U.S. patent application number 11/041756 was filed with the patent office on 2005-06-16 for intervertebral implant with reduced contact area and method.
This patent application is currently assigned to Zimmer Spine, Inc.. Invention is credited to Kohrs, Douglas W..
Application Number | 20050131539 11/041756 |
Document ID | / |
Family ID | 21936633 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050131539 |
Kind Code |
A1 |
Kohrs, Douglas W. |
June 16, 2005 |
Intervertebral implant with reduced contact area and method
Abstract
The disclosure provides fusion implants, instruments and methods
for insertion of the implants between opposing vertebral bodies to
facilitate stabilization or arthrodesis of an intervertebral joint.
A cross section through the longitudinal dimension of the implant
is substantially configured in an "I" shape. In addition to other
features, the implants of the invention provide a reduced contact
surface area with the interior surface of a bore formed for
receiving the implant.
Inventors: |
Kohrs, Douglas W.; (Edina,
MN) |
Correspondence
Address: |
FAEGRE & BENSON LLP
2200 Wells Fargo Center
90 South Seventh Street
Minneapolis
MN
55402-3901
US
|
Assignee: |
Zimmer Spine, Inc.
|
Family ID: |
21936633 |
Appl. No.: |
11/041756 |
Filed: |
January 24, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11041756 |
Jan 24, 2005 |
|
|
|
09777631 |
Feb 6, 2001 |
|
|
|
6855166 |
|
|
|
|
09777631 |
Feb 6, 2001 |
|
|
|
09045213 |
Mar 20, 1998 |
|
|
|
6224631 |
|
|
|
|
Current U.S.
Class: |
623/17.11 ;
623/17.16 |
Current CPC
Class: |
A61F 2002/30403
20130101; A61F 2002/30166 20130101; A61F 2310/00023 20130101; A61F
2002/30593 20130101; A61F 2002/2839 20130101; A61F 2220/0025
20130101; A61F 2/4611 20130101; A61F 2230/0069 20130101; A61F
2002/2817 20130101; A61F 2002/30777 20130101; A61F 2002/30789
20130101; A61F 2002/30873 20130101; A61F 2002/30904 20130101; A61F
2002/2835 20130101; A61F 2230/0058 20130101; A61F 2/446 20130101;
A61F 2310/00017 20130101; A61F 2002/30858 20130101; A61F 2002/30179
20130101; A61F 2002/30785 20130101; A61F 2002/448 20130101; A61F
2230/0028 20130101; A61F 2002/3023 20130101; A61F 2/447 20130101;
A61F 2002/3085 20130101 |
Class at
Publication: |
623/017.11 ;
623/017.16 |
International
Class: |
A61F 002/44 |
Claims
1-35. (canceled)
36. An implant for intervertebral fusion between opposing
vertebrae, said implant comprising: an implant body having a first
end and a second end, said body having first and second load
bearing surfaces extending along a longitudinal axis of the body
from the first end to the second end, the first and second load
bearing surfaces having a width extending perpendicular to the
longitudinal axis, said first and second load bearing surfaces
having a midline aligned with the longitudinal axis, said first and
second load bearing surfaces having opposing inner surfaces; and
said implant body comprising a central support member connecting
the first and second load bearing surfaces at their midlines, the
central support member having a width narrower than the width of
the first and second load bearing surfaces; wherein the opposing
inner surfaces of the first and second load bearing surfaces form
channels on either side of the central support member; wherein the
central support member is configured to provide rigid support of
the first and second load bearing surfaces.
37. The implant of claim 36, said channels extending along either
side of the central support member from the first end of the body
to the second end of the body.
38. An implant for intervertebral fusion between opposing
vertebrae, the implant comprising: an implant body having a first
end and a second end spaced along a longitudinal axis, the body
including: a central support member positioned in alignment with
the longitudinal axis of the implant body, the central support
member having a first support end and a second support end, the
central support member having a longitudinal dimension extending
from the first support end to the second support end; and a first
traverse member positioned at the first support end of the central
support member, the first traverse member being oriented in a
direction traverse to the longitudinal dimension of the central
support member; a second traverse member positioned at the second
support end of the central support member, the second traverse
member being oriented in a direction traverse to the longitudinal
dimension of the central support member; wherein each of the first
and second traverse member extends from the first end of the
implant body to the second end of the implant body; and wherein the
central support member in configured to maintain a spatial relation
between the first and second traverse members.
39. The implant of claim 38, wherein each of the first and second
traverse members has free ends, the central support member being
positioned between the free ends of the first and second traverse
members.
40. The implant of claim 39, wherein the central support member has
a first side and a second side, the first side and the
corresponding free ends of each of the first and second traverse
members defining a first channel, the second side and the
corresponding free ends of each of the first and second traverse
members defining a second channel.
41. The implant of claim 40, wherein the first and second channels
extend from the first end of the implant body to the second
end.
42. The implant of claim 38, wherein the central support member
extends from the first end of the implant body to the second
end.
43. An implant for intervertebral fusion between opposing
vertebrae, the implant comprising: an implant body having a first
end and a second end, the implant body including: a first traverse
member having opposite first free ends; a second traverse member
having opposite second free ends; a central support member that
bisects each of the first and second traverse members; wherein the
first and second traverse members extend from the first end to the
second end of the implant.
44. The implant of claim 43, wherein the central support member
maintains a spatial relation between the first and second traverse
members.
45. The implant of claim 43, wherein the central support member has
a first side and a second side, the first side and the
corresponding free ends of each of the first and second traverse
members defining a first channel, the second side and the
corresponding free ends of each of the first and second traverse
members defining a second channel.
46. The implant of claim 45, wherein the first and second channels
extend from the first end of the implant body to the second
end.
47. An implant for intervertebral fusion between opposing
vertebrae, the implant comprising: an implant body having length,
the length extending from a first end to a second end, the implant
body including first and second traverse members and a support
member that bisect each of the first and second traverse members; a
first channel centrally located between the first and second
traverse members, the first channel extending along the length of
the implant body; a second channel centrally located between the
first and second traverse member, the second channel extending
along the length of the implant body; wherein the first and second
channels are defined by continuous surfaces of each of the first
and second traverse members, the continuous surfaces of the first
and second traverse members extending along the length of the
implant body; and wherein the support member is configured to
provide rigid support of the first and second traverse member.
48. The implant of claim 36, wherein the first and second load
bearing surfaces contact the opposing vertebrae when the implant is
positioned between the opposing vertebrae.
49. The implant of claim 38, wherein the first and second traverse
members contact the opposing vertebrae when the implant is
positioned between the opposing vertebrae.
50. The implant of claim 43, wherein the first and second traverse
members contact the opposing vertebrae when the implant is
positioned between the opposing vertebrae.
51. The implant of claim 47, wherein the first and second traverse
members contact the opposing vertebrae when the implant is
positioned between the opposing vertebrae.
Description
FIELD OF THE INVENTION
[0001] This invention pertains to procedures for intervertebral
stabilization. Specifically, the disclosure provides implants,
instrumentation and methods to facilitate stabilization or fusion
between two vertebrae.
BACKGROUND OF THE INVENTION
[0002] Chronic back problems cause pain and disability for a large
segment of the population. Frequently, the cause of back pain is
traceable to diseased disk material between opposing vertebrae.
When the disk material is diseased, the opposing vertebrae may be
inadequately supported, resulting in persistent pain.
[0003] Surgical techniques have been developed to remove the
diseased disk material and fuse,the joint between opposing
vertebral bodies. Stabilization and/or arthrodesis of the
intervertebral joint can reduce the pain associated with movement
of an intervertebral joint having diseased disk material.
Generally, fusion techniques involve removal of the diseased disk
and packing the void area with a suitable matrix for facilitating a
bony union between the opposing vertebral bodies.
[0004] Surgical devices for facilitating interbody fusion have also
been developed. These devices typically provide for maintaining
appropriate intervertebral spacing and stabilization of the
vertebrae during the fusion process. Generally, these devices are
referred to as cages. Examples of such devices are disclosed in,
for example, U.S. Pat. Nos. 5,458,638, 5,489,307, 5,055,104,
5,026,373, 5,015,247, 4,961,740, 4,743,256 and 4,501,269, the
entire disclosures of which are incorporated herein by
reference.
[0005] Generally, the fusion device is implanted within a site
prepared between opposing vertebrae. Typically, the site is a bore
formed in the disk material and extends through the cortical end
plates and into the cancellous bone of the opposing vertebrae. Many
of the present fusion devices have a chamber enclosed by a
cylindrical or rectangular wall that substantially contacts the
entire interior surface of the bore. After placement of the device
into the bore, the enclosed chamber (interior of the cage) can be
filled with bone chips or other suitable material for facilitating
bony union between the vertebrae.
[0006] Most of the present fusion devices provide vertebral
stabilization during the fusion process by contact of the entire
outer wall of the fusion device with substantially the entire
interior surface of the wall of the insertion bore. While support
provided by contact of the device with the entire wall of the bore
provides adequate vertebral stabilization during the fusion
process, it also has many disadvantages. For example, the greater
the overall contact area of the device with the surface of the
bore, the slower the rate at which new bone can grow into the bore
to stabilize the joint In addition, the greater the surface area of
the device that contacts the surface area of the bore, the less
continuity that can occur between the bone that is external to the
device and the bone that is internal to the device. This lack of
continuity of bone can translate into reduced structural integrity
of the bony union. Furthermore, reducing the amount and continuity
of the bone growth into the fusion site can cause the patient's
body to rely on the device for long term stabilization rather than
relying on the structural integrity of the new bony union. The
potential orthopedic problems resulting from the body's reliance on
orthopedic implants for structural support are well known.
[0007] Moreover, because most fusion devices are manufactured with
materials that are radiopaque to typical diagnostic imaging
modalities, assessment of the status of new bone growth during the
fusion process can be limited.
[0008] Accordingly, there is a continuing need for improved
intervertebral stabilizing devices and methods. The present
invention is directed to addressing these needs.
SUMMARY OF THE INVENTION
[0009] The invention is directed to procedures for intervertebral
stabilization of opposing vertebrae. The disclosure provides
implants, instruments and methods for stabilization or fusion of
opposing vertebrae.
[0010] At various locations throughout the specification, lists of
examples are provided. It should be noted that the examples are
provided for illustrative purposes and are not intended to limit
the scope of the invention.
[0011] An implant according to the invention includes an implant
body having a first and second end spaced apart by a longitudinal
axis of the implant. The implant body includes a first transverse
member and a second transverse member maintained in spaced apart
relationship by a central support member. The transverse members
each include a bearing surface oriented to contact opposing
vertebral surfaces.
[0012] The bearing surfaces of the implant can be linear, curved or
other suitable configuration. In addition, the bearing surfaces can
include a pattern for anchoring the implant and/or resisting
displacement once the implant is inserted between opposing
vertebrae.
[0013] An implant of the invention provides a reduced displacement
volume relative to the insertion bore necessary to accommodate the
implant. The central support member or transverse members can also
include openings which further reduce the displacement volume of
the implants. In addition to enhancing the continuity of the new
bone growth between the stabilized vertebral bodies, the reduced
displacement volume of the implant facilitates assessment of the
fusion process using known imaging modalities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a perspective view of an implant embodiment of the
invention having a first and second curved bearing surfaces;
[0015] FIG. 2 is a side elevation view of the implant of FIG. 1
(the opposite side being identical in appearance);
[0016] FIG. 3 is a top plan view of a first transverse member of
the implant of FIG. 1 (the top view of the second transverse member
view being identical in appearance);
[0017] FIG. 4 is an elevation view of a trailing end of the implant
of FIG. 1;
[0018] FIG. 5 is an elevation view of a leading end of the implant
of FIG. 1;
[0019] FIG. 6 is a perspective view of a second embodiment of an
implant according to the invention;
[0020] FIG. 7 is a top plan view of a first transverse member of
the implant of FIG. 6 (the top view of the second transverse member
being identical in appearance);
[0021] FIG. 8 is a perspective view of a third embodiment of an
implant according to the invention;
[0022] FIG. 9 is a side elevation view of an embodiment of a
tapered implant according to the invention (the opposite side being
identical in appearance);
[0023] FIG. 10 is a top plan view of the implant of FIG. 9 taken
90.degree. from the view of FIG. 9 (the opposite side being
identical in appearance);
[0024] FIG. 11 is a side elevation view of an implant according to
the invention illustrating a first and second taper (the opposite
side being identical in appearance);
[0025] FIG. 12 is a top plan view of the implant of FIG. 11 taken
90.degree. from the view of FIG. 11 (the opposite side being
identical in appearance);
[0026] FIG. 13 is a side elevation view of another embodiment of an
implant according to the invention having a first and second
taper;
[0027] FIG. 14 is an end view of two opposing vertebrae stretched
apart and including two implants of FIGS. 1-5 disposed
therebetween;
[0028] FIG. 15 is a side elevation view of an insertion tool for
use with an implant of invention;
[0029] FIG. 16 is a side view of a distal end of the insertion tool
of FIG. 15;
[0030] FIG. 17 is perspective view of an implant of FIGS. 1-5 and
the distal end of the insertion tool of FIG. 15;
[0031] FIG. 18 is an end on view of the distal end of the insertion
tool of FIG. 15 with an implant of FIGS. 1-5;.
[0032] FIG. 19 is a side elevation view of an alternative
embodiment of an insertion tool according to the invention; and
[0033] FIG. 20 is an end on view of an implant of FIGS. 1-5 loaded
onto the distal end of the insertion tool of FIG. 19.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention is directed to intervertebral
stabilization and arthrodesis procedures that can provide for
greater structural integrity of the bony union between fused
vertebral bodies of the vertebral column. In addition, the devices
and methods disclosed herein facilitate greater continuity between
the bone formed at the fusion site and the remainder of the
vertebral body. In some embodiments, the invention provides
enhanced ability to assess new bone growth during the fusion
process using typical diagnostic imaging modalities such as
x-rays.
[0035] An implant of the invention can be prepared from known
implant materials including, for example, titanium, stainless
steel, porous titanium, bone or other suitable material used to
manufacture orthopedic implants. Unlike prior implants, the present
implants have no surrounding sidewalls and no chamber. The
disclosed implants support the axial load of the vertebral column
by a "central support member" that separates opposing bearing
surfaces of the implant.
[0036] The "central support member" provides for stabilization of
the vertebral bodies with a reduced area of contact between the
exterior surface of the implant and the inside surface of a bore
formed to accommodate the implant. In addition to promoting greater
structural integrity and continuity of the bony union, the reduced
contact area also reduces obstruction of assessment of the fusion
process. Further reduction in obstruction of assessment of the
fusion process can be provided by forming openings in the bearing
surfaces and/or providing the central support member in the form of
one or more columns having openings in between.
[0037] In some embodiments, in comparison to prior implants, the
present implants have a reduced displacement volume relative to the
cylindrical bore size necessary for insertion of the implant. For
example, in some embodiments, the displacement volume of the
implant takes up about 10% to 40% of the bore volume necessary to
accommodate the implant between opposing vertebrae. In one
preferred embodiment, the implant takes up about 24% or less of the
bore volume necessary to accommodate the implant. Thus, in this
embodiment, the remaining 76% of the bore volume can be filled with
bone or other suitable bone support matrix. In contrast, the BAK
implant (U.S. Pat. No. 5,489,308), commercially available from
Sulzer Spine-Tech, Inc., takes up about 41% of the bore volume on a
relative basis and the Proximity implant (U.S. Pat. No. 5,609,636),
also available from Sulzer Spine-Tech, Inc., takes up about 30% of
the bore volume on a relative basis.
[0038] According to the invention, the central support member is
located between the bearing surfaces of the implant and typically
does not extend to the lateral edges of the bearing surfaces. The
term "central" includes an implant having a support member located
away from the exact center of the bearing surfaces but providing
the same function of a herein described centrally located support
member. The "bearing surfaces" are the surfaces of the implant that
directly contact the opposing vertebral bodies. The "lateral edges"
of the bearing surfaces are the lateral most aspects of the bearing
surfaces.
[0039] The implants also have a leading end and trailing end that
are spaced apart along the longitudinal axis of the implant. In
general, a transverse cross section taken through the longitudinal
axis of the present implants has a substantially "I" shaped
configuration. The "central support member" forms the vertical arm
of the "I" and the "transverse members" form the horizontal arms of
the "I". In use, the central support member is typically oriented
parallel to the longitudinal axis of the vertebral column and the
transverse members are oriented perpendicular.
[0040] Each transverse member has a peripheral surface that is in
direct contact with one of the opposing vertebral bodies. The
traverse members also have an inner surface that is continuous with
the lateral aspect of the central support member. A "channel" is
present on either side of the central support member within the
inner surface of the transverse member. As will be appreciated from
the illustrated embodiment, the channel extends through the leading
and trailing ends of the implant and opens laterally between
opposing transverse members. As discussed below, after insertion of
the implant between opposing vertebrae, the channel can be filled
with a bone support matrix to facilitate new bone growth.
[0041] In some embodiments, the bearing surfaces are curved to
provide an external surface configured for insertion of the implant
into a circular bore formed between opposing vertebrae. In such
embodiments, the opposing bearing surfaces can be parallel to one
another along the longitudinal dimension of the implant from the
trailing end to leading end. Alternatively, the implant can include
a single or double taper including at least a first taper diverging
from the longitudinal axis of the implant from the leading end to
the trailing end. Implant embodiments having curved bearing
surfaces can include a pattern for anchoring the implant between
opposing vertebrae. The pattern can be, for example, knurls or
other intermittently raised surface. Alternatively, the pattern can
be a portion of a helical thread pattern which resists displacement
of the implant from an insertion bore and also provides for
threaded insertion of the implant into the bore.
[0042] In other embodiments, the bearing surfaces can be
substantially linear. According to this embodiment, preferably, at
least one of the bearing surfaces includes a pattern for anchoring
the implant and reducing the chance of displacement of the implant
from of the insertion bore.
[0043] The invention also provides a kit comprising a plurality of
incrementally sized implants which can be selected by the clinician
based on the size needed for a particular patient. In other
embodiments kits are provided which include instrumentation for
performing an implant procedure with or without a plurality of
incrementally sized implants.
[0044] Instruments and methods suitable for insertion of an implant
of the invention are disclosed in, for example, U.S. Pat. Nos.
5,489,308 and 5,458,638, and co-pending application U.S. Ser. Nos.
08/902,083 and 08/921,001, the entire disclosures of which are
incorporated herein by reference. Additional instruments
particularly advantageous for the implants disclosed herein are
described in detail below.
[0045] After the implant is inserted into the bore, the volume of
the bore not occupied by the implant, for example in the region of
the channels, can be filled with a bone support matrix. As used
herein, a "bone support matrix" is a material that facilitates new
bone growth between the opposing vertebral bodies. Suitable bone
support matrices can be resorbable or nonresorbable and
osteoconductive or osteoinductive. Examples of suitable matrices
according to the invention include synthetic materials, such as
Healous.TM., available from Orquest, Mountain View, Calif.; NeOsteo
.TM., available from Sulzer Orthopedic Biologics, Denver, Colo.; or
any of a variety of bone morphogenic proteins (BMPs). Suitable bone
support matrices also include heterologous, homologous, or
autologous bone and derivatives thereof. Preferably, the bone
support matrix is radiolucent on x-rays.
[0046] The bone support matrix can be packed into the bore after
insertion of the implant between the vertebral bodies.
Alternatively, a bone support matrix can be configured to fit into
the longitudinal channels on either side of the central support
member before or after installation of the implant into the site of
implantation. In one embodiment, the external surface of the bone
support matrix can include a portion of a helical thread. According
to this embodiment, when used with an implant having a portion of
helical threads on a bearing surface, the helical threads of the
bone matrix can be complimentary to the helical threads on the
implant such that when placed into the channel a complete helical
thread pattern is formed for threadedly inserting the implant into
the prepared site.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0047] The implants and instruments of the invention will now be
described by reference to the several drawing figures. The
illustrated embodiments are provided only for descriptive purposes
and are not intended to limit the implants which are within the
scope of the invention. It will be appreciated, however, that while
the illustrated embodiments share the general configuration of an
"I" in transverse cross section, each embodiment has additional
unique and advantageous features.
[0048] A. Implants
[0049] FIGS. 1-5 illustrate a first embodiment of an implant of the
invention having a first transverse member 1 and a second
transverse member 2 spaced apart by a central support member 3.
When inserted between opposing vertebrae, each transverse member is
oriented transverse to the longitudinal axis of the vertebral
column and the central support member is oriented parallel to the
longitudinal axis of the vertebral column. Thus, the transverse
members can also be referred to as a "cranial transverse member"
and a "caudal transverse member" to indicate that when inserted
between opposing vertebrae, one transverse member is oriented
cranially and the other transverse member is oriented caudally.
[0050] The first transverse member 1 has a first bearing surface 4
and the second transverse member 2 has a second bearing surface 5.
The first bearing surface 4 and the second bearing surface 5
include a pattern 7 for anchoring the implant within an insertion
bore. The illustrated pattern 7 is a portion of a helical thread 7a
which provides for threadedly inserting implant 10 into a bore
prepared between opposing vertebrae. The helical thread 7a is
generally rectangular in profile. However, a thread pattern having
sharp surfaces or a combination of rectangular and sharp threads
can be used. In addition, other surface patterns, such as knurls,
could be provided on the bearing surface and the device implanted
by impact into a bore.
[0051] The illustrated central support member 3 comprises a
plurality of columns 8a-8d with openings 9a-9c therebetween.
Columns 8a-8d of central support member 3 maintain transverse
members 1 and 2 in a fixed spatial relationship and provide rigid
support and stabilization of opposing vertebral bodies which
contact bearing surfaces 4 and 5. Openings 9a-9c between columns
8a-8d promote greater continuity of new bone growth through the
central support member as well as reduce the presence of radiopaque
material which can obstruct assessment of the fusion process using
typical diagnostic imaging modalities.
[0052] FIG. 3 illustrates a top view of the bearing surface 4 of
the first transverse member 1. Rotation of the implant 180.degree.
would show the bearing surface 5 of the second transverse member 2
which is substantially identical in appearance. The bearing surface
4 (and 5) includes rigid transverse supports, or trusses, 13a-13d
having openings 12a-12c therebetween. As illustrated, the portion
of helical thread 7a can be continuous in the region of the
transverse supports 13a-13d. In addition to facilitating greater
structural integrity of the bony union, the openings 12a-12d also
enhance the ability to assess new bone formation during the fusion
process.
[0053] FIG. 4 is an elevation view of the trailing end 20 of
implant 10. The inner surfaces 21a, 21b of transverse member 1
oppose the inner surfaces 22a, 22b of transverse member 2. The
inner surfaces of the transverse members are continuous with the
lateral surfaces 23a, 23b of the central support member 3. On
either side of the central support member 3, there are two
longitudinal channels 24a and 24b. Channel 24a is defined by
surfaces 21a, 22a and 23a and channel 24b is defined by surfaces
21b, 22b and 23b. Channels 24a and 24b not only provide a large
area for uninterrupted new bone growth around the implant, but they
also provide an arrangement for attachment of an insertion tool
described below.
[0054] Between each inner surface 21a, 22a, 21b and 22b and its
respective lateral edge 25a, 26a, 25b and 26b of transverse members
1 and 2, there are undercut segments 27a, 28a, 27b and 28b. The
angle A between undercut segments 27a and 28a and the angle B
between undercut segments 27b and 28b can be different. As will be
discussed below, asymmetry of angles A and B can provide for proper
orientation of the helical threads 7a of implant 10 with
complimentary threads of a below described insertion tool.
[0055] FIG. 5 is an elevation view of the leading end 30 of the
implant 10. In the illustrated embodiment, trailing column 8d of
central support member 3 includes lateral tabs 31a and 31b. Lateral
tabs 31a and 31b render the leading end distinguishable from the
trailing end such that implant 10 can only be loaded onto a below
described implant insertion tool in a certain orientation.
[0056] Referring to FIG. 2, the leading end 30 and trailing end 20
are spaced apart along the longitudinal axis X-X of implant 10 to
provide a length L. The implant 10 can be provided with different
lengths L between leading end 30 and trailing end 20 as well as
different heights H between the bearing surfaces 4 and 5 of
transverse members 1 and 2, respectively. Incrementally sized
length and height implants 10 can be provided in a kit for selected
use by the surgeon based on the particular patient's needs.
[0057] Once inserted into a prepared bore site, the channels 24a,
24b and any other area of the bore not occupied by the implant can
be filled with a bone support matrix. Referring again to FIG. 1,
one embodiment of a bone support matrix 40 is illustrated.
According to this embodiment, the bone support matrix 40 can be a
resorbable matrix 41 configured to fit within channels 24a or 24b.
The inner surface 42 of bone support matrix 40 can be shaped to
follow the contours of channels 24a or 24b. The outer surface 43 of
bone support matrix 40 can include a portion of helical threads 43
which are complimentary to portions of helical threads 7a of
implant 10. According to this embodiment, the implant 10 can be
threaded into a tapped insertion bore with bone support matrix 40
in place. In alternative embodiments, after placement of the
implant 10 into a bore, a bone support matrix configured to follow
the contours of channels 24a and 24b but without a threaded outer
surface can be inserted into the channels 24a and 24b of the
implant.
[0058] Referring now to FIGS. 6-7, a second embodiment of an
implant 100 is illustrated. The implant 100 includes four generally
linear thread segments 101, 102, 103 and 104. Linear thread
segments 101 and 103 provide a bearing surface 105 of a first
transverse member 106 and linear thread segments 102 and 104
provide a bearing surface 107 of a second transverse member 108. As
illustrated best in the top view of FIG. 7, thread segments 101 and
103 (and 102 and 104) are maintained in spaced apart alignment by
transverse supports 109, 110 and 111. In the illustrated embodiment
there are two openings 112 and 113 between transverse supports 109,
110 and 111. (The relative arrangement of the second transverse
member 108 having thread segments 102 and 104 is identical to that
just described for the first transverse segment 106). Transverse
members 106 and 108 are maintained in spaced apart alignment by
central support member 120. In the illustrated embodiment, central
support member 120 comprises columns 121, 122 and 123 and has
openings 124 and 125 therebetween.
[0059] It will be appreciated that the transverse members and
central support member of an implant need not include any openings
as described thus far. In addition, rather than comprising support
columns, and openings as illustrated, the central support member
can include several fine thickness support columns with several
fine openings interspersed therebetween giving a profile appearance
similar to the tines of a comb. A similar arrangement can be
provided for the transverse members rather than having the trusses
and openings illustrated.
[0060] Referring now to FIG. 8, another implant 200 is illustrated.
Implant 200 has a more classic "I-beam" appearance in cross
section. Similar to the previously discussed embodiments, first
transverse member 201 and second transverse member 202 are
maintained in spaced apart alignment by central support member 203.
Transverse member 201 also includes transverse supports 204, 205
and 206 having openings 207-210 therebetween. Transverse member 202
has an identical arrangement of transverse supports and openings.
In the illustration, central support member 203 comprises columns
211, 212, and 213 has openings 214-216 therebetween. Bearing
surfaces 220 and 221 include a pattern 223 of intermittent raised
edges 224 which reduce the chance of displacement of the implant
200 once inserted into a bore.
[0061] It should be noted that as an alternative to the helical
threads present on the bearing surface of other implants described
herein, a pattern such as intermittent raised surface 224 or other
non-helical thread pattern can be present on the bearing surface.
Thus, rather than threadedly inserting such an implant into an
insertion bore, the implant can simply be impacted by driving it
into the bore along the X-X axis of the implant.
[0062] FIGS. 9 and 10 illustrate an implant 300 having a first
taper diverging from longitudinal axis X-X from leading end 301 to
trailing end 302. In the side view of FIG. 9, implant 300 has a
substantially frusto-conical shape with a conical angle .alpha.
equal to a desired lordosis between the vertebrae into which the
implant 300 is to be placed as fully described in co-pending
application U.S. Ser. No. 08/902,083, the entire disclosure of
which is incorporated herein by reference. In the illustrated
embodiment, angle .alpha. is 8.degree.. However, it will be
appreciated that as with other implants, implant 300 will be
available in a wide variety of sizes. For example, such implants
may be provided having angles a ranging from 1.degree. to
20.degree. in 1.degree. increments to permit a physician to select
a desired implant to attain a desired lordosis. Further, such
implants can be provided in varying heights (i.e., the diameter of
the implants) to accommodate desired distraction and lordosis
between opposing vertebrae.
[0063] The first transverse member 304 and second transverse member
305 include a surface pattern 306 comprising a portion of helical
threads 306a along first bearing surface 308 and second bearing
surface 309. The threads 306a are generally square in cross-section
with their flat outer peripheral surfaces 310 set at an angle of
one-half .alpha. with respect to the longitudinal axis X-X and
defined valleys 311 between the threads 306a. At the leading end
301, the implant has a major diameter D.sub.M measured between
diametrically opposite outer radial surfaces 310 of the threads
306a at the leading end 301. At the leading end 301, the implant
300 has a minor diameter D.sub.m measured as the distance across
the implant 300 between the valleys 311 of the thread pattern
306a.
[0064] At the trailing end 302, the implant 300 has a major
diameter D'.sub.M measured between diametrically opposite outer
radial surfaces 310 of threads 306a at the trailing end 302.
Finally, at the trailing end 302, the implant 300 has a minor
diameter D'.sub.m measured between diametrically opposite valleys
311 at the trailing end 302.
[0065] The central support member 320 of implant 300 comprises
vertical columns 321, 322 and 323 including openings 324 and 325
therebetween. Referring to the top view of FIG. 10, it can be seen
that the first transverse member 304 (and also second transverse
member 305) include transverse supports 330, 331 and 332 and
include openings 333 and 334 therebetween. As with all implants
disclosed herein, the number of columns and transverse supports can
vary. The objective being to provide rigid support with the
greatest amount of free space.
[0066] Referring to FIGS. 11-13, another embodiment of an implant
400 is shown. According to this embodiment, the first transverse
member 401 and second transverse member 402 are maintained in
spaced apart relationship by central support member 403. Central
support member 403 includes columns 420, 421 and 422 with openings
423 and 424 therebetween. First transverse member 401 includes
transverse supports 425, 426 and 427 with openings 428 and 429
therebetween. The second transverse member 402 has an identical
arrangement.
[0067] Implant 400 has a first and second taper and a longitudinal
axis X-X extending from a leading end 404 to a trailing end 405.
The trailing end 405 of the present embodiment comprises a
"trailing end rise" (TER) 406 and a terminal end 407. The first
taper of implant 400 diverges from the axis from the leading end
404 to the trailing end rise 406 of the trailing end 405. The
second taper diverges from the axis from the terminal end 407 to
the TER 406. The trailing end rise 406 is the region of greatest
diameter of the implant 400.
[0068] The first taper provides the bi-tapered implant 400 with a
substantially frusto-conical shape with a conical angle a equal to
a desired lordosis between selected vertebrae. The angle a of the
illustrated embodiment, measured from the leading end 404 to the
TER 406 is 8.degree., however, as previously stated, the herein
disclosed implants will be available with a variety of angles and
sizes. Referring to FIG. 11, the leading end 404 has a major
diameter D.sub.M measured between diametrically opposite outer
radial surfaces 410 of the threads 411 at the leading end 404. The
leading end 404 also has a minor diameter D.sub.m measured between
diametrically opposite inner radial surfaces 412 of the valleys 413
of the thread pattern 411 of implant 400.
[0069] At the trailing end 405, the implant 400 has a major
diameter D'.sub.M measured between diametrically opposite outer
radial surfaces 414 of the threads 411 at the trailing end rise
406. The trailing end 405 also has a minor diameter D'.sub.m
measured across terminal end 407.
[0070] The second taper of the implant 400 has a second angle,
.delta., extending from the terminal end 407 to the TER 406. The
angle .delta. will vary with the diameter D'.sub.M of the TER 406,
the diameter D'.sub.m of the terminal end 407, and the longitudinal
distance L.sub.E therebetween. In the illustrated embodiment, the
diameter D'.sub.m of the terminal end 407 is equal to the major
diameter D.sub.M of the leading end 404.
[0071] The longitudinal distance L.sub.E can be about 5% to 25% of
the overall length L of the implant. Generally, L.sub.E is less
than 15% of the overall length L, typically about 8-10%.
[0072] It will be appreciated that the slope "m" of the second
taper, relative to the longitudinal axis X-X, can be calculated by
the equation:
D'.sub.M-D'.sub.m/L.sub.E
[0073] In the illustrated embodiment, m is about 1 (45.degree.).
However, the actual slope dimensions m can vary, typically, between
0.58 (30.degree.) and 1.73 (60.degree.).
[0074] The helical threads 411 can extend along the second taper as
illustrated at 415 of FIGS. 11-12. Alternatively, as illustrated in
FIG. 13, the threads 411 can stop at the terminal end rise 406 and
the second taper comprise a flat 416, undulating or other
non-threaded surface, from trailing end rise 406 to terminal end
407.
[0075] Implant 400 can also include other features as previously
described for an implant.
[0076] B. Instrumentation and Insertion
[0077] Instrumentation and methods for preparing an insertion bore
for placement of an implant between opposing vertebrae are known.
U.S. Pat. Nos. 5,458,638 and 5,489,308 and co-pending applications
U.S. Ser. Nos. 08/921,001 and ______ (M&G Docket No.
6683.22USI1 filed Mar. 6, 1998) describe preferred instrumentation
and methods for preparing an implant bore and inserting an implant
therein. The methods include the use of a distraction spacer,
boring tools and tapping tools. In addition, copending U.S. Ser.
Nos. 08/902,083, 08/902,407 and 08/902,431 disclose distraction
spacers, boring tools and tapping tools for preparing a tapered
insertion bore suitable for insertion of single tapered implant 300
or double tapered implant 400. The disclosure of each of these
patents and patent applications are incorporated herein by
reference.
[0078] FIG. 14 diagrammatically illustrates two implants 10
inserted into a threaded bore between opposing vertebral bodies
450, 451. It should be noted that in a preferred method, the
openings 12a-12c of implants 10 are beyond the cortical end plates
452, 453 and provide exposure to cancellous bone 454, 455. A bone
support matrix can be packed around the implants 10.
[0079] FIGS. 15-18 illustrate one preferred insertion tool 500.
Insertion tool 500 includes a tool body 502 extending from a
proximal end 504 to a distal end 506. In the illustrated
embodiment, an internal bore 508 extends completely through the
tool from the proximal end 504 to the distal end 506. At the
proximal end 504, the bore can be provided with internal threads
510. A handle 508 is provided at the proximal end 504 to permit a
surgeon to manipulate the tool 500.
[0080] At the distal end 506, a plurality of grips are provided as
best illustrated in FIGS. 16 and 17. The grips include threaded
grips 522,523. The threaded grips 522, 523 have opposing interior
surfaces 524, 525 configured to slide into channels 24a and 24b of
implant 10. The exterior surfaces of the grips 522, 523 are
provided with threads 526 and valleys 527 which are complimentary
to helical thread portions 7a of the implant 10.
[0081] FIG. 17 illustrates a perspective view of implant 10 and the
distal end 506 of insertion tool 500. The thread pattern 526 of the
threaded grips 522, 523 matches the helical thread pattern of the
threaded portions 7a of the implant 10 to defined a generally
continuous thread pattern through the combination of the implant 10
and the tool 500.
[0082] Referring now to the distal end view of tool 500 in FIG. 18
a preferred feature for assuring thread alignment between an
implant 10 and insertion tool 500 is described. As illustrated, the
lateral aspects 550 and 551 of each gripper 522 and 523,
respectively, each include a pair of tapered ridges 560 and 561.
The angle A formed between tapered ridges 561 is different than the
angle B formed between tapered ridges 560. However, angle A between
tapered ridges 561 is identical to angle A of implant 10 and angle
B of tapered ridges 560 is identical to angle B of implant 10 (see
FIG. 5). Thus, by providing different angles A and B on the distal
end 506 of tool 500 which match with angles A and B of implant 10
only in a particular orientation, proper alignment of thread
portions 7a of implant 10 and threads 526 of tool 500 is assured
for proper insertion of the implant into a tapped insertion bore.
In the illustrated embodiment, the opposing interior surfaces 524,
525 of the distal end 506 of grips 522 and 523 also include notches
570a and 570b which receive tabs 31a and 31b of implant 10,
respectively.
[0083] Referring now to FIGS. 19 and 20, an alternative embodiment
of the distal end 506 of a tool 500 is illustrated. According to
this embodiment, unthreaded grips 570 and 571 have opposing
interior surfaces 572, 573 that provide for sliding grips 570 and
571 into channels 24a and 24b of implant 10. However, as visualized
best in FIG. 20, the lateral aspects 574, 575 of grips 570, 571,
respectively, do not include threads and do not extend to the
lateral edges 25a, 25b, 26a and 26b of implant 10.
[0084] The insertion tool 500, with threaded or unthreaded grips as
just described, can also to include two additional grips that slide
into the regions between thread segments 101 and 103 and 102 and
104 of implant embodiment 100. Such additional grips are
illustrated, for example, in FIGS. 24, 27, 28 and 31 of co-assigned
U.S. Pat. No. 5,609,636, the entire disclosure of which is
incorporated herein by reference.
[0085] Finally, an insertion tool as described above can also be
prepared for tapered implants 300 and 400. The difference being
that grips 522 and 523 or 570 and 571 are tapered from the proximal
end to the distal end as disclosed in co-pending application U.S.
Ser. No. 08/902,083.
[0086] Having now described the present invention, it will be
apparent to one of ordinary skill in the art that many changes and
modifications can be made in the invention without departing from
the spirit or scope of the appended claims.
* * * * *