U.S. patent application number 10/773684 was filed with the patent office on 2007-12-27 for patello-femoral prosthesis.
Invention is credited to Paul A. Lotke.
Application Number | 20070299528 10/773684 |
Document ID | / |
Family ID | 34811317 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070299528 |
Kind Code |
A9 |
Lotke; Paul A. |
December 27, 2007 |
Patello-femoral prosthesis
Abstract
A patello-femoral prosthesis is provided for replacing the
engagement surfaces between the patella and the femur. The
prosthesis is configured to cover the trochlear groove and extend
into the intercondylar notch without extending onto the
articulating surfaces of the condyles. A method is also provided
for implanting a patello-femoral prosthesis in which a portion of
the trochlear groove and intercondylar notch are resected and the
prosthesis is implanted over the femur that had portions
resected.
Inventors: |
Lotke; Paul A.; (Gladwyne,
PA) |
Correspondence
Address: |
DANN, DORFMAN, HERRELL & SKILLMAN
1601 MARKET STREET
SUITE 2400
PHILADELPHIA
PA
19103-2307
US
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20050177242 A1 |
August 11, 2005 |
|
|
Family ID: |
34811317 |
Appl. No.: |
10/773684 |
Filed: |
February 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60535967 |
Jan 12, 2004 |
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Current U.S.
Class: |
623/20.19 ;
623/20.18; 623/908 |
Current CPC
Class: |
A61F 2310/00029
20130101; A61F 2310/00179 20130101; A61F 2/3877 20130101 |
Class at
Publication: |
623/020.19 ;
623/020.18; 623/908 |
International
Class: |
A61F 2/38 20060101
A61F002/38 |
Claims
1. A prosthesis, comprising: a femoral prosthesis configured to
cover a portion of the distal end of a femur, comprising: a
saddle-shaped trochlear groove portion comprising: a central
convexly-shaped grove extended toward a distal end of the femoral
prosthesis; a convexly-shaped medial portion extending upwardly
away from a first side of the central groove; and a convexly-shaped
lateral portion extending upwardly away from a second side of the
central groove; and an intercondylar notch portion intersecting the
trochlear groove portion, comprising a first wing extending
distally and curving posteriorally from the distal end of the
medial portion; and a second wing extending distally and curving
posteriorally from the distal end of the lateral portion and
curving away from the first wing; and a patellar prosthesis
configured to cover a posterior portion of a patella, comprising a
first surface configured to be attached to a patella, and a second
surface configured to cooperate with the trochlear groove and
intercondylar notch portions of the femoral prosthesis to
facilitate sliding engagement between the femoral prosthesis and
the patella prosthesis.
2. The prosthesis of claim 1 wherein the patellar prosthesis is
formed of a different material then the femoral prosthesis.
3. The prosthesis of claim 1 wherein the first and second wings
each have a length that is at least approximately one quarter the
length of the trochlear groove portion.
4. The prosthesis of claim 1 wherein the first and second wings are
tapered so that adjacent the trochlear groove portion the wings
have a width that is greater than terminal ends of the wings.
5. The prosthesis of claim 1 wherein the first and second wings
from a generally arch-shaped surface.
6. A femoral prosthesis configured to cooperate with a patellar
prosthesis, comprising: a first portion configured to cover a
portion of the length of the trochlear groove on the distal end of
a femur; a second portion connected to a distal end of the first
portion configured to cover a portion of the intercondylar notch on
the distal end of the femur; wherein the second portion comprises
first and second wings that flare outwardly from the distal end of
the first portion, wherein the first wing extends transverse the
first portion laterally and posteriorally of the first portion, and
the second wing extends transverse the first portion medially and
posteriorally of the first portion.
7. The prosthesis of claim 6 wherein the first portion comprises a
convex posterior surface configured to cooperate with the trochlear
groove of the knee and a concave anterior surface configured to
cooperate with a convex surface of the patellar prosthesis.
8. The prosthesis of claim 6 wherein the first portion tapers
inwardly from a medial and lateral direction to form a narrow waist
adjacent the intersection of the first and second portions.
9. The prosthesis of claim 6 wherein the first wing tapers so that
a distal end of the first wing remote from the first portion is
narrower than the width of the first wing adjacent the first
portion.
10. The prosthesis of claim 9 wherein the second wing tapers so
that a distal end of the second wing remote from the first portion
is narrower than the width of the second wing adjacent the first
portion.
11. The prosthesis of claim 6 wherein a lateral edge of the first
wing is configured to terminate on a lateral surface of the
intercondylar notch so that the first wing does not substantially
extend onto a distal surface of a lateral condyle of the femur.
12. The prosthesis of claim 6 wherein a medial edge of the first
wing is configured to terminate on a medial surface of the
intercondylar notch so that the first wing does not substantially
extend onto a distal surface of a medial condyle of the femur.
13. The prosthesis of claim 6 wherein the first and second wings
each form a generally triangular-shaped profile so that the wings
are configured to terminate within the intercondylar notch of the
femur.
14. A knee prosthesis for covering a portion of a patient's
patella, and trochlear groove and intercondylar notch of the femur,
comprising: a patellar prosthesis configured to cover a posterior
surface of a patella; and a femoral prosthesis comprising: a body
having a posterior surface configured to cover a portion of the
trochlear groove and an anterior surface forming a groove that is
cooperable with the posterior surface of the patellar prosthesis; a
medial extension projecting away from a distal end of the body
configured to extend along a medial edge of the intercondylar
notch; and a lateral extension projecting away from a distal end of
the body configured to extend along a lateral edge of the
intercondylar notch.
15. The knee prosthesis of claim 14 wherein the medial and lateral
extensions intersect the body to form a generally U-shaped
configuration.
16. The knee prosthesis of claim 14 wherein the medial and lateral
extensions form opposing sides of a bearing surface configured to
cooperate with the patellar prosthesis.
17. The knee prosthesis of claim 14 wherein the medial extension
has a length and a width and the length is substantially greater
than the width.
18. The knee prosthesis of claim 17 wherein the lateral extension
has a length and a width and the length is substantially greater
than the width.
19. The knee prosthesis of claim 14 wherein the medial extension
has an inner edge opposing the lateral extension and an outer edge,
wherein the outer edge is configured to terminate over the
intercondylar notch without extending over an articular surface of
the medial condyle.
20. The knee prosthesis of claim 14 wherein the medial extension
has an inner edge opposing the lateral extension and an outer edge,
wherein the outer edge comprises a generally convexly-shaped
curve.
21. The knee prosthesis of claim 14 wherein the lateral extension
has an inner edge opposing the medial extension and an outer edge,
wherein the outer edge is configured to terminate over the
intercondylar notch without extending over an articular surface of
the lateral condyle.
22. The knee prosthesis of claim 14 wherein the lateral extension
has an inner edge opposing the medial extension and an outer edge,
wherein the outer edge comprises a generally convexly-shaped
curve.
23. The knee prosthesis of claim 14 comprising a separate medial
condyle prosthesis configured to cover an articular surface of a
medial condyle, wherein the medial condyle prosthesis has an inner
edge configured to cooperate with an outer edge of the medial
extension.
24. The knee prosthesis of claim 14 comprising a separate lateral
condyle prosthesis configured to cover an articular surface of a
lateral condyle, wherein the lateral condyle prosthesis has an
inner edge configured to cooperate with an outer edge of the
lateral extension.
25. The knee prosthesis of claim 14 wherein the body, medial
extension and lateral extension are a unitary element.
26. A method for implanting a femoral prosthesis, comprising the
steps of: resecting a portion of a trochlear groove of a patient's
femur; resecting a portion of an intercondylar notch of a patient's
femur along a medial portion of the intercondylar notch, wherein
the step of resecting along the medial portion terminates without
resecting a portion of a medial condyle articular surface;
implanting a femoral prosthesis over the portions of the trochlear
groove and the intercondylar notch from which a portion was
resected wherein the prosthesis is positioned so as to cover the
intercondylar notch without covering the medial condyle articular
surface.
27. The method of claim 26 comprising the steps of; resecting
lateral portion of the intercondylar notch and a portion of a
lateral condyle articular surface; and implanting a lateral
condylar prosthesis over the portion of the lateral condyle from
which the articular surface was resected.
28. The method of claim 27 wherein the lateral condylar prosthesis
is separate from the femoral prosthesis, and the method includes
implanting the femoral prosthesis and the lateral condylar
prosthesis without overlapping the two prostheses.
29. The method of claim 26 wherein the femoral prosthesis comprises
a plurality of separate components and the step of implanting the
femoral prosthesis comprises implanting a trochlear groove element
over the trochlear groove and implanting a intercondylar notch
element over the intercondylar notch.
30. The method of claim 26 comprising the step of resecting a
portion of an anterior surface of a patella and implanting a
patellar prosthesis over the posterior surface, wherein the
patellar prosthesis comprises a posterior surface configured to
slidingly engage the femoral prosthesis.
31. The method of claim 30 wherein the femoral component comprises
a concave surface configured to cooperate with the patellar
prosthesis.
32. The method of claim 26 wherein the step of resecting a portion
of the intercondylar notch comprises resecting along a majority of
the length of the distal portion of the medial and lateral
condyles.
33. The method of claim 26 wherein the femoral prosthesis comprises
an central portion having an elongated channel, and opposing medial
and lateral extensions extending transverse the central portion,
wherein the channel is configured to cooperate with a patellar
prosthesis, and wherein the steps of resecting a portion of the
trochlear groove and resecting a portion of the intercondylar notch
comprise resecting a portion of the femur sufficient to receive the
femoral prosthesis.
34. The method of claim 33 wherein each of the medial and lateral
extensions have a width that is narrower than the width of the
central portion.
35. A method for implanting a femoral prosthesis, comprising the
steps of: resecting a portion of a troclear groove of a patient's
femur; resecting a portion of an intercondylar notch of a patient's
femur along a lateral portion of the intercondylar notch, wherein
the step of resecting along the lateral portion terminates without
resecting a portion of articular surface of a lateral condyle;
implanting a femoral prosthesis over the portions of the trochlear
groove and the intercondylar notch from which a portion was
resected wherein the prosthesis is positioned so as to cover the
intercondylar notch without covering the lateral condyle articular
surface.
36. The method of claim 35 comprising the steps of; resecting a
portion of a medial condyle articular surface; and implanting a
medial condylar prosthesis over the portion of the medial condyle
from which the articular surface was resected.
37. The method of claim 36 wherein the medial condylar prosthesis
is separate from the femoral prosthesis, and the method includes
implanting the femoral prosthesis and the medial condylar
prosthesis without overlapping the two prostheses.
38. The method of claim 35 wherein the femoral prosthesis comprises
a plurality of separate components and the step of implanting the
femoral prosthesis comprises implanting a trochlear groove element
over the trochlear groove and implanting a intercondylar notch
element over the intercondylar notch.
39. The method of claim 35 comprising the step of resecting a
portion of an anterior surface of a patella and implanting a
patellar prosthesis over the posterior surface, wherein the
patellar prosthesis comprises a posterior surface configured to
slidingly engage the femoral prosthesis.
40. The method of claim 39 wherein the femoral component comprises
a concave surface configured to cooperate with the patellar
prosthesis.
41. The method of claim 34 wherein the step of resecting a portion
of the intercondylar notch comprises resecting along a majority of
the length of the distal portion of the lateral condyle.
42. The method of claim 34 wherein the femoral prosthesis comprises
an central portion having an elongated channel, and opposing medial
and lateral extensions extending transverse the central portion,
wherein the channel is configured to cooperate with a patellar
prosthesis, and wherein the steps of resecting a portion of the
trochlear groove and resecting a portion of the intercondylar notch
comprise resecting a portion of the femur sufficient to receive the
femoral prosthesis.
43. The method of claim 42 wherein each of the medial and lateral
extensions have a width that is narrower than the width of the
central portion.
44. A method for implanting a femoral prosthesis on a knee having a
medial and lateral condyle, a trochlear groove and an intercondylar
notch between the medial and lateral condyles, comprising the steps
of: providing a femoral prosthesis comprising a central portion
having an elongated channel, and medial and lateral extensions
extending away from a distal end of the central portion, wherein
the medial and lateral extensions each have a width that is
narrower than the central portion; resecting a portion of the
trochlear groove and intercondylar groove, wherein the resecting
provides a recessed portion of the femur configured to receive the
femoral prosthesis; locating the femoral prosthesis over the
recessed portion without covering an articular surface of either
the medial or lateral condyle; and attaching the femoral prosthesis
to the femur.
45. The method of claim 44 comprising the steps of resecting an
posterior portion of the patella and attaching a patellar
prosthesis to the posterior portion of the patella, wherein the
patellar prosthesis is configured to cooperate with the channel and
medial and lateral extensions of the femoral prosthesis.
46. The method of claim 44 wherein the combined width of the medial
and lateral extensions is less than the width of the central
portion.
47. The method of claim 44 wherein the step of attaching comprises
cementing the femoral prosthesis to the femur.
48. The method of claim 44 wherein the femoral prosthesis provides
a generally L-shaped bearing surface cooperable with a patellar
prosthesis, wherein the bearing surface extends generally
vertically along the anterior surface of the femur and angles
inwardly at a distal end toward a posterior surface of the
condyles.
49. The method of claim 44 wherein the medial and lateral
extensions flare outwardly away from the central portion and away
from each other.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of prosthetics
for knee replacement. More particularly, the present invention
relates to a prosthesis for replacing the articulating surfaces of
the knee. Specifically, the invention relates to a prosthesis for
replacing the articulating surfaces of the patella and femur. In
addition, the present invention relates to a method of repairing a
knee, and specifically a method for repairing the articulating
surfaces of the patella and femur.
BACKGROUND OF THE INVENTION
[0002] The knee is formed where the thigh bone meets the shin bone.
The knee includes three bones, the femur (thigh bone), tibia (shin
bone) and patella (knee cap). The distal end of the femur sits on
top of the tibia, and the patella is on the front of the femur.
[0003] The three bones in the knee form two joints. The first is
the tibio-femoral joint, which relates to the joint where the femur
meets tibia. The second joint is the patello-femoral joint, which
relates to the joint where the patella meets the femur.
[0004] The joint elements that engage one another are covered by
articular cartilage. Specifically, the distal end of the femur and
the proximal end of the tibia are covered by articular cartilage,
as is the posterior surface of the patella. The articular cartilage
is a slippery substance that absorbs shock and allows the bone
surfaces to slide against one another without damage to either
surface.
[0005] If the articular cartilage becomes damaged, the contact
surface in the joint will not slide as well. The damaged area
becomes a weak point in the cartilage that is prone to continued
degradation over time. Ultimately, the damage can lead to
bone-to-bone contact during articulation of the joint, resulting in
significant pain and potential damage to the bone surfaces.
[0006] If the damage to the articular cartilage is sufficient
enough, a knee replacement procedure may be required. Depending on
the extent of the damage, the procedure may operate on either all
or only a portion of the knee. For instance, in a total knee
replacement, the ends of both the femur and the tibia are covered
by prosthetics, as well as a surface of the patella. In other
instances the procedure may be limited to portions of one of the
joints. For instance, in a patello-femoral procedure, the procedure
is limited to the engagement surfaces between the femur and the
patella.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0007] A patello femoral prosthesis is provided for repairing
surfaces of the patello-femoral joint. A patella prosthesis is
provided for replacing a surface of the patella and a femoral
prosthesis is provided for replacing surfaces of the femur. The
patella prosthesis is configured to cooperate with a groove in the
femoral prosthesis. The femoral prosthesis is configured to overlay
a portion of the trochlear groove and the intercondylar notch of
the femur. Preferably, the femoral prosthesis is configured to
cooperate with a unicompartmental prosthesis that is configured to
cover an articular surface of one of the condyles of the femur.
[0008] A method for implanting a patello-femoral prosthesis is also
provided. A portion of the patella is resected and a patellar
prosthesis is attached to the patella. A portion of the trochlear
groove and a portion of the intercondylar notch are also resected
to form a recess. Preferably, the resected portion of the
intercondylar notch extends along the medial and lateral condyles,
and terminates without extending onto an articular surface of one
of the condyles. A femoral prosthesis is inserted into the recess
formed by resecting the femur, and the prosthesis is attached by
either a cementing or non-cementing process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The foregoing summary and the following detailed description
of the preferred embodiments of the present invention will be best
understood when read in conjunction with the appended drawings, in
which:
[0010] FIG. 1 is an anterior view of a knee with a patello-femoral
prosthesis;
[0011] FIG. 2 is a lateral view partially in section of the knee
and prosthesis in FIG. 1;
[0012] FIG. 3 is a perspective view of a femoral component of the
prosthesis in FIG. 1;
[0013] FIG. 4 is a distal view of the femoral component shown in
FIG. 3;
[0014] FIG. 5 is a distal perspective view of the femoral component
shown in FIG. 3;
[0015] FIG. 6 is a distal perspective view of a distal end of a
partially resected femur;
[0016] FIG. 7 is a distal perspective view of the femur illustrated
in FIG. 6, illustrated with the femoral component illustrated in
FIG. 3 implanted; and
[0017] FIG. 8 is a a distal perspective view of a femur with the
femoral component illustrated in FIG. 3 combined with a
unicompartmental prosthesis.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Referring now to the figures, wherein like elements are
numbered alike throughout, a patello-femoral prosthesis 50 is
illustrated. In one aspect, the prosthesis includes a patellar
prosthesis 60 and a femoral prosthesis 70 that operate as
replacement surfaces for the interaction between the patella and
the femur. Specifically, the patellar prosthesis 60 covers a
surface of the patella and the femoral prosthesis 70 covers a
surface of the femur that cooperates with the patella during
flexion and extension of the leg.
[0019] The features of the patello-femoral prosthesis 50 are
configured to cooperate with various features of the femur 20 and
the patella 40. Accordingly, the following description details the
features of the femur and the patella related to the features of
the prosthesis, which are described more fully below.
[0020] The patella 40 is a small bone embedded within the patella
tendon in front of the intersection of the femur and the tibia (to
shown the details of the knee in FIG. 1, the patella is shown with
the patella tendon detached from the femur and folded over). The
patella 40 normally lies at the top of the groove, or trochlear 25,
of the femur 20. As the knee bends, it slides along the trochlear
groove 25, held in place by various ligaments and other tissues. As
the knee bends past about 30 degrees, the patella 40 moves slightly
towards the center of the body, centering it in this groove. As the
knee bends even farther, the patella continues to slide along the
trochlear groove.
[0021] As mentioned previously, the knee 10 includes two joints:
the joint between the femur and the tibia (referred to as the
tibio-femoral joint), and the joint between the femur and the
patella (referred to as the patello-femoral joint).
[0022] The tibio-femoral joint is characterized by interaction
between condyles 22, 24 at the distal end of the femur 20 and the
tibial plateau 32 at the proximal end of the tibia 30.
Specifically, the distal end of the femur includes a pair of
condyles: the medial condyle 22 and the lateral condyle 24. The
condyles are generally ovoid in shape and have articular surfaces
23 covered by articular cartilage that cooperates with the tibia.
Specifically, the condyles cooperate with the tibial plateau 32,
which also has portions covered by articular cartilage. The
articular surfaces are smooth surfaces configured to provide
bearing surfaces for the rotation of the tibia relative to the
femur during flexion of the knee.
[0023] The articular surfaces 23 of the condyles generally extend
from the distal end of the femur around to the posterior side of
the femur, as shown in FIGS. 2, 6 The articular surfaces of the
medial and lateral condyles 22, 24 are separated from one another.
An intercondylar notch 26 extends between the two condyles.
[0024] The trochlear groove 25 extends along the anterior surface
of the femur 20, extending toward the distal end of the femur. The
trochlear groove is a groove that the patella 40 slides within, as
discussed further below. The trochlear groove includes a central
groove, having sidewalls that curve upwardly, so that the sidewalls
from convex surfaces. More specifically, the groove 25 is a concave
groove that extends toward the distal end of the femur, while the
sidewalls extend upwardly and away from the groove, so that the
trochlear groove is saddle-shaped. The distal end of the trochlear
groove 25 intersects the intercondylar notch 26.
[0025] The patella is a small bone situated within the tendon of
the quadriceps muscle just above the point where the tendon joins
onto the tibia. The patellar bone provides a significant mechanical
advantage to the knee extensor mechanism, allowing the knee to
extend with a smaller contractile force of the quadriceps. In
addition, the patella redirects the force exerted by the
quadriceps, resulting in a large compressive stress on the
patello-femoral joint. The magnitude of this stress usually is at a
maximum with the knee flexed between about 45-60.degree. and the
foot planted, such as that occurring when one stands from a sitting
position.
[0026] The posterior surface of the patella 40 forms a surface that
is configured to slide within the trochlear groove 25 during
flexion of the knee. Specifically, as shown in FIG. 1 the posterior
surface of the patella forms a generally V-shaped surface that
cooperates with the trochlear groove. The confronting surfaces of
the patella and the trochlear groove are covered in articular
cartilage so that the two bones readily slide relative to one
another during knee flexion.
[0027] Only a portion of the patellar cartilage articulates with
the femoral trochlea at any one time. With the knee extended
0.degree., the patella rides laterally within the trochlear groove
and is not in direct contact with the trochlear cartilage. With
knee flexion, the patella moves distally, and the degree of surface
contact of the patello-femoral joint increases. For instance, the
initial contact of the patella with the femur occurs at
approximately 20.degree.. By 90.degree. of flexion a substantial
portion of the articular surface of the patella has made contact
with the femur. Beyond 90.degree. of flexion, the patella rides
down into the intercondylar notch and the quadriceps ride in the
trochlear groove.
[0028] The muscles and tendons of the quadriceps don't form a
straight line when viewed from the front. They point one way above
the patella and another way below the patella. Therefore when the
muscles contract, the kneecap has a tendency to be pulled off to
the side. The sidewalls of the trochlear groove retain the patella
within the trochlear groove. The contours of the posterior surface
of the patella and the trochlear groove determine the stability of
the patello-femoral joint. For instance, if the trochlear groove is
shallow, the patella is more easily pulled laterally out of the
trochlear groove during flexion of the knee (referred to as
patellar subluxation).
[0029] Since the two joints in the knee have different articular
surfaces and since the two joints are subject to different forces,
one of the joints may require replacement, but the other may be
sufficiently healthy that it does not need replacement. Therefore,
it is often desirable to replace select articular surfaces without
replacing all of the articular surfaces in the knee.
[0030] If there is damage to the patello-femoral joint, it is
desirable to replace the articulating surfaces of the patella 40
and the femur 20. Further, if the tibio-femoral joint does not need
repair, it is desirable to replace to patello-femoral surfaces
without affecting the tibio-femoral surfaces. This can be
accomplished by implanting a patellar prosthesis 60 and a femoral
prosthesis 70. Preferably, the femoral prosthesis replaces the
surfaces of the trochlear groove 25 and extends into the
intercondylar notch 26, without overlapping the articular surfaces
of the tibio-femoral joint. The patellar prosthesis 60 replaces a
posterior surface of the patella and is configured to slidingly
engage the femoral prosthesis 70.
[0031] The patellar prosthesis 60 is preferably a single element
that is configured to re-surface a portion of the posterior surface
of the patella. As described previously, the posterior surface of
the patella forms a generally V-shaped surface configured to ride
in the trochlear groove. Similarly, preferably the posterior
surface of the patellar implant forms a projection that is
configured to cooperate with a groove in the femoral implant as
discussed below. Preferably, but not necessarily, the interfacing
prostheses are formed of different materials. Accordingly, the
patellar prosthesis 60 and the femoral prosthesis 70 are preferably
formed of different materials, such as plastic and metal. In the
preferred embodiment, the patellar prosthesis is formed of a
plastic, such as ultra-high molecular weight (UHMW) polyethylene,
and the femoral prosthesis is formed of metal, such as
cobalt-chromium molybdenum. However, other materials may be
utilized, such as ceramics or other plastic or metals.
[0032] Referring now to FIGS. 3-5, the details of the femoral
prosthesis 70 will now be described in greater detail. The femoral
prosthesis includes two sections. Preferably the two sections form
a single unitary element. However, the femoral prosthesis may be
formed of a plurality of separate elements.
[0033] The first section of the femoral prosthesis is the central
or trochlear portion 72 that is configured to cover the trochlear
groove. The second section is the intercondylar section 76 that
intersects the distal end of the trochlear portion. The
intercondylar portion 76 preferably comprises a pair of tapered
extensions 77,78 configured to extend into away from the trochlear
portion along the intercondylar notch adjacent the interior edges
of the condyles.
[0034] In general, the trochlear portion 72 provides a channel for
retaining the patella 40 in place (i.e. preventing subluxation) and
providing a sliding surface in which the patella can slide during
moderate bending of the knee. The intercondylar portion 76 provides
a sliding portion on which the patella can slide during deep
bending of the knee.
[0035] The trochlear portion 72 is an elongated element that flares
outwardly adjacent its proximal end, and narrows adjacent the
distal end adjacent the intercondylar portion 76. A groove 75
extends along the top surface of the trochlear portion, extending
from the proximal end to the distal end. In certain configuration,
it may be desirable to center the groove between the sides of the
trochlear portion. Sidewalls 73, 74 extend upwardly and away from
the groove. The sidewalls 73, 74 are configured to retain the
patella 40 within the groove 75. In a preferred embodiment, the
sidewalls curve upwardly forming a convex surface. In this way, the
groove 75 is concave, having upwardly extending convex sidewalls.
Although the sidewalls have been described as convex curved
surfaces, the sidewalls need not be curved. The sidewalls can be
configured to extend upwardly generally straight to form a channel,
such as a V-groove. However, even such sidewalls would preferably
be convex, because preferably, the upper edge of the sidewalls
curves or bends over to overlie the femur (See e.g. FIG. 4).
[0036] As described above, the trochlear portion 72 has a groove
that is generally convex in the direction of the width of the
femur. In addition, preferably the trochlear portion curves
downwardly toward the posterior as the trochlear portion extends
toward the intercondylar notch. In this way, the trochlear portion
is generally convex in the direction of the length of the
femur.
[0037] The intercondylar portion 76 intersects the distal end of
the trochlear portion and extends downwardly in a posterior
direction and away from the trochlear portion. The intercondylar
portion has a pair of opposing extensions configured to extend
along the sides of the intercondylar notch. The first extension
projects is a medial extension 77 that extends in a medial
direction and downwardly in a posterior direction. The medial
extension is configured to overlie a medial portion of the
intercondylar notch 26 without extending onto an articular surface
23 of the medial condyle 22. The second extension is a lateral
extension 78 that is configured similarly to the medial extension
77, except that it extends in a lateral and posterior direction,
away from the medial extension. Further, the lateral extension 78
is configured to overlie a lateral portion of the intercondylar
notch 26 without extending onto an articular surface of the lateral
condyle 24.
[0038] Referring to FIG. 4, the medial and lateral extensions 77,
78 form a generally arch-shaped extension that curves outwardly and
posteriorly. Preferably, the extensions taper as they extend away
from trochlear portion 72. In this way, the ends of the extensions
remote from the trochlear portion are narrower than the width of
the extension adjacent the trochlear portion. The two extensions
are configured to provide a surface upon which the patella slides
when the knee is bent during deep flexion. Specifically, each
extension operates as a rail upon which the posterior surface of
the patella rides--the lateral side of the posterior patella
surface rides on the lateral extension, the medial side rides on
the medial extension.
[0039] As described above, the trochlear 72 and intercondylar
portions 76 of the femur prosthesis have been described as being
symmetric. However, the femoral prosthesis 70 need not be
symmetric. Since the femur and tibia do not form a straight line,
when the knee is bent, the patella is pulled distally and inwardly
(in a medial direction). Therefore, typically, the medial side of
the condyle is larger and the medial side of the trochlear groove
is higher than the lateral side to retain the patella within the
intercondylar groove. The femoral prosthesis 70 may be configured
to reflect this lack of symmetry. For instance, the medial sidewall
73 of the trochlear portion 72 may be higher than the lateral
sidewall 74. Similarly, the medial extension 77 may be wider and/or
longer than the lateral extension 78 of the intercondylar
portion.
[0040] The foregoing discussion has described features of the
femoral prosthesis for replacing the articular surfaces of the
patello-femoral joint. In some instances, it may be desirable to
replace some of the surfaces of the tibio-femoral joint in addition
to the patello-femoral joint. For instance, the interface between
the medial condyle and the tibial plateau may be damaged and need
replacement. Accordingly, it may be desirable to repair the
interface while repairing the patello-femoral joint. Furthermore,
if the interface between the lateral condyle and the tibial plateau
are not sufficiently damaged to justify replacement, it is
desirable to repair the patello-femoral joint and the medial
condyle/tibial plateau surfaces without altering the surfaces of
the lateral condyle/tibial plateau interface.
[0041] To facilitate selective repair of the knee joint surfaces, a
unicompartmental femoral prosthesis 90 is utilized to replace the
articular surface of the medial condyle. (see FIG. 8) Specifically,
the unicompartmental prosthesis 90 is configured to cover the
articular surface of the medial condyle. Preferably, the prosthesis
has a generally C-shaped configuration adapted to overly the outer
surface of the medial condyle. Further, preferably the
unicompartmental prosthesis is wide enough to cover the articular
surface, but it has a lateral side edge that terminate adjacent to
the lateral edge of the articular surface. In addition, preferably
the femoral prosthesis described above is configured to cooperate
with the unicompartmental prosthesis so that the edges of the two
prostheses cover the condylar and intercondylar articular surfaces
without overlapping each other.
Method of Implanting
[0042] The patello-femoral prostheses are preferably implanted as
follows. Since the patella is embedded within the patellar tendon
it is generally desirable to repair the patella rather than
replacing the patella. To implant the patellar prosthesis 60, a
portion of the patella is resected, and the patella prosthesis is
attached to the patella. Specifically, a portion of the posterior
prosthesis, preferably less than 10 mm thick, is resected from the
patella. The patella prosthesis is then attached using an adhesive.
In addition, the prosthesis may include a tab or post to improve
the bonding between the prosthesis and the patella. Therefore, in
addition to cutting-off a portion of the posterior patellar
surface, a recess may be drilled into the patella to receive the
post on the prosthesis. Adhesive cement is then applied to the
posterior surface of the patella and the prosthesis is pressed into
the cement to bond the prosthesis to the patella. In this way, the
patellar articulating surface is replaced by the prosthesis.
[0043] To replace the femoral surfaces, the surfaces of the
trochlear groove and the intercondylar notch are resected and the
femoral prosthesis is bonded onto the femoral surfaces from which
bone was resected. Specifically, the surface of the trochlear
groove is resected to form a recess of preferably no greater than
10 mm. In addition, preferably the recess extends to the anterior
surface of the femur adjacent the trochlear groove. The shape of
the recess is configured to be substantially similar to the outline
of the trochlear portion of the femoral prosthesis, and preferably
the recess is deeper than the thickness of the trochlear
portion.
[0044] In addition, the femur is further resected along the
intercondylar notch to accommodate the intercondylar notch portion
of the femoral prosthesis. The intercondylar notch is resected to
form a recess extending along the intercondylar groove. The recess
extends along the medial condyle terminating adjacent the articular
surface of the medial condyle so that the recess does not extend
onto the articular surface of the medial condyle. Similarly, the
recess extends along the intercondylar notch onto the lateral
condyle, terminating adjacent the articular surface of the lateral
condyle so that the recess does not extend onto the articular
surface of the lateral condyle. Preferably, the recess on the
intercondylar notch intersects the recess on the trochlear groove
to form one continuous recess.
[0045] After portions of the distal end of the femur are resected
as described above, preferably the femoral prosthesis is bonded
into the recess using adhesive cement. Specifically, adhesive
cement is applied to the recess and the femoral prosthesis is then
pressed into the cement to bond the prosthesis to the femur. The
femoral prosthesis may be a single unitary element so that the
entire prosthesis in implanted at once. Alternatively, the
prosthesis may be comprised of several separate elements that are
implanted separately. More specifically, after the cement is
applied to the recess each piece of the prosthesis is pressed into
the cement. By using a multi-element prosthesis, the size of the
incision necessary to insert the prosthesis can be reduced.
[0046] As discussed previously, in certain instances it may be
desirable to repair surfaces of the tibio-femoral joint during the
same procedure for repairing the patella-femoral joint. For
instance, to implant a unicompartmental prosthesis over one of the
condyles, the recess in the distal end of the femur is extended
onto the surface of one of the condyles. For instance, to repair
the lateral condyle, the recess along the lateral portion of the
intercondylar groove is extended onto the articular surface of the
lateral condyle. Adhesive cement is then applied to the recess and
the unicompartmental prosthesis is pressed into the cement so that
the unicompartmental prosthesis overlies the surface of the lateral
condyle. A unicompartmental prosthesis can be implanted over the
medial condyle in a similar fashion (i.e. extending the recess onto
the medial condyle and bonding the prosthesis over the medial
condyle). When inserting the femoral prosthesis with a
unicompartmental prosthesis, preferably the prostheses are
positioned so that the adjoining edges of the prostheses are
adjacent without overlapping.
[0047] In the above description, the prostheses are described as
being implanted by cementing the prostheses. However, the
prostheses may be implanted using any one of a variety of bonding
procedures. For instance, any of a variety of procedures using
adhesives or chemical can be used. Also, porous growth techniques
can be used in which the surface of the prosthesis has a fine mesh
of holes that allows bone to grow into the mesh to attach the
prosthesis to the bone. Accordingly, there is no intention to limit
the method of implanting to any particular bonding process.
[0048] It will be recognized by those skilled in the art that
changes or modifications may be made to the above-described
embodiments without departing from the broad inventive concepts of
the invention. It should therefore be understood that this
invention is not limited to the particular embodiments described
herein, but is intended to include all changes and modifications
that are within the scope and spirit of the invention as set forth
in the claims.
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