U.S. patent application number 14/985903 was filed with the patent office on 2016-04-28 for multi-thread bone screw and method.
The applicant listed for this patent is Warsaw Orthopedic, Inc.. Invention is credited to Francis Denis, Timothy A. Garvey, Joseph H. Perra, Manuel Pinto, James D. Schwender, Ensor Transfeldt, Michael Veldman.
Application Number | 20160113693 14/985903 |
Document ID | / |
Family ID | 37944107 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160113693 |
Kind Code |
A1 |
Denis; Francis ; et
al. |
April 28, 2016 |
MULTI-THREAD BONE SCREW AND METHOD
Abstract
A bone screw comprises a threaded shank including a distal end
portion and a proximal end portion, and defining a first threaded
section extending from the distal end portion toward the proximal
end portion and adapted for anchoring in cancellous bone. A second
threaded section extends contiguously from the first threaded
section toward the proximal end portion. The second threaded
section has a finer thread pattern relative to the first threaded
section. In one embodiment, the first threaded section includes a
first helical threading defining a single lead thread pattern for
anchoring in cancellous bone, and the second threaded section
includes a second helical threading interleaved with the first
threading to define a duel lead thread pattern for engagement in
cortical bone. In a further embodiment, the bone screw includes a
head portion extending from the threaded shank and configured for
coupling to a spinal implant.
Inventors: |
Denis; Francis;
(Minneapolis, MN) ; Garvey; Timothy A.; (Edna,
MN) ; Perra; Joseph H.; (Shoreview, MN) ;
Pinto; Manuel; (Minnetonka, MN) ; Schwender; James
D.; (Edna, MN) ; Transfeldt; Ensor; (Edna,
MN) ; Veldman; Michael; (Memphis, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Warsaw Orthopedic, Inc. |
Warsaw |
IN |
US |
|
|
Family ID: |
37944107 |
Appl. No.: |
14/985903 |
Filed: |
December 31, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13323546 |
Dec 12, 2011 |
9247976 |
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14985903 |
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11355877 |
Feb 16, 2006 |
8075604 |
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13323546 |
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Current U.S.
Class: |
606/308 ;
606/315 |
Current CPC
Class: |
A61B 17/7041 20130101;
A61B 17/7037 20130101; A61B 17/7038 20130101; A61B 17/863 20130101;
A61B 17/7059 20130101; A61B 17/7032 20130101; A61B 17/7007
20130101; A61B 17/701 20130101 |
International
Class: |
A61B 17/86 20060101
A61B017/86; A61B 17/70 20060101 A61B017/70 |
Claims
1-40. (canceled).
41. A system comprising: a screw comprising: a threaded shank
including a distal end portion and a proximal end portion, said
threaded shank defining a first threaded section extending from
said distal end portion toward said proximal end portion, said
threaded shank defining a second threaded section extending
contiguously from said first threaded section toward said proximal
end portion, said threaded shank including a first helical
threading extending along said threaded shank from said first
threaded section and into said second threaded section, said
threaded shank including a second helical threading interleaved
with said first helical threading to define said second threaded
section; and a structure comprising an inner first region having a
first hardness and an outer second region having a second hardness,
the second hardness being greater than the first hardness, wherein
said screw is configured for being inserted into said structure
such that said first threaded section penetrates said first region
after said first threaded section penetrates said second
region.
42. The system of claim 41, wherein said second threaded section
comprises a finer thread pattern relative to said first threaded
section.
43. The system of claim 41, wherein each of said first and second
helical threadings having a substantially equal thread pitch.
44. The system of claim 41, further comprising a spinal rod
positioned in U-shaped channel in a head portion of said screw that
extends from said proximal end portion.
45. The system of claim 41, wherein said second threading is
interleaved with and substantially centered between said first
threading to define a double helical thread pattern.
46. The system of claim 41, wherein said second threading is offset
about 180 degrees relative to said first threading.
47. The system of claim 41, wherein said first threading and the
second threading are buttress threads.
48. The system of claim 41, wherein said first threaded section
extends along at least about two-thirds of said threaded shank.
49. The system of claim 41, wherein said second threaded section
extends along about one-thirds of said threaded shank.
50. The system of claim 41, wherein: said first threaded section
extends along at least about two-thirds of said threaded shank; and
said second threaded section extends along about one-thirds of said
threaded shank.
51. The system of claim 41, wherein said screw comprises a head
portion that extends from said proximal end portion, said head
portion comprising a pair of spaced apart arms that together with a
surface of said head portion define a U-shaped channel.
52. The system of claim 51, wherein said U-shaped channel is
concavely curved between the arms.
53. The system of claim 51, wherein said threaded shank extends
along a longitudinal axis, said screw being coaxial with said
longitudinal axis from said proximal end portion to said head
portion.
54. The system of claim 51, further comprising a set screw having a
threaded outer surface, wherein inner surfaces of said arms are
threaded and are configured to engage the threaded outer surface to
couple said set screw to said head portion.
55. The system of claim 41, wherein said first threaded section has
a larger thread depth than said second threaded section.
56. A system, comprising: a screw comprising: a threaded shank
including a distal end portion, a proximal end portion, and a
middle portion extending between said distal end portion and said
proximal end portion, a first helical buttress threading extending
continuously from said distal end portion to said proximal end
portion of said threaded shank, a second helical threading
extending from said middle portion to said proximal end portion
such that said second helical threading does not extend to said
distal end portion, said first and second helical threadings having
a substantially similar thread pitch, and a head portion extending
from said proximal end portion of said threaded shank; and a
structure comprising an inner first region having a first hardness
and an outer second region having a second hardness, the second
hardness being greater than the first hardness, wherein said screw
is inserted into said structure such that said first helical
threading penetrates said first region after said first helical
threading penetrates said second region.
57. The system of claim 56, wherein said second threading is
substantially centered between said first threading to define said
double helical thread pattern that engages said second region.
58. The system of claim 56, wherein said second threading is offset
about 180 degrees relative to said first threading.
59. The system of claim 56, wherein said second threading is a
buttress thread.
60. A system comprising: a screw comprising: a threaded shank
including a distal end portion and a proximal end portion, said
threaded shank defining a first threaded section extending from
said distal end portion toward said proximal end portion, said
threaded shank defining a second threaded section extending
contiguously from said first threaded section toward said proximal
end portion, said threaded shank including a first helical
threading extending along said threaded shank from said first
threaded section and into said second threaded section, said
threaded shank including a second helical threading interleaved
with said first helical threading to define said second threaded
section, and a head portion extending from said proximal end
portion of said threaded shank, said head portion comprising a pair
of spaced apart arms that together with a surface of said head
portion define a U-shaped channel that is concavely curved between
the arms; a structure comprising an inner first region having a
first hardness and an outer second region having a second hardness,
the second hardness being greater than the first hardness; and a
set screw having a threaded outer surface, wherein inner surfaces
of said arms are threaded and are configured to engage the threaded
outer surface to couple said set screw to said head portion,
wherein said screw is configured for being inserted into said
structure such that said first threaded section penetrates said
first region after said first threaded section penetrates said
second region.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of bone
screws, and more particularly relates to a bone screw having
multiple threaded sections adapted for engagement with different
regions of bone, and a method for using the same.
BACKGROUND
[0002] Various types of fasteners are used to engage implants and
other devices to bone. In the spinal field, bone screws are
commonly used to attach plates, rods and other types of implants
and devices to one or more vertebrae. Referring to FIG. 1, shown
therein is a prior art bone screw 10 including a threaded shank
portion 12 adapted for engagement in bone, and a head portion 14
for coupling to an elongate member (not shown), such as a spinal
rod, via a connector mechanism (not shown). Examples of connector
mechanisms suitable for coupling a spinal rod to the head portion
14 of the bone screw 10 are illustrated and described, for example,
in U.S. Pat. No. 5,643,263 to Simonson, U.S. Pat. No. 5,947,967 to
Barker and U.S. Pat. No. 6,471,703 to Ashman.
[0003] The threaded shank portion 12 of the bone screw includes a
single, constant pitch threading 16. The threading 16 comprises a
relatively wide pitch that is particularly suitable for engagement
or purchase within cancellous bone, such as the cancellous bone
within the interior region of a vertebral body. Although the
threading 16 may be provided with finer pitched threads to increase
stability within the relatively harder and denser cortical region
of the hone, finer pitched threads tend to decrease purchase within
the cancellous region of the bone. Furthermore, finer pitched
threads require additional turns to fully engage the bone screw
within the bone.
[0004] Thus, there remains a need for an improved bone screw and a
method for using the same. The present invention satisfies this
need and provides other benefits and advantages in a novel and
unobvious manner.
SUMMARY
[0005] The present invention relates generally to a bone screw
having multiple threaded sections adapted for engagement with
different regions of bone, and a method for using the same. While
the actual nature of the invention covered herein can only be
determined with reference to the claims appended hereto, certain
forms of the invention that are characteristic of the preferred
embodiments disclosed herein are described briefly as follows.
[0006] In one form of the present invention, a bone screw is
provided having a threaded shank including a distal end portion and
a proximal end portion, with the threaded shank defining a first
threaded section extending from the distal end portion toward the
proximal end portion and adapted for anchoring in cancellous bone,
and with the threaded shank defining a second threaded section
extending contiguously from the first threaded section toward the
proximal end portion and adapted for engagement in cortical bone,
and wherein the second threaded section comprises a finer thread
pattern relative to the first threaded section.
[0007] In another form of the present invention, a spinal system is
provided including a bone screw with a threaded shank having a
distal end portion and a proximal end portion and a head portion
extending from the proximal end portion of the threaded shank, with
the threaded shank defining a first threaded section extending from
the distal end portion toward the proximal end portion and adapted
for anchoring in cancellous bone, and with the threaded shank
defining a second threaded section extending contiguously from the
first threaded section toward the proximal end portion and adapted
for engagement in cortical bone, and wherein the second threaded
section comprises a finer thread pattern relative to the first
threaded section. The spinal system further includes a spinal
implant coupled to the head portion of the bone screw.
[0008] In a further form of the present invention, a bone screw is
provided having a threaded shank including a distal end portion and
a proximal end portion, with the threaded shank including a first
helical threading extending from the distal end portion toward the
proximal end portion and defining a single lead thread pattern
adapted for anchoring in cancellous bone, and with the threaded
shank including a second helical threading interleaved with the
first threading to define a duel lead thread pattern adjacent the
proximal end portion of the threaded shank adapted for engagement
in cortical bone.
[0009] In still another form of the present invention, a method is
provided for engaging a bone screw to a bone having an inner
cancellous region and an outer cortical bone region. The method
includes the step of providing a bone screw having a threaded shank
including a distal end portion and a proximal end portion, with the
threaded shank defining a first threaded section extending from the
distal end portion toward the proximal end portion and adapted for
anchoring in cancellous bone, and with the threaded shank defining
a second threaded section extending contiguously from the first
threaded section toward the proximal end portion and adapted for
engagement in cortical bone, and wherein the second threaded
section comprises a finer thread pattern relative to the first
threaded section. The method further includes the steps of engaging
the first threaded section within the inner cancellous region of
the bone, and engaging the second threaded section within the outer
cortical region of the bone.
[0010] It is one object of the present invention to provide an
improved bone screw and a method for using the same. Further
objects, features, advantages, benefits, and aspects of the present
invention will become apparent from the drawings and description
contained herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is an elevational side view of a prior art bone
screw.
[0012] FIG. 2 is an elevational side view of a bone screw according
to one form of the present invention.
[0013] FIG. 3 is an elevational side view of the bone screw
illustrated in FIG. 2, as engaged to bone and as coupled to a
spinal rod.
[0014] FIG. 4 is an elevational side view of a bone screw according
to another form of the present invention, as engaged to bone and as
coupled to a spinal rod.
[0015] FIG. 5 is an elevational side view of a bone screw according
to another form of the present invention, as engaged to bone and as
coupled to a spinal plate.
[0016] FIG. 6 is an elevational side view of a bone screw according
to another form of the present invention, as engaged to bone and as
coupled to a spinal plate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated in the drawings and specific language will
be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is hereby
intended, and that alterations and further modifications to the
illustrated devices and/or further applications of the principles
of the invention as illustrated herein are contemplated as would
normally occur to one skilled in the art to which the invention
relates.
[0018] Referring to FIG. 2, shown therein is a bone screw 50
according to one form of the present invention. The bone screw 50
extends along a longitudinal axis L and includes a distal end
portion 50a and a proximal end portion 50b. The bone screw 50
generally includes a threaded shank portion 52 adapted for
engagement within bone, and a head portion 54 adapted for coupling
with an implant, further details of which will be set forth below.
The bone screw 50 may be formed of any suitable biocompatible
material such as, for example, titanium, a titanium alloy,
stainless steel, metallic alloys, or other materials known to those
of skill in the art that possess the mechanical and biocompatible
properties suitable for implantation within the body and attachment
to bone.
[0019] In one embodiment, the threaded shank 52 includes a distal
tip 56 that is configured to penetrate bone. In the illustrated
embodiment, the distal tip 56 is tapered or pointed to facilitate
entry into bone. However, in other embodiments, the distal tip 56
may define a blunt or rounded end. In further embodiments, the
distal tip 56 or other portions of the distal end portion 50a may
be provided with one or more cutting edges or flutes (not shown) to
provide the bone screw 50 with self-cutting or self-tapping
capabilities. In still other embodiments, the bone screw 50 may be
provided with an axial passage (not shown) extending from the
proximal end portion 50b and partially or entirely therethrough to
define a cannulation opening, and may be further provided with
transverse passages that communicate with the axial passage to
define fenestration openings. The cannulation and fenestration
openings may be used to deliver material such as, for example, bone
cement from the proximal end portion 50b of the bone screw 50 and
into areas of the bone axially or laterally adjacent the distal end
portion 50a or other portions of the threaded shank 52.
[0020] In the illustrated embodiment, the head portion 54 comprises
a relatively smooth shaft or stern 58 configured to slidably
receive an implant member or a connector for coupling to an implant
member. However, it should be understood that other types and
configuration of screw head portions 54 are also contemplated,
several examples of which will be discussed below. Additionally,
bone screw embodiments are also contemplated which do not include a
screw head portion. The bone screw 50, and particularly the screw
head portion 54, preferably includes features that allow for
releasable engagement with a driving tool or instrument (not shown)
such as, for example, a screwdriver. In one embodiment, the screw
head portion 54 may define a cavity or recess (not shown) sized and
shaped to receive a distal end portion of a driver tool. The cavity
or recess is preferably non-circular such as, for example,
hexagonal or rectangular shaped to provide non-rotational
engagement between the head portion 54 and the driver tool to
facilitate driving engagement of the bone screw 50 into bone.
Alternatively, the screw head portion 54 may define external
surface features for engagement by the distal end portion of a
driver tool.
[0021] The threaded shank 52 has an overall length l and defines a
first threaded section 60 extending along a first shank length
l.sub.1 from the distal end portion 50a toward the proximal end
portion 50b, and a second threaded section 62 extending
contiguously from the first threaded section 60 to the proximal end
portion 50b along a second shank length l.sub.2. As will be
discussed in greater detail below, the first threaded section 60
includes a first threading 64 that is adapted for anchoring in the
cancellous region of a bone, and the second threaded section 62
includes a relatively finer threading 66 that is adapted for
anchoring in the cortical region of the bone. Additionally, the
second threaded section 62 may define a thread run out 68 adjacent
the proximal end portion 50b of the threaded shank 52.
[0022] In one embodiment, the length l.sub.1 of the first threaded
section 60 extends along at least about one half of the overall
length l of the threaded shank 52, with the length l.sub.2 of the
second threaded section 62 extending along the remainder of the
overall shank length l. In another embodiment, the length l.sub.1
of the first threaded section 60 extends along at least about
two-thirds of the overall length l of the threaded shank 52, with
the length l.sub.2 of the second threaded section 62 extending
along the remainder of the overall shank length l. In a further
embodiment, the length l.sub.1 of the first threaded section 60
extends along at least about three-quarters of the overall length l
of the threaded shank 52, with the length l.sub.2 of the second
threaded section 62 extending along the remainder of the overall
shank length l. However, it should be understood that other lengths
l.sub.1 of the first threaded section 60 relative to the overall
length l of the threaded shank 52 are also contemplated as falling
within the scope of the present invention.
[0023] As should be appreciated, the particular ratio between the
shank lengths l.sub.1, l.sub.2 associated with the first and second
threaded sections 60, 62 should preferably be selected based on the
characteristics of the bone to which the bone screw 50 is to be
engaged. As discussed above, the first threaded section 60 includes
thread features that are particularly suited for anchoring in the
cancellous region of bone, and the second threaded section 62
includes thread features that are particularly suited for anchoring
in the cortical region of bone. In order to maximize the anchoring
effectiveness of the bone screw 50, the lengths l.sub.1, l.sub.2 of
the first and second threaded sections should preferably correspond
to the desired anchoring depth within the cancellous region of bone
and the thickness of the cortical region of bone, respectively.
[0024] In the illustrated embodiment of the invention, the first
threading 64 includes a single lead in the form of a helical thread
pattern which defines the first threaded section 60, and the second
threading 66 cooperates with the first threading 64 to provide a
dual lead in the form of double helical thread pattern which
defines the second threaded section 62. In the illustrated
embodiment, the first and second threadings or leads 64, 66 are
provided in the form of a helix that extends substantially
continuously about the longitudinal axis L and along the length of
the shank portion 52. Because the second threading 66 is preferably
uniformly and centrally offset relative to the first threading 64,
the threadings 64, 66 appear to spiral together along the length
l.sub.2 of the second threaded section 62 as a continuous thread,
but which in actuality comprise separate threadings. As will be
discussed below, providing separate threadings along the second
threaded section 62 allows the thread pitch associated with each of
the first and second threaded sections 60 and 62 to be equal if so
desired.
[0025] In one specific embodiment, the first threading 64 has a
first thread pitch p.sub.1, and the second threading 66 is
interleaved with the first threading 64 and has a second thread
pitch p.sub.2 that is substantially equal to the first thread pitch
p.sub.1. As should be appreciated, since the first and second
threadings 64, 66 cooperate with one another to provide a dual lead
thread defining the second threaded section 62, and since the first
and second threadings 64, 66 have a substantially equal thread
pitch p, engagement of the second threaded section 62 into bone
will not require any additional turns relative to the first
threaded section 60. Additionally, in the illustrated embodiment,
the second threading 66 is offset about 180 degrees relative to the
first threading 64 such that the turns of the second threading 66
are substantially centered between adjacent turns of the first
threading 64. Although a specific thread configuration and
arrangement has been illustrated with regard to the bone screw 50,
it should be understood that other configurations and arrangements
of threadings are also contemplated for use in association with the
present invention.
[0026] As should be appreciated, providing the first threading 64
with a single lead thread having a relatively large thread pitch
tends to increase cancellous bone purchase capabilities, while at
the same time maintaining the strength and structural integrity of
the cancellous bone.
[0027] Additionally, providing the second threading 66 with a dual
lead thread provides increased fixation strength and stability
within the relatively harder and denser cortical bone. Moreover, as
indicated above, providing the second threaded section 62 with a
dual lead thread having the e thread pitch p as the first threaded
section 60 will not require any additional turns of the bone screw
50 for engagement within cortical bone as compared to engagement of
the first threaded section 60 within cancellous bone.
[0028] In another aspect of the invention, the first and second
threaded sections 60, 62 define an inner thread root diameter
d.sub.i that varies between the distal end portion 50a and the
proximal end portion 50b. In one embodiment, the inner thread root
diameter d.sub.i increases from a first root diameter d.sub.1
adjacent the distal end portion 50a, to a larger second root
diameter d.sub.2 adjacent a mid-section of the threaded shank 52,
to an even larger third root diameter d.sub.3 adjacent the proximal
end portion 50b. In another embodiment, the inner thread root
diameter d.sub.i increases uniformly between the root diameter
d.sub.1 adjacent the distal end portion 50a and the root diameter
d.sub.3 adjacent the proximal end portion 50b. In a further
embodiment, the inner thread root diameter d.sub.i increases along
substantially the entire length l of the threaded shank 52 between
the distal end portion 50a and the proximal end portion 50b. In one
specific embodiment, the inner thread root diameter d.sub.i
increases by at least about 15% between the root diameter d.sub.1
adjacent the distal end portion 50a and the root diameter d.sub.3
adjacent the proximal end portion 50b. In another specific
embodiment, the inner thread root diameter d.sub.i increases by at
least about 25% between the root diameter d.sub.1 and the root
diameter d.sub.3. In a further specific embodiment, the inner
thread root diameter d.sub.i increases by at least about 50%
between the root diameter d.sub.1 and the diameter d.sub.3.
[0029] As should be appreciated, increasing the inner thread root
diameter d.sub.i from the distal end portion 50a toward the
proximal end portion 50b, results in a decrease or reduction in the
depth of the first and second threadings 64, 66 (as measured from
the thread root diameter to the outer thread diameter) from the
distal end portion 50a toward the proximal end portion 50b. It
should further be appreciated that providing the first threading 64
with a relatively large thread depth (or a relatively small root
diameter d.sub.i) provides increased cancellous bone purchase
capabilities and desirable pullout characteristics compared to the
smaller thread depth associated with the second threading 66.
Additionally, providing the second threading 66 with a reduced
thread depth (or a relatively larger inner thread root diameter
d.sub.i) relative to the first threading 64 provides increased
fixation strength and stability, which is particularly advantageous
for fixation within the relatively harder and denser cortical bone,
and also tends to reduce resistance to threading engagement within
the cortical bone. In one specific embodiment, the thread depth of
the first and second threadings 64, 66 decreases by at least about
50% from the distal end portion 50a toward the proximal end portion
50b. As should be appreciated, the thread depth of the threadings
64, 66 is maximized along the first threaded section 60, and
particularly adjacent the distal end portion 50a, to provided
increased cancellous bone purchase capabilities and desirable
pullout characteristics.
[0030] In another aspect of the invention, the first and second
threaded sections 60, 62 define a substantially uniform outer
thread diameter d.sub.c between the distal end portion 50a and the
proximal end portion 50b. In one specific embodiment, the outer
thread diameter d.sub.o is at least about 15% greater than the
inner thread root diameter d.sub.i adjacent the distal end portion
50a. In another specific embodiment, the outer thread diameter
d.sub.o is at least about 25% greater than the inner thread root
diameter d.sub.i adjacent the distal end portion 50a. In a further
specific embodiment, the outer thread diameter d.sub.o is at least
about 50% greater than the inner thread root diameter d.sub.i
adjacent the distal end portion 50a. As should be appreciated, a
larger variation between the outer thread diameter d.sub.o and the
inner thread root diameter d.sub.i tends to increase bone purchase
capabilities, which is particularly suitable along the first
threaded section 60 that is engaged in cancellous bone.
[0031] In a further aspect of the invention, the thread pitch p
adjacent the distal end portion 50a is equal to or greater than the
inner thread root diameter d.sub.i adjacent the distal end portion
50a. In one embodiment, the thread pitch p is equal to or greater
than the inner thread root diameter d.sub.i along substantially the
entire length l.sub.1 of the first threaded section 60 of the
threaded shank 52. In another embodiment, the thread pitch p is
equal to or greater than the inner thread root diameter d.sub.i
along substantially the entire overall length l of the threaded
shank 52.
[0032] As indicated above, the head portion 54 of the bone screw 50
is preferably adapted for coupling with an implant. As illustrated
in FIG. 3, in one embodiment, the screw head portion 54 comprises
an unthreaded stem portion or shaft 58, and the implant comprises
an elongate spinal rod R that is coupled to the screw head 54 via a
connector mechanism 70. The connector mechanism 70 includes a
connector body 72 defining a first passage 74a for receiving the
stem portion 58 of the screw head 54, and a second passage 74b for
receiving the spinal rod R. An interface member 76 may be
positioned between the spinal rod R and the stem portion 58, and a
fastener or et screw 78 is threaded through an opening in the
connector body 72 and into contact with the spinal rod R, which in
turn engages the interface member 76 with the stem portion 58 of
the screw head 54 to fix the angular relationship between the
spinal rod R and the bone screw 50. Further details regarding the
connector mechanism 70 and other types of connector mechanisms are
illustrated and described, for example, in U.S. Pat. No. 5,643,263
to Simonson. U.S. Pat. No. 5,947,967 to Barker and U.S. Pat. No.
6,471,703 to Ashman, the contents of each patent reference hereby
incorporated by reference in its entirety.
[0033] Referring to FIG. 4, shown therein is a bone screw 80
according to another form of the invention for coupling with a
spinal rod R. Specifically, the bone screw 80 includes a threaded
shank 52 and a head 84 that is adapted for coupling with a spinal
rod R. The threaded shank 52 is identical to that described above
and illustrated in FIGS. 2 and 3. However, the bone screw head 84
defines a U-shaped channel 86 that is sized to receive the spinal
rod R therein, with the spinal rod R captured within the channel 86
via a fastener or set screw 88 engaged with the bone screw head
84.
[0034] Referring to FIG. 5, shown therein is a bone screw 90
according to another form of the invention which is adapted for
coupling with an implant, such as a spinal plate P. In one
embodiment, the spinal plate P includes one or more openings 92 for
receiving one or more of the bone screws 90, with the bone screw 90
including an enlarged head portion 94. In the illustrated
embodiment, the opening 92 includes a lower portion sized to
receive the threaded shank 52 therethrough, and an upper portion
sized to receive the enlarged bone screw head 94. As should be
appreciated, threading of the bone screw 90 into the bone
compresses the spinal plate P against an outer surface of the bone,
thereby capturing the spinal plate P between the enlarged head 94
and the outer surface of the bone.
[0035] Referring to FIG. 6, shown therein is a bone screw 90'
according to a further think of the invention for coupling with a
spinal plate P'. Specifically, the bone screw 90' includes a
threaded shank 52, an enlarged head portion 94', and a threaded
stem portion 96 extending from the enlarged head 94', with the
spinal plate P' including one or more openings 92' for receiving
the threaded stem portion 96 of one or more of the bone screws 90'
therethrough, and with the spinal plate P' secured to the bone
screw 90' via a lock nut 98 threaded onto the stem portion 96,
thereby capturing the spinal plate P between the enlarged head 94'
and the lock nut 98. As should be appreciated, the bone screw 90'
illustrated in FIG. 6 allows the spinal plate P' to be spaced from
the outer surface of the bone.
[0036] Having described the components and features associated with
the present invention, reference will now be made to a method for
engaging the bone screw to bone according to one form of the
invention. As shown in FIGS. 3-6, in one embodiment, the bone
comprises a vertebral body V having an inner cancellous bone region
100 and an outer cortical bone region 102. As discussed above, the
outer cortical bone region 102 of the vertebral body V is
relatively harder and denser compared to the inner cancellous bone
region 100. The threaded shank 52 of the bone screw is driven into
engagement with the vertebral body V, with the first threaded
section 60 including the single lead threading 64 engaged within
the inner cancellous bone region 100, and with the relatively finer
second threaded section 62 including the dual lead threading 66
engaged within the outer cortical bone region 102.
[0037] As should be appreciated, the relatively course single lead
threading 64 provides increased bone purchase capabilities and
desirable pullout characteristics compared to the finer dual lead
threading 66, which is particularly advantageous for anchoring
within soft cancellous bone. As should be further appreciated, the
relatively fine dual lead threading 66 provides increased fixation
strength and stability compared to the courser single lead
threading 64, which is particularly advantageous for fixation
within relatively harder and denser cortical bone. Additionally,
since the single lead threading 64 and the dual lead threading 66
each have substantially equal thread pitches p.sub.1, p.sub.2,
threading of the second threaded section 62 into the cortical bone
102 will not require any additional turns relative to threading of
the first threaded section 60 into the cancellous bone 100 to fully
engage the bone screw within the vertebral body V. As should be
appreciated a spinal implant such as a rod or plate may be coupled
to one or more bone screws which are in turn anchored to
corresponding vertebral bodies V for treatment of the spinal
column.
[0038] It should be understood that the bone screws of the present
invention may be anchored within any number of vertebral bodies V,
including a single vertebral body or two or more vertebral bodies.
In one embodiment of the invention, the bone screws are anchored
within the pedicle region of a vertebral body. However, it should
be understood that the bone screws may be anchored to other
portions or regions of a vertebral body. It should also be
understood that the bone screws of the present invention may be
anchored to a posterior, anterior, lateral, posterolateral or
anterolateral aspect of the vertebral body V. It should further be
understood that the bone screws of the present invention may be
attached to any region of the spinal column, including the
cervical, thoracic, or lumbar regions of spinal column. It should
likewise be understood that the bone screws of the present
invention may be attached to bone structures other than vertebral
bodies, such as, for example, hones associated with the arm or
leg.
[0039] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiments have been
shown and described and that all changes and modifications that
come within the spirit of the invention are desired to be
protected.
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