U.S. patent application number 10/192324 was filed with the patent office on 2003-09-11 for surgical implant.
This patent application is currently assigned to CORIN LIMITED. Invention is credited to Collins, Simon Nicholas, Fletcher, David Mark.
Application Number | 20030171753 10/192324 |
Document ID | / |
Family ID | 9924467 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030171753 |
Kind Code |
A1 |
Collins, Simon Nicholas ; et
al. |
September 11, 2003 |
SURGICAL IMPLANT
Abstract
A surgical implant, typically a cervical plate assembly,
comprises a plate having at least two apertures and two screw
threaded fastening devices for securing the plate to bone. Each
aperture in the plate has an annular groove intermediate opposite
ends of the aperture and each fastening device comprises an outer
screw and an inner plug. The screw has a head at one end, a tip at
the other end, an externally threaded shank between the head and
the tip and an internal bore extending axially through the head and
at least part way into the shank for receiving the inner plug. The
head comprises a plurality of resiliently deformable fingers
separated by one another by axially extending slits. Each finger
has an outwardly projecting rib extending circumferentially of the
head intermediate opposite ends of the finger for snap fit
engagement in the annular groove of a respective plate aperture.
The inner plug is arranged so that when it is inserted into the
internal bore of the screw it will prevent contraction of the head
of the screw thereby preventing the ribs disengaging from the
groove.
Inventors: |
Collins, Simon Nicholas;
(Gloucestershire, GB) ; Fletcher, David Mark;
(Gloucestershire, GB) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
CORIN LIMITED
CIRENCESTER
GB
|
Family ID: |
9924467 |
Appl. No.: |
10/192324 |
Filed: |
July 11, 2002 |
Current U.S.
Class: |
606/293 ;
606/289 |
Current CPC
Class: |
A61B 17/8685 20130101;
A61B 17/8635 20130101; A61B 17/7059 20130101; A61B 17/8038
20130101 |
Class at
Publication: |
606/69 |
International
Class: |
A61B 017/56 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2001 |
GB |
0125565.2 |
Claims
What is claimed is:--
1. A surgical implant comprising a plate having at least two
apertures and two screw threaded fastening devices for securing the
plate to bone, each aperture in the plate having an annular groove
intermediate opposite ends of the aperture and each fastening
device comprising an outer screw and an inner plug, the screw
having a head at one end, a tip at the other end, an externally
threaded shank between the head and the tip and an internal bore
extending axially through the head and at least part way into the
shank for receiving the inner plug, the head comprising a plurality
of resiliently deformable fingers separated from one another by
axially extending slits, each finger having an outwardly projecting
rib intermediate opposite ends of the finger for snap fit
engagement in the annular groove of a respective plate aperture,
and the inner plug being arranged so that, when it is inserted into
the internal bore of the screw, it will prevent contraction of the
head of the screw thereby preventing the ribs disengaging from the
groove.
2. A surgical implant as claimed in claim 1, wherein the plug
comprises a head which is a close fit in that part of the internal
bore extending through the head of the screw and an externally
threaded shank which is screw threadably engageable with an
internal thread on at least part of the bore in the shank of the
screw.
3. A surgical implant as claimed in claim 1, wherein each plate
aperture has an annular ledge between the annular groove and the
inner end of the aperture for engagement by the inner end of the
screw head when the ribs are in snap fit engagement with the
annular groove.
4. A surgical implant as claimed in claim 1, wherein the head of
the plug has a non-circular socket for receiving a tool for
inserting the plug in the internal bore of the screw.
5. A surgical implant as claimed in claim 1, wherein the internal
bore extends throughout the entire length of the screw, the tip end
of the screw being outwardly deformable and the tip end of the plug
including an expansion element for outwardly deforming the tip end
of the screw as the plug is inserted in the internal bore.
6. A surgical implant as claimed in claim 5, wherein the tip end of
the screw has a plurality of axially extending slits.
7. A surgical implant as claimed in claim 1, wherein each rib is
tapered inwards towards the tip of the screw.
8. A surgical implant as claimed in claim 1, wherein the plug is
snap fittably engageable in the screw.
9. A surgical implant as claimed in claim 1, wherein the plate is a
cervical plate.
10. A surgical implant as claimed in claim 9, wherein the plate has
at least four apertures.
11. A surgical implant as claimed in claim 9, wherein the plate is
non-planar.
Description
INTRODUCTION
[0001] This invention relates to a surgical implant and more
particularly, but not exclusively, to a cervical plate assembly for
stabilising the cervical spine.
[0002] Plates are commonly used to connect two separated pieces of
bone. These plates immobilise the broken bone pieces while the bone
pieces fuse together. Cervical plates are commonly used for
anterior spine stabilisation to assist fusion in cases of
degenerative disease, tumours, fractures and partial or total
vertebrectomy. The plates are fixed to the bone by screws. It is
known to provide the screws with expansion cones to expand the tip
of the screw after insertion of the latter in the bone. This
results in secure fixation. However, it is often difficult in young
patients or in good quality bone to expand the tip of the
screw.
[0003] It is known from U.S. Pat. No. 4,484,570 to expand the head
of the screw to provide secure fixation of the screw to the plate.
However, this suffers from the disadvantage that a force arises
from the tapered mating of the inner and outer screws which may
contribute to loosening and subsequent screw pull out leading to
failure of the device.
SUMMARY OF THE INVENTION
[0004] According to the present invention there is provided a
surgical implant comprising a plate having at least two apertures
and two screw threaded fastening devices for securing the plate to
bone, each aperture in the plate having an annular groove
intermediate opposite ends of the aperture and each fastening
device comprising an outer screw and an inner plug, the screw
having a head at one end, a tip at the other end, an externally
threaded shank between the head and the tip and an internal bore
extending axially through the head and at least part way into the
shank for receiving the inner plug, the head comprising a plurality
of resiliently deformable fingers separated from one another by
axially extending slits, each finger having an outwardly projecting
rib extending circumferentially of the head intermediate opposite
ends of the finger for snap fit engagement in the annular groove of
a respective plate aperture, and the inner plug being arranged so
that when it is inserted into the internal bore of the screw it
will prevent contraction of the head of the screw thereby
preventing the ribs disengaging from the groove.
[0005] The invention will now be more particularly described, by
way of example, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a perspective, partially exploded, view of one
embodiment of a surgical implant according to the present
invention,
[0007] FIG. 2 is a section taken through FIG. 1, and
[0008] FIG. 3 is a view similar to FIG. 2 of a second
embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0009] Referring to the drawings, the surgical implant shown
therein is in the form of a cervical plate assembly used for
stabilising the cervical spine of a patient. The assembly comprises
a cervical plate 10 having an aperture 11 adjacent each corner. It
may also have a central aperture (not shown) to allow attachment of
a bone graft to aid fusion. The plate 10 is of contoured non-planar
shape and is available in various sizes so that a surgeon can
select an appropriate plate which will not result in penetration of
the intervertebral disc space by the fastening devices referred to
below.
[0010] The assembly comprises four screw threaded fastening devices
13 for securing the plate 10 to bone. Each fastening device 13
comprises an outer screw 14 and an inner plug 15.
[0011] Each aperture 11 in the plate has an annular groove 16
intermediate the outer and inner ends of the aperture and an
annular ledge 17 between the annular groove 16 and the inner end of
the aperture 11.
[0012] Each outer screw 14 comprises a head 18, an externally
threaded shank 19 and an internal bore 20 extending axially through
the head 18 and through the shank 19 for receiving the plug 15.
[0013] The bore 20 has a first portion 20a in the head 18 of the
screw 14, a second portion 20b extending into the shank 19 from the
portion 20a and a third portion 20c extending from the portion 20b
through the tip of the screw 13. The portion 20b is of larger
diameter than the portion 20c and the portion 20a is of larger
diameter than the portion 20b. The portion 20b of the bore 20 is
internally screw threaded for a purpose which will become
apparent.
[0014] The tip of the screw 13 has four equi-angularly spaced,
axially extending slits 21 which allow the tip to be outwardly
deformed in a manner to be described hereinafter.
[0015] The plug 15 has a head portion 15a which is a close fit in
the portion 20a of the bore 20, an externally threaded shank 15b
which threadably engages the portion 20b of the bore 20 and an
expansion element 15c of slightly larger diameter than the portion
20c of the bore 20 for outwardly deforming the tip end of the screw
14.
[0016] The tip of the expansion element 15c is tapered or part
spherical in order to assist insertion of the expansion element 15c
into the bore portion 20c.
[0017] The head 18 of the screw 14 comprises a plurality of
resiliently deformable fingers (in this case three) 22 separated
from one another by axially extending slits 23. Each finger 22 has
an outwardly projecting rib 24 extending circumferentially of the
head 18 intermediate opposite ends of the finger 22 for snap fit
engagement in the annular groove 16 of a plate aperture 11. As
shown, the rib 24 is inwardly tapered towards the tip of the screw
but this need not necessarily be the case.
[0018] The head portion 15a of the plug 15 has a non-circular, and
as shown hexagonal, socket 15d for receiving an insertion tool.
[0019] In order to fix the cervical plate assembly to the cervical
spine, the outer screws 14 are screwed into bone through the
apertures 11 by a known tubular screw driver until the head 18 of
the screw 14 abuts the ledge 17 in the aperture and the ribs 24
snap fittably engage in the groove 16. The plug 15 is then inserted
and screwed into place by a hexagonal screw driver inserted through
the tubular screw driver, the latter acting as a guide and
preventing the screw 14 from turning during insertion of the plug
15. When the plug 15 is fully in place, the head 15a of the plug is
a close fit in the portion 20a of the bore 20 in the screw and this
prevents contraction of the head 18 of the screw thereby preventing
the ribs 24 disengaging from the groove 16. Also, the expansion
element 15c expands the tip of the screw 13 to improve the overall
fixation and prevent pull out of the fastening devices.
[0020] In some circumstances, it will be difficult to expand the
tip of the screw 13 and in such cases a different plug having no
expansion element will be used.
[0021] The plate 10, screws 14 and plugs 15 are made of suitable
biocompatible material, typically commercially pure or alloyed
titanium.
[0022] The embodiment shown in FIG. 3 differs from that shown in
FIG. 2 in that the portion 20a' of the bore 20' in the screw has an
annular groove 30 to receive an annular rib 31 on the head 15a' of
the plug 15' as a snap fit.
[0023] The implant described above is in the form of a cervical
plate assembly. However, the invention is equally applicable to any
plates used to immobilise broken bone pieces. Thus, the plate may
take other forms and may, for example, have only two apertures.
[0024] The embodiments described above are given by way of example
only and various modifications will be apparent to persons skilled
in the art without departing from the scope of the invention as
defined by the appended claims. For example, the plug could be a
push fit in the bore of the screw.
* * * * *