U.S. patent application number 10/748824 was filed with the patent office on 2005-06-30 for junction for a modular implant.
Invention is credited to Gilbertson, Leslie N..
Application Number | 20050143835 10/748824 |
Document ID | / |
Family ID | 34552897 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050143835 |
Kind Code |
A1 |
Gilbertson, Leslie N. |
June 30, 2005 |
JUNCTION FOR A MODULAR IMPLANT
Abstract
The present invention provides an improved junction for modular
implant components.
Inventors: |
Gilbertson, Leslie N.;
(Warsaw, IN) |
Correspondence
Address: |
ZIMMER TECHNOLOGY - REEVES
P. O. BOX 1268
ALEDO
TX
76008
US
|
Family ID: |
34552897 |
Appl. No.: |
10/748824 |
Filed: |
December 27, 2003 |
Current U.S.
Class: |
623/22.4 ;
623/22.42; 623/22.43 |
Current CPC
Class: |
A61F 2002/3079 20130101;
A61F 2002/365 20130101; A61F 2/34 20130101; A61F 2/3676 20130101;
A61F 2002/3611 20130101; A61F 2002/30332 20130101; A61F 2250/0036
20130101; A61F 2002/3694 20130101; A61F 2002/3625 20130101; A61F
2002/30886 20130101; A61F 2/36 20130101; A61F 2002/30349 20130101;
A61F 2002/30014 20130101; A61F 2002/30507 20130101; A61F 2002/3674
20130101; A61F 2250/0018 20130101; A61F 2002/30326 20130101; A61F
2002/30433 20130101; A61F 2/367 20130101; A61F 2002/30405 20130101;
A61F 2/30767 20130101; A61F 2/32 20130101; A61F 2002/30324
20130101; A61F 2002/30354 20130101; A61F 2220/0025 20130101; A61F
2002/30604 20130101; A61F 2220/0041 20130101; A61F 2250/0037
20130101; A61F 2002/30339 20130101; A61F 2220/0033 20130101 |
Class at
Publication: |
623/022.4 ;
623/022.42; 623/022.43 |
International
Class: |
A61F 002/32 |
Claims
1-9. (canceled)
10. A modular implant for insertion into a femur adjacent a hip
joint, the implant comprising: a proximal body component having a
top end for engaging the hip joint, a bottom end for insertion into
the femur, a medial side, a lateral side, a neck formed adjacent
the top end and a bore formed into the bottom end, the bore having
a bore opening and an interior surface forming a female side of a
male/female junction, the bore having a longitudinal junction axis;
a stem component having a first end for engaging the proximal body
component a second end for insertion into the femur, and a
projection formed adjacent the first end, the projection having an
exterior surface forming a male side of the male/female junction,
the projection being engageable with the bore in male/female
seating arrangement along the junction axis, the male and female
sides contacting one another adjacent the bore opening, the contact
between the male and female sides adjacent to the bore opening on
the lateral side being offset longitudinally toward the top end
relative to the contact between the male and female sides adjacent
the bore opening on the medial side.
11. The implant of claim 10 wherein the bore and the projection
form complimentary tapers, the tapers narrowing from the bottom end
toward the top end and from the second end toward the first
end.
12. The implant of claim 10 wherein the proximal body component has
an exterior surface spaced from the interior surface of the bore,
the exterior and interior surfaces defining a wall between them,
the wall having a wall thickness that increases over a portion of
the wall between the bottom end and the top end as the bore taper
diverges inwardly from the exterior wall in a direction generally
parallel to the junction axis such that the contact between the
male and female sides adjacent the bore opening on the lateral side
is offset in the direction of increasing wall thickness.
13. The implant of claim 10 further comprising a femoral head
component supported on the neck of the proximal body component and
an acetabular component engageable with the femoral head
component.
14. (canceled)
15. (canceled)
16. The implant of claim 10 wherein the bore opening is transverse
to the junction axis.
17. The implant of claim 10 wherein the implant further includes a
joint load receiving head and further wherein the medial side is
generally in compression in use and the lateral side is generally
in tension in use such that the contact between the male and female
sides adjacent the bore opening is offset longitudinally toward the
top end on the tensile side of the implant.
18. The implant of claim 10 wherein the proximal body component has
an exterior surface spaced from the interior surface of the bore,
the exterior and interior surfaces defining a wall between them,
the wall having a stiffness that increases over a portion of the
wall between the bottom end and the top end in a direction
generally parallel to the junction axis, the projection further
having a stiffness, such that the contact between the male and
female sides adjacent to the bore opening on the lateral side is
offset in the direction of increasing wall stiffness.
19. The implant of claim 10 wherein the bore opening adjacent the
lateral side is offset radially away from the projection.
Description
BACKGROUND
[0001] Medical implants to replace or augment various parts of the
mammalian body have been successfully used to reduce pain and
improve function. For example, orthopaedic implants for replacing
portions of bones and joints damaged by disease and/or trauma often
eliminate pain and/or increase mobility. Orthopaedic implants for
hips, knees, shoulders, ankles, elbows, wrists, the digits of the
hands and feet, vertebral bodies, spinal discs, and other bones and
joints have been developed. Many medical implants are made more
versatile by providing them as separate modular components that can
be combined to form an implant suited to a particular patient's
condition. Where such modular components are supplied, a means for
attaching them to one another is provided.
SUMMARY
[0002] The present invention provides a junction for modular
implant components.
[0003] In one aspect of the invention, a modular joint implant
includes a male/female junction between first and second joint
components. The first component includes a bore having a
longitudinal junction axis and a bore opening. The second component
includes a projection engageable with the bore in male/female
seating arrangement. A first portion of the bore opening is offset
axially relative to a second portion of the bore opening.
[0004] In another aspect of the invention, the first portion is
offset in a direction of increasing stiffness of the wall
surrounding the bore.
[0005] In another aspect of the invention, the first portion is
offset in a direction of increasing wall thickness.
[0006] In another aspect of the invention, the first portion is
offset on a side of the implant that is generally in tension when
the implant is loaded.
[0007] In another aspect of the invention, a modular joint implant
includes a male/female junction having a side that is predominately
in compression in use and a side that is predominately in tension
in use. The implant includes a first component including a bore
having a bore opening and an interior surface forming a female side
of the male/female junction. The first component further has an
exterior surface. The interior and exterior surfaces define a wall
between them having a wall thickness. The wall thickness on the
tensile side of the implant being greater than the wall thickness
on the compressive side of the implant.
[0008] In another aspect of the invention, a modular joint implant
includes a male/female junction having a side that is predominately
in compression in use and a side that is predominately in tension
in use. The implant includes a first component including a bore
having a bore opening and an interior surface forming a female side
of the male/female junction. The bore has a side on the tensile
side of the implant that is shifted axially relative to a side of
the bore on the compressive side of the implant.
[0009] These and other aspects of the invention will be described
in reference to the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Various embodiments of the present invention will be
discussed with reference to the appended drawings. These drawings
depict only illustrative embodiments of the invention and are not
to be considered limiting of its scope.
[0011] FIG. 1 is an exploded perspective view of a modular implant
junction according to the present invention;
[0012] FIG. 2 is a side section view of the modular implant
junction of FIG. 1; and
[0013] FIG. 3 is a side section view of an optional configuration
of the lateral side of the modular implant junction of the present
invention.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0014] Embodiments of a junction for a modular implant are
applicable to a variety of implants for use throughout the body. A
femoral hip stem has been used to illustrate the invention.
However, the invention may also be applied to various other
implants including orthopaedic implants for hips, knees, shoulders,
ankles, elbows, wrists, the digits of the hands and feet, vertebral
bodies, spinal discs, and other suitable implants.
[0015] FIGS. 1-2 depict a modular femoral hip implant 10 for
replacing the proximal head and neck of a femur of a hip joint that
has been damaged due to injury or disease. In use, the proximal
head and neck are surgically removed and the femoral hip implant 10
is inserted into the proximal femur. The femoral hip implant 10
supports a femoral head 12 that may be a modular and separate
component as shown. Optionally, the femoral head 12 may be integral
to the femoral hip implant 10. An acetabular component 14 may be
implanted in the acetabulum of the pelvis to articulate with the
femoral head 12. Optionally, the femoral head 12 may articulate
with the natural acetabulum. The femoral hip implant 10 has a
medial aspect 16 and a lateral aspect 18. When the patient loads
the joint, such as by standing, walking, or other activities,
forces are transmitted to the femoral hip implant 10 through the
head 12. These forces tend to create a bending moment that places
the medial aspect 16 of the femoral hip implant in compression and
the lateral aspect 18 in tension.
[0016] The femoral hip implant 10 may include modular components
such as a proximal body 20 and a stem 22. The proximal body 20 has
a top end 24 and a bottom end 26. A neck 28 extends upwardly and
medially from the top end 24 to support the femoral head 12 for
articulation with the acetabular component 14. The proximal body 20
and stem 22 include a male/female junction for holding them
together. In the illustrative embodiment, the female side of the
junction is depicted in the proximal body 20 and the male side of
the junction is depicted on the stem 22. It is contemplated that
the male/female portions may be reversed and still fall within the
scope of the invention. The proximal body 20 includes a bore 30
(FIG. 2) having a bore opening 32 and an interior surface 34
forming the female side of the male/female junction. The bore 30
has a longitudinal junction axis 36. The proximal body 20 has an
exterior surface 38 spaced from the interior surface 34 of the bore
30. The exterior 38 and interior 34 surfaces define a wall 40
between them. The wall 40 has a wall thickness 42 that may be
constant or that may increase from the bore opening 32 toward the
top end 24 as shown in FIG. 2. An increasing wall thickness may be
accomplished by tapering the bore such that it narrows from the
bore opening 32 toward the top end 24 as in the illustrative
embodiment. A tapered bore can be made self-locking as is known in
the art.
[0017] The stem 22 includes a bottom end 44 and a top end 46. The
bottom end 44 is configured for insertion into the intramedullary
canal of the patient's femur. The top end 46 includes a projection
48 having an exterior surface 50 forming the male side of the
male/female junction. The projection 48 is engageable with the bore
30 in male/female seating arrangement along the junction axis 36. A
threaded stud 33 extends from the projection 48 and is received by
a counter bore 35 formed in the proximal body 20. A nut 37 threads
onto the stud 33 to secure the male/female junction.
[0018] When the femoral hip implant 10 is loaded, the medial
aspects of the proximal body 20 and stem 22 are placed in
compression and the lateral aspects of the proximal body 20 and
stem 22 are placed in tension. Due to differences in the bending
stiffness of the proximal body 20 and stem 22 in the region of the
male/female junction, the bore wall 40 may move relative to the
exterior surface 50 of the projection 48. Cyclic loading can lead
to fretting between the interior surface 34 of the bore 30 and
exterior surface 50 of the projection 48. This may be more
problematic on the tension side since tensile forces may initiate
and propagate fatigue cracks.
[0019] The magnitude of the fretting motion is related to the
relative stiffness of the male and female parts of the junction.
The relative motion at the opening 32 of the bore 30 is an
accumulation of the relative motion along the entire length of the
junction. This accumulated relative motion may be decreased by
decreasing the length along which the relative motion accumulates
on the tensile side of the junction. However, it is ineffective to
simply make the junction shorter, because this will create higher
stresses on the smaller diameter male cross section where such a
shortened junction would end. However, by shortening only the
tensile side, the compressive side is still supported and the
tensile stress at the end of the tensile side increases only
slightly while the relative fretting motion decreases
significantly. In the illustrative embodiment, a lateral portion 52
of the bore opening 32 is offset axially upwardly relative to a
medial portion 54. This offset, or relieved, portion 52 can be
created by stepping up the lateral portion 52, sloping up the
lateral side such that the bore opening 32 is transverse to the
junction axis 36, or by forming the bore opening in some other
suitable shape.
[0020] Fretting in the male/female junction can also be reduced by
better matching the stiffness of the male and female sides of the
male/female junction. The present investigators have found that one
way to better match the stiffness of the male and female sides is
to increase the stiffness of the bore wall 40 adjacent the bore
opening 32 on the tensile side of the implant 10. Increasing the
stiffness can be accomplished by increasing the outer diameter of
the proximal body 20 adjacent the bore opening 32 to move material
radially away from the junction axis 36 such that the bending
moment of inertia is increased. Increasing this stiffness can also
be accomplished by increasing the wall thickness of the proximal
body 20 at the junction of the proximal body 20 and projection 48.
In the illustrative embodiment, the bore 30 is tapered so that it
narrows proximally and the wall thickness 42 increases proximally.
By offsetting a lateral portion 52 of the bore opening 32 axially
upwardly relative to a medial portion 54 the wall thickness on the
lateral side 18 of the bore opening 32 is increased. This offset,
or relieved, portion 52 can be created by sloping the lateral side
such that the bore opening 32 is transverse to the junction axis 36
as shown, by stepping up the lateral portion 52, or by forming the
bore opening in some other suitable shape. In the illustrative
embodiment, the projection 48 forming the male side of the junction
narrows upwardly. Thus, moving the lateral portion 52 upwardly also
moves the lateral interface to an area of decreased stiffness of
the projection 48 to further match the stiffness of the male and
female portions laterally. Finally, by moving the lateral side
upwardly while having the medial, anterior, and posterior sides of
the junction extend further downwardly, the fatigue properties of
the lateral side are improved while the overall interface of the
male and female parts is kept relatively large to facilitate secure
engagement between them.
[0021] Another way increase the stiffness of the bore wall 40 is to
enlarge the bore 30 on just the tensile side of the junction as
shown in FIG. 3 such that the bore wall is offset away from the
projection 48. This has the same effect as moving the tensile side
axially upwardly as described above. Other ways of better matching
the stiffness of the male and female sides of the junction may also
be used and are considered within the scope of this invention.
[0022] It will be understood by those skilled in the art that the
foregoing has described illustrative embodiments of the present
invention and that variations may be made to these embodiments
without departing from the spirit and scope of the invention
defined by the appended claims.
* * * * *