U.S. patent application number 14/100289 was filed with the patent office on 2014-04-03 for spinal stabilization device.
This patent application is currently assigned to DePuy Synthes Products, LLC. The applicant listed for this patent is DePuy Synthes Products, LLC. Invention is credited to Brian Scott Bowman, Tae-anh Jahng, Jason Yim.
Application Number | 20140094852 14/100289 |
Document ID | / |
Family ID | 46206121 |
Filed Date | 2014-04-03 |
United States Patent
Application |
20140094852 |
Kind Code |
A1 |
Jahng; Tae-anh ; et
al. |
April 3, 2014 |
Spinal Stabilization Device
Abstract
A flexible connection unit for use in a spinal fixation device
that includes: a longitudinal member having first and second ends
and a flexible member interposed between the first and second ends,
at least one of the first end and second end configured to be
engaged by a first bone securing member; and at least one spacer
located between the first and second ends, the spacer comprising a
resilient element and a ring element encircling at least a portion
of the resilient element, wherein the ring element is configured to
be engaged by a second bone securing member.
Inventors: |
Jahng; Tae-anh; (Iksan,
KR) ; Yim; Jason; (San Diego, CA) ; Bowman;
Brian Scott; (Solana Beach, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DePuy Synthes Products, LLC |
Raynham |
MA |
US |
|
|
Assignee: |
DePuy Synthes Products, LLC
Raynham
MA
|
Family ID: |
46206121 |
Appl. No.: |
14/100289 |
Filed: |
December 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13163217 |
Jun 17, 2011 |
8623057 |
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14100289 |
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11705953 |
Feb 13, 2007 |
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13163217 |
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11072886 |
Mar 3, 2005 |
7326210 |
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11705953 |
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11009097 |
Dec 10, 2004 |
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11072886 |
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10798014 |
Mar 10, 2004 |
7763052 |
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11009097 |
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10728566 |
Dec 5, 2003 |
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10798014 |
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Current U.S.
Class: |
606/264 ;
606/279 |
Current CPC
Class: |
A61B 17/1757 20130101;
A61B 17/7032 20130101; A61B 2017/00862 20130101; A61B 17/3423
20130101; A61B 2090/3916 20160201; A61B 17/8897 20130101; A61B
17/88 20130101; A61B 17/3468 20130101; A61B 17/7007 20130101; A61B
90/39 20160201; A61B 2017/0256 20130101; A61B 17/701 20130101; A61B
17/02 20130101; A61B 2090/363 20160201; A61B 17/3472 20130101; A61B
2090/3987 20160201; A61B 17/7004 20130101; A61B 2017/00004
20130101; A61B 17/3421 20130101; A61B 17/3439 20130101 |
Class at
Publication: |
606/264 ;
606/279 |
International
Class: |
A61B 17/70 20060101
A61B017/70; A61B 17/88 20060101 A61B017/88 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 24, 2003 |
KR |
2003-0066108 |
Claims
1. A flexible, elongated connection unit for stabilizing a human
spine where the flexible connection unit is configured to be
surgically implanted into the human body adjacent the spine and
held in place by a first and a second pedicle screw assembly that
are configured to be anchored into a first and second, adjacent
vertebra, respectively, the flexible, elongated connection unit
comprising: (a) a first, metallic rigid portion having an outer
surface configured to be secured within the first pedicle screw
assembly; (b) a second, metallic rigid portion; (c) a cylindrical
flexible member extending from the first rigid portion to the
second rigid portion and directly secured to the second rigid
portion; and (d) a longitudinally compressible spacer comprising:
(1) a metallic, rigid portion having a length and having an inner
bore extending the length of the spacer metallic portion, the
flexible member extending through the bore of the spacer metallic
portion, the inner bore of the spacer metallic portion having a
larger dimension than a diameter of an outer surface of the
flexible member along the length of the spacer metallic portion
bore such that the spacer metallic portion can slide over the outer
surface of the flexible member along a length of the flexible
member, and where the spacer metallic portion has an outer surface
configured to be secured within the second pedicle screw assembly,
the spacer metallic portion being located entirely between the
first rigid portion and the second rigid portion such that along
the length of the connection unit no portion of the spacer metallic
portion overlaps with any portion of the first or second rigid
portion; (2) a first elastomeric portion located between the first
rigid portion and the spacer metallic portion, the first
elastomeric portion having a length and having an inner bore
extending the length of the first elastomeric portion with the
flexible member extending through the bore of the first elastomeric
portion; and (3) a second elastomeric portion located between the
second rigid portion and the spacer metallic portion, the second
elastomeric portion having a length and having an inner bore
extending the length of the second elastomeric portion with the
flexible member extending through the bore of the second
elastomeric portion; whereby the first and second elastomeric
spacer portions limit sliding of the spacer metallic portion over
the flexible member along the length of the flexible member.
2. The flexible connection unit of claim 1, wherein the spacer
metallic portion is physically separate from and does not
physically contact the first rigid portion or the second rigid
portion.
3. The flexible connection unit of claim 1, wherein the spacer
metallic portion is not integral with the first rigid portion or
the second rigid portion.
4. The flexible connection unit of claim 1, wherein the second
rigid portion has a longitudinal dimension that is shorter than the
longitudinal dimension of both the first elastomeric portion and
the second elastomeric portion individually.
5. The flexible connection unit of claim 1, wherein the first and
second elastomeric spacer portions limit sliding of the spacer
metallic portion over the flexible member in response to external
forces of the magnitude experienced from movement of the spine
applied to the first rigid portion and the spacer metallic
portion.
6. The flexible connection unit of claim 1, wherein the spacer is
constructed such that the first elastomeric portion physically
separates the first rigid portion and the spacer metallic portion
and the second elastomeric portion physically separates the second
rigid portion and the spacer metallic portion.
7. The flexible connection unit of claim 6, wherein the spacer
metallic portion physically separates the first and second
elastomeric portions.
8. The flexible connection unit of claim 6, wherein both the first
and second spacer elastomeric portions comprise polycarbonate
urethane.
9. The flexible connection unit of claim 6, wherein the first rigid
portion is longer than the second rigid portion.
10. The flexible connection unit of claim 1, wherein the flexible
member is metallic.
11. A method for stabilizing a human spine with a flexible,
elongated connection unit, comprising: (a) securing a first pedicle
screw assembly to a first vertebra and a second pedicle screw
assembly to a second vertebra; (b) securing the flexible connection
unit to the first and second pedicle screw assemblies, wherein the
flexible connection unit comprises: (1) a first, metallic rigid
portion; (2) a second, metallic rigid portion; (3) a flexible
member extending from the first rigid portion to the second rigid
portion and directly secured to the second rigid portion; (4) a
longitudinally compressible spacer extending between the first
rigid portion and the second rigid portion, the spacer comprising:
(i) a metallic, rigid portion having a length and having an outer
surface and an inner bore extending the length of the spacer
metallic portion, the flexible member extending through the inner
bore of the spacer metallic portion, the inner bore of the spacer
metallic portion having a larger dimension than an outer surface of
the flexible member along the length of the spacer metallic portion
bore such that the spacer metallic portion can slide over the outer
surface of the flexible member along a length of the flexible
member; (ii) a first elastomeric portion located between the first
rigid portion and the spacer metallic portion, the first
elastomeric portion having a length and having an inner bore
extending the length of the first elastomeric portion with the
flexible member extending through the bore of the first elastomeric
portion; (iii) a second elastomeric portion located between the
second rigid portion and the spacer metallic portion, the second
elastomeric portion having a length and having an inner bore
extending the length of the second elastomeric portion with the
flexible member extending through the bore of the second
elastomeric portion; wherein the flexible connection unit is
secured by securing the first, metallic rigid portion to the first
pedicle screw assembly and securing the spacer metallic, rigid
portion to the second pedicle screw assembly; whereby the first and
second elastomeric spacer portions limit sliding of the spacer
metallic portion along the length of the flexible member.
12. The method of claim 11, wherein the spacer metallic portion is
physically separate from and does not physically contact the first
rigid portion or the second rigid portion.
13. The method of claim 11, wherein the second rigid portion has a
longitudinal dimension that is shorter than the longitudinal
dimension of both the first elastomeric portion and the second
elastomeric portion individually.
14. The method of claim 11, wherein the spacer is constructed such
that the first elastomeric portion physically separates the first
rigid portion and the spacer metallic portion and the second
elastomeric portion physically separates the second rigid portion
and the spacer metallic portion.
15. The method of claim 14, wherein the spacer metallic portion
physically separates the first and second elastomeric portions.
16. The method of claim 15, wherein the outer, longitudinal surface
of each of the first rigid portion and the spacer metallic portion
is cylindrical.
17. The method of claim 15, wherein the first rigid portion is
longer than the second rigid portion.
18. The method of claim 17, wherein the spacer metallic portion is
longer than the second rigid portion.
19. The method of claim 11, wherein the second elastomeric portion
can be compressed between the spacer metallic portion and the
second rigid portion.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/163,217, filed Jun. 17, 2011, which is a
continuation U.S. patent application Ser. No. 11/705,953, filed
Feb. 13, 2007, which is continuation-in-part of U.S. patent
application Ser. No. 11/072,886, filed Mar. 3, 2005 now U.S. Pat.
No. 7,326,210 issued Feb. 5, 2008, which is a continuation-in-part
of U.S. patent application Ser. No. 11/009,097, filed Dec. 10,
2004, which is continuation-in-part of U.S. patent application Ser.
No. 10/798,014, filed Mar. 10, 2004 now U.S. Pat. No. 7,763,052
issued Jul. 27, 2010, which is a continuation-in-part of U.S.
patent application Ser. No. 10/728,566, filed on Dec. 5, 2003,
which claims the benefit of priority under 35 U.S.C. .sctn.119(a)
to Korean Application Serial No. 2003-0066108, filed on Sep. 24,
2003, the entireties of which are incorporated by reference
herein.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to a method and system for
stabilizing a spinal column and, more particularly, to a method and
system of spinal fixation in which one or more screw type securing
members are implanted and fixed into a portion of a patient's
spinal column and a longitudinal member including flexible,
semi-rigid rod-like or plate-like structures of various
cross-sections (hereinafter referred to as "rods" or "plates",
respectively) are connected and fixed to the upper ends of the
securing members to provide stabilization of the spinal column.
[0004] 2. Description of the Related Art
[0005] Degenerative spinal column diseases, such as disc
degenerative diseases (DDD), spinal stenosis, spondylolisthesis,
and so on, need surgical operation if they do not take a turn for
the better by conservative management. Typically, spinal
decompression is the first surgical procedure that is performed.
The primary purpose of decompression is to reduce pressure in the
spinal canal and on nerve roots located therein by removing a
certain tissue of the spinal column to reduce or eliminate the
pressure and pain caused by the pressure. If the tissue of the
spinal column is removed the pain is reduced but the spinal column
is weakened. Therefore, fusion surgery (e.g., ALIF, PLIF or
posterolateral fusion) is often necessary for spinal stability
following the decompression procedure. However, following the
surgical procedure, fusion takes additional time to achieve maximum
stability and a spinal fixation device is typically used to support
the spinal column until a desired level of fusion is achieved.
Depending on a patient's particular circumstances and condition, a
spinal fixation surgery can sometimes be performed immediately
following decompression, without performing the fusion procedure.
The fixation surgery is performed in most cases because it provides
immediate postoperative stability and, if fusion surgery has also
been performed, it provides support of the spine until sufficient
fusion and stability has been achieved.
[0006] Conventional methods of spinal fixation utilize a rigid
spinal fixation device to support an injured spinal part and
prevent movement of the injured part. These conventional spinal
fixation devices include: fixing screws configured to be inserted
into the spinal pedicle or sacral of the backbone to a
predetermined depth and angle, rods or plates configured to be
positioned adjacent to the injured spinal part, and coupling
elements for connecting and coupling the rods or plates to the
fixing screws such that the injured spinal part is supported and
held in a relatively fixed position by the rods or plates.
[0007] U.S. Pat. No. 6,193,720 discloses a conventional spinal
fixation device, in which connection members of a rod or plate type
are mounted on the upper ends of at least one or more screws
inserted into the spinal pedicle or sacral of the backbone. The
connection units, such as the rods and plates, are used to
stabilize the injured part of the spinal column which has been
weakened by decompression. The connection units also prevent
further pain and injury to the patient by substantially restraining
the movement of the spinal column. However, because the connection
units prevent normal movement of the spinal column, after prolonged
use, the spinal fixation device can cause ill effects, such as
"junctional syndrome" (transitional syndrome) or "fusion disease"
resulting in further complications and abnormalities associated
with the spinal column. In particular, due to the high rigidity of
the rods or plates used in conventional fixation devices, the
patient's fixed joints are not allowed to move after the surgical
operation, and the movement of the spinal joints located above or
under the operated area is increased. Consequently, such spinal
fixation devices cause decreased mobility of the patient and
increased stress and instability to the spinal column joints
adjacent to the operated area.
[0008] It has been reported that excessive rigid spinal fixation is
not helpful to the fusion process due to load shielding caused by
rigid fixation. Thus, trials using load sharing semi-rigid spinal
fixation devices have been performed to eliminate this problem and
assist the bone fusion process. For example, U.S. Pat. No.
5,672,175, U.S. Pat. No. 5,540,688, and U.S. Pub No 2001/0037111
disclose dynamic spine stabilization devices having flexible
designs that permit axial load translation (i.e., along the
vertical axis of the spine) for bone fusion promotion. However,
because these devices are intended for use following a bone fusion
procedure, they are not well-suited for spinal fixation without
fusion. Thus, in the end result, these devices do not prevent the
problem of rigid fixation resulting from fusion.
[0009] To solve the above-described problems associated with rigid
fixation, non-fusion technologies have been developed. The Graf
band is one example of a non-fusion fixation device that is applied
after decompression without bone fusion. The Graf band is composed
of a polyethylene band and pedicle screws to couple the
polyethylene band to the spinal vertebrae requiring stabilization.
The primary purpose of the Graf band is to prevent sagittal
rotation (flexion instability) of the injured spinal parts. Thus,
it is effective in selected cases but is not appropriate for cases
that require greater stability and fixation. See, Kanayama et al,
Journal of Neurosurgery 95(1 Suppl):5-10, 2001, Markwalder &
Wenger, Acta Neurochrgica 145(3):209-14). Another non-fusion
fixation device called "Dynesys" has recently been introduced. See
Stoll et al, European Spine Journal 11 Suppl 2:S170-8, 2002,
Schmoelz et. al., J. of Spinal Disorder & Techniques
16(4):418-23, 2003. The Dynesys device is similar to the Graf band
except it uses a polycarburethane spacer between the screws to
maintain the distance between the heads of two corresponding
pedicle screws and, hence, adjacent vertebrae in which the screws
are fixed. Early reports by the inventors of the Dynesys device
indicate it has been successful in many cases. However, it has not
yet been determined whether the Dynesys device can maintain
long-term stability with flexibility and durability in a controlled
study. Because it has polyethylene components and interfaces, there
is a risk of mechanical failure. Furthermore, due to the mechanical
configuration of the device, the surgical technique required to
attach the device to the spinal column is complex and
complicated.
[0010] U.S. Pat. Nos. 5,282,863 and 4,748,260 disclose a flexible
spinal stabilization system and method using a plastic,
non-metallic rod. U.S. patent publication no. 2003/0083657
discloses another example of a flexible spinal stabilization device
that uses a flexible elongate member. These devices are flexible
but they are not well-suited for enduring long-term axial loading
and stress. Additionally, the degree of desired flexibility vs.
rigidity may vary from patient to patient. The design of existing
flexible fixation devices are not well suited to provide varying
levels of flexibility to provide optimum results for each
individual candidate. For example, U.S. Pat. No. 5,672,175
discloses a flexible spinal fixation device which utilizes a
flexible rod made of metal alloy and/or a composite material.
Additionally, compression or extension springs are coiled around
the rod for the purpose of providing de-rotation forces on the
vertebrae in a desired direction. However, this patent is primarily
concerned with providing a spinal fixation device that permits
"relative longitudinal translational sliding movement along [the]
vertical axis" of the spine and neither teaches nor suggests any
particular designs of connection units (e.g., rods or plates) that
can provide various flexibility characteristics. Prior flexible
rods such as that mentioned in U.S. Pat. No. 5,672,175 typically
have solid construction with a relatively small diameter in order
to provide a desired level of flexibility. Because they are
typically very thin to provide suitable flexibility, such prior art
rods are prone to mechanical failure and have been known to break
after implantation in patients.
[0011] Therefore, conventional spinal fixation devices have not
provided a comprehensive and balanced solution to the problems
associated with curing spinal diseases. Many of the prior devices
are characterized by excessive rigidity, which leads to the
problems discussed above while others, though providing some
flexibility, are not well-adapted to provide long-term stability
and/or varying degrees of flexibility. Therefore, there is a need
for an improved dynamic spinal fixation device that provides a
desired level of flexibility to the injured parts of the spinal
column, while also providing long-term durability and consistent
stabilization of the spinal column.
[0012] Additionally, in a conventional surgical method for fixing
the spinal fixation device to the spinal column, a doctor incises
the midline of the back to about 10-15 centimeters, and then,
dissects and retracts it to both sides. In this way, the doctor
performs muscular dissection to expose the outer part of the facet
joint. Next, after the dissection, the doctor finds an entrance
point to the spinal pedicle using radiographic devices (e.g., C-arm
flouroscopy), and inserts securing members of the spinal fixation
device (referred to as "spinal pedicle screws") into the spinal
pedicle. Thereafter, the connection units (e.g., rods or plates)
are attached to the upper portions of the pedicle screws in order
to provide support and stability to the injured portion of the
spinal column. Thus, in conventional spinal fixation procedures,
the patient's back is incised about 10.about.15 cm, and as a
result, the back muscle, which is important for maintaining the
spinal column, is incised or injured, resulting in significant
post-operative pain to the patient and a slow recovery period.
[0013] Recently, to reduce patient trauma, a minimally invasive
surgical procedure has been developed which is capable of
performing spinal fixation surgery through a relatively small hole
or "window" that is created in the patient's back at the location
of the surgical procedure. Through the use of an endoscope, or
microscope, minimally invasive surgery allows a much smaller
incision of the patient's affected area. Through this smaller
incision, two or more securing members (e.g., pedicle screws) of
the spinal fixation device are screwed into respective spinal
pedicle areas using a navigation system. Thereafter, special tools
are used to connect the stabilizing members (e.g., rods or plates)
of the fixation device to the securing members. Alternatively, or
additionally, the surgical procedure may include inserting a step
dilator into the incision and then gradually increasing the
diameter of the dilator. Thereafter, a tubular retractor is
inserted into the dilated area to retract the patient's muscle and
provide a visual field for surgery. After establishing this visual
field, decompression and, if desired, fusion procedures may be
performed, followed by a fixation procedure, which includes the
steps of finding the position of the spinal pedicle, inserting
pedicle screws into the spinal pedicle, using an endoscope or a
microscope, and securing the stabilization members (e.g., rods or
plates) to the pedicle screws in order to stabilize and support the
weakened spinal column.
[0014] One of the most challenging aspects of performing the
minimally invasive spinal fixation procedure is locating the entry
point for the pedicle screw under endoscopic or microscopic
visualization. Usually anatomical landmarks and/or radiographic
devices are used to find the entry point, but clear anatomical
relationships are often difficult to identify due to the confined
working space. Additionally, the minimally invasive procedure
requires that a significant amount of the soft tissue must be
removed to reveal the anatomy of the regions for pedicle screw
insertion. The removal of this soft tissue results in bleeding in
the affected area, thereby adding to the difficulty of finding the
correct position to insert the securing members and causing damage
to the muscles and soft tissue surrounding the surgical area.
Furthermore, because it is difficult to accurately locate the point
of insertion for the securing members, conventional procedures are
unnecessarily traumatic.
[0015] Radiography techniques have been proposed and implemented in
an attempt to more accurately and quickly find the position of the
spinal pedicle in which the securing members will be inserted.
However, it is often difficult to obtain clear images required for
finding the corresponding position of the spinal pedicle using
radiography techniques due to radiographic interference caused by
metallic tools and equipment used during the surgical operation.
Moreover, reading and interpreting radiographic images is a complex
task requiring significant training and expertise. Radiography
poses a further problem in that the patient is exposed to
significant amounts of radiation.
[0016] Although some guidance systems have been developed which
guide the insertion of a pedicle screw to the desired entry point
on the spinal pedicle, these prior systems have proven difficult to
use and, furthermore, hinder the operation procedure. For example,
prior guidance systems for pedicle screw insertion utilize a long
wire that is inserted through a guide tube that is inserted through
a patient's back muscle and tissue. The location of insertion of
the guide tube is determined by radiographic means (e.g., C-arm
fluoroscope) and driven until a first end portion of the guide tube
reaches the desired location on the surface of the pedicle bone.
Thereafter, a first end portion of the guide wire, typically made
of a biocompatible metal material, is inserted into the guide tube
and pushed into the pedicle bone, while the opposite end of the
wire remains protruding out of the patient's back. After the guide
wire has been fixed into the pedicle bone, the guide tube is
removed, and a hole centered around the guide wire is dilated and
retracted. Finally, a pedicle screw having an axial hole or channel
configured to receive the guide wire therethrough is guided by the
guide wire to the desired location on the pedicle bone, where the
pedicle screw is screw-driven into the pedicle.
[0017] Although the concept of the wire guidance system is a good
one, in practice, the guide wire has been very difficult to use.
Because it is a relatively long and thin wire, the structural
integrity of the guide wire often fails during attempts to drive
one end of the wire into the pedicle bone, making the process
unnecessarily time-consuming and laborious. Furthermore, because
the wire bends and crimps during insertion, it does not provide a
smooth and secure anchor for guiding subsequent tooling and pedicle
screws to the entry point on the pedicle. Furthermore, current
percutaneous wire guiding systems are used in conjunction with
C-arm flouroscopy (or other radiographic device) without direct
visualization with the use of an endoscope or microscope. Thus,
current wire guidance systems pose a potential risk of misplacement
or pedicle breakage. Finally, because one end of the wire remains
protruding out of the head of the pedicle screw, and the patient's
back, this wire hinders freedom of motion by the surgeon in
performing the various subsequent procedures involved in spinal
fixation surgery. Thus, there is a need to provide an improved
guidance system, adaptable for use in minimally invasive pedicle
screw fixation procedures under endoscopic or microscopic
visualization, which is easier to implant into the spinal pedicle
and will not hinder subsequent procedures performed by the
surgeon.
[0018] As discussed above, existing methods and devices used to
cure spinal diseases are in need of much improvement. Most
conventional spinal fixation devices are too rigid and inflexible.
This excessive rigidity causes further abnormalities and diseases
of the spine, as well as significant discomfort to the patient.
Although some existing spinal fixation devices do provide some
level of flexibility, these devices are not designed or
manufactured so that varying levels of flexibility may be easily
obtained to provide a desired level of flexibility for each
particular patient. Additionally, prior art devices having flexible
connection units (e.g., rods or plates) pose a greater risk of
mechanical failure and do not provide long-term durability and
stabilization of the spine. Furthermore, existing methods of
performing the spinal fixation procedure are unnecessarily
traumatic to the patient due to the difficulty in finding the
precise location of the spinal pedicle or sacral of the backbone
where the spinal fixation device will be secured.
SUMMARY
[0019] The invention addresses the above and other needs by
providing an improved method and system for stabilizing an injured
or weakened spinal column.
[0020] To overcome the deficiencies of conventional spinal fixation
devices, in one embodiment, the inventor of the present invention
has invented a novel flexible spinal fixation device with an
improved construction and design that is durable and provides a
desired level of flexibility and stability.
[0021] As a result of long-term studies to reduce the operation
time required for minimally invasive spinal surgery, to minimize
injury to tissues near the surgical area, in another embodiment,
the invention provides a method and device for accurately and
quickly finding a position of the spinal column in which securing
members of the spinal fixation device will be inserted. A novel
guidance/marking device is used to indicate the position in the
spinal column where the securing members will be inserted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 illustrates a perspective view of a spinal fixation
device in accordance with one embodiment of the invention.
[0023] FIG. 2 illustrates a perspective view of spinal fixation
device in accordance with another embodiment of the invention.
[0024] FIG. 3 illustrates an exploded view of the coupling assembly
14 of the pedicle screw 2 of FIGS. 1 and 2, in accordance with one
embodiment of the invention.
[0025] FIG. 4 illustrates a perspective view of a flexible rod
connection unit in accordance with one embodiment of the
invention.
[0026] FIG. 5 illustrates a perspective view of a flexible rod
connection unit in accordance with another embodiment of the
invention.
[0027] FIG. 6 illustrates a perspective view of a flexible rod
connection unit in accordance with a further embodiment of the
invention.
[0028] FIG. 7 illustrates a perspective view of a pre-bent flexible
rod connection unit in accordance with one embodiment of the
invention.
[0029] FIG. 8 illustrates a perspective, cross-sectional view of a
flexible portion of connection unit in accordance with one
embodiment of the invention.
[0030] FIG. 9 illustrates a perspective, cross-sectional view of a
flexible portion of connection unit in accordance with another
embodiment of the invention.
[0031] FIG. 10 illustrates a perspective, cross-sectional view of a
flexible portion of connection unit in accordance with a further
embodiment of the invention.
[0032] FIG. 11 illustrates a perspective view of a flexible rod
connection unit in accordance with one embodiment of the
invention.
[0033] FIG. 12A illustrates a perspective view of a flexible
connection unit having one or more spacers in between two end
portions, in accordance with one embodiment of the invention.
[0034] FIG. 12B illustrates an exploded view of the flexible
connection unit of FIG. 12A.
[0035] FIG. 12C provides a view of the male and female interlocking
elements of the flexible connection unit of FIGS. 12A and 12B, in
accordance with one embodiment of the invention.
[0036] FIG. 13 shows a perspective view of a flexible connection
unit, in accordance with a further embodiment of the invention.
[0037] FIG. 14 illustrates a perspective view of a spinal fixation
device in accordance with another embodiment of the invention.
[0038] FIG. 15 illustrates an exploded view of the spinal fixation
device of FIG. 14.
[0039] FIG. 16A shows a perspective view of a flexible plate
connection unit in accordance with one embodiment of the
invention.
[0040] FIG. 16B illustrates a perspective view of a flexible plate
connection unit in accordance with a further embodiment of the
invention.
[0041] FIG. 16C shows a side view of the flexible plate connection
unit of FIG. 16A.
[0042] FIG. 16D shows a top view of the flexible plate connection
unit of FIG. 16A.
[0043] FIG. 16E illustrates a side view of the flexible plate
connection unit of FIG. 16A having a pre-bent configuration in
accordance with a further embodiment of the invention.
[0044] FIG. 17 is a perspective view of a flexible plate connection
unit in accordance with another embodiment of the invention.
[0045] FIG. 18 illustrates a perspective view of a flexible plate
connection unit in accordance with another embodiment of the
invention.
[0046] FIG. 19 illustrates a perspective view of a hybrid rod-plate
connection unit having a flexible middle portion according to a
further embodiment of the present invention.
[0047] FIG. 20 is a perspective view of a spinal fixation device
that utilizes the hybrid rod-plate connection unit of FIG. 19.
[0048] FIG. 21 illustrates a perspective view of the spinal
fixation device of FIG. 1 after it has been implanted into a
patient's spinal column.
[0049] FIGS. 22A and 22B provide perspective views of spinal
fixation devices utilizing the plate connection units of FIGS. 16A
and 16B, respectively.
[0050] FIG. 23A illustrates a perspective view of two pedicle
screws inserted into the pedicles of two adjacent vertebrae at a
skewed angle, in accordance with one embodiment of the
invention.
[0051] FIG. 23B illustrates a structural view of a coupling
assembly of a pedicle screw in accordance with one embodiment of
the invention.
[0052] FIG. 23C provides a perspective view of a slanted
stabilizing spacer in accordance with one embodiment of the
invention.
[0053] FIG. 23D illustrates a side view of the slanted stabilizing
spacer of FIG. 23C.
[0054] FIG. 23E is a top view of the cylindrical head of the
pedicle screw of FIG. 23.
[0055] FIG. 24 illustrates a perspective view of a marking and
guiding device in accordance with one embodiment of the
invention.
[0056] FIG. 25 is an exploded view of the marking and guidance
device of FIG. 24.
[0057] FIG. 26A provides a perspective, cross-section view of a
patient's spine after the marking and guiding device of FIG. 24 has
been inserted during surgery.
[0058] FIG. 26B provides a perspective, cross-section view of a
patient's spine as an inner trocar of the marking and guiding
device of FIG. 24 is being removed.
[0059] FIGS. 27A and 27B illustrate perspective views of two
embodiments of a fiducial pin, respectively.
[0060] FIG. 28 is a perspective view of a pushing trocar in
accordance with a further embodiment of the invention.
[0061] FIG. 29A illustrates a perspective, cross-sectional view of
a patient's spine as the pushing trocar of FIG. 28 is used to drive
a fiducial pin into a designate location of a spinal pedicle, in
accordance with one embodiment of the invention.
[0062] FIG. 29B illustrates a perspective, cross-sectional view of
a patient's spine after two fiducial pins have been implanted into
two adjacent spinal pedicles, in accordance with one embodiment of
the invention.
[0063] FIG. 30 is a perspective view of a cannulated awl in
accordance with one embodiment of the invention.
[0064] FIG. 31 is a perspective, cross-sectional view of a
patient's spine as the cannulated awl of FIG. 30 is being used to
enlarge an entry hole for a pedicle screw, in accordance with one
embodiment of the invention.
[0065] FIG. 32 provides a perspective view of fiducial pin
retrieving device, in accordance with one embodiment of the
invention.
[0066] FIG. 33 is a perspective view of a pedicle screw having an
axial cylindrical cavity for receiving at least a portion of a
fiducial pin therein, in accordance with a further embodiment of
the invention.
[0067] FIG. 34 is a perspective, cross-sectional view of a
patient's spine after one pedicle screw has been implanted into a
designated location of a spinal pedicle, in accordance with one
embodiment of the invention.
[0068] FIG. 35 is a perspective, cross-sectional view of a
patient's spine after two pedicle screws have been implanted into
designated locations of two adjacent spinal pedicles, in accordance
with one embodiment of the invention.
[0069] FIG. 36A is perspective view of a flexible rod for spinal
fixation having a spiral groove cut therein, in accordance with one
embodiment of the present invention.
[0070] FIG. 36B provides a cross-sectional view of the flexible rod
of FIG. 36A, taken along lines B-B of FIG. 36A.
[0071] FIG. 37A illustrates a perspective view of a flexible rod
for spinal fixation having transverse tunnels within the body of
the rod, in accordance with one embodiment of the invention.
[0072] FIG. 37B is a cross-sectional view of the flexible rod of
FIG. 37A, taken along lines B-B of FIG. 37A.
[0073] FIG. 38A is a perspective view of a flexible rod for spinal
fixation having a spiral groove cut therein and transverse tunnels
in the body of the rod, in accordance with a further embodiment of
the invention.
[0074] FIG. 38B is a top view of the flexible rod of FIG. 38A, from
the perspective of lines B-B of FIG. 38A.
[0075] FIG. 39A is a perspective view of a flexible rod for spinal
fixation having transverse tunnels within the body of the rod, in
accordance with another embodiment of the invention.
[0076] FIG. 39B is a cross-sectional view of the flexible rod of
FIG. 39A, taken along lines B-B of that figure.
[0077] FIG. 39C is an alternative cross-sectional view of the
flexible rod of FIG. 39A, taken along lines B-B of that figure,
having substantially orthogonal transverse tunnels in the body of
the rod, in accordance with a further embodiment of the
invention.
[0078] FIG. 40A illustrates a perspective view of a flexible rod
for spinal fixation, in accordance with a further embodiment of the
invention.
[0079] FIG. 40B illustrates a cross-sectional view of a flexible
rod for spinal fixation in accordance with a further embodiment of
the invention.
[0080] FIG. 41A illustrates a perspective view of a flexible
longitudinal member connection unit in accordance with one
embodiment of the invention.
[0081] FIG. 41B illustrates a perspective view of the connection
unit of FIG. 41A assembled with securing members.
[0082] FIG. 41C illustrates a perspective view of a flexible
longitudinal member trimmed to length and assembled with securing
members.
[0083] FIG. 42A illustrates a side view of a flexible longitudinal
member connection unit in accordance with a further embodiment of
the invention.
[0084] FIG. 42B illustrates a side view of a flexible longitudinal
member connection unit in accordance with another embodiment of the
invention.
[0085] FIG. 43A illustrates a side view of a flexible longitudinal
member connection unit in accordance with another embodiment of the
invention.
[0086] FIG. 43B illustrates a perspective view of a flexible
longitudinal member connection unit in accordance with another
embodiment of the invention.
[0087] FIG. 43C illustrates a side view of a flexible longitudinal
member connection unit in accordance with another embodiment of the
invention.
[0088] FIG. 43D illustrates a side view of a flexible longitudinal
member connection unit in accordance with another embodiment of the
invention.
[0089] FIG. 44 illustrates a perspective view of a flexible
longitudinal member connection unit in accordance with a further
embodiment of the invention.
[0090] FIG. 45A illustrates a cross-section view of a flexible
longitudinal member connection unit in accordance with an
embodiment of the invention.
[0091] FIG. 45B illustrates a cross-section view of a flexible
longitudinal member made of two types of material in accordance
with another embodiment of the invention.
[0092] FIGS. 46A-C illustrate perspective views of a metal-hybrid
longitudinal member with an elastomer cladding, in accordance with
various embodiments of the invention.
[0093] FIGS. 47A-B illustrate perspective views of a longitudinal
member having at least one spacer and an elastomer, in accordance
with various embodiments of the invention.
[0094] FIG. 48 illustrates a flexible connection unit having a
spacer and an elastomer cladding, in accordance with another
embodiment of the invention.
[0095] FIG. 49 illustrates a flexible connection unit having a
spacer and an elastomer cladding, in accordance with another
embodiment of the invention.
[0096] FIGS. 50A-D illustrate a variety of features for improved
fixation of the elastomer cladding to a rigid surface, in
accordance with various embodiments of the invention.
[0097] FIGS. 51-52 illustrates two respective embodiments of a
flexible connection unit having at least one spacer and an
elastomer cladding, in accordance with the invention.
[0098] FIG. 53 illustrates two flexible connection units as shown
in FIG. 52 attached to a patient's spine, in accordance with one
embodiment of the present invention.
[0099] FIGS. 54-55 illustrates additional embodiments of a flexible
connection unit having at least one spacer and an elastomer
cladding, in accordance with the invention.
[0100] FIG. 56 illustrates an exploded view of a further embodiment
of a flexible connection unit in accordance with the present
invention.
[0101] FIG. 57 illustrates the flexible connection unit of FIG. 56
in an assembled state in accordance with an embodiment of the
present invention.
[0102] FIG. 58 illustrates a cross sectional view of a metal-hybrid
spacer in accordance with an embodiment of the present
invention.
[0103] FIGS. 59a-b illustrate a perspective view and front
cross-sectional view of an embodiment of a D-ring metal ring in
accordance with the present invention.
[0104] FIG. 60 illustrates a flexible connection unit in accordance
with one embodiment of the invention.
[0105] FIG. 61 illustrates a flexible connection unit in accordance
with one embodiment of the invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0106] The invention is described in detail below with reference to
the figures wherein like elements are referenced with like numerals
throughout.
[0107] FIG. 1 depicts a spinal fixation device in accordance with
one embodiment of the present invention. The spinal fixation device
includes two securing members 2 (designated as 2' and 2''), and a
flexible fixation rod 4 configured to be received and secured
within a coupling assembly 14, as described in further detail below
with respect to FIG. 3. Each securing member 2 includes a threaded
screw-type shaft 10 configured to be inserted and screwed into a
patient's spinal pedicle. As shown in FIG. 1, the screw-type shaft
10 includes an external spiral screw thread 12 formed over the
length of the shaft 10 and a conical tip at the end of the shaft 10
configured to be inserted into the patient's spinal column at a
designated location. Other known forms of the securing member 2 may
be used in connection with the present invention provided the
securing member 2 can be inserted and fixed into the spinal column
and securely coupled to the rod 4.
[0108] As described above, the spinal fixation device is used for
surgical treatment of spinal diseases by mounting securing members
2 at desired positions in the spinal column. In one embodiment, the
rod 4 extends across two or more vertebrae of the spinal column and
is secured by the securing members 2 so as to stabilize movement of
the two or more vertebrae.
[0109] FIG. 2 illustrates a perspective view of a spinal fixation
device in accordance with a further embodiment of the present
invention. The spinal fixation device of FIG. 2 is similar to the
spinal fixation device of FIG. 1 except that the rod 4 comprises a
flexible middle portion 8 juxtaposed between two rigid end portions
9 of the rod 4.
[0110] FIG. 3 provides an exploded view of the securing member 2 of
FIGS. 1 and 2 illustrating various components of the coupling
assembly 14, in accordance with one embodiment of the invention. As
shown in FIG. 3, the coupling assembly 14 includes: a cylindrical
head 16 located at a top end of the screw-type shaft 10, a spiral
thread or groove 18 formed along portions of the inner wall surface
of the cylindrical head 16, and a U-shaped seating groove 20
configured to receive the rod 4 therein. The coupling assembly 14
further comprises an outside-threaded nut 22 having a spiral thread
24 formed on the outside lateral surface of the nut 22, wherein the
spiral thread 24 is configured to mate with the internal spiral
thread 18 of the cylindrical head 16. In a further embodiment, the
coupling assembly 14 includes a fixing cap 26 configured to be
mounted over a portion of the cylindrical head 16 to cover and
protect the outside-threaded nut 22 and more securely hold rod 4
within seating groove 20. In one embodiment an inner diameter of
the fixing gap 26 is configured to securely mate with the outer
diameter of the cylindrical head 16. Other methods of securing the
fixing cap 26 to the cylindrical head, such as correspondingly
located notches and groove (not shown), would be readily apparent
to those of skill in the art. In preferred embodiments, the
components and parts of the securing member 2 may be made of highly
rigid and durable bio-compatible materials such as stainless steel,
iron steel, titanium or titanium alloy. Additionally or
alternatively, non-metal biocompatible materials may also be
utilized such as polymers, elastomers, resins, ceramics, and
composites thereof. Such materials are known in the art. As also
known in the art, and used herein, "bio-compatible" materials
refers to those materials that will not cause any adverse chemical
or immunological reactions after being implanted into a patient's
body.
[0111] As shown in FIGS. 1 and 2, in preferred embodiments, the rod
4 is coupled to the securing means 2 by seating the rod 4
horizontally into the seating groove 20 of the coupling means 14
perpendicularly to the direction of the length of the threaded
shaft 10 of securing member 2. The outside threaded nut 22 is then
received and screwed into the cylindrical head 16 above the rod 4
so as to secure the rod 4 in the seating groove 20. The fixing cap
26 is then placed over the cylindrical head 16 to cover, protect
and more firmly secure the components in the internal cavity of the
cylindrical head 16. FIGS. 4-7 illustrate perspective views of
various embodiments of a rod 4 that may be used in a fixation
device, in accordance with the present invention. FIG. 4
illustrates the rod 4 of FIG. 1 wherein the entire rod is made and
designed to be flexible. In one embodiment, rod 4 comprises a metal
tube or pipe having a cylindrical wall 5 of a predefined thickness.
In alternative embodiments, the rod 4 may comprise a tube made from
a biocompatible metal-synthetic hybrid material or entirely from a
biocompatible synthetic material. Examples of biocompatible metals
are: titanium, stainless steel, zirconium, tantalum, cobalt,
chromium, nickel and alloys thereof. Examples of biocompatible
synthetic materials are: polymers, elastomers, resins, plastics,
carbon graphite and composites thereof. Such materials are well
known in the art.
[0112] In one embodiment, in order to provide flexibility to the
rod 4, the cylindrical wall 5 is cut in a spiral fashion along the
length of the rod 4 to form spiral cuts or grooves 6. As would be
apparent to one of ordinary skill in the art, the width and density
of the spiral grooves 6 may be adjusted to provide a desired level
of flexibility. In one embodiment, the grooves 6 are formed from
very thin spiral cuts or incisions that penetrate through the
entire thickness of the cylindrical wall of the rod 4. As known to
those skilled in the art, the thickness and material of the tubular
walls 5 also affect the level of flexibility.
[0113] In one embodiment, the rod 4 is designed to have a
flexibility that substantially equals that of a normal back.
Flexibility ranges for a normal back are known by those skilled in
the art, and one of ordinary skill can easily determine a thickness
and material of the tubular walls 5 and a width and density of the
grooves 6 to achieve a desired flexibility or flexibility range
within the range for a normal back. When referring to the grooves 6
herein, the term "density" refers to tightness of the spiral
grooves 6 or, in other words, the distance between adjacent groove
lines 6 as shown in FIG. 4, for example. However, it is understood
that the present invention is not limited to a particular,
predefined flexibility range. In one embodiment, in addition to
having desired lateral flexibility characteristics, the rigidity of
the rod 4 should be able to endure a vertical axial load applied to
the patient's spinal column along a vertical axis of the spine in a
uniform manner with respect to the rest of the patient's natural
spine.
[0114] FIG. 5 illustrates the rod 4 of FIG. 2 wherein only a middle
portion 8 is made and designed to be flexible and two end portions
9 are made to be rigid. In one embodiment, metal end rings or caps
9', having no grooves therein, may be placed over respective ends
of the rod 4 of FIG. 4 so as make the end portions 9 rigid. The
rings or caps 9' may be permanently affixed to the ends of the rod
4 using known methods such as pressing and/or welding the metals
together. In another embodiment, the spiral groove 6 is only cut
along the length of the middle portion 8 and the end portions 9
comprise the tubular wall 5 without grooves 6. Without the grooves
6, the tubular wall 5, which is made of a rigid metal or metal
hybrid material, exhibits high rigidity.
[0115] FIG. 6 illustrates a further embodiment of the rod 4 having
multiple sections, two flexible sections 8 interleaved between
three rigid sections 9. This embodiment may be used, for example,
to stabilize three adjacent vertebrae with respect to each other,
wherein three pedicle screws are fixed to a respective one of the
vertebrae and the three rigid sections 9 are connected to a
coupling assembly 14 of a respective pedicle screw 2, as described
above with respect to FIG. 3. Each of the flexible sections 8 and
rigid sections 9 may be made as described above with respect to
FIG. 5.
[0116] FIG. 7 illustrates another embodiment of the rod 4 having a
pre-bent structure and configuration to conform to and maintain a
patient's curvature of the spine, known as "lordosis," while
stabilizing the spinal column. Generally, a patient's lumbar is in
the shape of a `C` form, and the structure of the rod 4 is formed
to coincide to the normal lumbar shape when utilized in the spinal
fixation device of FIG. 2, in accordance with one embodiment of the
invention. In one embodiment, the pre-bent rod 4 includes a middle
portion 8 that is made and designed to be flexible interposed
between two rigid end portions 9. The middle portion 8 and end
portions 9 may be made as described above with respect to FIG. 5.
Methods of manufacturing metallic or metallic-hybrid tubular rods
of various sizes, lengths and pre-bent configurations are
well-known in the art. Additionally, or alternatively, the pre-bent
structure and design of the rod 4 may offset a skew angle when two
adjacent pedicle screws are not inserted parallel to one another,
as described in further detail below with respect to FIG. 23A.
[0117] Additional designs and materials used to create a flexible
tubular rod 4 or flexible middle portion 8 are described below with
respect to FIGS. 8-10. FIG. 8 illustrates a perspective,
cross-sectional view of a flexible tubular rod 4, or rod portion 8
in accordance with one embodiment of the invention. In this
embodiment, the flexible rod 4, 8 is made from a first metal tube 5
having a spiral groove 6 cut therein as described above with
respect to FIGS. 4-7. A second tube 30 having spiral grooves 31 cut
therein and having a smaller diameter than the first tube 5 is
inserted into the cylindrical cavity of the first tube 5. In one
embodiment, the second tube 30 has spiral grooves 31 which are cut
in an opposite spiral direction with respect to the spiral grooves
6 cut in the first tube 5, such that the rotational torsion
characteristics of the second tube 30 offset at least some of the
rotational torsion characteristics of the first tube 5. The second
flexible tube 30 is inserted into the core of the first tube to
provide further durability and strength to the flexible rod 4, 8.
The second tube 30 may be made of the same or different material
than the first tube 5. In preferred embodiments, the material used
to manufacture the first and second tubes 5 and 30, respectively,
may be any one or combination of the following exemplary
biocompatible metals: titanium, stainless steel, zirconium,
tantalum, cobalt, chromium, nickel, aluminum, vanadium, and alloys
thereof. In alternative embodiments, the tubes 5 and 30 may be made
from a biocompatible metal-synthetic hybrid material or entirely
from a biocompatible synthetic material. Examples of biocompatible
synthetic materials are: polymers, elastomers, resins, plastics,
carbon graphite and composites thereof. Such materials are well
known in the art.
[0118] FIG. 9 illustrates a perspective, cross-sectional view of a
flexible rod 4, 8 in accordance with a further embodiment of the
invention. In one embodiment, the flexible rod 4, 8 includes an
inner core made of a biocompatible metallic wire 32 comprising a
plurality of overlapping thin metallic yarns, such as steel yarns,
titanium yarns, or titanium-alloy yarns. The wire 32 is encased by
a metal, or metal hybrid, flexible tube 5 having spiral grooves 6
cut therein, as discussed above. The number and thickness of the
metallic yarns in the wire 32 also affects the rigidity and
flexibility of the rod 4, 8. By changing the number, thickness or
material of the yarns flexibility can be increased or decreased.
Thus, the number, thickness and/or material of the metallic yarns
in the wire 32 can be adjusted to provide a desired rigidity and
flexibility in accordance with a patient's particular needs. Those
of ordinary skill in the art can easily determine the number,
thickness and material of the yarns, in conjunction with a given
flexibility of the tube 5 in order to achieve a desired rigidity v.
flexibility profile for the rod 4, 8. In alternative embodiments,
the wire 32 and plurality of yarns may be made from a biocompatible
metal-synthetic hybrid material or entirely from biocompatible
synthetic materials, as discussed above.
[0119] FIG. 10 shows yet another embodiment of a flexible rod 4
wherein the flexible tube 5 encases a non-metallic, flexible core
34. In various embodiments, the core 34 may be made from, for
example, known biocompatible metals, biocompatible shape memory
alloys (e.g., NITINOL), or biocompatible synthetic materials such
as carbon fiber, Poly Ether Ether Ketone (PEEK), Poly Ether Ketone
Ketone Ether Ketone (PEKKEK), or Ultra High Molecular Weight Poly
Ethylene (UHMWPE).
[0120] FIG. 11 illustrates a perspective view of another embodiment
of the flexible rod 35 in which a plurality of wires 32, as
described above with respect to FIG. 9, are interweaved or braided
together to form a braided wire rod 35. The braided wire rod 35 can
be made from the same materials as the wire 32 discussed above. In
addition to the variability of the rigidity and flexibility of the
wire 32 as explained above, the rigidity and flexibility of the
braided rod 35 can be further modified to achieve desired
characteristics by varying the number and thickness of the wires 32
used in the braided structure 35. For example, in order to achieve
various flexion levels or ranges within the known flexion range of
a normal healthy spine, those of ordinary skill in the art can
easily manufacture various designs of the braided wire rod 35 by
varying and measuring the flexion provided by different gauges,
numbers and materials of the wire used to create the braided wire
rod 35. In a further embodiment each end of the braided wire rod 35
is encased by a rigid cap or ring 9' as described above with
respect to FIGS. 5-7, to provide a rod 4 having a flexible middle
portion 8 and rigid end portions 9. In a further embodiment (not
shown), the braided wire rod 35 may be utilized as a flexible inner
core encased by a tube 5 having spiral grooves 6 cut therein to
create a flexible rod 4 or rod portion 8, in a similar fashion to
the embodiments shown in FIGS. 8-10. As used herein the term
"braid" or "braided structure" encompasses two or more wires,
strips, strands, ribbons and/or other shapes of material interwoven
in an overlapping fashion. Various methods of interweaving wires,
strips, strands, ribbons and/or other shapes of material are known
in the art. Such interweaving techniques are encompassed by the
present invention. In another exemplary embodiment (not shown), the
flexible rod 35 includes a braided structure having two or more
strips, strands or ribbons interweaved in a diagonally overlapping
pattern.
[0121] FIG. 12A illustrates a further embodiment of a flexible
connection unit 36 having two rigid end portions 9' and an
exemplary number of spacers 37 interposed between the end portions.
In one embodiment, the rigid end portions 9' and spacers can be
made of bio-compatible metal, metal-hybrid, and/or synthetic
materials as discussed above. The connection unit 36 further
includes a flexible member or wire 32, as discussed above with
respect to FIG. 9, which traverses an axial cavity or hole (not
shown) in each of the rigid end portions 9' and spacers 37. FIG.
12B illustrates an exploded view of the connection unit 36 that
further shows how the wire 32 is inserted through longitudinal axis
holes of the rigid end portions 9' and spacers 37. As further shown
in FIG. 12B, each of the end portions 9' and spacers 37 include a
male interlocking member 38 which is configured to mate with a
female interlocking cavity (not shown) in the immediately adjacent
end portion 9' or spacer 37. FIG. 12 C illustrates an exploded side
view and indicates with dashed lines the location and configuration
of the female interlocking cavity 39 for receiving corresponding
male interlocking members 38.
[0122] FIG. 13 shows a perspective view of a flexible connection
unit 40 in accordance with another embodiment of the invention. The
connection unit 40 is similar to the connection unit 36 described
above, however, the spacers 42 are configured to have the same
shape and design as the rigid end portions 9'. Additionally, the
end portions 9' have an exit hole or groove 44 located on a lateral
side surface through which the wire 32 may exit, be pulled taut,
and clamped or secured using a metal clip (not shown) or other
known techniques. In this way, the length of the flexible
connection unit 36 or 40 may be varied at the time of surgery to
fit each patient's unique anatomical characteristics. In one
embodiment, the wire 32 may be secured using a metallic clip or
stopper (not shown). For example, a clip or stopper may include a
small tubular cylinder having an inner diameter that is slightly
larger than the diameter of the wire 32 to allow the wire 32 to
pass therethrough. After the wire 32 is pulled to a desired tension
through the tubular stopper, the stopper is compressed so as to
pinch the wire 32 contained therein. Alternatively, the wire 32 may
be pre-secured using known techniques during the manufacture of the
connection units 36, 40 having a predetermined number of spacers
37, 42 therein.
[0123] FIG. 14 depicts a spinal fixation device according to
another embodiment of the present invention. The spinal fixation
device includes: at least two securing members 2 containing an
elongate screw type shaft 10 having an external spiral thread 12,
and a coupling assembly 14. The device further includes a plate
connection unit 50, or simply "plate 50," configured to be securely
connected to the coupling parts 14 of the two securing members 2.
The plate 50 comprises two rigid connection members 51 each having
a planar surface and joined to each other by a flexible middle
portion 8. The flexible middle portion 8 may be made in accordance
with any of the embodiments described above with respect to FIGS.
4-11. Each connection member 51 contains a coupling hole 52
configured to receive therethrough a second threaded shaft 54 (FIG.
15) of the coupling assembly 14.
[0124] As shown in FIG. 15, the coupling assembly 14 of the
securing member 2 includes a bolt head 56 adjoining the top of the
first threaded shaft 10 and having a circumference or diameter
greater than the circumference of the first threaded shaft 10. The
second threaded shaft 54 extends upwardly from the bolt head 56.
The coupling assembly 14 further includes a nut 58 having an
internal screw thread configured to mate with the second threaded
shaft 54, and one or more washers 60, for clamping the connection
member 51 against the top surface of the bolt head 56, thereby
securely attaching the plate 50 to the pedicle screw 2.
[0125] FIGS. 16A and 16B illustrate two embodiments of a plate
connection unit 40 having at least two coupling members 51 and at
least one flexible portion 8 interposed between and attached to two
adjacent connection members 51. As shown in FIGS. 16A and 16B, the
flexible middle portion 8 comprises a flexible braided wire
structure 36 as described above with respect to FIG. 11. However,
the flexible portion 8 can be designed and manufactured in
accordance with any of the embodiments described above with respect
to FIGS. 4-11, or combinations thereof. FIGS. 16C and 16D
illustrate a side view and top view, respectively, of the plate 50
of FIG. 16A. The manufacture of different embodiments of the
flexible connection units 50 and 58 having different types of
flexible middle portions 8, as described above, is easily
accomplished using known metallurgical, organic polymer, natural
resin, or composite materials, and compatible manufacturing and
machining processes.
[0126] FIG. 16E illustrate a side view of a pre-bent plate
connection unit 50', in accordance with a further embodiment of the
invention. This plate connection unit 50' is similar to the plate
50 except that connection members 51' are formed or bent at an
angle .theta. from a parallel plane 53 during manufacture of the
plate connection unit 50'. As discussed above with respect to the
pre-bent rod-like connection unit 4 of FIG. 7, this pre-bent
configuration is designed to emulate and support a natural
curvature of the spine (e.g., lordosis). Additionally, or
alternatively, this pre-bent structure may offset a skew angle when
two adjacent pedicle screws are not inserted parallel to one
another, as described in further detail below with respect to FIG.
23A.
[0127] FIG. 17 illustrates a perspective view of a plate connection
unit 60 having two planar connection members 62 each having a
coupling hole 64 therein for receiving the second threaded shaft 44
of the pedicle screw 2. A flexible middle portion 8 is interposed
between the two connection members 62 and attached thereto. In one
embodiment, the flexible middle portion 8 is made in a similar
fashion to wire 32 described above with respect to FIG. 9, except
it has a rectangular configuration instead of a cylindrical or
circular configuration as shown in FIG. 9. It is understood,
however, that the flexible middle portion 8 may be made in
accordance with the design and materials of any of the embodiments
previously discussed.
[0128] FIG. 18 illustrates a perspective view of a further
embodiment of the plate 60 of FIG. 17 wherein the coupling hole 64
includes one or more nut guide grooves 66 cut into the top portion
of the connection member 62 to seat and fix the nut 58 (FIG. 15)
into the coupling hole 64. The nut guide groove 66 is configured to
receive and hold at least a portion of the nut 58 therein and
prevent lateral sliding of the nut 58 within the coupling hole 64
after the connection member 62 has been clamped to the bolt head 56
of the pedicle screw 2.
[0129] FIG. 19 illustrates a perspective view of a hybrid plate and
rod connection unit 70 having a rigid rod-like connection member 4,
9 or 9', as described above with respect to FIGS. 4-7, at one end
of the connection unit 70 and a plate-like connection member 51 or
62, as described above with respect to FIGS. 14-18, at the other
end of the connection unit 70. In one embodiment, interposed
between rod-like connection member 9 (9') and the plate-like
connection member 52 (64) is a flexible member 8. The flexible
member 8 may be designed and manufactured in accordance with any of
the embodiments discussed above with reference to FIGS. 8-13.
[0130] FIG. 20 illustrates a perspective view of a spinal fixation
device that utilizes the hybrid plate and rod connection unit 70 of
FIG. 19. As shown in FIG. 20, this fixation device utilizes two
types of securing members 2 (e.g., pedicle screws), the first
securing member 2' being configured to securely hold the plate
connection member 42 (64) as described above with respect to FIG.
15, and the second securing member 2'' being configured to securely
hold the rod connection member 4, 9 or 9', as described above with
respect to FIG. 3.
[0131] FIG. 21 illustrates a perspective top view of two spinal
fixation devices, in accordance with the embodiment illustrated in
FIG. 1, after they are attached to two adjacent vertebrae 80 and 82
to flexibly stabilize the vertebrae. FIGS. 22A and 22B illustrate
perspective top views of spinal fixation devices using the flexible
stabilizing members 50 and 58 of FIGS. 16A and 16B, respectively,
after they are attached to two or more adjacent vertebrae of the
spine.
[0132] FIG. 23A illustrates a side view of a spinal fixation device
after it has been implanted into the pedicles of two adjacent
vertebrae. As shown in this figure, the pedicle screws 2 are
mounted into the pedicle bone such that a center axis 80 of the
screws 2 are offset by an angle .theta. from a parallel plane 82
and the center axes 80 of the two screws 2 are offset by an angle
of approximately 2.theta. from each other. This type of
non-parallel insertion of the pedicle screws 2 often results due to
the limited amount of space that is available when performing
minimally invasive surgery. Additionally, the pedicle screws 2 may
have a tendency to be skewed from parallel due to a patient's
natural curvature of the spine (e.g., lordosis). Thus, due to the
non-parallel nature of how the pedicle screws 2 are ultimately
fixed to the spinal pedicle, it is desirable to offset this skew
when attaching a rod or plate connection unit to each of the
pedicle screws 2.
[0133] FIG. 23B illustrates a side view of the head of the pedicle
screw in accordance with one embodiment of the invention. The screw
2 includes a cylindrical head 84 which is similar to the
cylindrical head 16 described above with respect to FIG. 3 except
that the cylindrical head 84 includes a slanted seat 86 configured
to receive and hold a flexible rod 4 in a slanted orientation that
offsets the slant or skew .theta. of the pedicle screw 2 as
described above. The improved pedicle screw 2 further includes a
slanted stabilizing spacer 88 which is configured to securely fit
inside the cavity of the cylindrical head 84 and hold down the rod
4 at the same slant as the slanted seat 86. The pedicle screw 2
further includes an outside threaded nut 22 configured to mate with
spiral threads along the interior surface (not shown) of the
cylindrical head 84 for clamping down and securing the slanted
spacer 88 and the rod 4 to the slanted seat 86 and, hence, to the
cylindrical head 84 of the pedicle screw 2.
[0134] FIG. 23C shows a perspective view of the slanted spacer 88,
in accordance with one embodiment of the invention. The spacer 88
includes a circular middle portion 90 and two rectangular-shaped
end portions 92 extending outwardly from opposite sides of the
circular middle portion 90. FIG. 23D shows a side view of the
spacer 88 that further illustrates the slant from one end to
another to compensate or offset the skew angle .theta. of the
pedicle screw 2. FIG. 23E illustrates a top view of the cylindrical
head 84 configured to receive a rod 4 and slanted spacer 88
therein. The rod 4 is received through two openings or slots 94 in
the cylindrical walls of the cylindrical head 84, which allow the
rod 4 to enter the circular or cylindrical cavity 96 of the
cylindrical head 84 and rest on top of the slanted seat 86 formed
within the circular or cylindrical cavity 94. After the rod 4 is
positioned on the slanted seat 86, the slanted stabilizing spacer
88 is received in the cavity 96 such that the two
rectangular-shaped end portions 92 are received within the two
slots 94, thereby preventing lateral rotation of the spacer 88
within the cylindrical cavity 96. Finally, the outside threaded nut
22 and fixing cap 26 are inserted on top of the slanted spacer 88
to securely hold the spacer 88 and rod 4 within the cylindrical
head 84.
[0135] FIG. 24 illustrates a perspective view of a marking and
guidance device 100 for marking a desired location on the spinal
pedicle where a pedicle screw 2 will be inserted and guiding the
pedicle screw 2 to the marked location using a minimally invasive
surgical technique. As shown in FIG. 24, the marking device 100
includes a tubular hollow guider 52 which receives within its
hollow an inner trocar 104 having a sharp tip 105 at one end that
penetrates a patient's muscle and tissue to reach the spinal
pedicle. The inner trocar 104 further includes a trocar grip 106 at
the other end for easy insertion and removal of the trocar 104. In
one embodiment, the marking and guidance device 100 includes a
guider handle 108 to allow for easier handling of the device
100.
[0136] As shown in FIG. 25, the trocar 104 is in the form of a long
tube or cylinder having a diameter smaller than the inner diameter
of the hollow of the guider 102 so as to be inserted into the
hollow of the tubular guider 102. The trocar 104 further includes a
sharp or pointed tip 105 for penetrating the vertebral body through
the pedicle. The trocar 104 further includes a trocar grip 106
having a diameter larger than the diameter of the hollow of the
guider tube 102 in order to stop the trocar 104 from sliding
completely through the hollow. The trocar grip 106 also allows for
easier handling of the trocar 104.
[0137] FIGS. 26A and 26B provide perspective views of the marking
and guidance device 100 after it has been inserted into a patient's
back and pushed through the muscle and soft tissue to reach a
desired location on the spinal pedicle. The desired location is
determined using known techniques such as x-ray or radiographic
imaging for a relatively short duration of time. After the marking
and guidance device 100 has been inserted, prolonged exposure of
the patient to x-ray radiation is unnecessary. As shown in FIG.
26B, after the guidance tube 102 is positioned over the desired
location on the pedicle, the inner trocar 104 is removed to allow
fiducial pins (not shown) to be inserted into the hollow of the
guidance tube 102 and thereafter be fixed into the pedicle.
[0138] FIGS. 27A and 27B illustrate perspective views of two
embodiments of the fiducial pins 110 and 112, respectively. As
mentioned above, the fiducial pins 110 and 112 according to the
present invention are inserted and fixed into the spinal pedicle
after passing through the hollow guider 102. The pins 110 and 112
have a cylindrical shape with a diameter smaller than the inner
diameter of the hollow of the guider tube 102 in order to pass
through the hollow of the guider 102. An end of each fiducial pin
is a sharp point 111 configured to be easily inserted and fixed
into the spinal pedicle of the spinal column. In one embodiment, as
shown in FIG. 27B, the other end of the fiducial pin incorporates a
threaded shaft 114 which is configured to mate with an internally
threaded tube of a retriever (not shown) for extraction of the pin
112. This retriever is described in further detail below with
respect to FIG. 32.
[0139] The fiducial pins 110, 112 are preferably made of a durable
and rigid biocompatible metal (e.g., stainless steel, iron steel,
titanium, titanium alloy) for easy insertion into the pedicle bone.
In contrast to prior art guide wires, because of its comparatively
shorter length and more rigid construction, the fiducial pins 110,
112 are easily driven into the spinal pedicle without risk of
bending or structural failure. As explained above, the process of
driving in prior art guidance wires was often very difficult and
time-consuming. The insertion of the fiducial pins 110, 112 into
the entry point on the spinal pedicle is much easier and convenient
for the surgeon and, furthermore, does not hinder subsequent
procedures due to a guide wire protruding out of the patient's
back.
[0140] FIG. 28 shows a cylindrical pushing trocar 116 having a
cylindrical head 118 of larger diameter than the body of the
pushing trocar 116. The pushing trocar 116, according to the
present invention, is inserted into the hollow of the guider 102
after the fiducial pin 110 or 112 has been inserted into the hollow
of the guider 102 to drive and fix the fiducial pin 110 or 112 into
the spinal pedicle. During this pin insertion procedure, a doctor
strikes the trocar head 118 with a chisel or a hammer to drive the
fiducial pin 110 and 112 into the spinal pedicle. In preferred
embodiments, the pushing trocar 116 is in the form of a cylindrical
tube, which has a diameter smaller than the inner diameter of the
hollow of the guider tube 112. The pushing trocar 116 also includes
a cylindrical head 118 having a diameter larger than the diameter
of the pushing trocar 116 to allow the doctor to strike it with a
chisel or hammer with greater ease. Of course, in alternative
embodiments, a hammer or chisel is not necessarily required. For
example, depending on the circumstances of each case, a surgeon may
choose to push or tap the head 118 of the pushing trocar 116 with
the palm of his or her hand or other object.
[0141] FIG. 29A illustrates how a hammer or mallet 120 and the
pushing trocar 116 may be used to drive the pin 110, 112 through
the hollow of the guider tube 102 and into the designated location
of the spinal pedicle. FIG. 29B illustrates a perspective
cross-sectional view of the spinal column after two fiducial pins
110, 112 have been driven and fixed into two adjacent
vertebrae.
[0142] After the fiducial pins 110 or 112 have been inserted into
the spinal pedicle as discussed above, in one embodiment, a larger
hole or area centered around each pin 110, 112 is created to allow
easier insertion and mounting of a pedicle screw 2 into the pedicle
bone. The larger hole is created using a cannulated awl 122 as
shown in FIG. 30. The cannulated awl 122 is inserted over the
fiducial pin 110, 112 fixed at the desired position of the spinal
pedicle. The awl 122 is in the form of a cylindrical hollow tube
wherein an internal diameter of the hollow is larger than the outer
diameter of the fiducial pins 110 and 112 so that the pins 110, 112
may be inserted into the hollow of the awl 122. The awl 122 further
includes one or more sharp teeth 124 at a first end portion for
cutting and grinding tissue and bone so as to create the larger
entry point centered around the fiducial pin 110, 112 so that the
pedicle screw 2 may be more easily implanted into the spinal
pedicle. FIG. 31 illustrates a perspective cross-sectional view of
a patient's spinal column when the cannulated awl 122 is inserted
into a minimally invasive incision in the patient's back, over a
fiducial pin 110, 112 to create a larger insertion hole for a
pedicle screw 2 (not shown). As shown in FIG. 31, a retractor 130
has been inserted into the minimally invasive incision over the
surgical area and a lower tubular body of the retractor 130 is
expanded to outwardly push surrounding tissue away from the
surgical area and provide more space and a visual field for the
surgeon to operate. In order to insert the retractor 130, in one
embodiment, the minimally invasive incision is made in the
patient's back between and connecting the two entry points of the
guide tube 102 used to insert the two fiducial pins 110, 112.
Before the refractor 130 is inserted, prior expansion of the
minimally invasive incision is typically required using a series of
step dilators (not shown), each subsequent dilator having a larger
diameter than the previous dilator. After the last step dilator is
in place, the retractor 130 is inserted with its lower tubular body
in a retracted, non-expanded state. After the retractor 130 is
pushed toward the spinal pedicle to a desired depth, the lower
tubular portion is then expanded as shown in FIG. 31. The use of
step dilators and retractors are well known in the art.
[0143] After the cannulated awl 122 has created a larger insertion
hole for the pedicle screw 2, in one embodiment, the fiducial pin
110, 112 is removed. As discussed above, if the fiducial pin 112
has been used, a retrieving device 140 may be used to remove the
fiducial pin 112 before implantation of a pedicle screw 2. As shown
in FIG. 32, the retriever 140 comprises a long tubular or
cylindrical portion having an internally threaded end 142
configured to mate with the externally threaded top portion 114 of
the fiducial pin 112. After the retriever end 142 has been screwed
onto the threaded end 114, a doctor my pull the fiducial pin 112
out of the spinal pedicle. In another embodiment, if the fiducial
pin 110 without a threaded top portion has been used, appropriate
tools (e.g., specially designed needle nose pliers) may be used to
pull the pin 110 out.
[0144] In alternate embodiments, the fiducial pins 110, 112 are not
extracted from the spinal pedicle. Instead, a specially designed
pedicle screw 144 may be inserted into the spinal pedicle over the
pin 110, 112 without prior removal of the pin 110, 112. As shown in
FIG. 33, the specially designed pedicle screw 144 includes an
externally threaded shaft 10 and a coupling assembly 14 (FIG. 3)
that includes a cylindrical head 16 (FIG. 3) for receiving a
flexible rod-shaped connection unit 4 (FIGS. 4-13). Alternatively,
the coupling assembly 14 may be configured to receive a plate-like
connection unit as shown in FIGS. 14-20. The pedicle screw 144
further includes a longitudinal axial channel (not shown) inside
the threaded shaft 10 having an opening 146 at the tip of the shaft
10 and configured to receive the fiducial pin 110, 112 therein.
[0145] FIG. 34 illustrates a perspective cross-sectional view of
the patient's spinal column after a pedicle screw 2 has been
inserted into a first pedicle of the spine using an insertion
device 150. Various types of insertion devices 150 known in the art
may be used to insert the pedicle screw 2. As shown in FIG. 34,
after a first pedicle screw 2 has been implanted, the retractor 130
is adjusted and moved slightly to provide space and a visual field
for insertion of a second pedicle screw at the location of the
second fiducial pin 110, 112.
[0146] FIG. 35 provides a perspective, cross sectional view of the
patient's spinal column after two pedicle screws 2 have been
implanted in two respective adjacent pedicles of the spine, in
accordance with the present invention. After the pedicle screws 2
are in place, a flexible rod, plate or hybrid connection unit as
described above with respect to FIGS. 4-20 may be connected to the
pedicle screws to provide flexible stabilization of the spine.
Thereafter, the retractor 130 is removed and the minimally invasive
incision is closed and/or stitched.
[0147] FIG. 36A illustrates a perspective view of a flexible rod
200 for spinal fixation, in accordance with a further embodiment of
the invention. The rod 200 is configured to be secured by securing
members 2 as described above with reference to FIGS. 1-3. In
preferred embodiments, the rod 200, and rods 210, 220, 230 and 240
described below, are comprised of a solid, cylindrically-shaped rod
made of known biocompatible materials such as: stainless steel,
iron steel, titanium, titanium alloy, NITINOL, and other suitable
metal, metal-synthetic hybrid or non-metal materials or
compositions, as discussed above. As shown in FIG. 36A, spiral
grooves 202 are cut or formed along at least a portion of the
length of the cylindrical body of the rod 200. In an exemplary
embodiment, the length of the rod "l" may be between 4 and 8
centimeters (cm), and its cylindrical diameter "D" is between 4-8
millimeters (mm). The spiral grooves 202 have a width "w" between
0.1 and 0.5 mm and a spiral angle .theta. between 50 and 85 degrees
from horizontal. The distance between spiral grooves 202 can be
between 3 and 6 mm. However, as understood by those skilled in the
art, the above dimensions are exemplary only and may be varied to
achieve desired flexibility, torsion and strength characteristics
that are suitable for a particular patient or application.
[0148] FIG. 36B illustrates a cross-sectional view of the flexible
rod 200, taken along lines B-B of FIG. 36A. As shown, spiral groove
202 is cut toward the center longitudinal axis of the cylindrical
rod 200. The groove may be formed continuously in a spiral fashion,
as a helix or an interrupted helix for a solid or hollow rod, or
are as disconnected circumferential grooves for a solid rod. If
hollow rods have disconnected circumferential grooves formed in
them, the grooves can only partially penetrate the rod material to
avoid discontinuities. In one embodiment, the depth of the groove
202 is approximately equal to the cylindrical radius of the rod
200, as shown in FIG. 36B, and penetrates as deep as the center
longitudinal axis of the cylindrical rod 200. However, the cross
sectional area and shape of the rod, groove depth, groove width,
groove cross-section shape, and groove to groove spacing of the
grooved portion of the longitudinal member can be varied to adjust
mechanical and structural characteristics as desired. For example,
deepening or widening grooves increases flexibility, while
increasing groove-to-groove spacing decreases flexibility. This can
be used to modify extent of rod bending at a fixed bending force,
custom tailor the bent shape of the rod, and equalize mechanical
stresses in the rod during bending in order to minimize material
fatigue and improve rod reliability.
[0149] FIG. 37A illustrates a flexible rod 210 for spinal fixation
in accordance with another embodiment of the invention. The rod 210
includes a plurality of transverse holes or tunnels 212 drilled or
formed within the body of the rod 210. In one embodiment, the
tunnels 212 pass through a center longitudinal axis of the
cylindrical rod 210 at an angle .PHI. from horizontal. The openings
for each respective tunnel 212 are located on opposite sides of the
cylindrical wall of the rod 210 and adjacent tunnels 212 share a
common opening on one side of the cylindrical wall, forming a
zigzag pattern of interior tunnels 212 passing transversely through
the central longitudinal axis of the rod 210, as shown in FIG. 37A.
In one embodiment, the diameter D of each tunnel 212 may be varied
between 0.2 to 3 mm, depending the desired mechanical and
structural characteristics (e.g., flexibility, torsion and
strength) of the rod 210. However, it is understood that these
dimensions are exemplary and other diameters D may be desired
depending on the materials used and the desired structural and
mechanical characteristics. Similarly, the angle from horizontal
.PHI. may be varied to change the number of tunnels 212 or the
distance between adjacent tunnels 212.
[0150] FIG. 37B illustrates a cross-sectional view of the flexible
rod 210 taken along lines B-B of FIG. 37A. The tunnel 212 cuts
through the center cylindrical axis of the rod 210 such that
openings of the tunnel 212 are formed at opposite sides of the
cylindrical wall of the rod 210.
[0151] FIG. 38A illustrates a perspective view of a flexible rod
220 for spinal fixation, in accordance with a further embodiment of
the invention. Rod 220 incorporates the spiral grooves 202
described above with reference to FIGS. 36A and 36B as well as the
transverse tunnels 212 described above with respect to FIGS. 37A
and 37B. The spiral grooves 202 are cut into the surface of the
cylindrical wall of the rod 220 toward a center longitudinal axis
of the rod 220. As discussed above, the dimensions of the spiral
grooves 202 and their angle from horizontal .theta. (FIG. 36A) may
be varied in accordance with desired mechanical and structural
characteristics. Similarly, the dimensions of the transverse
tunnels 212 and their angle from horizontal .PHI. (FIG. 37A) may be
varied in accordance with desired mechanical and structural
characteristics. In one embodiment, the angles .theta. and .PHI.
are substantially similar such that the openings of the tunnels 212
substantially coincide with the spiral grooves 202 on opposite
sides of the cylindrical wall of the rod 220.
[0152] FIG. 38B shows a top view of the flexible rod 220 taken
along the perspective indicated by lines B-B of FIG. 38A. As shown
in FIG. 38B, the openings of the tunnels 212 coincide with the
spiral grooves 202. By providing both spiral grooves 202 and
transverse tunnels 212 within a solid rod 220, many desired
mechanical and structural characteristics that are suitable for
different patients, applications and levels of spinal fixation may
be achieved.
[0153] FIG. 39A illustrates a flexible rod 230 for spinal fixation,
in accordance with another embodiment of the invention. The rod 230
includes a plurality of transverse tunnels 232 formed in the body
of the rod 230. The tunnels 232 are substantially similar to the
tunnels 212 described above with respect to FIGS. 37A and 37B,
however, the tunnels 232 are not linked together in a zigzag
pattern. Rather, each tunnel 232 is substantially parallel to its
immediate adjacent tunnels 232 and the openings of one tunnel 232
do not coincide with the openings of adjacent tunnels 232. As shown
in FIG. 39A, the angle from horizontal. .PHI. in this embodiment is
approximately 90 degrees. However, it is understood that other
angles .PHI. may be incorporated in accordance with the present
invention. It is further understood that the dimensions, size and
shape of the tunnels 232 (as well as tunnels 212) may be varied to
achieve desired mechanical and structural characteristics. For
example, the cross-sectional shape of the tunnels 212 and 232 need
not be circular. Instead, for example, they may be an oval or
diamond shape, or other desired shape.
[0154] FIG. 39B illustrates a cross-sectional view of the rod 230
taken along lines B-B of FIG. 39A. As shown in FIG. 39B, the
transverse tunnel 232 travels vertically and transversely through
the center longitudinal axis of the rod 230. FIG. 39C illustrates a
cross-sectional view of a further embodiment of the rod 230,
wherein an additional transverse tunnel 232' is formed
substantially orthogonal to the first transverse tunnel 232 and
intersect the first transverse tunnel 232 at the center,
cylindrical axis point. In this way, further flexibility of the rod
230 may be provided as desired.
[0155] FIG. 40A illustrates a perspective view of a flexible rod
240, in accordance with a further embodiment of the invention. The
rod 240 includes a plurality of interleaved transverse tunnels 232
and 242 which are substantially orthogonal to each other and which
do not intersect, as shown in FIG. 40A. In another embodiment, a
cross-sectional view of which is shown in FIG. 40B, adjacent
tunnels 232 and 242 need not be orthogonal to one another. Each
tunnel 232, 242 can be offset at a desired angle .omega. from its
immediately preceding adjacent tunnel 232, 242. As can be verified
by those of skill in the art, without undue experimentation, by
varying the dimensions of the tunnels, their numbers, and their
angular directions with respect to one another, various desired
mechanical and structural characteristics for flexible rods used in
spinal fixation devices may be achieved.
[0156] Sometimes for multi-level spinal fixation procedures, as
shown in FIG. 22B for example, it may be desirable for one spinal
joint to be rigidly fixed, while an adjacent spinal joint is
dynamically (flexibly) stabilized. An embodiment of a longitudinal
member to accomplish this function is shown in FIG. 41A. Axial
portion 254 of longitudinal member 250 is grooved to provide
increased flexibility for bending, whereas axial portions 252 and
256 are not grooved and remain relatively rigid. The hole 258 is
used to terminate the groove to prevent the formation of cracks and
improve reliability. The use of such holes of expanded diameter to
terminate grooves or slots in materials is well known in the art as
a means of reducing peak mechanical stresses in materials and
reducing the likelihood of material failure.
[0157] FIG. 41B illustrates the assembly of the rod 250 of FIG. 41A
configured to be secured to a patient's spine using at least three
securing members 2 (FIG. 3) having a flexible section 254 disposed
between a first pair of securing members 2 and a non-flexible
section 252 disposed between a second pair for securing members
2.
[0158] As a further embodiment illustrated in FIG. 41C, an extended
ungrooved section 252 can accommodate a range of positions for a
single securing member 2 to be placed. In another embodiment,
extended ungrooved sections can be symmetrically disposed at either
end of a grooved section. It is appreciated that the extended
length of section 252 provides a "one size fits all" longitudinal
member 250 that can accommodate various distances between the
pedicle bones of adjacent vertebrae. As shown in FIG. 41C, the
distance between the adjacent securing members, 2 and 2', may be
adjusted by selecting the location of the securing member 2 on
section 252. Any excess length of section 252 can then be trimmed
away or removed.
[0159] Groove parameters such as groove depth, groove width, groove
cross-section shape or profile, and groove to groove spacing of the
grooved portion 254 can be uniformly constant for uniform
structural and mechanical characteristics along the axis of the
grooved portion 254. Sometimes it is advantageous to have axially
varying structural and mechanical characteristics for the
longitudinal member in order to control local mechanical stress
levels, custom tailor bending shapes, or affect resistance to
bending in all bending directions or in selected bending
directions. The cross-sectional area of a cylindrical (for example)
hollow longitudinal member can be changed by changing the outer
diameter, while maintaining constant wall thickness for the hollow
cylinder. Another embodiment is to modify the wall thickness by
adjusting the internal diameter (i.e. the diameter of the cavity
within the cylinder) while keeping the outer diameter of the hollow
cylinder constant. Still other embodiments simultaneously vary the
external diameter and the internal diameter. It is easily seen how
the above arguments also apply to longitudinal members with shapes
that are not cylindrical.
[0160] FIG. 42A illustrates a side view of a flexible, spirally
grooved stabilization device 270 in accordance with an embodiment
of the invention. The spirally grooved section 271 has an expanded
outer diameter relative to ungrooved sections 262 and 262'. Whereas
the spiral groove imparts increased flexibility to section 271, it
would also impart greater per unit area material strain to section
271 relative to ungrooved sections 262 and 262' because of reduced
cross-sectional material area in section 271, due to the presence
of the grooves, if the outer diameter of spirally grooved section
271 were the same as the outer diameter of the ungrooved sections
262 and 262'. Expanding the outer diameter of section 271 can
maintain acceptable material stress levels during the flexing of
the spirally grooved section 271 for both the spirally grooved
section 271, and the ungrooved sections 262 and 262'.
[0161] In one embodiment, if the longitudinal member of FIG. 42A is
hollow, the inner diameter of the cavity of the spirally grooved
section 271 can be the same as the inner diameter of the cavity of
the ungrooved sections 262 and 262', whereas the outer diameter of
the grooved flexible section 271 is increased to reduce material
stresses during bending and/or vary the flexibility of the grooved
section 271.
[0162] FIGS. 42A and 42B (discussed below) illustrate examples of a
longitudinal spinal stabilization device wherein a flexible section
has a different cross-sectional profile (e.g., outer diameter (in
the case of a cylindrical rod) or perimetric shape than that of
corresponding end portions of the longitudinal stabilization
device.
[0163] In a further embodiment, the cross-sectional profile (e.g.,
outer diameter) of the grooved flexible section is kept the same as
the cross-sectional profile (e.g., outer diameter) of the ungrooved
sections, whereas the inner diameter of the cavity of the grooved
flexible section is reduced relative to the inner diameters of the
cavities of the ungrooved sections. This has a similar material
stress reduction effect as described above.
[0164] In still further embodiments of the present invention, both
inner and outer diameters of the grooved flexible section can be
varied with respect to the inner and outer diameters of the
ungrooved sections to reduce material strain differences between
the sections.
[0165] FIG. 42B illustrates a side view of another embodiment of
the present invention that accomplishes variation in flexibility
along a longitudinal axis by adjusting the cylindrical diameter or
cross-sectional profile of the grooved section 266 (while
maintaining a constant inner cavity diameter for the case of a
hollow longitudinal member) in order to achieve reduced mechanical
stresses in the vicinity of transition sections 264 and 264',
between the grooved section 266 and ungrooved sections 262 and
262', respectively. The outer diameter of the grooved section 266
is smallest near a central portion of the grooved section 266 and
gradually expands toward the ungrooved sections 262. This provides
more cross-sectional material area to distribute forces through,
thereby reducing per unit area stress in the regions of the grooved
section 266 near the transition sections 264 and 264'.
[0166] In another embodiment, axial variations of groove depth,
groove width, groove cross-section shape, and groove to groove
spacing can also achieve axially variant flexibility and mechanical
characteristics, either alone or in combination with variance of
the cylindrical cross-section as discussed above. For example: (i)
tapering the groove depth from a maximum near the center of a
grooved section to near zero at a boundary with a non grooved
section (FIG. 43A); (ii) tapering the groove width from a maximum
near the center of a grooved section to near zero at a boundary
with a non grooved section (FIG. 43B); (iii) transitioning groove
shape from one permitting maximum flexure near the center of a
grooved section to a shape providing reduced flexure at a boundary
with a non grooved section (FIG. 43C); or (iv) expanding groove to
groove spacing from a minimum near the center of a grooved section
to a maximum at a boundary with a non grooved section (FIG.
43D).
[0167] FIG. 44 illustrates a longitudinal member with an elastomer
cladding 278 around the grooved section 276. In this embodiment,
elastomer cladding 278 covers only grooved section 276 and does not
cover ungrooved sections 272. Also optional tapers 274 are formed
in the longitudinal member to provide for a smooth surface
transition between clad and unclad sections. These optional tapers
274 also fixate the longitudinal position of the cladding.
Alternately the cladding may be extended onto an ungrooved section
272. The elastomer cladding may (i) contact only the surface of the
longitudinal member, (2) additionally penetrate into the grooves of
the longitudinal member, or (3) if the longitudinal member is
hollow, additionally penetrate to and at least partially fill the
inside of the longitudinal member. The elastomer cladding provides
additional control over the axial and flexural stability of the
longitudinal member, as well as providing a barrier between tissues
and the grooved section.
[0168] The elastomer cladding can consist of any of a variety of
medical grade elastomers, including, for example, silicone,
polyurethane, polycarbonateurethane and silicone-urethane
copolymers. The cladding can be applied to the longitudinal member
using a variety of techniques that are well known in the art. In
one technique, a thermoplastic or thermosetting resin can be
injected into a heated mold surrounding the desired section of the
longitudinal member, while it is affixed within a mold. An
advantage of this injection molding process is that it can
accommodate cladding material that are not of sufficiently low
viscosity for application by alternate means at room temperature
and pressure. A further advantage of injection molding is that the
shape of the exterior of the cladding is determined by the shape of
the mold that is used. Another injection molding advantage is the
reproducible penetration of groove interstices and the interior of
hollow longitudinal members. Alternative molding techniques include
compression molding and transfer molding.
[0169] Other cladding application methods include liquid injection
molding, dipping, spraying, or painting with a mechanical
applicator such as a paintbrush. These methods require that the
cladding material be applied in a low viscosity form. For an
example a resin for application could be suspended in a solvent
that evaporates after application. In another example, the cladding
material is applied in a low viscosity form and subsequently cured
through chemical, heat, or radiation methods. It is sometime useful
to mask parts of the longitudinal member where application of the
cladding material is not desired.
[0170] FIG. 45A illustrates a uniform cross-section of the flexible
section of a longitudinal member made of a material 277. FIG. 44B
illustrates a non-uniform cross-section of a rod as a flexible
section of a longitudinal member made of a material 277 that
includes a section made of another material 279. Clearly the rod of
FIG. 45A will exhibit the same bending behavior with applied force
in both the x and y directions. If the materials of sections 320
and 330 have different bending characteristics, the rod of FIG. 45B
will exhibit different bending behavior with applied force for the
x and y directions. For example, if material 279 in FIG. 45B is
stiffer than material 277, the rod will bend more easily in the x
direction than in the y direction.
[0171] FIG. 46A illustrates another embodiment of a metal hybrid
longitudinal member with an elastomer cladding 278 around a wire
portion 280 of the longitudinal member. In this embodiment,
elastomer cladding 278 surrounds a braided wire 280 between two
unclad end portions 262. The wire may also be a single wire,
multiple wires that are not braided (not shown), and may be coaxial
with the end portions 262 or positioned eccentrically with respect
to the longitudinal axis of the end portions 262 as shown in FIG.
46B. The wire portion 280 may be straight as shown in FIG. 46A or
curved, such as the wire 281 shown in FIG. 46C. A straight wire 280
between end portions 262 provides greater resistance to tension
than a curved wire 281, which straightens as the longitudinal
member elongates under tension. In one embodiment, the end portions
262 and wire 280 may be made from any desired and suitable
biocompatible metal or metal-synthetic hybrid material discussed
above with respect to rod 4 and wire 32. In further embodiments,
the cladding 278 may be made from any one or combination of
suitable biocompatible synthetic or non-metal materials discussed
above.
[0172] The stiffness of the metal hybrid longitudinal member in
FIGS. 46A-C may be modified by varying the wire configuration
within the elastomer cladding 278 as described above, or by varying
the physical geometry of the wire 280 and/or cladding 278. Those
skilled in the art will recognize that stiffness may be altered by
changing the length and/or diameter of the wire portion 280 and
cladding 278, the ratio of diameters, or the number and placement
of wires, for example.
[0173] FIG. 47A illustrates yet another embodiment of a flexible
connection unit having one or more spacers 37 between two rigid end
portions 9' with an elastomer cladding 278 covering the one or more
spacers 37. The connection unit further includes a wire 32, which
traverses a longitudinal axial channel or hole in each of the
spacers 37. In one embodiment, as shown in FIG. 47A, the spacers 37
occupy substantially all of the space between the end portions 9'
such that the plurality of spacers 37 are maintained in a
substantially fixed position along a longitudinal axis direction
between the end portions 9'. In other words, the spacers 37 do not
move or slide substantially with respect to the wire 32 in the
longitudinal direction because there is no space between the end
portions 9' to do so. Each spacer 37 abuts an adjacent spacer 37
and/or end portion 9' such that it does not have room to slide with
respect to the wire 32 or other flexible member located in the
longitudinal axial channels of the spacers 37 between the end
portions 9'. A cladding 278 is formed around each spacer 37 or
around the entire group of spacers 37. It is appreciated that the
combination of the spacer 37 and cladding 278 forms a composite or
hybrid spacer wherein the spacer 37 provides a first material of
the hybrid spacer and the cladding provides a second material of
the hybrid spacer. In one embodiment, the spacers 37 may be made
from a biocompatible metal or metal-synthetic hybrid materials, as
discussed above, and the cladding 278 may be made from any one or
combination of suitable biocompatible synthetic or non-metal
materials discussed above.
[0174] In another embodiment, the spacers 37 may be positioned
along the wire 32 such that there is room between adjacent spacers
37 and the end portions 9', as shown in FIG. 47B. A cladding 278 is
formed around the spacers 37 and the wire 32 such that
substantially all of the space between adjacent spacers 37 and the
end portions 9' is occupied by the cladding 278. Thus, the cladding
278 limits the motion of spacers 37 and the wire 32 encased therein
and provides additional rigidity to the flexible portion between
the end portions 9'. The cladding 278, spacers 37 and wire 32 may
be made from any suitable material, including those discussed above
with respect FIGS. 9, 10 and 47A, for example.
[0175] The cladding 278 in FIGS. 47A & B is shown to
encapsulate all of each of the metal-hybrid spacers 37 between the
end portions 9'. Those skilled in the art will recognize that the
stiffness of the connection unit 36 may be altered by cladding only
a portion of the spacers 37, for example the space between the
metal portion of the spacers 37 and the wire 32, or the spaces
between the spacers 37 and between the spacers 37 and the end
portions 9'.
[0176] The stiffness of the flexible connection unit described in
the various embodiments above may be altered by selecting various
biocompatible materials. For example, the spacers 37 may be made of
biocompatible metals (e.g. stainless steel, titanium, titanium
alloys, tantalum, zirconium, cobalt chromium, and alloys of such
materials). The spacers 37 may also be made from materials
comprising known rigid polymers (e.g. UHMWPE, PEEK and
polyurethane) or ceramics (e.g. alumina or zirconia).
[0177] FIG. 48 illustrates a further embodiment of a flexible
connection unit 36 having a metal spacer 37 between rigid end
portions 9', with an elastomer cladding 278 surrounding at least
part of the rigid spacer 37. The connection unit 36 further
includes a flexible wire 32 positioned axially through the spacers
37 and end portions 9', wherein the spacer 37, end portions 9' and
wire 32 are all physically separated by the elastomer cladding 278.
In such an embodiment, all elements of the flexible connection unit
can move relative to any other element under mechanical load,
restricted only by the flex, stretch and compression
characteristics of the elastomer cladding 278. Thus, the size and
shape of the elements may be selected to withstand the loads on the
human spinal column and to allow normal motion of the vertebrae to
which the connection unit is attached. The metal spacer 37 and
cladding 278 together form a metal-synthetic hybrid or composite
spacer, wherein the elastomer cladding 278 separates the metal
spacer 37 from respective rigid end portions 9' and the metal wire
32 so that they do not rub against each other, thereby minimizing
the generation of wear debris. It is a further advantage of this
embodiment that the connection unit is flexible in all directions
or degrees of freedom, and therefore will permit flexion,
extension, lateral bending and axial rotation of the spinal column
without a fixed or rigid mechanical restriction in any direction.
The elastomer cladding 278 in FIG. 48 is concentric with the
flexible wire 32. In other embodiments (not shown), the wire 32 may
be eccentrically located in the axial cavity of the spacer 37, or
multiple wires 32, may be distributed throughout the axial cavity
of the spacer 37.
[0178] The wire 32 shown in FIG. 48 is physically separated at both
ends from the end portions 9'. This may be accomplished by cladding
the wire 32 individually to create a metal-hybrid wire and
assembling it with the end portions 9' prior to cladding the spacer
37. Alternatively the metal-hybrid wire 32 may be clad by extruding
elastomer around the wire 32 or sliding it into a pre-formed
extruded elastomer prior to assembly. The latter method of
manufacturing has the advantage of allowing the wire 32 to slide
along its axis within the elastomer cladding 278, thereby
decreasing axial stiffness of the connection unit 36 relative to
its flexural and shear stiffness. Those skilled in the art will
recognize that if the flexible wire 32 is free to slide as
described herein, then the flexural and shear stiffness of the
connection unit 36 may be altered by varying the diameter of the
wire 32, with minimal change in the axial stiffness of the
connection unit 36. As known in the art, "flexural stiffness"
relates to an amount that an object may bend and "shear stiffness"
relates to an amount that an object can withstand lateral shear
forces. "Axial stiffness" relates to an amount that an object can
be stretched or compressed.
[0179] FIG. 49 illustrates a flexible connection unit identical to
FIG. 48, except that each end of the wire 32, is in contact with
the end portions 9'. In an alternate embodiment (not shown) one end
of the wire 32 may be in contact with one end portion 9', while the
opposite end of the wire 32 is separated from the other end portion
9' by cladding as described above. Contact between the wire 32 and
the end portions 9' may be sliding contact or fixed contact such as
a press fit assembly, welded assembly or brazed assembly. If both
ends of the wire 32 are in fixed contact with the end portions 9',
i.e. rigidly connected, the axial stiffness of the flexible
connection unit is increased. A fixed contact at only one end of
the wire 32, will have less effect on axial stiffness of the
connection unit.
[0180] FIGS. 48 and 49 illustrate a metal-hybrid spacer that
includes a metal spacer 37 that circumferentially surrounds an
elastomer cladding 278. Thus, the spacer 37 is primarily clad on
its inside surface. These embodiments may be easily manufactured by
holding the metal portion of the spacer 37 in place relative to the
end portions 9' in a mold, while the cladding 278 is applied. It is
a further advantage of this embodiment that the circumferentially
located spacer 37 limits the expansion and bending of the cladding
278 when the connection unit 36 is mechanically loaded. This
limiting effect results in varying stiffness of the connection unit
36, particularly in axial compression, bending and shear. Those
skilled in the art will recognize that stiffness of the connection
unit 36 may be varied by varying the inside diameter, length and
number of spacers 37.
[0181] The elastomer cladding 278 in various embodiments may be
formed by a variety of methods, including a variety of molding
techniques, extrusion, dipping and painting as described earlier.
In an alternate embodiment, the elastomer cladding 278 is molded in
place using an injection molded process and a biocompatible
thermoplastic elastomer such as polycarbonate urethane (PCU). PCU
has advantages of favorable biocompatibility, resistance to
degradation and cracking, favorable fatigue properties and good
adhesion to metal substrates in addition to its compatibility with
the injection molding process. It is understood, however, that the
cladding may be made from other suitable non-metal materials such
as those described above. In further embodiments the surface of the
spacers 37 and end portions 9' are prepared with one or more
features or surface treatments to improve the durability of
fixation of the elastomer cladding 278.
[0182] FIGS. 50A-D illustrate a variety of features for improved
fixation of the elastomer cladding 278 to the surface of any rigid
element 281. FIG. 50A illustrates an undercut cavity in the rigid
element 281 wherein the body of the cavity 282 is larger than the
neck 283, thereby capturing the elastomer cladding 278 within the
cavity 282. The cavity further includes smaller undercut grooves
283 in the wall of the cavity for interdigitation of the elastomer
cladding 278. The undercut grooves 283 and undercut cavity 282 may
be utilized independently as well. FIG. 50B illustrates an external
barb 284 on the rigid element 281 around which the elastomer
cladding 278 is molded. FIG. 50C illustrates holes 285 through the
wall of the rigid element 281 through which the elastomer cladding
278 is molded. In one embodiment, the elastomer cladding 278 covers
both the interior and exterior surfaces of the wall around the hole
285. FIG. 50D illustrates a roughened surface 281' of the rigid
element 281 at the interface with the elastomer cladding 278. The
roughened surface may be formed by a variety of methods, including
for example, grit blasting, bead blasting, plasma spraying,
chemical etching and a variety of machining techniques. Any of the
features illustrated in FIG. 50A-D may be used in combination with
each other or in combination with surface treatments such as
cleaning, passivation or chemical priming of the surface of the
rigid element 281.
[0183] FIG. 51 illustrates a further embodiment of a spacer 37 and
end portions 9' in which the spacer 37 and end portions 9' are
physically separated by the elastomer cladding 278 and are
configured such that they reinforce the elastomer cladding 278 when
the connection unit 36 is mechanically loaded. The spacer 37 and
end portions 9' include overlapping portions that physically limit
the shear displacement of the end portions 9' relative to each
other without necessarily limiting axial displacement of the end
portions 9' relative to each other. FIG. 51 is exemplary of any
number of combinations of shapes of a spacer 37 and end portions 9'
that may be used to vary stiffness of the connection unit 36 in one
or more directions. Those skilled in the art will recognize that
this objective may be accomplished with overlapping features or
simply by increasing or reducing the spacing between the rigid
spacer 37 and the end portions 9', or by adding additional spacers
(not shown) and varying the spacing between adjacent spacers.
[0184] FIG. 52 illustrates another embodiment of a connection unit
284 having two rigid end portions 285 and 286, and a middle portion
in which a flexible member 287 connects end portions 285 and 286
and traverses an axial hole in a metal-hybrid spacer 288. In one
embodiment, metal-hybrid spacer 288 is formed from at least one
metal and one elastomer material, such that the metal part of the
spacer 289 is configured to be accepted and retained by a securing
member such as a pedicle screw or laminar hook, and the elastomer
part 290 of the spacer 288 is located on opposite sides of the
metal part 289 and adjacent to respective end portions 285 and
286.
[0185] Referring to FIG. 52, when end portion 285 and metal spacer
289 are retained by respective securing members 2 (FIG. 2), for
example, and affixed to adjacent vertebrae, the connection unit 284
provides stability while simultaneously permitting motion to the
vertebrae in six degrees of freedom (i.e., x-axis, y-axis, z-axis,
pitch, roll and yaw). Although the end portions 285 and 286
substantially limit the motion of the metal-hybrid spacer 288 in
the longitudinal axial direction, the compressibility and
elasticity of the elastomer part 290 on both sides of the metal
spacer 289 allows for stabilized motion of the metal spacer 289
relative to the end portions 285 and 286 and/or flexible connecting
member 287 in each of the six degrees of freedom while also
providing a resistance and stability of motion in each of the six
degrees of freedom. Thus, in one embodiment, the connection unit
provides a greater range of dynamically stabilized motion.
Additionally, in one embodiment, the elastomer cladding 290
comprises a high-friction material that resists sliding of the
metal-hybrid spacer 288 on flexible middle portion 287, thereby
providing further resistance to movement of the metal spacer 289 in
the longitudinal axial direction. End portions 285 and 286 are
connected to respective ends of metal-hybrid spacer 288 using any
of the techniques discussed above or other known methods. End
portion 285 is configured to have sufficient length to be accepted
and retained by a pedicle screw or other type of securing member.
When the metal part 289 of the hybrid spacer 288 is coupled to and
secured to a securing member 2 (FIG. 3), for example, end portion
286 extends beyond the securing member 2 (on the side opposite the
space between the two securing members 2). Thus, end portion 286 is
configured to be short along the axis of the connection unit 284,
in order to minimize the length of the connection unit 284 that
extends beyond the securing member 2.
[0186] In another embodiment (not shown), the flexible member 287
may be located eccentric from the central longitudinal axis of the
connection unit 284. This eccentric configuration provides
different levels of stiffness, depending on the direction the
connection unit 284 is bent. This may be advantageous if it is
desired to provide a greater level of stiffness when the connection
unit 284 is flexed during spinal extension (e.g., when a patient
bends backward) and a lesser level of stiffness when the connection
unit 284 is flexed during spinal flexion (e.g. when a patient bends
forward). Additionally, or alternatively, different levels of
stiffness v. direction of bending profiles may be achieved by
applying different amounts or thicknesses of cladding 290 on one
side of the connection unit 284 than on other sides of the
connection unit 284. Additionally, different amounts and/or types
of cladding materials 290 may be applied on either side of the
spacer 289. Thus, the connection unit 284 can provide different
levels of stiffness in different directions of movement of the
spacer 289 and, hence, varying levels of stability can be provided
to different directions of movement of a vertebra secured to the
spacer 289 via a securing member 2. In these embodiments wherein
the level of stiffness of the connection unit 284 depends on the
direction of bending, appropriate markings (e.g., laser etchings,
physical features, etc.) may be placed on the connection unit 284
to indicate the proper orientation of the connection unit 284 prior
to securing the connection unit 284 to a patient's spine.
[0187] FIG. 53 illustrates the position of two connection units 284
after they have been implanted and secured to respective vertebrae
of the spine. For each connection unit 284, the metal hybrid spacer
288 is fixed to the inferior vertebra 291, and end portion 285 is
fixed to the superior vertebra 292. As shown in FIG. 53, the
connection unit 284 provides allows for flexibility that takes into
account the natural and anatomical motion of the spine. Because the
intravertebral disc 293 and facet joint 294 are closer to the
pedicle of the inferior vertebra 291 than the pedicle of the
superior vertebra 292, the flexible portion of the connection unit
284 provided by metal hybrid spacer 288, when it is secured to the
inferior vertebra 291, is located off-center at or near the level
of the natural joint in the spine, namely, the level of the
intravertebral disc 293 and the facet joints 294. This flexibility
at the level of the natural joint allows for natural and
anatomically correct motion of the spine.
[0188] Of course, if flexibility is desired at additional areas
this may be achieved by duplicating the metal-hybrid spacer 288 and
connecting member 287 at the opposite end of the connection unit
294 as shown in FIG. 54. Connection unit 295 is configured to be
retained by respective securing members attached to both spacers
288. The spacers 288 in connection unit 295 may be longer than the
spacer 288 in connection unit 284 so that variability in the
distance between vertebrae may be accommodated. In further
embodiments, the connection units described above can be extended
to stabilize two or more joints or spinal motion segments between
three or more adjacent vertebrae, and affixed to respective
vertebrae by three or more securing members (e.g., pedicle screws).
Thus, in one embodiment, a connection unit includes a plurality of
metal-hybrid spacers 288 for providing flexible stabilization to a
plurality of joints or spinal motion segments. Additionally, the
metal-hybrid spacers 288 may be alternated with rigid end portions
285 in any order or combination as needed by the surgeon. In this
way, a hybrid multi-level or multi-spine segment connection unit
may be designed, wherein each segment of the connection unit can
provide a desired level of flexibility suited for each respective
pair of inferior and superior vertebrae to be stabilized. For
example, a first section of the connection unit that stabilizes a
first pair of vertebrae may be very rigid, while a second section
of the connection unit that stabilizes a second pair of vertebrae
may be more flexible when compared to the first section. Numerous
desired combinations of sections may be achieved to create a hybrid
multi-level or multi-segment connection unit, in accordance with
the present invention.
[0189] In various embodiments, the flexible member 287 as shown in
FIGS. 52, 54 and 55 may be a solid member of rigid material, such
as a biocompatible metal, preferably the same material as end
portions 285 and 286 integrally formed with end portion 285 and
permanently fixed to end portion 286. Alternatively, connecting
member 287 may be a wire, plurality of wires, braided cable or
other structure for connecting end portions 285 and 286. It will be
clear to one skilled in the art that the structure, length and
diameter of the connecting member will affect the flexibility of
the connection unit 284. Similarly, the metal-hybrid spacer 288 may
be made of a biocompatible metal, preferably the same material as
end portions 285 and 286, and a biocompatible elastomer, for
example, silicone or polyurethane and preferably polycarbonate
urethane. The metal-hybrid spacer 288 is shown to be of
substantially the same outside diameter as the rigid end portions
285 and 286. Alternatively, the elastomer part of the spacer 290
may be smaller or larger in diameter, or may be variable in
diameter. It will be clear to one skilled in the art that the
flexibility of the connection unit 284 may be changed by the
selection of the cladding material and varying its dimensions.
[0190] The non-metal or elastomer portion 290 of the metal-hybrid
spacer 288 may be attached to the surfaces of the respective end
portions 285 and 286, the metal spacer 289 and/or the flexible
member 287 by a variety of methods including those shown in FIGS.
50A-50D. As shown in FIGS. 52-55, the elastomer cladding 290
maintains the metal spacer 289 in a substantially fixed position
with respect to the end portions 285 and 286, while allowing some
relative movement of the spacer 289 when external forces cause the
cladding to bend or compress in any direction. Thus, in one
embodiment, the flexibility of the connection unit 284 is
substantially limited by the compressibility of the elastomer part
290 of the hybrid spacer 288, which may be compressed in various
directions by the motion of the metal part 289 of the spacer 288,
when the metal part 289 is fixed to the vertebral bone by a
securing member 2.
[0191] FIG. 55 illustrates an embodiment of a connection unit 296
with a metal-hybrid spacer 297 comprised of more than two different
materials. The spacer 297 has a metal part 289 and an elastomer
part 290 as described in FIG. 52 and an additional bio-absorbable
part 298, shown external to the elastomer part 290. The
bio-absorbable part 298 of the metal-hybrid spacer is configured to
substantially extend from each end of the metal part of the spacer
289 to the nearest end of respective rigid end portions 285 and 286
and to restrict motion of the metal part 297, until bio-absorbable
part 298 is softened or degraded in the body. The bio-absorbable
part of the spacer 298 may be comprised of at least one material
selected from a group of known bio-absorbable materials consisting
of: polylactic acid, polyglycolic acid, polyglactic acid,
polydioxanone, polyglyconate, calcium sulfate, calcium phosphate
and combinations thereof. Other known bio-absorbable materials, and
even those that will be discovered in the future, may be utilized
in accordance with the present invention.
[0192] In one embodiment, the connection unit 296 can be used after
a spinal fusion procedure. In many cases, it is desirable to
rigidly secure the spine with implanted devices during the period
immediately postoperative to a fusion procedure, in order to allow
the surgically placed bone graft to heal and effectively fuse the
adjacent vertebrae together. After fusion is successfully achieved,
it is desirable to remove the implanted devices to allow the bone
graft to stabilize the spine independently. This creates load on
the graft site and healthy remodeling of the bone graft for secure
fixation long term. However, it is highly undesirable to perform a
second surgery to remove the implanted devices. The connection unit
296 in FIG. 55 initially provides a more rigid stabilization
following spinal fusion and then through a natural process the
bio-absorbable portion 298 of the connection unit 296 degrades and
becomes absorbed by the body, thereby reducing the stiffness of the
connection unit 296 and allowing the bone graft to share a greater
percentage of the load to stabilize the spine long term. The
flexible connection unit 296 therefore allows a surgeon to
transition the level of flexible stabilization from a first more
rigid state to a second less rigid state, with only one surgical
procedure. Needless to say, the elimination of a surgical procedure
is a tremendous advantage to patients both from a health standpoint
and a financial one.
[0193] The flexible connection unit 296 can be advantageously
utilized in any situation where it is desirable to provide varying
levels of stability. Additionally, the relative amount and type of
bio-absorbable material incorporated into the connection unit 298
can be varied to alter the initial stiffness of the connection unit
296 and the time required to fully absorb all of the bio-absorbable
portion(s) 298. In one embodiment, two or more different types of
bio-absorbable materials having different stiffness characteristics
and/or absorption times can be utilized to provide transitions from
multiple levels of stiffness. In a further embodiment, a connection
unit configured to stabilize multiple spine segments can
incorporate bio-absorbable materials in one or more flexible
portions of the connection unit to provide varying states of
flexibility by various flexible portions of the multi-spine segment
connection unit. Additionally, the bio-absorbable material 298 may
be applied to completely encapsulate a flexible portion (e.g., the
metal-hybrid spacer portion) of a connection unit, or simply cover
select portions of the connection unit, or fill gaps, spaces and/or
channels of the connection unit. In other words, the application of
one or more bio-absorbable materials 298 can be implemented in
various ways to achieve desired initial and final stiffness
characteristics for one or more flexible portions of a connection
unit. Additionally, it is not necessary to combine bio-absorbable
claddings 298 with non-bio-absorbable claddings 290. Thus, in one
embodiment, the elastomer cladding 290 of the connection unit 296
illustrated in FIG. 55 may be omitted altogether or replaced by the
bio-absorbable cladding 298, or another bio-absorbable cladding
(not shown) having different stiffness and/or
degradation/absorption characteristics.
[0194] FIG. 56 is an exploded view illustrating several features of
a connection unit 300 in accordance with one embodiment of the
present invention. The connection unit 300 has first and second end
portions 301 and 302 and a middle portion 304 in which a flexible
member 306 connects end portions 301 and 302 and traverses an axial
hole in a collar 308 and an axial hole in a metal-hybrid spacer
310. The second end portion 302 is also referred to in this
disclosure from time to time as the end cap 302. The flexible
member 306 can be formed integrally with the first end portion 301,
so that the first end portion 301 and a flexible member 306 are a
rod-like element. In an alternative embodiment, the first end
portion 301 and the flexible member 306 can be formed as two
separate elements and secured together using any number of
different securing methods, such as by use of adhesives, machine
threads, welding, laser welding, press fitting, morse taper, or any
other suitable method of securing presently known or that will be
known in the future.
[0195] The first end portion 301 and the flexible member 306 may be
designed in a number of different ways for providing a desired
stability to a patient's back, for example, substantially equal to
that of a normal back. As is appreciated, varying the physical
characteristics of the first end portion 301 and flexible member
306, such as respective sizes and material composition, can change
the flexibility characteristics of the connection unit 300. For
example, the first end portion 301 of the connection unit 300, as
shown in FIG. 56, has a larger diameter than the flexible member
306. However, the dimensions need not be so limited, as other
embodiments can have other dimensions such having the first end
portion 301 and flexible member 306 with the same diameter or the
flexible member 306 having a larger diameter than the first end
portion 301. The first end portion 301 can also be rigid,
semi-rigid or flexible. In one embodiment, the first end portion
301 is flexible, but less flexible than the flexible member 306. In
addition, the first end portion 301 and the flexile member can be
made of the same type of material or each can be made of different
materials. In one embodiment, the first end portion 301 and
flexible member 306 can be made of any suitable biocompatible
metal, metal-hybrid or synthetic material discussed above with
respect to the end portion 285 and flexible middle portion 287
described with reference to FIG. 52. It is also understood that the
first end portion 301 and the flexible member 306 can be made in
accordance with the design and material specifications of any of
the embodiments previously discussed.
[0196] Further to FIG. 56, a transition area 312 can be provided
where first end portion 301 and the flexible member 306 connect.
The transition area 312 can be tapered or stepped so that the
change in diameter between the first end portion 301 and the
flexible member 306 is gradual. This can reduce or eliminate stress
points caused by a sudden change in diameter, as is understood by
those skilled in the art. Thus, the transition area 312 can provide
further strength to the device by, for example, reducing the stress
associated with a change in diameter between the first end portion
301 and the flexible portion. In one embodiment, the transition
area 312 is integral with the first end portion 301 and the
flexible member 306 and is made of the same material as the first
end portion 301 and the flexible member 306.
[0197] With reference to FIG. 57, which shows the connection unit
300 of FIG. 56 in an assembled state, the collar 308 can be
positioned between the first end portion 301 and the metal-hybrid
spacer 310 and over some or all of the transition area 312 (FIG.
56). The collar 308 can provide an even surface for an end of the
metal-hybrid spacer 310 to abut against; as opposed to the spacer
310 contacting the transition area 312, which can provide an uneven
contact surface. In one embodiment, the collar 308 is made of the
same type of material as the first end portion 301 and the flexible
member 306 discussed above, but may comprise a different type of
material in other embodiments. Moreover, the collar 308 can be
secured to the first end portion 301 or the collar 308 can be
separate and "float" between the first end portion 301 and the
spacer 310. If secured, the collar 308 can be secured to the first
end portion 301 using any number of different securing methods,
such as by use of adhesives, machine threads, welding, laser
welding, press fitting, morse taper, or any other suitable method
of securing presently known or known in the future.
[0198] Further to FIG. 56, the metal-hybrid spacer 310 can be
similar to the metal-hybrid spacer 310 of FIG. 52. The metal-hybrid
spacer 310 can include at least one metal ring element 314 and at
least one resilient element or portion 316. As best seen in the
cross-sectional view of the spacer 310 shown in FIG. 58, the
resilient element 316 can comprise multiple sections: a first
bumper section 318 located on one side of the metal ring element
314, a second bumper section 320 located on the other side of the
metal ring element 314, and an internal bumper section 322 located
between the first and second bumpers 318 and 320 and substantially
or completely inside the core of the metal ring element 314. In one
embodiment, each of the bumper sections 318, 320 and 322 is formed
integral with one another. However, in other embodiments, the
bumper sections 318, 320 and 322 can be non-integral or separate.
In alternative embodiments, the resilient element 316 can comprise
more that three bumper sections or fewer than three bumper sections
for providing desired flexibility characteristics to the connection
unit 300.
[0199] The resilient element 316 can consist of any of a variety of
medical grade elastomers, including, for example, silicone,
polyurethane, polycarbonateurethane and silicone-urethane
copolymers. It is understood that the resilient element 316 can be
made from other suitable non-metal materials such as those
described above. In alternative embodiments, the resilient element
316 may be implemented as a helical metal spring, disc spring, wave
spring or other resilient structures. The resilient element 316 can
be formed on the sides of and within the core of the metal ring
element 314 using a variety of techniques that are well known in
the art. In one technique, a thermoplastic or thermosetting resin
can be injected into a heated mold, while the metal ring element
314 is affixed within a mold. An advantage of this injection
molding process is that it can accommodate elastomer materials that
are not of sufficiently low viscosity for application by alternate
means at room temperature and pressure. As is understood, the mold
can be shaped to form the hollow axial core of the spacer 310, or
the hollow axial core can be formed by cutting out elastomer after
the molding process is finished. A further advantage of injection
molding is that the shape of the exterior of the cladding is
determined by the shape of the mold that is used. Alternative
molding techniques include compression molding and transfer
molding.
[0200] In accordance with one embodiment, the stiffness of one of
the bumper sections 318, 320 or 322 can be different from one or
more of the other bumper sections 318, 320 or 322. Specifically,
the stiffness of each bumper can be independently tuned by
adjusting the physical properties of the bumper. For example, as is
appreciated by those skilled in the art, the stiffness can be
modified by changing the length, diameter, ratio of diameters,
placement and material composition of one or more of the bumper
sections. Additionally, the resistance provided by bumper regions
may be adjusted by changing the length of the spacing provided for
the resilient element between the first and second ends of the
connection unit, thereby compressively biasing the resilient
element. In one embodiment, the length of the spacing provided
between the first and second ends may be adjusted by selecting a
collar 308 of desired dimensions. Other techniques for adjusting
this length would be readily apparent to those of skill in the
art.
[0201] Deformation zones can also be provided for controlling the
deformation of the resilient element 316. Deformations zones can
have the desired effect of providing a more predictive and
consistent response to compressive forces. For example, because
most buckling of an resilient element 316 having deformation zones
occurs at the deformation zones, it can be easier to predict the
resilient element's 316 response. In contrast, an absence of
deformation zones can result in deformation at any number of
different locations about the elastomer portion 316. For example, a
resilient element 316 not having a defined deformation zone may
buckle at one location in response to a compressive force that is
applied a first time, but buckle at a different, second location
when the exact same compressive force is applied a second time. As
is appreciated by those skilled in the art, buckling at different
locations can provide different responses to the same compressive
force. Consequently, it can be difficult to predict the response of
an elastomer portion that does not have predefined deformation
zones.
[0202] In one embodiment of the present invention, predefined
deformation zones are formed by contouring the shape of the
resilient element 316 so that it buckles at the predefined
deformation zones. In the embodiment shown in FIG. 58, the first
bumper 318 is contoured to have a reduced diameter its center,
thereby defining a first predefined deformation zone 324, and the
second bumper is contoured to have a reduced diameter its center,
thereby defining a second predefined deformation zone 326.
Accordingly, the resilient element 316 is configured to buckle at
the first deformation zone 324 when ring element 314 translates in,
for example, a longitudinal axial direction toward the first
deformation zone 324, and buckle at the second deformation zone 326
when the ring element 314 translates in, for example, a
longitudinal axial direction toward the second deformation zone
326.
[0203] Similar to the metal part 289 referenced in FIG. 52, the
metal ring element 314 can be configured to be accepted and
retained by a securing member such as the securing member 2
described with reference to FIG. 3. To help properly position the
ring element 314 in a securing member, shoulders 328a and 328b can
be provided at respective ends of the ring element 314, as best
seen in FIGS. 57 and 58. For example, positioning the head 16 (FIG.
3) of the securing member 2 between the shoulders 328a and 328b can
provide assurance that the ring element 314 is positioned correctly
in the securing member 2.
[0204] In one embodiment, the shoulders 328a and 328b may also be
sized so that a fastening member, such as the threaded nut 22 or
the cap member 26 of FIG. 3, cannot be fastened to a screw mount,
such as head 16 of FIG. 3, if the shoulders 328a and 328b are not
positioned properly. For example, the shoulders 328a and 328b may
be required to be positioned on either side of the screw head 16;
otherwise, if one of the shoulders 328a or 328b is inside the screw
head 16, then the nut 22 cannot be properly inserted into the head
16 because the shoulder 328 extends at least partially into the
area of the head 16 configured to receive the nut 22. As a result,
a person securing the ring element 314 to the securing member 2
should realize that the ring element 314 is not positioned properly
in the head 16 if the nut 22 cannot be properly fastened to the
securing member 2. Thus, if unable to fasten the nut 22, the person
installing the connection unit 300 should reposition the ring
element 314 within the head 16.
[0205] With further reference to FIG. 58, in particular the
magnified view of the spacer 310, the interior edges of the ring
element 314 may be trumpeted. As used herein, the term trumpeted
can be defined as rounded out or flared. In one embodiment, the
inner diameter of the ring element 314 is substantially constant in
the center portion of the metal ring element 314, but increases
(i.e., is trumpeted) near the ends of the ring element 314. In a
further embodiment, the inner diameter is smallest at the center
and gradually increases toward the ends of the ring element 314 so
that the longitudinal cross-sectional shape of the interior surface
of the ring element 314 has a constant radius of curvature.
[0206] Trumpeting the ends of the ring element 314 can provide
several benefits. First, trumpeting the ends can provide more
surface area between the ring element 314 and the resilient element
316 than if the inner surface of the ring element 314 had, for
example, sharp corners at the edges. The additional surface area
can result in less contact stress, which can reduce the likelihood
of the ring element 314 cutting the resilient element 316,
especially at the edges of the ring element 314. Trumpeting the
ends can also facilitate toggling rotation of the ring element 314.
Toggling rotation permits a more natural motion of the spine, and
is discussed in more detail below.
[0207] FIGS. 59a and 59b depict a further embodiment of a ring
element 414 in accordance with the present invention. FIG. 59a is a
perspective view of the ring element 414 and FIG. 59b is a front
cross-sectional view of the ring element 414. As shown, the ring
element 414 is similar to the ring element 314 shown in FIGS.
56-58, except that the ring element 414 has a generally D-like
cross-sectional shape. The ring element 414 is referred to in this
disclosure from time to time as a "D-ring." Also, similar to the
ring element 314, the D-ring 414 can have trumpeted ends 330 as
well as shoulders 328a, 328b. It is believed that the
cross-sectional shape of the D-ring 414 can distribute a
compressive load resulting from a locking cap (e.g. nut 22 of FIG.
3) compressing down onto a flat top surface 332 of the ring 414
better than most other configurations. The D-ring's 414 ability to
better distribute this type of compressive load can reduce or
altogether avoid localized buckling, thereby enabling higher
locking torques and the use of thinner ring walls.
[0208] Referring back to FIG. 56, the end cap 302 is fastened to an
end of the flexible member 306 and retains the collar 308 and the
spacer 310 between the first end 301 and the end cap 302. In one
embodiment, the end cap 302 has an axial core with internal threads
(not shown). The end cap 302 can be secured to the flexible member
306 by threading the internal threads with corresponding external
threads 334 located at an end of the flexible member 306. Once
threaded together, an outside seam (not shown) between the flexible
member 306 and the end cap 302 can be laser welded to further
secure the end cap 302 to the flexible member 306. In other
embodiments, the end cap 302 may be secured to the first end
portion 301 using any number of different securing methods,
including but not limited to press fitting, use of adhesives,
swaging and morse taper.
[0209] With reference to FIG. 56, a shoulder 336 can be formed on
the flexible member 306 for preventing the end cap 302 from
traveling along the longitudinal axis of the flexible member 306
past a predetermined distance when being secured to the flexible
member 306. Advantageously, the predetermined distance can be
associated with a desired preload on the spacer 310. This is
because when assembling the connection unit 300, the resilient
element 316 of the spacer 310 may be compressed to some extent
after the end cap 302 is attached. This may happen, for example, if
the spacer 310 in its uncompressed state has a longitudinal length
that is longer than the length between the collar 308 and the end
cap 302. Accordingly, the amount the spacer 310 is compressed after
the end cap 302 is attached can correspond to a preload amount.
[0210] In one embodiment, the spacer 310 having a preload provides
a first level of resistance to a longitudinal movement of the metal
ring 314 until the preload is overcome. Once the preload is
overcome, the spacer 310 provides a second level of resistance,
which is less than the first level of resistance. Because it is
believed that most people dealing with spine pain typically feel
most the their pain during an initial range of motion of the spine,
but do not feel as much pain after the initial range of motion, the
spacer 310 can be configured with a preload that provides more
support (e.g. more resistance) during the initial, painful range of
motion and less support (e.g. less resistance) after the initial
range of motion.
[0211] As described above, in one embodiment, the spacer 310 is not
affixed to the collar 308, end cap 302 or of flexible member 306
and, therefore, can separate from the end cap 302 or collar 308
after a preload associated with the spacer 310 has been overcome.
Accordingly, in this embodiment, the spacer 310 only resists
compression and does not resist motion by tension or elongation. By
configuring the spacer 310 to resist compression only, it is
believed that the connection unit 300 can provide better dynamic
support during motion of the spine.
[0212] Referring to FIG. 57, when end portion 301 and spacer 310
are retained by respective securing members 2 (FIG. 2), for
example, and affixed to adjacent vertebrae, the connection unit 300
provides stability while simultaneously permitting motion to the
vertebrae in six degrees of freedom (i.e., x-axis, y-axis, z-axis,
pitch, roll and yaw). Movement of the metal ring element 314 in a
pitch, roll, yaw or combination thereof may also be referred to in
this disclosure as a "toggling" motion. Although the end portions
301 and 302 substantially limit the motion of the spacer 310 in the
longitudinal axial direction, the compressibility and elasticity of
the resilient element 316 on both sides of the metal ring element
314 and between the metal ring element 314 and the flexible member
306 allows for stabilized motion of the metal ring element 314
relative to the end portions 301 and 302 and/or flexible member 306
in each of the six degrees of freedom while also providing a
resistance and stability of motion in each of the six degrees of
freedom. Thus, in one embodiment, the connection unit 300 provides
a greater range of dynamically stabilized motion. Additionally, in
one embodiment, the resilient element 316 permits sliding of the
metal-hybrid spacer 310 on flexible member 306, thereby providing
further movement of the metal ring element 314 in the longitudinal
axial direction. In one embodiment, the metal hybrid spacer 310
floats between end portions 301 and 302 (i.e. the spacer 310 is not
affixed to respective ends portions 301 and 302 or collar 308) so
that the metal-hybrid spacer 310 can be physically separated from
the end cap 302 or collar 308 in response to a sufficient
longitudinal axial force.
[0213] FIG. 60 illustrates an alternative embodiment of a
connection unit 500 in accordance with the present invention.
Connection unit 500 is similar to connection unit 300 of FIG. 56,
except that the spacer 310 is comprised of single resilient element
510 rather than the metal-hybrid spacer 310 shown in FIG. 56. In
this embodiment, the single resilient element 510 is configured to
be directly received within a correspondingly shaped securing head
of a bone securing member (e.g., ring-shaped head of a pedicle
screw). Thus, the securing head of the bone securing member assumes
the functionality of the ring element 314 of the metal-hybrid
spacer. When the resilient element 510 is received within and
secured to the securing head of a bone securing member, the
resilient element 510 functions to provide dynamic resistance
against relative motion of the bone securing member in at least
five degrees of freedom, excluding rotation about a longitudinal
axis of the connection unit. In an alternative embodiment, the
resilient element 510 provides sufficient friction against the
flexible member 306 located within the axial channel of the
resilient element 510 so as to provide resistance to motion of the
bone securing member in all six degrees of freedom.
[0214] FIG. 61 is a perspective view of a flexible connection unit
600, in accordance with another embodiment of the invention.
Connection unit 600 is similar to connection units 300 and 500 of
FIGS. 56 and 60, respectively, except that the spacer 610 of
connection unit 600 includes a ring element 612 interposed between
resilient spring elements 614 and 616. The ring element 612 is
configured to be engaged with a securing head of a bone securing
member (e.g., pedicle screw) and the resilient spring elements 614
and 616 provide resistance to longitudinal movement (e.g., sliding)
of the ring element 612 along a longitudinal axis of the flexible
element 306 (FIG. 56). As shown in FIG. 61, the spacer 610 is
positioned between a first end 301 and a second end 302, comprising
end cap 302, as described above. A collar 308 is interposed between
the spacer 610 and the first end 301. As discussed above, the
collar 308 can provide an even surface for an end of the
metal-hybrid spacer 310 to abut against; as opposed to the spacer
310 contacting a transition area 312 (FIG. 56), which can provide
an uneven contact surface.
[0215] Various embodiments of the connection units discussed in
this disclosure can have several other advantages. First, some of
the embodiments have a similar profile to conventional spinal
fixation devices consisting of a metal rod secured to vertebrae via
securing members. Because embodiments of connection units in
accordance with the present invention can have a similar profile to
a metal rod, the embodiments disclosed herein can have the
advantage of being installed using conventional spinal fixation
instrumentation. Furthermore, the low profile associated with many
of the connection unit embodiments occupies less room in the
patient, thereby resulting in less interference with the patient's
range of motion, among other things.
[0216] Various embodiments of the invention have been described
above. However, those of ordinary skill in the art will appreciate
that the above descriptions of the preferred embodiments are
exemplary only and that the invention may be practiced with
modifications or variations of the devices and techniques disclosed
above. Those of ordinary skill in the art will know, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments of the invention described
herein. Such modifications, variations and equivalents are
contemplated to be within the spirit and scope of the present
invention as set forth in the claims below.
* * * * *