U.S. patent application number 13/709864 was filed with the patent office on 2013-06-27 for static compression device.
This patent application is currently assigned to IB MEDICAL, LLC. The applicant listed for this patent is IB MEDICAL, LLC. Invention is credited to Theodore P. Bertele, Zaki G. Ibrahim.
Application Number | 20130165934 13/709864 |
Document ID | / |
Family ID | 38655977 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130165934 |
Kind Code |
A1 |
Ibrahim; Zaki G. ; et
al. |
June 27, 2013 |
Static Compression Device
Abstract
A device for compressing two or more adjacent bones includes a
male plate attachable to a first one bones and having a central
protrusion extending away from the male plate along a longitudinal
axis, a female plate attachable to a second one of the bones and
having a channel substantially parallel to the longitudinal axis
and adapted to conformally receive the central protrusion when the
plates are aligned, and a locking mechanism configured to: hold the
male plate and the female plate together when the plates are
aligned; allow the male plate and the female plate to move with
respect to each other under compression along the longitudinal axis
when the protrusion is engaged with the channel; and prevent
movement of the male plate with respect to the female plate when a
desired, measurable amount of force is applied to the first bone
with respect to the second bone.
Inventors: |
Ibrahim; Zaki G.; (Greenwood
Village, CO) ; Bertele; Theodore P.; (Longmont,
CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IB MEDICAL, LLC; |
Longmont |
CO |
US |
|
|
Assignee: |
IB MEDICAL, LLC
Longmont
CO
|
Family ID: |
38655977 |
Appl. No.: |
13/709864 |
Filed: |
December 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12522147 |
Jul 2, 2009 |
8328853 |
|
|
PCT/US07/06830 |
Mar 20, 2007 |
|
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13709864 |
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Current U.S.
Class: |
606/71 |
Current CPC
Class: |
A61B 17/8023 20130101;
A61B 17/7059 20130101; A61B 17/8019 20130101; A61B 17/8042
20130101; A61B 17/8004 20130101; A61B 2090/064 20160201; A61B
2017/564 20130101 |
Class at
Publication: |
606/71 |
International
Class: |
A61B 17/80 20060101
A61B017/80 |
Claims
1. A device for compressing two or more adjacent bones, comprising:
a male plate having a central protrusion extending away from the
male plate along a longitudinal axis, the male plate being
attachable to a first one of the two or more adjacent bones; a
female plate having a channel substantially parallel to the
longitudinal axis, the channel being adapted to conformally receive
the central protrusion when the male plate is aligned with the
female plate, and the female plate being attachable to a second one
of the two or more adjacent bones; a locking mechanism configured
to: (a) hold the male plate and the female plate together when the
male plate is aligned with the female plate; (b) allow the male
plate and the female plate to move with respect to each other under
compression along the longitudinal axis when the protrusion is
engaged with the channel; and (c) prevent movement of the male
plate with respect to the female plate when a desired, measurable
amount of force is applied to the first adjacent bone with respect
to the second adjacent bone.
Description
RELATED APPLICATION
[0001] This application is a Continuation of application Ser. No.
12/522,147, filed Jul. 2, 2009 which is a US 371 National Stage
Entry of PCT/US07/06830 filed Mar. 20, 2007 which claims the
benefit of priority from Provisional Application Ser. No.
60/788,607 filed Apr. 3, 2006. Each of the aforementioned
applications is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is directed to devices and methods to
compress two or more adjacent vertebrae across an adjacent bone
graft to facilitate fusion of these vertebrae to treat pain
produced by pressure from the disks between such vertebrae bulging
and resulting in contact with and pressure on the spinal cord and
adjacent nerve roots.
[0004] 2. Description of Related Art
[0005] For nearly half a century, anterior cervical discectomy and
fusion has been performed for individuals complaining of
intractable upper extremity pain due to cervical disc herniation or
bone spurs at single or multiple levels. This procedure has
undergone several significant modifications since its inception.
The introduction of the Smith-Robinson technique of using
tricortical iliac crest bone graft, the technique of denuding
vertebral endplates of cartilage described by Zdeblick et al., and
the present use of cervical plates have all represented significant
technical advances which have increased fusion rates and improved
patient outcomes. Currently it is possible to expect greater than
85% good or excellent outcomes for individuals with appropriate
indications who undergo this surgical procedure.
[0006] However, several problems remain. Although fusion rates for
one level anterior cervical fusion with autograft (patient's own
bone) may approach 95%, these rates decrease significantly for each
additional level incorporated in the fusion. Additionally, using
autograft bone typically involves the use of a second incision,
which significantly increases patient morbidity. Allograft bone
(bone from another human) is a viable option, but has considerably
lower fusion rates than autograft and is generally not considered a
good choice in multiple level fusion surgery.
[0007] The use of anterior cervical plates has been credited with
increasing fusion rates in multiple level fusions. It is thought
that the immediate stability provided by the plate provides a more
favorable environment for fusion to occur. The vast majority of
plates on the market provide for static stabilization of the
vertebral body-graft construct (no compression, no dynamization).
More recently dynamic plates have been introduced. These plates
provide for passive dynamic compression of the vertebral body-graft
construct. This compression occurs post-operatively when the weight
of the patient's head loads the construct, allowing for passive
compression of the graft to occur. Wolff s law (the concept that
bone heals best under compression) suggests that the use of dynamic
compression plates should lead to increased fusion rates. However,
this has not been found to be the case. Several studies have
indicated that dynamic compression plates do not lead to higher
fusion rates than static plates. In addition, the possibility of
uncontrolled settling over time which may lead to kyphosis
(reversal of the normal curvature of the neck) has caused these
plates to fall out of favor with many surgeons.
[0008] Wolff s law is a well-accepted orthopedic principle,
championed and reported in the trauma literature by the Swiss AO
Foundation, a non-profit surgeon-driven organization dedicated to
progress in research, development, and education in the field of
trauma and corrective surgery. Several studies have shown that long
bones heal best under rigid compression. This has led to the
development of special compression plates that are currently widely
used in surgical techniques of open reduction and internal fixation
of fractures.
[0009] It is believed that there is no plate on the market that
truly invokes Wolff s law in spinal fusion surgery by providing
rigid static loading of the graft-vertebral body construct.
Mechanisms for achieving compression on adjacent vertebrae are
known. But, most of these devices either utilize compression across
individual screws (risking cut out due to lessened surface area) or
attempt to achieve compression prior to the plate being applied
(making this a cumbersome technique).
SUMMARY OF THE INVENTION
[0010] The Static Compression Device (SC device) of the present
invention allows for active, measurable compression of a fusion
graft by the surgeon at the time of surgery. The SC device is
attachable to adjacent vertebral bodies or other pieces of bone and
has a device that applies compressive force to the adjacent
vertebral bodies or other pieces of bone to assist fusion according
to Wolff s law. The SC device has a locking mechanism that
maintains the compression applied at surgery, but prevents further
compression (settling) from occurring after surgery. So, the SC
device allows the surgeon the ability to compress a segment or
other adjacent pieces of bone, measure the applied compression, and
to lock the segment or pieces of bone in the compressed position.
In one embodiment of the invention, the pressure is applied to the
SC device through a compression device that applies a desired and
measurable amount of force. In this embodiment, the combination of
the SC device with a pressure applying and measuring device allows
the surgeon more control over the force applied to a cervical,
lumbar or thoracic implant or implant applied to other pieces of
bone than has previously been available.
[0011] The SC device of the present invention in one embodiment
compresses two or more adjacent vertebrae across an adjacent bone
graft to facilitate fusion of these vertebrae to treat pain
produced by pressure from the disks between such vertebrae,
adjacent bone spurs or both bulging and resulting in contact with
and pressure on the spinal cord and adjacent nerve roots or any
other disorder of the spine. The vertebrae may be in the cervical,
thoracic or lumbar spine. In fact, in various embodiments, the SC
device may be used to apply measurable compression across any type
of bony interface (e.g. fractures) to facilitate union.
[0012] The SC device has four unique characteristics which together
provide for static compression of the vertebral body-graft
interface: [0012] The use of fixed angle screws to secure the SC
device to the vertebral bodies; [0013] The use of a compression
device to apply and measure the pressure applied to the vertebral
bodies by the SC device; [0014] The technique of using active,
static compression to assist the fusion process; and [0015] The use
of a locking mechanism that maintains compression during the fusion
process to facilitate bone growth. This SC device differs from
currently known static plates by providing controlled loading
(compression) of the graft at the time of surgery. The SC device
also differs from currently known dynamic plates in that the
compression achieved is "static" (rigid) and prevents further
"dynamic" settling from occurring after the procedure is completed.
The resulting major advantage of the SC device over previously
known devices is that the SC device may significantly increase
fusion rates (especially in multiple level cervical fusion) and
maintain the anatomy of the cervical spine (preventing excessive
compression leading to kyphosis). In fact, it is believed that
using the SC device to provide static loading at each level in
multiple level fusions may allow the use of allograft bone to
approach fusion rates now only attainable by using autograft
techniques.
[0013] The invention will be described hereafter in detail with
particular reference to the drawings. Throughout this description,
like elements, in whatever embodiment described, refer to common
elements wherever referred to and referenced by the same reference
number. The characteristics, attributes, functions, interrelations
ascribed to a particular element in one location apply to that
element when referred to by the same reference number in another
location unless specifically stated otherwise.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a perspective view of one embodiment of the static
compression device of the present invention.
[0015] FIG. 2 is a top view of the static compression device of
FIG. 1.
[0016] FIG. 3 is a bottom view of the static compression device of
FIG. 1.
[0017] FIG. 4 is a side view of the static compression device of
FIG. 1.
[0018] FIG. 5 is a bottom end view of the static compression device
of FIG. 1.
[0019] FIG. 6 is a perspective view of the male plate of the static
compression device of FIG. 1.
[0020] FIG. 7 is a side view of the male plate of the static
compression device of FIG. 1.
[0021] FIG. 8 is a top view of the male plate of the static
compression device of FIG. 1.
[0022] FIG. 9 is a bottom end view of the male plate of the static
compression device of FIG. 1.
[0023] FIG. 10 is a perspective view of the female plate of the
static compression device of FIG. 1.
[0024] FIG. 11 is an end view of the female plate of the static
compression device of FIG. 1.
[0025] FIG. 12 is a bottom view of the female plate of the static
compression device of FIG. 1.
[0026] FIG. 13 is a perspective view of the interconnecting plate
of the static compression device of FIG. 1
[0027] FIG. 14 is a top view of the interconnecting plate of the
static compression device of FIG. 1.
[0028] FIG. 15 is a perspective view of the static compression
device of FIG. 1 in an embodiment without the interconnecting
plate.
[0029] FIG. 16 is a perspective view of the static compression
device of FIG. 15 in an unlocked configuration.
[0030] FIG. 17 is a perspective view of the static compression
device of FIG. 15 in a locked configuration.
[0031] FIG. 18 is a perspective view of the locking clamp of the
static compression device of FIGS. 1 and 15.
[0032] FIG. 19 is a side view of the locking screw of the static
compression device of FIG. 1.
[0033] FIG. 20 is a perspective view of one embodiment of the
compression tool of the present invention.
[0034] FIG. 21 is a perspective view of the embodiment of the
compression tool of FIG. 20 from the opposite side of the view of
FIG. 20.
[0035] FIG. 22 is a perspective view of the preferred embodiment of
the compression tool of the present invention with cannula for
receiving a screwdriver.
[0036] FIG. 23 is a close up perspective view of the distal end of
the compression tools of the present invention.
[0037] FIG. 24 is a perspective view of another embodiment of the
compression tool of the present invention.
[0038] FIG. 25 is a side view of the embodiment of the compression
tool of FIG. 24.
[0039] FIG. 26 is an exploded perspective view of the turnbuckle of
the embodiment of the compression tool of FIG. 24.
[0040] FIG. 27 is an exploded perspective view of the compression
tool of FIG. 24.
[0041] FIG. 28 is a perspective view of an embodiment of the static
compression device of the present invention.
[0042] FIG. 29 is a perspective view of the static compression
device of FIG. 28 without the locking screw in place.
[0043] FIG. 30 is a side view of the locking screw of the static
compression device of FIG. 28.
[0044] FIG. 31 is a cross-sectional perspective view of the static
compression device of FIG. 28 without the locking screw in
place.
[0045] FIG. 32 is a perspective view of the static compression
device of FIG. 28 without an alternate embodiment of the locking
screw in place.
[0046] FIG. 33 is a perspective view of an alternate embodiment of
the static compression device.
[0047] FIG. 34 is an end view of the female plate of the static
compression device of FIG. 33 with the locking screw and cam in
place.
[0048] FIG. 35 is a perspective view of the locking screw and cam
of the static compression device of FIG. 33.
[0049] FIG. 36 is a perspective view of one embodiment of the
static compression device of the present invention.
[0050] FIG. 37 is a top view of the static compression device of
FIG. 36.
[0051] FIG. 38 is a bottom view of the static compression device of
FIG. 36.
[0052] FIG. 39 is a side view of the static compression device of
FIG. 36.
[0053] FIG. 40 is a bottom end view of the static compression
device of FIG. 36.
[0054] FIG. 41 is a top end view of the static compression device
of FIG. 36.
[0055] FIG. 42 is a perspective view of the male plate of the
static compression device of FIG. 36.
[0056] FIG. 43 is a side view of the male plate of the static
compression device of FIG. 36.
[0057] FIG. 44 is a bottom view of the male plate of the static
compression device of FIG. 36.
[0058] FIG. 45 is a perspective view of the female plate of the
static compression device of FIG. 36.
[0059] FIG. 46 is an end view of the female plate of the static
compression device of FIG. 36.
[0060] FIG. 47 is a bottom view of the female plate of the static
compression device of FIG. 36.
[0061] FIG. 48 is a perspective view of the male plate and female
plate of the static compression device of FIG. 36 in an
interconnected relationship.
[0062] FIG. 49 is a perspective view of the male plate and female
plate of the static compression device of FIG. 36 in an
interconnected relationship and with the locking plate in
place.
[0063] FIG. 50 is a perspective view of the male plate and female
plate of the static compression device of FIG. 36 in an
interconnected relationship and with the locking plate and locking
screw in place.
[0064] FIG. 51 is a top view of the static compression device of
FIG. 36 with the male plate interconnected to the female plate and
with the locking plate in place and in the uncompressed
position.
[0065] FIG. 52 is a top view of the static compression device of
FIG. 36 with the male plate interconnected to the female plate and
with the locking plate in place and in the compressed position.
[0066] FIG. 53 is a bottom view of the locking plate of the static
compression device of FIG. 36.
[0067] FIG. 54 is a side view of the locking screw of the static
compression device of FIG. 36.
[0068] FIG. 55 is a perspective view of an alternate embodiment of
the static compression device.
[0069] FIG. 56 is a perspective view of the static compression
device of FIG. 55 with the guide plate shown in phantom.
[0070] FIG. 57 is a perspective view of a series of trial spacers
and corresponding handle of one aspect of the present
invention.
[0071] FIG. 58 is a perspective view of an embodiment of the static
compression device designed to be used in the thoracic or lumbar
region of the spine.
[0072] FIG. 59 is a perspective view of an embodiment of the static
compression device designed to be used to treat fractures.
[0073] FIG. 60 is a perspective view of an embodiment of the static
compression device designed to be used to treat fractures.
DETAILED DESCRIPTION OF THE INVENTION
[0074] The SC device 10 in a preferred embodiment shown in FIGS.
1-14 and 18 has five main parts, a male plate 12, a female plate
14, an interconnecting plate 15, a locking clamp 16 and a locking
screw 18 that, in combination with standard cancellous bone screws
(not shown) fix the SC device 10 to the patient's vertebrae. The SC
device 10 has a top side 20, a bottom side 22 and opposed medial
sides 24.
[0075] The male plate 12 has a male main body 26 and a central
protrusion 28 extending away from the male main body 26. The
central protrusion 28 has a top surface 30, a longitudinal axis 32,
a bottom surface 33 and parallel sides 36. Central protrusion 28
also has a threaded hole 35 in the top surface 30.
[0076] The male plate 12 also has a pair of side protrusions 29
extending away from the male main body 26 on opposite sides of the
central protrusion 28. Each of the side protrusions 29 has an inner
surface 37 and an outer surface 39. The inner surfaces 37 are
directed toward the central protrusion 28 and are preferably curved
in a concave fashion to mate with the outer surfaces 63 of the left
guide 58 and right guide 60 of the interconnecting plate 15 or the
female plate 14 as will be described hereafter.
[0077] The male main body 26 is relatively flat with a top side 34
and a bottom side 36 and, in a preferred embodiment, has two screw
receiving holes 38. The screw receiving holes 38 each have a
bowl-shaped basin 40 on the top side 34 to receive the heads of the
screws 43 and a throughhole 42 through which the main body of the
screws 43 pass to come into contact with the vertebral body. The
throughholes 42 are configured in a manner that allows the
cancellous bone screws 43 to be rigidly fixed to the plate once
inserted in bone. The method of fixing the screws 43 to the plate
may utilize any number of mechanisms well understood in the art
that allow the screws 43 and the male plate 12 to maintain a rigid
relationship once the screws 43 are inserted in bone.
[0078] The bottom side 36 of the male plate 12, female plate 14 and
interconnecting plate 15 is preferable roughened, thereby allowing
the bottom side 22 of the SC device 10 to "grip" the vertebral body
when the bottom side 22 of the SC device 10 is brought into contact
with and secured to the vertebral body by the interaction of the
screws 43 and the body of the SC device 10 as described herein.
[0079] As mentioned, the male plate 12 has a central protrusion 28
with a top surface 30 and a longitudinal axis 32. Central
protrusion 28 is dimensioned to mate with and secure the male plate
12 with the interconnecting plate 15 or the female plate 14 as will
be described in detail hereafter. Where the interconnecting plate
15 is used, the combined length of the central protrusion 28 on the
male plate 12 and the central protrusion 28' on the interconnecting
plate 15 will be slightly longer than the distance the SC device 10
is intended to provide compression over.
[0080] Central protrusion 28 has a boss 44 extending entirely
through it approximately parallel to the top surface 30 that is
designed to mate with a relief cut 62 in the interconnecting plate
15/female plate 14.
[0081] The interconnecting plate 15 combines the features of the
male plate 12 and the female plate 14 on its opposite ends. As a
result, on one end of interconnecting plate there is a central
protrusion 28' essentially as described in connection with the
central protrusion 28 of male plate 12. On the opposite end of
interconnection plate 15, there is a protrusion receiving channel
56 essentially as described hereafter in connection with the
protrusion receiving channel 56 of female plate 14. In addition,
interconnecting plate 15 has at least a pair of screw receiving
holes 38 essentially as described in connection with the screw
receiving holes 38 of the male plate 12.
[0082] The purpose of the interconnecting plate 15 is to allow the
SC device 10 to be secured to three or more adjacent vertebrae and
allow the SC device 10 to apply compression across these vertebrae
to facilitate healing as described herein. As a result, a single
interconnecting plate 15 may be placed between the male plate 12
and the female plate 14 and attached to the vertebra between the
vertebrae that the male and females plates 12, 14 are attached to.
Alternately, several interconnecting plates 15 can be connected end
to end (i.e., the protrusion receiving channel 56 of one
interconnecting plate 15 receives the central protrusion 28' of an
adjacent interconnecting plate 15 and the process continues until
all the interconnecting plates 15 are joined together) to form an
interconnecting span with a male plate 12 and a female plate 14
attached to the ultimate ends of this chain of interconnecting
plates 15. In this embodiment of the invention, each of the
interconnecting plates 15 would have screw receiving holes 38
allowing each interconnecting plate 15 to be attached to a single
vertebra by bone screws 43. In a variant of this embodiment, a
single interconnecting plate 15 could have several sets of screw
receiving holes 38 so that this single interconnecting plate 15
could be attached to several adjacent vertebrae or could span a
previously fused segment.
[0083] The female plate 14 has a female main body 52 with a bottom
side 54 and a protrusion receiving channel 56. Protrusion receiving
channel 56 is formed between a left guide 58 and a right guide 60
that extend away from the female main body 52. Left guide 58 and
right guide 60 each have an inner surface 61, an outer surface 63,
a bottom surface 65 and a top surface 67. Left guide 58 and right
guide 60 are basically rectangular in cross-section with inner
surfaces 61 being preferably essentially planar and with outer
surfaces 63 being essentially outwardly curved with a series of
ridges 71 extending outwardly. On the bottom surface 65 of the left
and right guides 58, 60 facing the protrusion receiving channel 56,
there is a relief cut 62 machined to accept the boss 44 on the
central protrusion 28' of the interconnecting plate 15 or the male
plate 14.
[0084] Protrusion receiving channel 56 is dimensioned to snugly
receive the central protrusion 28' with the locking clamp 16 in
place on the central protrusion 28' as will be described hereafter
so that the central protrusion 28' is "captured" and held in the
protrusion receiving channel 56 by physical contact between the
outer surface of the locking clamp 16 and the inner surfaces of the
left guide 58 and right guide 60 as well as by the interaction
between the central protrusion 28' and the boss 44 on the inferior
aspect of the central protrusion 28' and relief cut 62.
[0085] The outer surfaces 63 of the left and right guides 58, 60
contact the inner surfaces 37 of the side protrusions 29 under the
influence of the locking clamp 16, as will be described hereafter,
to securely locate the female plate 14 with respect to the
interconnecting plate 15 and the interconnecting plate 15 with the
male plate 12.
[0086] The female plate 14, also in a preferred embodiment, has two
screw receiving holes 82. These screw receiving holes 82 receive
standard cancellous bone screws 43 that are threaded into the bone
of the vertebrae. In similar fashion to screw receiving holes 38,
the screw receiving holes 82 also have a bowl-shaped basin 84 on
the upper surface 78 to receive the heads of the bone screws 43 and
a throughhole 86 through which the main body of the bone screws 43
pass to come into contact with the vertebral body. The throughholes
86 are configured in a manner that allows the cancellous bone
screws 43 to be rigidly fixed to the plate once inserted in bone by
the interaction of the screws 43 with the basins 84. The method of
fixing the screws 43 to the female plate 14 may utilize any number
of mechanisms well understood in the art that allow the screws 43
and the female plate 14 to maintain a rigid relationship once the
screws 43 are inserted in bone.
[0087] The SC device 10 has a locking mechanism 88. Locking
mechanism 88 converts "active" compression applied by the surgeon
using the compression device 90 described below interacting with
the device 10 at the time of surgery to "static" compression after
surgery. The locking mechanism 88 also provides rigid fixation to
the SC device 10 to optimize bone healing and preventing further
settling from occurring.
[0088] The locking mechanism 88 in one embodiment includes locking
clamp 16 and locking screw 18. The locking clamp 16 has a top
surface 92 with a hole 93 extending through it, a bottom surface
94, parallel sides 96, a longitudinal axis 97 and an inner channel
99 between the parallel sides 96 and below the top surface 92. The
inner width of the inner channel 99 of the locking clamp 16 (i.e.,
the inside distance between the parallel sides 96) is such that the
locking clamp 16 will fit snugly over the central protrusion 28.
The width of the locking clamp 16 (i.e., the distance between the
parallel sides 96) is such that the locking clamp 16 will fit
snugly between the left and right guides 58, 60 in the protrusion
receiving channel 56.
[0089] A single large locking screw 18, dimensioned to rotate
freely within the hole 93 of the locking clamp 16, activates the
locking mechanism 88. In the embodiment of the invention shown in
FIGS. 1-19, the locking screw 18 has a head 106, a body 108 and a
distal end 110 opposite the head 106. The head 106 has a larger
cross-sectional diameter than the threaded body 108. The body 108
is threaded at least on the distal end 110 to correspond to the
threads of the threaded hole 35 in the protrusion 28.
[0090] The parallel sides 96 of locking clamp 16 preferably have a
series of ridges 46 and valleys 48, preferably placed substantially
perpendicular to the longitudinal axis 97 and tapered from top to
bottom, to locate and affix the locking clamp 16 to the inner
surfaces of the left guide 58 and right guide 60 of the
interconnecting plate 15 and female plate 14. Through this
configuration, the ridges 46 and valleys 48 on the sides 96 of the
locking clamp 16 preferably contact and engage with the inner
surfaces of left and right guides 58, 60 in frictional or
mechanical contact to precisely locate and affix the locking clamp
16 within the protrusion receiving channel 56. Because the series
of ridges 46 and 48 are tapered, as the series of ridges 46, 48 are
moved into contact with and engage the inner surfaces of left and
right guides 58, 60, this engagement adds compressive force to the
adjacent vertebral bodies through the SC device 10. The locking
clamp 16 is preferably made of a material that is harder than the
material of the interconnecting plate 15 or the female plate
14.
[0091] The present invention also includes a compression device 90
(FIGS. 20-23) that allows the surgeon to provide active, controlled
compression between the two sliding components of the SC device 10
(male plate 12 and female plate 14) at the time of surgery. This
compression device 90 allows the surgeon to accurately measure the
force applied across the graft by the SC device 10 and allows the
surgeon to stop compressing when a predetermined amount of force
has been obtained. Since both the male plate 12 and the female
plate 14 are each connected to adjacent vertebral bodies by two
fixed angle bone screws 43, this provides for even,
surgeon-controlled compression across the interbody graft.
[0092] The compression device 90 has two arms 114, 116 that each
have a handle 118, 120 at one end and a foot 122, 124, located at a
distal end 126, 128, respectively. The arms 114, 116 are connected
via a pivot 130 that connects the respective arms 114, 116 and
allows them to move in scissors-like movement with respect to each
other. By connecting the arms 114, 116 through a pivot 130, a
surgeon squeezing the handles 118, 120 moves the distal ends 126,
128 together. By connecting these distal ends 126, 128 to the
device 10, a surgeon squeezing the handles 118, 120 together is
able to apply compression to the SC device 10 and thus to adjacent
vertebral bodies through the interaction of the feet 122, 124 and
the male plate 12 and female plate 14 as will be explained
hereafter.
[0093] Each foot 122, 124 of the compression device 90 engages the
male plate 12 or female plate 14 (or interconnecting plate 15),
respectively, to apply pressure to move the male plate 12 and
female plate 14 toward each other as the physician squeezes the
handles 118, 120 together. In the embodiment of compression device
90 and SC device 10 shown in FIG. 23, the distal ends 126, 128 of
feet 122, 124, respectively, are shaped with pins 132 that protrude
from the distal ends 126, 128.
[0094] In the embodiment shown in FIGS. 21-23, pins 132 protrude
from adaptor plates 134 having throughholes 136. Adaptor plates 134
are secured to the distal ends 126, 128 of feet 122, 124,
respectively by screws 138 that pass through throughholes 136. The
distal ends 126, 128 of feet 122, 124, respectively each have a
threaded secure hole 140 that receives a screw 138. In this way,
adaptor plates 134 are secured to the distal ends 126, 128 of feet
122, 124, respectively. The adaptor plates 134 may be removed and
replaced with hooks protruding from the distal ends 126, 128 of
feet 122, 124, respectively, that each engage a slot on the
outermost aspects of the male and female plates 12, 14 placed or
formed in the top side 34 of the male plate 12 and the top surface
78 of the female plate 14. This enables the ends of compression
device 90 to be modular (i.e., replaceable so that the appropriate
end for a desired application can be placed on the compression
device 90) with respect to using different techniques to achieve
compression.
[0095] The male plate 12 and female plate 14 each have a notch 142,
144, respectively, located on opposite ends of the SC device 10 and
shaped to receive the pins 132 in a snug, conforming fashion so
that compression applied to the feet 122, 124 by squeezing the
handles 118, 120 together is transferred from the distal ends 126,
128 to the male plate 12 and female plate 14, respectively, through
the interaction of the pins 132 with the notches 142, 144.
[0096] In an alternate embodiment of the invention, the distal ends
126, 128 of feet 122, 124, respectively, again engage the male
plate 12 and the female plate 14, respectively, through pins 132.
However, in this embodiment, the notches 142, 144 are located in
the outer edge of the top surfaces 26 and upper surface 78 of the
male plate 12 and female plate 14, respectively, sized and shaped
to receive the pins 132 in a snug fashion so that compression
applied to the feet 122, 124 by squeezing the handles 118, 120
together is transferred from the pins 132 to the male plate 12 and
female plate 14, respectively, through the notches 142, 144.
[0097] The compression device 90 also preferably has a gauge 146
that allows the physician to measure the compression force being
applied to the SC device 10, and thus to the vertebral bodies, by
the squeezing together of the handles 118, 120. The gauge 146, by
quantifying the deflection of the handles 118, 120 when they are
squeezed together, gives an accurate measurement of force applied
across the SC device 10. In the embodiment of the compression
device 90 shown in FIG. 20, gauge 146 includes an arm 148 attached
to pivot 130 and located between handles 118, 120. The arm 148
preferably has a circular, oval, square or rectangular
cross-section and a horizontal and a vertical component 149, 151,
respectively. The arm 148 has indicia 150 located on at least a
portion of the horizontal component 149.
[0098] The gauge 146 has an indicator 152 that is an annular spacer
located along the horizontal component 149 of arm 148. The
indicator 152 has a central opening 154 sized to be approximately
the same size and shape as the cross-sectional size and shape of
the horizontal component 149 of arm 148 so that indicator 152 is
attached to the horizontal component 149 by sliding the horizontal
component 149 through the first central opening 154. A frictional
fit between the first central opening 154 and the horizontal
component 149 holds the indicator 152 in position on the horizontal
component 149.
[0099] As mentioned above, when the handles 118, 120 are squeezed
together, the resulting amount of deflection of the handles 118,
120 is directly related to the force applied by the physician as he
or she squeezes the handles 118, 120 together. Because the vertical
component 151 of the arm 148 is rigidly attached to the pivot 130,
as the handles 118, 120 move together as a result of being
squeezed, the horizontal component of the arm 148 and its associate
indicator 152 does not move. As a result, the handle 120 will be
deflected along the horizontal component 149 of the arm 148 and
along the indicia 150 located on the horizontal component 149. By
observing the location of the handle 120 with respect to the
indicia 150 on the horizontal component 149, the amount of force
applied to handles 118, 120 and, therefore to the distal ends 126,
128 of feet 122, 124, is indicated. When the distal ends 126, 128
are placed in functional contact with the notches 142, 144 of the
male plate 12 and female plate 14, the gauge 146 indirectly
measures the compression being applied to the graft, and allows the
surgeon to stop compressing once a predetermined force has been
achieved.
[0100] By placing the indicator 152 at a desired location on the
horizontal component 149 of arm 148, the physician can squeeze the
handles 118, 120 together until the handle 120 moves into contact
with the indicator 152. At this point, the physician knows that the
desired amount of force has been applied to the compression device
90 and thereby to the SC device 10 to the graft.
[0101] In another embodiment of the compression device 90 shown in
FIG. 22, gauge 146 again includes an arm 148. But, in this
embodiment, the arm 148 is connected to a rigid arm 156 located on
the outside of handle 118. Rigid arm 156 is attached to handle 118
near the pivot 130. Arm 148 extends from the rigid arm 156 in the
direction that handle 118 moves when it is squeezed together with
handle 120 and may extend through a slot in handle 118 or may be
formed around handle 118 so that arm 148 extends toward handle 120.
In this embodiment as well, indicator 152 is located between
handles 118, 120.
[0102] As mentioned above, when the handles 118, 120 are squeezed
together, the resulting amount of deflection of the handles 118,
120 is directly related to the force applied by the physician as he
or she squeezes the handles 118, 120 together. Because the arm 148
is rigidly attached to the rigid arm 156, as the handle 118, 120
move together as a result of being squeezed, the arm 148 and its
associate indicator 152 does not move. As a result, the handle 118
will be deflected along arm 148 and along the indicia 150 located
on arm 148. By observing the location of the handle 118 with
respect to the indicia 150 on arm 148, the amount of force applied
to handles 118, 120 and, therefore to the distal ends 126, 128 of
feet 122, 124, is indicated. When the distal ends 126, 128 are
placed in functional contact with the notches 142. 144 of the male
plate 12 and female plate 14, the gauge 146 indirectly measures the
compression being applied to the graft, and allows the surgeon to
stop compressing once a predetermined force has been achieved.
Again, by observing the location of the handle 118 versus the
indictor, the surgeon will know that the desired amount of force
has been applied to the compression device 90 and thereby to the SC
device 10 to the graft.
[0103] An alternative embodiment of the compression device 90 is
referred to as the static compensating compressor 590 and shown in
FIGS. 24-27. The static compensating compressor 590 utilizes a
force indicator 592 and a method to measure static compressive
forces applied by the patient's own anatomy to allow the surgeon to
factor the patient's own static compressive forces out to ensure
the correct value of the absolute compression applied through the
SC device 10 to the vertebral bodies. The static compensating
compressor 590 includes a turnbuckle 594 that uses a threaded nut
596, threaded inserts 598, along with a series of compression
springs 600 and guide rods 602, collectively known as the
distraction mechanism 604, to allow the surgeon to apply a
measurable distraction force (a force in the opposite direction to
the compressive force) to unload the vertebral segment. By unload,
we mean to take compression pressure, usually applied by the
patient's own muscles and ligaments, off the vertebral segments.
Once compression pressure on the vertebral segment has been
unloaded from the vertebral segment, a null point (i.e., a point
where there is no compression or distraction force on the vertebral
bodies) is established and therapeutically useful compression can
be applied to the vertebral segment at a known rate.
[0104] The force indicator 592 has a central processing unit (CPU)
606 and a display 608 to determine and indicate the amount of force
applied in either compression or distraction to the SC device 10
and a zeroing function that allows the surgeon to compensate for
static anatomical compression. The force indicator 592 also
includes a strain gauge 610. The force indicator 592 is a simple
electronic device that measures the resistance across the strain
gauge 610 that is secured to one of the arms 114, 116 of the
compressor 90 and then uses the CPU 606 to determine, by formula or
through a lookup table, and indicate the amount of force applied by
the compressor 90 and then indicate this amount of force on the
display 608. The CPU 606 may be an application specific integrated
circuit (ASIC), a digitally based central processing unit or
discrete components.
[0105] The display 608 is preferably attached to one of the handles
118, 120 of the arms 114, 116 and the CPU 606 and the display 608
are preferably combined into a single unit. However, either or both
the CPU 606 and the display 608 may be located remotely from the
static compensating compressor 590 and the CPU 606 and the display
608 may be located separately from each other.
[0106] The strain gauge 610 is preferably located on a distal end
126, 128 of a respective arm 114, 116 of the compression device 90
although the strain gauge may be located anywhere on an arm 114,
116 or on the pivot 130. As the physician applies compression
through the compression device 90 to the SC device 10 and thus to
the vertebral bodies by squeezing the handles 118, 120 of the
compression device 90 together, the distal ends 126, 128 will flex
or bend slightly. The strain gauge 610 measures this flexing or
bending of the distal ends 126, 128 and communicates the value to
the CPU 606 where the force value, once determined, indicates the
amount of force applied to the SC device 10, and thus to the
vertebral bodies, as is well understood in the art.
[0107] As mentioned above, the static compensating compressor 590
is able to apply distraction pressure to the vertebral bodies
through the use of a turnbuckle 594 (FIG. 26). The threaded nut 596
has a pair of threaded holes 612. The threaded holes 612 are
threaded in opposite directions (i.e., with right and left handed
threads) as is well understood in turnbuckles. The threaded inserts
598 each have a threaded end 614 and a non-threaded end 616 to
which a guide rod 602 is attached. The guide rods 602 are
preferably attached to the non-threaded ends 616 through springs
600 that have a low spring force. Springs 600, when used, apply a
low biasing force to the turnbuckle 594 to remove looseness in the
connection between the turnbuckle 594 and the arms 114, 116. In
another embodiment, the guide rods 602 may be attached directly to
the non-threaded ends 616. The threaded inserts 598 are also each
threaded on their threaded ends 614 in opposite directions (i.e.,
with right and left handed threads) and are mated with the threaded
holes 612 of the threaded nut 596 so that as the threaded nut 596
is rotated in a first direction, the threaded inserts 598 are drawn
into the threaded holes 612 and as the threaded nut 596 is rotated
in a second direction, the threaded inserts 598 are moved out of
the threaded holes 612. As a result, as the threaded nut 596 is
rotated in a first direction, the turnbuckle 594 expands in length
and as the turnbuckle 594 is rotated in a second direction opposite
the first direction, the turnbuckle contracts in length.
[0108] The turnbuckle 594 is preferably attached between and
applies a preload to the handles 118, 120 of the arms 114, 166 of
the compressor 90. However, the turnbuckle 594 may also be attached
between and apply a preload to the distal ends 126, 128 of the arms
114, 166 of the compressor 90. In either embodiment, the turnbuckle
594 is fitted between the arms 114, 116, either between the handles
118, 120 or distal ends 126, 128 preferably in slots 618, secured
with pins 620 or other suitable retaining devices well understood
in the art. In a variant of this embodiment, the pins 620 could be
quick release pins, allowing the turnbuckle 594 to be quickly
removed once the null point is found, as explained below, so that
the compressor 90 would be used thereafter without the turnbuckle
594.
[0109] Once the turnbuckle 594 is attached to the arms 114, 116, by
turning the threaded nut 596, the turnbuckle 594 expands or
contracts (depending on the direction the threaded nut 596 is
rotated) thereby applying a preload in either a compression or
distraction direction to the arms 114, 166 of the compressor 90 and
thus to the SC device 10 and ultimately to the vertebral bodies.
This preload allows the vertebral segment that the SC device 10 is
spanning to become unloaded or lifted. By "lifted" or "lift-off" we
mean that a distraction force has been applied to the vertebral
segment by the compressor 90 and SC device 10 to the point where
the distraction force is equal to the anatomical compression force
applied to the vertebral segment by the patient's own muscles and
ligaments. At this point, called the null point, there is a net
zero force applied to the affected vertebral segment so that the
affected vertebral bodies separate or "lift-off" of each other
slightly which separation is visually ascertained by the
physician.
[0110] Once lift-off has been determined, and consequently, the
null point established, a button is pushed on the display 608, on
the CPU 606 itself or otherwise, including remotely, to alert the
CPU 606 that strain measured by the strain gauge 610 at that point
is the null point. As a result, the CPU 606 directs the display 608
to indicate a zero reading at that point.
[0111] At this point, the turnbuckle 594 is preferably removed from
the compressor 90. As the turnbuckle 594 is removed, the patient's
anatomical compression force will be applied to the affected
vertebral segment. This compression force will be transferred
through the SC device 10 to the compressor 90 where the strain
gauge 610 will measure the anatomically applied compression force
and the CPU 606 will direct the display 608 to indicate the
anatomically applied compression force. Thereafter, the surgeon
applies an additional compressive force to the SC device 10 which
additional compressive force will be sensed by the strain gauge 610
combined with the compressive force applied by the patient's own
anatomy. As a result, the CPU 606 will determine the total
compressive force applied to the vertebral segment (i.e., the
summation of the patient's own anatomical compressive force and the
compressive force being applied by the physician by the compressor
90) which total compressive force is displayed on the display 608.
The physician then applies the additional compressive force to the
vertebral segment until a desired total compressive force for
maximum therapeutic value is obtained.
[0112] If the force indicator 592 is set to a null point before
distraction pressure is applied to the vertebral segment by the
turnbuckle 594, the force indicator 592 will also indicate the
distraction pressure applied to the vertebral segment by the
turnbuckle 594. At the point where lift-off occurs, the display 608
will indicate the amount of distraction pressure being applied by
the turnbuckle 594 which equals the amount of compression force
that is applied by the patient's own anatomy. This amount of
compression force is also potentially valuable information in that
the amount of compression force anatomically applied by the patient
may be used by the physician to determine the overall health and
strength of the patient's inherent anatomical compression
mechanism. Thereafter, the physician may set the force indicator
592 to zero as described above to indicate the null point for the
application of compression force also as described above.
[0113] In a variant to the embodiments of the compression device 90
described above, a small cannula 158 is attached to the compression
device 90 at the pivot 130. The cannula 158 is directed downward
toward the SC device 10. This cannula 158 is intended to receive a
special screwdriver 160 that activates the locking mechanism 88 of
the SC device 10 when the desired compression is achieved. The
screwdriver 160 is inserted through the cannula 158 into the
loosened locking mechanism 88 as the compression device 90 engages
the male plate 12 and female plate 14. Thus, it is possible for the
surgeon to maintain compression across the graft with one hand on
the compression device 90, to determine the degree of compression
achieved on the SC device 10 by visualizing the compression gauge
146, and to activate the locking mechanism 88 of the SC device 10
with the other hand, causing the SC device 10 to become a rigid
construct and preventing further movement of the vertebral bodies
from occurring.
[0114] Alternately, the physician may use the screwdriver 160
without inserting it through the cannula 158 or may use the
screwdriver 160 in an embodiment of the compression device 90 that
does not include a cannula 158. Further, in any of the embodiments
of the compressor 90, the compressor 90 may be disposable or
reusable.
[0115] One mechanism of fixing the bone screws 43 to the male plate
12 at a rigid predetermined angle is described as follows. As
mentioned above, bone screws 43 fix the male plate 12, the female
plate 14 and the interconnecting plate, 15, if present, to the
vertebral bodies. The bone screws 43 may be machined, as is common
for such screws, with two separate sets of threads, one on the
shaft of the screw 43, the second set on the head of the screw 43.
These threads are distinct from each other in that they have
different pitches and distinct outer diameters. The pitch and outer
diameter of the threads on the shaft of the screw 43 are that of a
standard cancellous bone screw. In order to engage the main male
plate 12, the diameter of the head 45 of the bone screw 43 head is
significantly larger than the diameter of the threads on the shaft
of the bone screw 43. However, the threads on the bone screw 43 are
smaller in outer diameter and tighter in pitch than the bore of the
screw receiving holes 38. These threads are machined to engage
threads of similar pitch and diameter in the screw receiving holes
38 of the male plate 12.
[0116] The screw receiving holes 38 are machined to project the
screw 43 into the vertebral body at a predetermined angle
determined to be most advantageous for fixing the SC device 10 to
the vertebral bodies. Thus, by engaging the threads on the head 45
of the screw 43 with those in the screw receiving hole 38, the
screw 43 projects into the vertebral body at the predetermined
angle and maintains a rigid fixed relationship with the male plate
12.
[0117] The interaction between the bone screws 43 and the SC device
10 described above is one of the many ways that bone screws 43 can
be connected to the SC device 10. However, it is well understood in
the art that there are other commercially available ways to connect
devices like the SC device 10 to vertebrae that could also be used.
As a result, it is intended that any method of connecting the SC
device 10 to vertebral bone so that there is a rigid fixed
relationship between the SC device 10 and the bone may be used with
the SC device 10 of the present invention.
[0118] The mechanism of fixing the screws 43 to the female plate 14
at a rigid predetermined angle is similar to the mechanism for
fixing the screws 43 to the male plate 12 at a rigid predetermined
angle as described above. Again, the bone screws 43 are machined,
as is common for such screws, with two separate sets of threads,
one on the shaft of the screw 43, the second set on the head of the
screw 43. These threads are distinct from each other in that they
have different pitches and distinct outer diameters. The pitch and
outer diameter of the threads on the shaft of the screw 43 are that
of a standard cancellous bone screw. In order to engage the female
plate 14, the inner diameter of the screw head 45 is significantly
larger than the inner diameter of the threads on the shaft.
However, the threads on the screw head 45 are smaller in outer
diameter and tighter in pitch than the bore of the screw receiving
holes 82. These threads are machined to engage threads of similar
pitch and diameter in the screw receiving holes 82 of the female
plate 14. The screw receiving holes 82 are machined to project the
screw 43 into the vertebral body at a predetermined angle. Thus, by
engaging the threads on the head 45 of the screw 43 with those in
the screw receiving holes 82, the screw 43 projects into the
vertebral body at the predetermined angle and maintains a rigid
fixed relationship with the female plate 14.
[0119] The SC device 10 as described in the embodiment above has
the option of using fixed angle screws. However, variable angle
screws 43 may be used with the SCD device 10 as long as when these
screws 43 are placed through the male plate 12, female plate 14 or
interconnecting plate 15 into bone, their relationship with the
respective plate 12, 14 or 15 becomes rigid. There are numerous
methods of attaching bone screws to plates well understood in the
art, all of which may be used with this device. It is important
that the relationship between the screws and the plates 12, 14, 15
becomes rigid once the screws are placed in order to avoid "toggle"
of the screws during the compression maneuver. "Toggle" must be
avoided, because if it occurs, actual compression may be
significantly less than measured.
[0120] Most currently available non-adjustable plates have the
option to place screws into the bone at a variety of different
angles to obtain optimum purchase. While this is necessary to
position static plates, it is not necessary in the SC device 10. In
fact the sliding capability that the SC device 10 has in the
unlocked arrangement renders the common use of variable screws
superfluous. Nevertheless, any type of screw may be used with the
SC device 10 as long as a mechanism exists for rigidly fixing the
screw to the plate.
[0121] The importance of having screws 43 that are rigidly fixed to
the male plate 12 and female plate 14 at a predetermined angle is
that compression occurs through the entire SC device 10 (the
sliding components of the SC device 10 (male plate 12 and female
plate 14 and the two rigidly attached screws), rather than through
the screws individually. Also, as mentioned, the bottom side 36 of
the male plate 12 and the bottom side 54 of the female plate 14,
and of the interconnecting plate 15 if present, are roughened,
allowing the SC device 10 to "grip" the vertebral body. These
characteristics in combination provide for a much larger surface
area to compress against (the contact of the bottom side 36 and
bottom side 54 on the anterior surface of the vertebrae as well as
the two rigidly fixed bone screws in the male plate 12 and female
plate 14, respectively). This results in a much more even
compression against the entirety of the interbody graft and
minimizes the potential for screw cutout or bony failure.
[0122] For purposes of illustrating the operation of locking
mechanism 88 of the invention in the embodiment shown in FIGS.
1-14, a variant of the embodiment described above will be used. In
this variant, shown in FIGS. 15-17, there is no interconnecting
plate 15. Instead, the male plate 12 and female plate 14 intermesh
directly through the interaction of the central protrusion 28 and
side protrusions 29 of the male plate 12 and the left and right
guides 58, 60 of the female plate 14. In describing the operation
of the SC device 10, it is to be understood that the concepts
described apply as well to the interaction between the male plate
12 and one end of the interconnecting plate 15 and the interaction
between the opposite end of the interconnecting plate 15 and the
female plate 14.
[0123] In use, the central protrusion 28 is inserted into the
protrusion receiving channel 56 (FIG. 15). Because protrusion
receiving channel 56 is dimensioned to receive central protrusion
28 with the locking clamp 16 in place, central protrusion 28 is
precisely located and retained within the protrusion receiving
channel 56. In this position with the locking clamp 16 in place on
the top surface 30 of central protrusion 28, the ridges 46 and
valleys 48 on the parallel sides 96 of locking clamp 16 come into
loose contact with the inner surface 61 of left guide 58 and right
guide 60 of the female plate 14. (FIG. 15) The locking screw 18 is
passed through the screw hole 93 so that its distal end 110 comes
into contact with and is threaded into the threaded hole 35 a
sufficient amount to locate the distal end 110 of the locking screw
18 in the threaded hole 35 but not a sufficient amount to deform
the locking clamp 16.
[0124] Bone screws are passed through the screw receiving holes 38
and 82 and into the vertebral bone. These bone screws are screwed
into the vertebral bone until the heads of the bone screws seat
into the basins 40, 84 of the male plate 12 and female plate 14,
respectively.
[0125] The compression device 90 is then used to apply the desired
compression to the SC device 10. The pins 132 are placed in the
notches 142, 144 and the handles 118, 120 are squeezed together. As
a result, compression pressure is applied to the male plate 12,
female plate 14 and interconnecting plate 15 if present, and
thereby to the vertebral bone through the bone screws.
[0126] As mentioned above, where a gauge 146 is present, the amount
of compressive force applied to the device 10 can be
ascertained.
[0127] As shown in FIGS. 16 and 17, when the male plate 12 is moved
into an intermeshing position with the female plate 14 and the
appropriate amount of compression is applied to the SC device 10
through the compression device 90, the screwdriver 160 is coupled
to the head 106 of the locking screw 18. The screwdriver 160 is
rotated so that the threaded body 108 of locking screw 18 is
threaded into the threaded hole 35. The locking screw 18 is then
screwed further onto the central protrusion 28 on the male plate 12
so that the head 106 contacts the top surface 92 of the locking
clamp 16.
[0128] Once the head 106 has contacted the top surface 92, further
rotation of the locking screw 18 will cause the head to be forced
into the material of the top surface 92 of the locking clamp 16.
This will cause the locking clamp 16 to interfere so that the
parallel sides 96 will be forced into engaging and locking contact
with the inner surfaces 61 of the left and right guides 58, 60 on
the female plate 14 or the interconnecting plate 15. This outward
compression from the interference fit is transferred through the
left and right guides 58, 60 to cause engaging and locking contact
between the outer surface 63 of the left and right guides 58, 60
and the inner surface 37 of the side protrusions 29. The
interaction between the head 106 and the screw hole 35 locks the
locking clamp 16 against the right and left guides 58, 60. Once
male plate 12 is secured with respect to the female plate 14, the
compression device 90 is removed. As a result, the compression
applied to the SC device 10 through the compression device 90 will
be locked to the vertebral bone through the male plate 12 and
female plate 14 (and interconnecting plate 15 if used) because
these various components are locked in a fixed relationship to each
other.
[0129] An alternate embodiment of the locking mechanism 88 is shown
in FIGS. 28-32 and is described as follows. In this embodiment
there is no locking clamp 16 and the locking screw 18 (FIG. 30) is
large in diameter and is tapered from the head 106 to the distal
end 110 so that the diameter of the head 106 is significantly
larger than the diameter of the distal end 110. In addition, the
diameter of head 106 of the locking screw 18 is greater than the
width of the central protrusion 28. Further, the threaded hole 35
of the central protrusion 28 of the male plate 12 is fashioned in a
threaded tapered fashion so that the locking screw 18 fits into the
threaded hole 35. In this embodiment the central protrusion 28 may
include a slot 41 through which the threaded hole 35 passes to
allow maximal deformation of the central protrusion 28 along the
length of the central protrusion 28.
[0130] Thus, when appropriate compression has been applied to the
vertebral bodies by the SC device 10, the locking mechanism 88 is
engaged by advancing the locking screw 18 into the threaded hole
35. The advancement of the locking screw 18 into the threaded hole
35 deforms the outer aspect of the central protrusion 28 which
surrounds the threaded hole 35 thereby causing this portion of the
central protrusion 28 to expand and interfere with the inner
surface 61 of left guide 58 and right guide 60 of the female plate
14. The presence of the slot 41 helps the deformation of the outer
aspects of the central protrusion 28 by making it easier for the
two sides of the central protrusion 28 to move away from the
threaded hole 35 under the influence of the locking screw 18. This
outward compression from the interference between expanded central
protrusion 28 and left and right guides 58, 60 is transferred
through the left and right guides 58, 60 to cause engaging and
locking contact between the outer surfaces 63 of the left and right
guides 58, 60 and the inner surface 37 of the side protrusions
29.
[0131] It should be noted that the SC device 10 is a modular and
expandable device. The characteristics of this device allow it to
be disassembled in vivo and expanded to immobilize adjacent
vertebral segments (or other bone pieces or segments) by the
insertion of one or more interconnecting plates 15 to form an
interconnecting span as described above.
[0132] Thus, should subsequent surgery be required, as for example,
in the case of adjacent segment disease (the segment adjacent to a
fused segment undergoing accelerated degeneration), it is not
necessary to expose the entirety of the SC device 10 and remove it
to extend the fusion to the adjacent segment (as is the case with
nearly all current plates). Instead, an end portion of the SC
device 10 (e.g., either the male plate 12 or female plate 14) may
be removed (leaving the remainder of the SC device 10 intact), the
fusion completed and the SC device 10 simply expanded to include
the newly fused segment by inserting one or more interconnecting
plate 15, then reapplying the end portion (either the male plate 12
or female plate 14, respectively) of the SC device 10 to the newly
fused vertebrae, applying compression as explained herein and
locking and securing the SC device 10.
[0133] An alternate embodiment of the SC device 10 is shown in
FIGS. 33-35. In this embodiment, the locking screw 18 of the
locking mechanism 88 is modified to include a cam 162 that rotates
around the locking screw 18 below the head 106 (FIG. 35). Further,
the edges of channel 80 form a track 164 (FIG. 34) dimensioned to
receive and constrain the cam 162 within the track 164 in a
relatively conformal manner. In addition, in this embodiment of the
locking mechanism 88, there is no locking clamp 16 and the central
protrusion 28 does not have the protrusion ridges 50.
[0134] Cam 162 is relatively disk shaped with elongated opposed
outer edges 166. The outer edges 166 resemble somewhat a "V" with
the bottom of the V being farther from the body 108 than the open
mouth of the V which rotates around the body 108 of locking screw
18. The locking screw 18 in this embodiment rotates freely with
respect to cam 162. However, the cam portion can be rotated into
contact with and engage the track 164 when rotated 90 degrees about
the body 108. When the locking screw 18 is in the unlocked
position, the male plate 12 is inserted into the protrusion
receiving channel 56. With the cam 162 rotated so that the cam 162
does not contact the track 164, the cam 162 and the locking screw
18 move easily into the channel 80. Then the male plate 12 and the
female plate 14 are moved to the desired position relative to each
other, the cam 162 is rotated 90 degrees so that the cam 162
contacts the wall of the track 164 where such frictional contact
prevents the male plate 12 from moving relative to the female plate
14. In addition, though both the locking screw 18 and the female
plate 14, including the track 164 are preferably made of titanium,
the locking screw 18 is of a significantly harder grade. In this
way, as the locking screw 18 is rotated 90 degrees, because the cam
162 is present and has a cam shape, the cam 162 is forced into the
track 164, effectively deforming the cam 162 and forming a "cold
weld" with the track 164. In this way, a rigid, permanent fixation
between the locking screw 18 and the male plate 12 to which it is
attached and the female plate 14 through track 164 is achieved and
compression is maintained. The SC device 10 in this embodiment is
also designed to work with the compression device 90.
[0135] An alternate embodiment of the SC device 10 in a preferred
embodiment shown in FIGS. 36-54 also has a male plate 12 and a
female plate 14. In addition, the SC device 10 in this embodiment
also has a locking plate 316 and a locking screw 318 that, in
combination with standard cancellous bone screws (not shown) fix
the SC device 10 to the patient's vertebrae. This SC device 10 has
a top side 320, a bottom side 322 and opposed medial sides 324.
[0136] The male plate 12 has a male main body 326 and a protrusion
328 extending away from the male main body 326. The protrusion 328
has a top surface 330 and a longitudinal axis 332. The male main
body 326 is relatively flat with a top side 334 and a bottom side
336 and, in a preferred embodiment, has two screw receiving holes
338. The screw receiving holes 338 each have a bowl-shaped basin
340 on the top side 334 to receive the heads of the screws and a
throughhole 342 through which the main body of the screws pass to
come into contact with the vertebral body. The throughholes 342 are
machined to have a rigid relationship with the bone screws as will
be described hereafter.
[0137] The bottom side 336 of male plate 12 is preferably
roughened, thereby allowing the bottom side 336 of male plate 12 to
"grip" the vertebral body when the bottom side 336 is brought into
contact with and is secured to the vertebral body by the
interaction of the screws and the male main body 326 as described
above.
[0138] As mentioned, the male plate 12 has a protrusion 328 with a
top surface 330 and a longitudinal axis 332. Protrusion 328 is
dimensioned to mate with and secure the male plate 12 with the
female plate 14 as will be described in detail hereafter. The
length of protrusion 328 along the longitudinal axis 332 is chosen
to be slightly longer than the distance the SC device 10 is
intended to provide compression over.
[0139] Protrusion 328 has a slot 344 extending entirely through it
approximately perpendicular to the top surface 330. Protrusion 328
also has a series of alternating ridges 346 and valleys 348,
collectively protrusion ridges 350, located on a portion of its top
surface 330. Ridges 350 are preferable angled slightly with respect
to the longitudinal axis 332 for a purpose to be explained
hereafter.
[0140] The female plate 14 has a female main body 352 with a bottom
side 354 and a protrusion receiving channel 356. Protrusion
receiving channel 356 is comprised of a left channel 358, a right
channel 360 and a connecting piece 362. Left channel 358 is
basically "C" shaped with a top piece 370, bottom piece 372 and an
outer piece 374. Although left channel 358 has been described as
having a top piece 370, bottom piece 372 and outer piece 374, left
channel 358 is preferable a single contiguous piece although it
could be made of these separate segments connected together.
[0141] Right channel 360 has a top piece 370, a bottom piece 372
and an outer piece 374. Although right channel 360 has been
described as having a top piece 370, bottom piece 372 and outer
piece 374, right channel 360, like left channel 358, is preferably
a single contiguous piece although it could be made of these
separate segments connected together.
[0142] Connecting piece 362 connects the left channel 358 to the
right channel 360 at the respective bottom pieces 372. In the
preferred embodiment, connecting piece 362 is integrally formed
with the bottom pieces 372 although it could be made of these
separate segments connected together. Connecting piece 362 has a
threaded hole 376 that extends into connecting piece 362.
[0143] Protrusion receiving channel 356 is dimensioned to snugly
receive the protrusion 328 so that the protrusion 328 is "captured"
and held in the protrusion receiving channel 356 by relatively
conformal physical contact between the outer surface of the
protrusion 328 and the inner surfaces of the left channel 358,
right channel 360 and connecting piece 362.
[0144] The female main body 352 also has an upper surface 378 and a
channel 380 formed in the upper surface 378 between the left
channel 358 and the right channel 360. Channel 380 extends entirely
through the upper surface 378.
[0145] The female plate 14, also in a preferred embodiment, has two
screw receiving holes 382. These screw receiving holes 382 receive
standard cancellous bone screws (not shown) that are threaded into
the bone of the vertebrae. In similar fashion to screw receiving
holes 338, the screw receiving holes 382 also have a bowl-shaped
basin 384 on the upper surface 378 to receive the heads of the bone
screws and a throughhole 386 through which the main body of the
bone screws pass to come into contact with the vertebral body. The
throughholes 386 are machined to provide a rigid relationship with
the bone screws. The SC device 10 has a locking mechanism 388. The
locking mechanism 388 includes locking plate 316 and locking screw
318 as well as the ridges 346 and valleys 348 on the top surface
330 of protrusion 328 of the male plate 12 and the threaded hole
376 and channel 380 of female plate 14 as described below. Locking
mechanism 388 converts "active" compression applied by the surgeon
using the compression device 90 described above interacting with
the SC device 10 at the time of surgery to "static" compression
after surgery. The locking mechanism 388 also provides rigid
fixation to the SC device 10 to optimize bone healing and
preventing further settling from occurring.
[0146] The locking plate 316 has a top surface 392, a bottom
surface 394 and parallel sides 396. The bottom surface of locking
plate 316 preferably has a series of ridges 398 and valleys 400,
collectively locking ridges 402, of similar dimensions to the
ridges 346 and valleys 348 of the protrusion 328 to locate and
affix the locking plate 316 to the protrusion 328 as will be
described hereafter. In a most preferred embodiment of the
invention, the ridges 346 and valleys 348 of the protrusion 328 and
the ridges 398 and valleys 400 of the locking plate 316 are angled
slightly with respect to the longitudinal axis 332. Through this
configuration, the ridges 398 and valleys 400 of the bottom surface
394 of the locking plate 316 preferably contact and engage with the
ridges 346 and valleys 348 of the protrusion 328 in frictional or
mechanical contact to precisely locate and affix the locking plate
316 to the protrusion 328. Further, as shown in FIGS. 42 and 48-53,
because the protrusion ridges 350 and the locking ridges 402 are
angled, as the locking plate 316 is moved from one side of the
channel 380 to the other, as the locking ridges 402 seat with the
protrusion ridges 350, the male plate 12 is moved into compression
with the female plate 14. This compression is transferred through
the male plate 12 and female plate 14 to the vertebral bone.
[0147] The width of the locking plate 316 (i.e, the distance
between the parallel sides 396) is such that the locking plate 316
will fit snugly into the channel 380 formed in the upper surface
378 of the female plate 14 of the SC device 10 but still allow the
locking plate 316 to move in a direction perpendicular to the
parallel sides 396 within the channel 380.
[0148] Locking plate 316 has a slot 404. Slot 404 is aligned with
channel 344 of the protrusion 328 and allows a locking screw 318,
as explained hereafter, to pass through both the slot 404 and mate
with the threaded hole 376 as described hereafter. Slot 404 is also
dimensioned to conformally mate with the head 406 of screw 318 so
that contact between the head 406 and slot 404 as the locking screw
318 is threaded into threaded hole 376 moves the locking ridges 402
into contact with the protrusion ridges 350.
[0149] A single large locking screw 318, dimensioned to rotate
freely within the slot 404 of the locking plate 316, activates the
locking mechanism 388. In the embodiment of the invention shown in
FIGS. 36-54, the locking screw 318 has a head 406, a threaded body
408 and a distal end 410 where the head 406 has a larger
cross-sectional diameter than the threaded body 408.
[0150] In use, the protrusion 328 is inserted into the protrusion
receiving channel 356 (FIGS. 39 and 48). Because protrusion
receiving channel 356 is dimensioned to conformally receive
protrusion 328, protrusion is precisely located and retained within
the protrusion receiving channel 356. Locking plate 316 is placed
on the top surface 330 of protrusion 328 within the channel 380 so
that the protrusion ridges 350 come into contact with the locking
ridges 402 (FIG. 49). The locking screw 318 is passed through the
slot 404 so that its distal end 410 comes into contact with and is
threaded into the threaded hole 376 a sufficient amount to locate
the distal end 410 of the locking screw 318 in the threaded hole
376 but not a sufficient amount to secure the locking ridges 402 of
the locking plate 316 into secure contact with the protrusion
ridges 350 (FIGS. 50-51).
[0151] Bone screws are passed through the screw receiving holes 338
and 376 and into the vertebral bone. These bone screws are screwed
into the vertebral bone until the heads of the bone screws seat
into the basins 334, 378 of the male plate 12 and female plate 14,
respectively.
[0152] The compression device 90 is then used to apply the desired
compression to the SC device 10. The pins 132 are placed in the
notches 442, 444 and the handles 118, 120 are squeezed together. As
a result, compression pressure is applied to the male plate 12 and
female plate 14 and thereby to the vertebral bone through the bone
screws. As mentioned above, where a gauge 146 is present, the
amount of compressive force applied to the SC device 10 can be
ascertained. Once the desired amount of compressive force is
applied to the SC device 10, the screwdriver 160 is coupled to the
head 406 of the locking screw 318. The screwdriver 160 is rotated
so that the threaded body 408 of locking screw 318 is threaded into
the threaded hole 376. In this process, the locking ridges 402 are
brought into secure contact with the protrusion ridges 350. But, to
secure an optimum fit between the locking ridges 402 and the
protrusion ridges 350, it may be necessary to move the locking
plate 316 from side to side within the channel 380 until they mate
optimally and impart a compression on the male plate 12 and female
plate 14 (FIG. 52). Once this optimal mating occurs, the
screwdriver 160 is rotated further. The interaction between the
head 406 and the slot 404 locks the locking plate 316 against the
protrusion 328. Locking screw 318 is tightened into the threaded
hole 376 so that the male plate 12 is securely positioned with
respect to the female plate 14. Once male plate 12 is secured with
respect to the female plate 14, the compression device 90 is
removed.
[0153] Another alternate embodiment of the SC device 10 is shown in
FIGS. 55-56. In this embodiment, the SC device 10 is as described
above except that the SC device 10 has a spring mechanism 168
integral between the ends of the male plate 12 and female plate 14
that provides a near constant force applied to a fixed vertebral
segment (or segments) through a standard buttressing or tension
band construct. Spring mechanism 168 has three parts, a relatively
flat spring plate 170, guide pins 184, 186 and a guide plate 172.
Spring plate 170 has ends suitable for attaching to bone via one or
more bone screws.
[0154] Spring 178 is preferably a plurality of flexible members
that resist being moved in a lateral direction, in this case, in
the direction of moving the one plate end 174 away from the other
plate end 176. In a preferred version of this embodiment, the
spring 178 is a plurality of flat serpentine shaped members made of
a spring metal such as spring steel. However, the spring 178 could
also be made of a single member that has spring-like attributes and
could be made of materials other than metal so long as the elements
of spring 178 possess the ability to resist stretching according to
a linear restoring force (i.e., follows Hooke's law).
[0155] Guide plate 172 reinforces spring plate 170 and provides
over extension protection as well as flexion/extension moment
buffering. Over extension protection is provided by guide pins 184,
186 attached to spring plate 12 via slots and limit the extension
of the spring 178. Flexion/extension is controlled by the guide
plate 172 in close contact with the spring plate 12.
[0156] This embodiment of SC device 10 allows the SC device 10 to
settle into position on the vertebral bone and minimize the
deflection of the male plate 12 and the female plate 14 without a
drastic reduction in the SC device 10's ability to provide a
consistent tension force. Further, after the SC device 10 is
implanted, the surgeon can determine the actual level of
compression by measuring the overall change in length of the
construct and applying Hooke's law to determine the relative rate
of compression.
[0157] Another feature of an embodiment of the invention shown in
FIG. 57 is that of a series of trial spacers 202 that include a
strain gauge capable of measuring compressive strain through
electromagnetic techniques as are well understood in the art. These
spacers 202 are preferably cylindrical in shape with a handle which
allows them to be inserted between the vertebral bodies. The
spacers are machined to have the approximate dimensions of the bone
graft which is to be placed between adjacent vertebrae (in the disc
space once the disc has been removed). This embodiment also
includes a handle 204 attached to the spacer 202 in order to allow
the surgeon ease in facilitating insertion and extraction of the
spacer 202. The cylinders of the spacer 202 are preferably machined
in height increments (e.g. one millimeter) in order to accommodate
a variety of disc space heights.
[0158] The spacer 202 serves two purposes. First, it enables the
surgeon to "size" the disc space in order to place an appropriate
sized graft, in the same manner that many allograft spacers
currently have "trials". Second, each spacer 202 has the
characteristics of a strain gauge which is able to directly measure
the "passive" force applied to that spacer 202 by the adjacent
vertebral bodies, once the spacer 202 is inserted. In this way the
surgeon may estimate the approximate "passive" force which would be
applied to a similar sized bone graft. The total force applied to
that graft, then, would be the sum of the passive force applied to
the graft (as measured by the spacer of similar dimensions) and the
active force applied by the surgeon through the compression device
90. Thus, by using the strain-gauge spacer 202 in conjunction with
the compression device 90, the surgeon may obtain an accurate
assessment of total force applied to the graft. This is beneficial
in that it allows further study of the "optimal" force which must
be applied in order to reliably achieve fusion.
[0159] In all the embodiments shown, the SC device 10 is a unique
device that utilizes Wolff s law to compress two or more adjacent
cervical vertebrae while fusion between the vertebrae occurs by
allowing static, rigid compression to be applied to interbody graft
in the cervical spine. Static, rigid compression has definitively
been shown to increase bony union in a long bone fracture model.
Lumbar interbody fusions have been shown to heal at a higher rate
than intertransverse fusions, presumably because of the constant
loading of the graft. No other currently available cervical device
allows for active, static compression.
[0160] It should be noted that use of the SC device 10 is by no
means limited to use in the cervical spine. Any of the
aforementioned embodiments, in a somewhat larger version or having
a curved bottom side 22 (FIG. 58) as will be clear to those skilled
in the art, may be used for the same or similar purposes in the
thoracic or lumbar spine, or in instances where static compression
is desired outside of the spine (e.g., and without limitation, bone
fractures, as for example, of long bones like the femur or bones of
the skull, hip or scapula) (FIG. 59).
[0161] In the thoracic spine a larger version of the SC device 10
may be placed on the side of the thoracic spine (as opposed to the
front) in order to facilitate approach to the thoracic spine and to
avoid large vascular structures that reside immediately in front of
the thoracic spine.
[0162] In the lumbar spine, a larger version of the SC device 10
may be placed either on the side of the spine to facilitate
exposure and avoid vascular structures or directly on the front of
the spine, especially at the lumbosacral junction. It is believed
that in order to obtain anterior fusion at L5-S1, it is important
to have a fully contoured SC device 10 (FIG. 58) that is simply
comprised of a male plate 12 and a female plate 14 with a curved
bottom side 22 matching the curvature of the vertebral segments in
the L5-S1 region.
[0163] As mentioned above, the SC device 10 may be used to obtain
union of fractures, nonunions, osteotomies and other bony defects
in regions other than the spine. In the embodiment suited for use
with other bones, the SC device 10 should be sized appropriately to
the bone and have the option of placing more than two screws 138 on
either side of the defect where union is desired (FIG. 59). The SC
device 10 allows for maximum utilization of Wolff s Law to
facilitate healing in that reproducible measurable compression is
applied in each of these scenarios to obtain bony union.
[0164] FIG. 60 is a perspective view of an embodiment of the static
compression device designed to be used to treat fractures. The
reference numerals correspond to elements described in other
embodiments above. Reference numerals designed with a prime symbol
simply refer to the same element disposed in a different structural
configuration.
[0165] The SC device 10 described herein has the following four
unique characteristics which together provide for static
compression of the vertebral body-graft interface: [0166] The use
of fixed-angle screws to secure the SC device 10 to the vertebral
bodies; [0167] The use of a compression device to apply and measure
the pressure applied to the vertebral bodies by the SC device 10;
[0168] The technique of using active, static compression to assist
the fusion process; and [0169] The use of a locking mechanism 88
that maintains compression during the fusion process to facilitate
bone growth. These four characteristics of the SC device 10 are not
currently found in any other spinal device. As a result, it is
believed that the SC device 10 in any of the disclosed embodiments
provides an optimal environment for spinal fusions to consolidate
while preventing frequent non-unions and occasional deformities
seen with the use of current dynamic plates.
[0170] The SC device 10 in several embodiments has been described
in detail above. However, it is to be understood that the specific
features of the various components may be modified as will occur to
those skilled in the art and still fall within the parameters of
the invention. For example, the specific cross-sectional shape of
the protrusion 28, left and right guides 58, 60 and side
protrusions 29 may be modified so long as these components
interlock with each other as described herein. Further, the shape
of the locking clamp 16 may be modified so long as it is able to be
deformed to force frictional or mechanical contact between the
various components as described above.
[0171] Further, the invention has been described as having a
protrusion 28 with side protrusions 29 on a male plate 12 or
interconnecting plate 15 and a left guide 58 and right guide 60 on
a female plate 14 or interconnecting plate 15. It is clear that the
invention could also be practiced with the male plate 12 or
interconnecting plate 15 having a single protrusion 28 with the
female plate 14 or interconnecting plate 15 still having the left
guide 58 and right guide 60. Also, the SC device 10 could have two
or more protrusions 28 on the male plate 12 or interconnecting
plate 15 with a corresponding number of protrusion receiving
channels 56 to receive these protrusions 28 and a corresponding
number of locking clamps 16.
[0172] The present invention has been described in connection with
certain embodiments, configurations and relative dimensions. It is
to be understood, however, that the description given herein has
been given for the purpose of explaining and illustrating the
invention and are not intended to limit the scope of the invention.
For example, complimentary versions of the mating aspects of the SC
device 10 could be formed and still be within the scope of the
invention. In addition, it is clear that an almost infinite number
of minor variations to the form and function of the disclosed
invention could be made and also still be within the scope of the
invention. Consequently, it is not intended that the invention be
limited to the specific embodiments and variants of the invention
disclosed. It is to be further understood that changes and
modifications to the descriptions given herein will occur to those
skilled in the art. Therefore, the scope of the invention should be
limited only by the scope of the claims.
* * * * *