U.S. patent application number 13/854923 was filed with the patent office on 2014-05-08 for knee prosthesis.
This patent application is currently assigned to SEVIKA HOLDING AG. The applicant listed for this patent is SEVIKA HOLDING AG. Invention is credited to Michael J. HOWARD, Kenneth D. JOHANNABER.
Application Number | 20140128973 13/854923 |
Document ID | / |
Family ID | 47989749 |
Filed Date | 2014-05-08 |
United States Patent
Application |
20140128973 |
Kind Code |
A1 |
HOWARD; Michael J. ; et
al. |
May 8, 2014 |
KNEE PROSTHESIS
Abstract
A knee prosthesis for use in a total knee replacement surgical
procedure may include a femoral component, a tibial component and a
meniscal component. Optionally, the prosthesis may also include a
patellar component. The femoral component may include a bone
attachment side and a joint facing side, the latter including an
anterior joint surface, a posterior joint surface having a
cross-sectional shape defining a portion of a cylinder, and medial
and lateral grooves between the anterior and posterior joint
surfaces. The meniscal component may include a number of features
designed to mate with the femoral component to provide relatively
natural movement and range of motion about the knee joint as well
as stability and resistance to wear and tear.
Inventors: |
HOWARD; Michael J.;
(Sammamish, WA) ; JOHANNABER; Kenneth D.; (Reno,
NV) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEVIKA HOLDING AG; |
|
|
US |
|
|
Assignee: |
SEVIKA HOLDING AG
Baar
CH
|
Family ID: |
47989749 |
Appl. No.: |
13/854923 |
Filed: |
April 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13281748 |
Oct 26, 2011 |
8409293 |
|
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13854923 |
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Current U.S.
Class: |
623/14.12 |
Current CPC
Class: |
A61F 2/3877 20130101;
A61F 2002/30884 20130101; A61F 2/3872 20130101; A61F 2/3886
20130101; A61F 2002/30934 20130101 |
Class at
Publication: |
623/14.12 |
International
Class: |
A61F 2/38 20060101
A61F002/38 |
Claims
1. A knee prosthesis for use in a total knee replacement surgical
procedure, the knee prosthesis comprising: a femoral component
comprising: a bone attachment side for attaching to a cut distal
end of a femur; a joint facing side opposite the bone attachment
side comprising: an anterior joint surface; a posterior joint
surface having a cross-sectional shape defining a portion of a
cylinder, wherein the posterior joint surface extends along at
least 135 degrees of the cylinder and comprises: a lateral condyle;
a medial condyle; and an intercondylar opening disposed between the
lateral and medial condyles; and medial and lateral grooves
extending across the femoral component between the anterior joint
surface and the medial and lateral condyles; a tibial component
comprising: a bone attachment side for attaching to a cut proximal
end of a tibia; and a joint facing side opposite the bone
attachment side; and a meniscal component, having an inferior side
for mating with the tibial component, a superior side for mating
with the femoral component, an anterior side, a posterior side, a
lateral side and a medial side, the meniscal component further
comprising: an anterior articulating surface on the superior side
for mating with the anterior joint surface of the femoral
component; a posterior lateral articulating surface on the superior
side for mating with the lateral condyle of the femoral component,
the posterior lateral articulating surface having an approximately
horizontal profile in an anterior-to-posterior direction; a
posterior medial articulating surface on the superior side for
mating with the medial condyle of the femoral component, the
posterior medial articulating surface having an upward sloping
profile in an anterior-to-posterior direction; medial and lateral
projections on the superior side for mating with the medial and
lateral grooves of the femoral component; a post extending from the
superior surface and configured to mate with the intercondylar
opening of the femoral component, wherein a central axis of the
post is disposed closer to the posterior side than to the anterior
side of the meniscal component; and an anterior cutout on the
anterior side of the superior surface to prevent injury to a
patellar tendon.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention is related to surgical devices for total knee
replacement surgery. More specifically, the invention is related to
a knee prosthesis for total knee replacement surgery.
[0003] 2. Description of the Related Art
[0004] Approximately 581,000 total knee replacement surgeries (also
referred to as total knee arthroplasty ("TKA")) are performed
annually in the U.S. for the treatment of chronic knee pain and
dysfunction. As the U.S. and world populations become older and
more obese and knee joints endure greater wear and tear from
increased loads and years of stress, TKA becomes a more and more
commonly performed surgical procedure. The goals of TKA are to
provide the patient with a knee joint that is pain free, moves
naturally through a full range of motion, provides stability during
motion and rest, and lasts as long as possible. Many different
total knee implants (or "knee prostheses") have been developed in
pursuit of these goals, but no total knee prosthesis is perfect.
Some knee prostheses, for example, sacrifice some amount of
stability in order to provide greater range of motion, while other
prostheses do just the opposite. Other prostheses may provide
certain kinematic advantages but may wear out more easily, thus
requiring revision surgery more frequently. Although much of the
success of TKA procedures can be attributed to surgeon skill and
experience, rather than the prostheses themselves, improvements in
total knee prostheses are still being sought.
[0005] The knee joint is generally defined as the point of
articulation of the femur with the tibia. Structures that make up
the knee include the distal femur, the proximal tibia, the patella,
and the soft tissues within and surrounding the knee joint. Four
ligaments are especially important in the functioning of the
knee--the anterior cruciate ligament, the posterior cruciate
ligament, the medial collateral ligament, and the lateral
collateral ligament. In an arthritic knee, protective cartilage at
the point of articulation of the femur with the tibia has been worn
away, which causes significant pain and discomfort. In a TKA
procedure, the distal end of the femur, the proximal end of the
tibia, and often the inner surface of the patella are replaced with
prosthetic parts to provide smooth, well-aligned surfaces for joint
movement, while also creating a stable knee joint that moves
through a wide range of motion.
[0006] A typical knee prosthesis includes a femoral component, a
tibial tray or plateau and a tibial bearing insert (or "meniscal
component") coupled to the tibial tray. The prosthesis may also
include a patellar component, if replacing that bone surface is
necessary. The femoral component generally includes a pair of
laterally spaced apart condylar portions that have distal surfaces
that articulate with complementary condylar elements formed in a
tibial bearing insert.
[0007] As mentioned above, the TKA procedure and total knee
prostheses generally try to achieve several basic goals: (1) Pain
reduction/elimination; (2) Natural and full range of motion about
the knee joint; (3) Joint stability; (4) Correctly sized and
implanted joint to minimize wear and tear of the prosthesis; and
(5) Preservation of as much of the patient's existing bone and soft
tissue (ligaments and tendons) as possible. The goals of freedom of
motion and stability can conflict with one another, since creating
a more stable knee joint often means reducing freedom of motion. In
trying to achieve these various goals, three categories of total
knee prostheses/procedures have been developed.
[0008] In a knee joint resurfacing procedure, the articular surface
of the distal femur and proximal tibia are "resurfaced" with
respective condylar-type articular bearing components. These knee
prostheses provide substantial rotational and translational freedom
and require minimal bone resection to accommodate the components in
the available joint space. The patellofemoral joint may also be
resurfaced by a third prosthetic component. The femoral, tibial and
patellar prosthetic resurfacing components are affixed to
respective adjacent bone structure by a cementing or by a
biological bone ingrowth fixation means or any other suitable
technique.
[0009] In a second type of TKA, a mechanically linked or hinged
knee prosthesis provides a fixed fulcrum flexion-extension
capability. The hinged knee, therefore, is usually surgically
indicated in selected cases where the surrounding soft tissue
structures are grossly degenerated and incapable of providing
functionally acceptable knee joint stability.
[0010] The third category of total knee prosthesis, the posterior
stabilized total knee, provides more predictable kinematics than
the first category. The posterior stabilized total knee prostheses
essentially incorporate all of the functional features of the first
category, that is, the resurfacing condylar-type of knee
prostheses, in addition to incorporating a mechanical cam/follower
mechanism for providing posterior (tibia-to-femur) constraint. The
cam/follower mechanism is positioned within the intercondylar space
of the femoral component and provides substitutional posterior
constraint to compensate for lost anterior and/or posterior
cruciate ligament function or for compromised posterior knee
stability. This cam/follower mechanism enables the femur to roll
back on the tibia, providing a mechanical advantage to the
quadriceps during flexion.
[0011] Although many different posterior stabilized total knee
prostheses have been developed and some work well, there is still
much room for improvement. For example, most currently available
prostheses compromise either knee joint stability or natural, full
range of motion to an extent that is suboptimal for a patient.
Additionally, most prostheses wear out more quickly than would be
ideal, often in predictable wear patterns. Another limitation with
conventional posterior cruciate substituting knee designs is that
they require excess removal of bone for implantation. Excessive
bone removal can lead to intraoperative fractures due to the stress
concentration created by cutting out bone to accommodate the box of
the design. Bone removal is also disadvantageous, because, in the
event of revision surgery, the more bone available, the easier the
revision surgery will be.
[0012] Therefore, a need exists for an improved knee prosthesis for
a total knee arthroplasty procedure. Ideally, an improved
prosthesis would provide natural kinematics, full range of motion
through the knee joint, as well as a stable feeling joint. Also
ideally, the knee prosthesis would have improved wear
characteristics compared with most currently available prostheses.
At least some of these objectives will be met by various
embodiments of present invention.
SUMMARY OF THE INVENTION
[0013] The present invention provides an improved knee prosthesis
for total knee arthroplasty. The prosthesis may have a number of
advantages, such as but not limited to effectively replicating
natural knee kinematics and reducing wear and tear of the
prosthesis thus prolonging its useful life in situ. In various
embodiments, the prosthesis may be provided as a system including
multiple components, such as a femoral component, tibial component,
meniscal component and patellar component, or some subset of those
components.
[0014] In one aspect of the invention, a knee prosthesis for use in
a total knee replacement surgical procedure may include a femoral
component, a tibial component and a meniscal component. The femoral
component may include a bone attachment side for attaching to a cut
distal end of a femur and a joint facing side opposite the bone
attachment side. The joint facing side of the femoral component may
include: an anterior joint surface; a posterior joint surface
having a cross-sectional shape defining a portion of a cylinder,
wherein the posterior joint surface extends along at least 135
degrees of the cylinder and includes a lateral condyle, a medial
condyle, and an intercondylar opening disposed between the lateral
and medial condyles; and medial and lateral grooves extending
across the femoral component between the anterior joint surface and
the medial and lateral condyles. The tibial component may also
include a bone attachment side for attaching to a cut proximal end
of a tibia and a joint facing side opposite the bone attachment
side.
[0015] The meniscal component may include an inferior side for
mating with the tibial component, a superior side for mating with
the femoral component, an anterior side, a posterior side, a
lateral side and a medial side. The meniscal component may also
include: an anterior articulating surface on the superior side for
mating with the anterior joint surface of the femoral component; a
posterior lateral articulating surface on the superior side for
mating with the lateral condyle of the femoral component, the
posterior lateral articulating surface having an approximately
horizontal profile in an anterior-to-posterior direction; a
posterior medial articulating surface on the superior side for
mating with the medial condyle of the femoral component, the
posterior medial articulating surface having an upward sloping
profile in an anterior-to-posterior direction; medial and lateral
projections on the superior side for mating with the medial and
lateral grooves of the femoral component; a post extending from the
superior surface and configured to mate with the intercondylar
opening of the femoral component, wherein a central axis of the
post is disposed closer to the posterior side than to the anterior
side of the meniscal component; and an anterior cutout on the
anterior side of the superior surface to prevent injury to a
patellar tendon.
[0016] In one embodiment, the bone attachment side of the femoral
component may include three surfaces for attaching to a three-cut
configuration of the distal end of the femur. In one embodiment,
the anterior joint surface of the femoral component may include a
trochlear groove that is offset from a midline axis of the femoral
component in a direction slanting from medial to lateral as the
groove extends toward an anterior, superior edge of the femoral
component. In one embodiment, the post of the meniscal component
may have an asymmetrical shape in at least two dimensions. For
example, in some embodiments, the post may have a helical twist
shape as viewed from a superior aspect. Optionally, an anterior
convex surface of the post may conform to an anterior concave
surface of the intercondylar opening of the femoral component, and
a posterior convex surface of the post may conform to a posterior
concave surface of the intercondylar opening of the femoral
component. Additionally, in some embodiments a posterior portion of
the post may be wider than an anterior portion of the post. Also
optionally, a superior surface of the post may slope downward in a
posterior-to-anterior direction, and the superior surface may have
an asymmetric convex configuration.
[0017] In some embodiments, the anterior cutout on the meniscal
component may be asymmetrically disposed along the anterior side,
biased toward the lateral side. Also in some embodiments, the
prosthesis may further include a patellar component having a cutout
portion on an inferior edge.
[0018] In another aspect of the invention, a meniscal component of
a knee prosthesis for use in a total knee replacement surgical
procedure may include: an inferior side for mating with a tibial
component of a knee prosthesis; a superior side for mating with a
femoral component of the knee prosthesis; an anterior side, a
posterior side, a lateral side and a medial side; a concave
anterior articulating surface on the superior side toward the
anterior side for mating with a convex anterior joint surface of a
femoral component; a posterior lateral articulating surface on the
superior side for mating with a lateral condyle of the femoral
component, the posterior lateral articulating surface having an
approximately horizontal profile in an anterior-to-posterior
direction; a posterior medial articulating surface on the superior
side for mating with a medial condyle of the femoral component, the
posterior medial articulating surface having an upward sloping
profile in an anterior-to-posterior direction; medial and lateral
projections on the superior side for mating with medial and lateral
grooves on the femoral component; a post extending from the
superior surface and configured to mate with the intercondylar
opening of the femoral component, wherein a central axis of the
post is disposed closer to the posterior side than to the anterior
side of the meniscal component; and an anterior cutout on the
anterior side of the superior surface to prevent injury to a
patellar tendon. As described above, the post of the meniscal
component may have an asymmetrical shape in at least two
dimensions.
[0019] In another aspect of the present invention, a knee
prosthesis for use in a total knee replacement surgical procedure
may include a femoral component as described above and a meniscal
component. The meniscal component may be largely as describe above
but may include a bone attachment side for attaching to a cut
proximal end of a tibia and a superior side for mating with the
femoral component, thus eliminating the need for a separate tibial
component. In some embodiments, the meniscal component may be made
entirely of a polymer such as ultra-high-molecular-weight
polyethylene (UHMWPE). As in previously described embodiments, the
prosthesis may optionally also include a patellar component having
a cutout portion on an inferior edge.
[0020] For a further understanding of the nature and advantages of
the invention, reference should be made to the following
description taken in conjunction with the accompanying figures.
However, each of the figures is provided for the purpose of
illustration and description only and is not intended to limit the
scope of the embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1A is a perspective view of a knee prosthesis,
including femoral, meniscal, tibial and patellar components, in
place within a knee joint, according to one embodiment;
[0022] FIG. 1B is a perspective view of the knee prosthesis of FIG.
1A, with the patellar component removed;
[0023] FIG. 1C is a perspective view of the knee prosthesis of
FIGS. 1A and 1B without the femur or tibia shown;
[0024] FIG. 1D is an exploded view of the knee prosthesis of FIGS.
1A-1C;
[0025] FIGS. 2A-2E are top, perspective, posterior, medial and
anterior views, respectively, of a femoral component of a knee
prosthesis, according to one embodiment;
[0026] FIG. 2F is a side, diagrammatic view of a femoral component,
according to one embodiment;
[0027] FIG. 2G is a side view of a prior art femoral component of a
knee prosthesis;
[0028] FIGS. 2H-2K are posterior comparison views of two femoral
components, according to two different embodiments;
[0029] FIGS. 3A-3E are top, perspective, medial, anterior and
lateral views, respectively, of a meniscal component of a knee
prosthesis, according to one embodiment;
[0030] FIG. 3F is a top, cross-sectional view of meniscal and
femoral components of a knee prosthesis, showing conforming
posterior surfaces according to one embodiment;
[0031] FIG. 3G is a top, cross-sectional view of meniscal and
femoral components of a knee prosthesis, showing conforming
anterior surfaces, according to one embodiment;
[0032] FIG. 3H is a top view of a meniscal component of a knee
prosthesis, according to one embodiment;
[0033] FIGS. 3I and 3J are a top view of a meniscal component and a
side view of meniscal, femoral and patellar components of a knee
prosthesis, respectively, according to one embodiment;
[0034] FIG. 3K is a top view of a meniscal component of a knee
prosthesis, according to one embodiment;
[0035] FIGS. 3L-3N are posterior, medial and lateral views,
respectively, of a meniscal component of a knee prosthesis,
according to one embodiment;
[0036] FIGS. 4A-4D are top, perspective, posterior and side views,
respectively, of a tibial component of a knee prosthesis, according
to one embodiment.
[0037] FIGS. 5A and 5B are anterior and perspective/posterior
views, respectively, of a patellar component of a knee prosthesis,
according to one embodiment;
[0038] FIG. 5C is an anterior view of a prior art patellar
component of a knee prosthesis;
[0039] FIGS. 6A-6E are perspective views of femoral and meniscal
components of a knee prosthesis, according to one embodiment,
demonstrating how the components move during a range of motion of a
knee joint from extension to flexion as follows: 4 degrees
hyperextension (FIG. 6A); 0 degrees flexion (FIG. 6B); 45 degrees
flexion (FIG. 6C); 90 degrees flexion (FIG. 6D); and 135 degrees
flexion (FIG. 6E);
[0040] FIGS. 7A-7E are side views of the femoral and meniscal
components through the same range of motion shown in FIGS.
6A-6E;
[0041] FIGS. 8A-8E are posterior views of the femoral and meniscal
components through the same range of motion shown in FIGS. 6A-6E
and 7A-7E; and
[0042] FIGS. 9A-9E are anterior views of the femoral and meniscal
components through the same range of motion shown in FIGS. 6A-6E,
7A-7E and 8A-8E.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] Referring to FIGS. 1A-1D, in one embodiment, a knee
prosthesis system 10 may include a femoral component 12, a meniscal
component 14, a tibial component 16, and optionally a patellar
component 18. In FIG. 1A, knee prosthesis system 10 is shown with
patellar component 18, while in FIGS. 1B-1D, it is shown without
patellar component 18. In other embodiments, system 10 may be
provided without tibial component 16, for example when meniscal
component 14 attaches directly to the cut tibia (not shown). In yet
other embodiments, multiple sizes of one or more components may be
provided as part of system 10, for example as a kit or suite of
operating room tools so that a surgeon can select a desired size of
each component or set of components. Generally, therefore, system
10 may include any two or more components of a knee prosthesis as
described herein. Although system 10 is typically described below
as including femoral 12, meniscal 14 and tibial 16 components, with
an optional patellar component 18, this description is provided for
exemplary purposes and should not be interpreted to limit the scope
of the claims.
[0044] FIG. 1A shows knee prosthesis system 10 in place within a
knee joint of a left leg. Here, femoral component 12 is attached to
the femur F, tibial component 16 is attached to the tibia T,
meniscal component 14 is disposed between the two, and patellar
component is floating in a position generally located where it
would be when attached to a patella (not shown for ease of
illustration). The ligaments or tendons of the knee joint are not
shown in FIG. 1, so that system 10 may be more easily seen.
[0045] The embodiment of system 10 and components 12, 14, 16, 18
shown in FIG. 1A and many of the subsequent figures in this
application is configured for a left knee. It is described as
having a lateral side L and a medial side M, conforming to the
lateral and medial sides of the knee, respectively. Of course, in
another embodiment, system 10 is provided in mirror image for use
on a right knee, and in some embodiments a kit or system may
include multiple knee prostheses for a left knee and a right knee
or even for multiple sizes of left and right knees. Therefore,
although many references will be made to the lateral side L and
medial side M of components 12, 14, 16, 18 and system 10, these
sides may be reversed in alternative embodiments, and the
descriptions thus should not be interpreted as limiting the
invention as claimed.
[0046] FIG. 1B illustrates knee prosthesis system 10 in place
within a knee joint with patellar component 18 removed. FIG. 1C is
a perspective view of knee prosthesis system 10 by itself, also
without patellar component 18.
[0047] Referring now to FIG. 1D, an exploded view of knee
prosthesis system 10 helps illustrate further details of femoral
component 12, meniscal component 14 and tibial component 16. For
example, in the embodiment shown, femoral component 12 includes a
bone attachment side 20 and a joint facing side 22. Bone attachment
side 20 has three surfaces at different angled orientations from
one another (see FIGS. 2A-2D), to provide for attachment to a 3-cut
distal end of a femur F. In an alternative embodiment, bone
attachment side 20 may include five surfaces, for attachment to a
5-cut distal end of a femur F, or any other suitable number of
surfaces to provide for alternative femoral bone cut
configurations. Generally, the 3-cut configuration is used for
revision TKA procedures, while the 5-cut configuration is used for
original (or "primary") TKA procedures. This is not a requirement
for the present application, however, and although the 3-cut bone
attachment side 20 is shown and described herein, system 10 may be
used for primary or revision TKA procedures in various
embodiments.
[0048] Joint facing side 22 of femoral component 12 may include an
anterior articulating surface 24, a posterior articulating surface
25 including a medial condyle 25a and a lateral condyle 25b, a
medial groove 26a and a lateral groove 26b between the articulating
surfaces 24, 25, an intercondylar opening 28, and a trochlear
groove 30 extending vertically along anterior articulating surface
24. These and other features of femoral component 12 are described
in greater detail below.
[0049] Still referring to FIG. 1D, meniscal component 14 may
include a post 32 for mating with the intercondylar opening 28 of
femoral component 12, a medial projection 34a and a lateral
projection 34b (not visible in this figure) for mating with lateral
grooves 26a, 26b of femoral component 12, and an anterior cutout 36
on its anterior/superior side for preventing injury to the patellar
tendon. These and other features of meniscal component 14 are
described in greater detail below.
[0050] Tibial component 16 includes a joint facing side 40, a bone
attachment side 38, and a bone attachment stem 43 for extending
into the tibia to facilitate bone attachment. Tibial component 16
is also described in greater detail below.
[0051] All components 12, 14, 16, 18 of knee prosthesis system 10
may be made of any suitable material for manufacturing knee
prostheses. For example, in some embodiments, femoral component 12
and tibial component 16 may be made of a metal, while meniscal
component 14 and patellar component 18 may be made of a polymer. In
other embodiments, tibial component 16 may also be made of a
polymer. In some embodiments, one of more of the components may be
made of ceramic. Knee prosthesis system 10, therefore, may
incorporate any suitable material(s) and combinations thereof.
Typical implant metals include CoCr (Cobalt-Chrome), and Ti-6Al-4V
(Titanium Alloy). A typical polymer is UHMWPE (Ultra-High Molecular
Weight Polyethylene). Ceramics include Zirconia, Zirconia-Toughened
Alumina (ZTA), Alumina, and oxidized zirconium (metal-ceramic).
Some implants may also be coated (or part of an implant may be
coated) with any of a number of suitable coating materials. For
example, some coatings are used on implants to increase
bone-cement-implant adhesion and promote ingrowth. Potential
coatings include HA (Hydroxyapatite), TPS (Titanium Plasma Spray),
RBM (Resorbable blast media) and porous Ccoatings (spherical beads,
asymmetrical powder and irregular particle coatings).
[0052] Components 12, 14, 16, 18 of knee prosthesis system 10 may
also be provided in any suitable size, combinations of sizes, kits
including multiple sizes, or the like. For example, in one
embodiment, femoral component 12 may have any of a number of
different distal thicknesses (or "heights") while maintaining the
distal profile, posterior thickness and anterior thickness of joint
facing surface 22. These femoral components 12 of multiple
thicknesses may be provided to allow a surgeon to select a desired
thickness without needing to use augments or offsets. One example
of such a kit of different distal thicknesses of a femoral
component is described in U.S. Pat. No. 7,837,737, the disclosure
of which is hereby incorporated by reference. Thus, knee prosthesis
system 10 is not dependent on sizes of components and may be
provided in any suitable size or combination of sizes as
desired.
[0053] FIGS. 2A-2E show femoral component 12 in greater detail.
FIG. 2A, a top view, shows the three surfaces 20a, 20b and 20c of
this embodiment of bone attachment side 20, a bone attachment
member 27, an anterior/superior edge 21, a posterior/superior edge
23, and intercondylar opening 28, which has an anterior surface 28a
and a posterior surface 28b. This view also shows that anterior
joint surface 24 is asymmetric, slanting toward the lateral side L
toward the anterior/superior edge 21. Bone attachment member 27 may
have any of a number of suitable configurations and may include a
post, as shown. Ideally, bone attachment member 27 is made as small
as possible while also helping provide secure attachment to the
femur, so that as small a femoral cut as possible may be made.
[0054] The shape and location of intercondylar opening 28 and its
anterior 28a and posterior 28b surfaces are configured for mating
with post 32 on meniscal member 14. Surfaces 28a, 28b may be
regarded as cam surfaces, which interact with corresponding
anterior and posterior surfaces of post 32 during rotation of the
knee joint. Posterior cam surface 28b produces rollback in the form
of posterior translation of the femur relative to the tibia as it
rides against meniscal component post 32. Anterior cam surface 28a
is used to stabilize femoral component 12 with meniscal component
14 in full extension.
[0055] Shape of intercondylar opening 28 is designed to conform
closely to the shape of post 32, so that the two parts conform to
one another during movement to enhance stability while still
allowing for a full range of motion.
[0056] Referring now to FIG. 2B, a perspective view of femoral
component 12, trochlear groove 30 on anterior surface 24 is shown
in greater detail, as are medial groove 26a and lateral groove 26b.
The asymmetry of anterior surface 24 is also demonstrated in this
figure. As mentioned above, anterior articulating surface 24 of
femoral component 12 is asymmetrically slanted toward the lateral
side of femoral component 12 toward its anterior/superior edge 21.
Trochlear groove 30 is also offset laterally. In other words,
instead of traveling vertically up anterior articulating surface
24, trochlear groove 30 angles toward the lateral side in the
anterior/superior direction. This offset configuration of trochlear
groove 30 improves patellar tracking.
[0057] Medial and lateral grooves 26a, 26b divide femoral component
12 into anterior and posterior articulating surfaces 24, 25, the
latter having two parts-medial condyle 25a and lateral condyle 25b.
Together with protrusions 34a, 34b of meniscal component 14,
grooves 26a. 26b help provide knee prosthesis 10 with
anterior-posterior stability, help reduce paradoxical
shift/translation of the knee, and enhance patellofemoral tracking
when implanted in a knee joint.
[0058] FIG. 2C is a posterior view of femoral component 12. From
this viewpoint, intercondylar opening 28 and its anterior surface
28a are visible. Also, the cylindrical shape of posterior
articulating surface 25 is evident. This cylindrical shape is
discussed further below, and an alternative embodiment is discussed
in relation to FIG. 3A.
[0059] In FIGS. 2D and 2F, medial side views, the cylindrical shape
of posterior articulating surface 25 is again shown. As the knee
rotates through its range of motion from extension to flexion and
back to extension, the tibia rotates about the femur around an axis
of rotation A (FIG. 2F). Posterior articulating surface 25,
including medial condyle 25a and lateral condyle 25b, are the
portion of femoral component 12 about which the majority of this
rotation occurs. Posterior articulating surface 25 may thus be said
to have an axis of rotation A about which the cylindrical shape of
surface 25 is formed. This cylinder may be said to have a radius R
from axis A to posterior surface 25, One of the advantageous
features of femoral component 12 is that posterior joint surface 25
conforms to the radius R of the cylinder drawn about the axis of
rotation A for at least about 120 degrees, and more preferably at
least about 135 degrees, and even more preferably about 180 degrees
or more. This configuration of posterior articulating surface 25
may be referred to as a "cylindrical radius," which ends in grooves
26a, 26b. By contrast, and referring to FIG. 2G, currently
available femoral components of knee prosthesis generally have a
posterior portion that conforms to the radius of a cylinder for
only 90 degrees at most. The posterior shapes of these currently
available devices then move away from the radius. The advantage of
having posterior surface 25 that conforms to the radius of the
cylinder for at least 120 degrees (and preferably closer to or
equal to 180 degrees) is that, along with grooves 26a, 26b, this
feature enhances stability and the natural kinematics (motion) of
the knee. Tests have shown that this shape provides a more natural
knee movement.
[0060] Still referring to FIGS. 2D and 2F, femoral component 12 may
also be described as having an anterior radius of curvature
involving anterior articulating surface 24 and a posterior radius
of curvature R involving posterior articulating surface 25.
Posterior radius of curvature R was just described and involves the
tibiofemoral portion of the knee joint. The anterior radius of
curvature refers to the radius of rotation of the patella about the
femur (or femoral component 12)--i.e., the patellofemoral joint.
The anterior and posterior curvatures intersect at the location of
grooves 26a and 26b.
[0061] FIG. 2E is an anterior/superior view of femoral component
12, again demonstrating the asymmetrical shape of anterior
articulating surface 24 and trochlear groove 30. As mentioned
previously, this asymmetry is reversed in a knee prosthesis
configured for the opposite (right) knee.
[0062] Referring now to FIGS. 211 and 21, an alternative embodiment
of femoral component 12 is explained. FIG. 2H is a posterior view
of the previously described embodiment of femoral component 12 and
meniscal component 14 with post 32. Femoral component 12 has medial
25a and lateral 25b condyles, which have a generally cylindrical
overall shape, and intercondylar opening 28 between the two. In an
alternative embodiment, however, as shown in FIG. 2I, a femoral
component 112 may have an intercondylar opening 128 and a medial
condyle 125a and a lateral condyle 125b that conform to more of a
spherical shape. In this embodiment, meniscal component 114 also
has a more concave shape to mate with the spherical shape of
femoral component 112. In alternative embodiments, either of these
configurations of femoral component 12, 112 and meniscal component
14, 114 may be used.
[0063] Referring now to FIGS. 3A-3E, meniscal component 14 is shown
in greater detail. Meniscal component 14 may be described as having
a superior side 50 for mating with femoral component 12, an
inferior side 52 for mating with tibial component 16, an anterior
side 54, a lateral side 56, a medial side 58 and a posterior side
60. On superior side 50, as mentioned previously, meniscal
component 14 includes posterior stabilization post 32, medial
protrusion 34a for mating with medial groove 26a of femoral
component, lateral protrusion 34b for mating with lateral groove
26b of femoral component, and anterior cutout 36 for preventing
injury to a patellar tendon. Superior side 50 may also include an
anterior articulating surface 62 for mating with anterior joint
surface 24 of femoral component 12, a posterior medial articulating
surface 64a for mating with medial condyle 25a of femoral component
12, and a posterior lateral articulating surface 64b for mating
with lateral condyle 25b of femoral component 12.
[0064] As shown in FIG. 3A (a top view of meniscal component 14),
post 32 may be described as having an anterior surface 66a and a
posterior surface 66b. These surfaces 66a, 66b interact with
anterior cam surface 28a and posterior cam surface 28b of
intercondylar opening 28 of femoral component 12. Compared to
currently available knee prostheses, post 32 is located farther
toward posterior side 60 of meniscal component 14. For example, a
central axis drawn vertically through approximately the center of
post 32 is located closer to posterior side 60 than to anterior
side 54. In one embodiment, post 32 is located approximately one
third of the total anterior/posterior distance from posterior side
60. The advantages of this more posterior location of post 32 may
include: (1) It better replicates natural knee motion/kinematics by
allowing for greater rollback of the tibia over the femur; (2) By
placing the post more posterior, and having a cylindrical radius
with a center that is close to the insertion point of the PCL, this
design engages the posterior stabilizer earlier and transitions
easily from rotation to posterior "rollback" at the correct time to
replicate natural kinematics; (3) It makes posterior surface 66b of
post 32 engage with posterior cam surface 28b of femoral component
12 earlier in flexion (i.e., at a smaller angle of flexion, such as
about 20 degrees instead of about 45 degrees with conventional
prostheses), which increases stability; (4) It increases the range
of motion about the knee; and (5) It allows less bone removal from
the distal femur during the surgical procedure.
[0065] Referring now to FIGS. 3A and 3F, in at least one
embodiment, posterior stabilization post 32 has a shape that
conforms in multiple different ways to intercondylar opening 28 of
femoral component 12. Post 32 is also asymmetrical in multiple
ways. For example, as illustrated by FIGS. 3A and 3F, post 32 may
have a slight helical twist from a top down view (in a
counterclockwise direction in the figure). The helical twist shape
may allow posterior cam surface 28b of femoral component 12 to
better conform to posterior surface 66b of post during the range of
motion of the knee and especially during internal tibial rotation,
which may reduce wear and tear on post 32. The twist shape may also
help facilitate natural knee kinematics by encouraging posterior
translation of lateral condyle 25b and pivoting of medial condyle
25a during flexion (illustrated by curved arrow in FIG. 3F).
[0066] With reference to FIGS. 3A and 3G, anterior surface 66a of
post 32 may also have a shape that conforms to anterior cam surface
28a of intercondylar opening 28. This conformity of the
corresponding surfaces helps stabilize the knee when returning from
flexion to extension or when simply in a state of extension or low
flexion. The conformity of the surfaces also reduces peak stresses
on anterior cam surface 66a, reducing potential for wear and
premature fatigue.
[0067] Referring to FIGS. 3A and 3H, post 32 may also have a
tapered profile, looking from a top down view, going from a wider
profile posteriorly to a narrower profile anteriorly. This tapered
profile may be produced by making an angular cut down the medial
side of post 32, thus creating another asymmetry. Again, this
asymmetry helps facilitate internal tibial rotation during flexion
of the knee. The tapered profile maintains prosthesis
constraint/stability between post 32 and intercondylar opening 28
in early flexion and extension, while allowing internal tibial
rotation at higher flexion angles in the kinematic range of
motion.
[0068] Turning now to FIGS. 3B, 3I and 3J, post 32 may also include
a sloped anterior/superior surface 68 with a small, asymmetric
concavity (or "cutout"). The concavity generally has a tapered
posterior-to-anterior profile. As illustrated by FIG. 33, the slope
and especially the asymmetric concavity of anterior/superior
surface 68 are configured to reduce contact with patellar component
18 as the knee moves into deep flexion. This reduced contact, in
turn, reduces wear and tear on post 32 and patellar component
18.
[0069] Referring to FIGS. 3A, 3B and 3K, meniscal component 14 may
also include an asymmetric anterior cutout 36 at the juncture of
superior side 50 and anterior side 54. Cutout 36 is configured to
minimize tenting of the patellar tendon over the meniscal component
14 as the knee flexes. Relief 36 also reduces the risk of patellar
component 18 contacting the meniscal component 14 in situations in
which the joint line has moved, either purposefully or as an
unintended effect of the surgical procedure, proximally and
anteriorly. As best seen in FIG. 3K, anterior/superior cutout 36 is
positioned asymmetrically, closer to lateral side 56, to compensate
for internal rotation of the tibia relative to the femur during
flexion.
[0070] Referring to FIGS. 3C (medial side view), 3E (lateral side
view), 3L (posterior view), 3M (medial cross-section), and 3N
(lateral cross-section), meniscal component 14 may include yet
another feature to enhance the kinematics of a knee in which knee
prosthesis system 10 is implanted. FIG. 3L shows that the superior
edge of posterior medial articulating surface 64a is higher than
the superior edge of posterior lateral articulating surface 64b. In
other words, posterior side 60 has a height H1 at the medial side
that is greater than its height H2 at the lateral side. This is due
to the fact that, in this embodiment, posterior medial articulating
surface 64a has an upward slope or slam in an anterior-to-posterior
direction, while posterior lateral articulation surface 64b has an
approximately horizontal (or "flat") profile in an
anterior-to-posterior direction. The difference between the two
posterior articulating surfaces is best shown in FIGS. 3M (medial
sloping surface 64a) and 3N (lateral horizontal surface 64b). These
surfaces 64a, 64b are also shown in FIGS. 3C and 3E. In the
embodiment shown, for example, the upward slope angle of medial
articulating surface 64a is approximately 3 degrees, and the
profile angle of the posterior articulating surface 64b is
approximately 0 degrees. In alternative embodiments, slight changes
to these angles may be made. For example, in one alternative
embodiment, medial articulating surface 64a may have a slightly
larger slope such as between about 4 degrees and about 5 degrees,
and posterior articulating surface 64b may have a slight slope such
as between about 1 degree and about 2 degrees. Thus, although the
3-degree/0-degree combination has been shown in tests to provide
natural knee kinematics, other combinations might be possible. This
configuration of medial articulating surface 64a and posterior
articulating surface 64b is another feature that helps replicate
natural knee kinematics in knee prosthesis 10 by helping keep
medial condyle 25a of femoral component 12 in place while allowing
lateral condyle 25b to translate posteriorly relative to meniscal
component 14. Again, this facilitates tibial rotation and posterior
translation during flexion.
[0071] Turning now to FIGS. 4A-4D, tibial component 16 according to
one embodiment is shown in greater detail. In this embodiment,
tibial component 16 generally includes a joint facing surface 40
for mating with meniscal component 14, a bone attachment surface
38, one or more attachment features 41 for attaching to meniscal
component 14, and anterior 55, posterior 61, medial 57 and lateral
59 sides. Tibial component may also include a post 43 for extending
into the tibia to enhance attachment to the bone. According to
various embodiments, tibial component 16 may have any of a number
of suitable sizes and shapes to attach to tibial bone and to
meniscal component 14, and thus the embodiment shown is only one
example. Tibial component may be made of any suitable material,
typically but not necessarily metal or polymer.
[0072] Referring now to FIGS. 5A and 5B, patellar component 18 is
shown in greater detail. Patellar component 18 may have any
suitable shape (domed, symmetric, asymmetric, etc.) and may include
an inferior relief 42 (or "cutout"). In contrast, traditional
patellar components have a circular anterior-view profile (FIG.
7C). Relief 42 reduces the risk of patellar component 18 contacting
the meniscal component 14 during mid-to-deep flexion in situations
(known as patella baja) in which the joint line has moved, either
purposefully or as an unintended effect of the surgical procedure,
proximally and anteriorly.
[0073] FIGS. 6-9 illustrate femoral component 12 and meniscal
component 14 in various stages of motion of a knee through a range
of motion from extension to flexion, to show how these two
components 12, 14 interact with one another to facilitate natural
knee kinematics. In each set of figures, the first figure (the "A"
figure) shows components 12, 14 in 4 degrees of hyperextension, the
second figure (the "B" figure) shows components 12, 14 in 0 degrees
of flexion, the third figure (the "C" figure) shows components 12,
14 in 45 degrees of flexion, the fourth figure (the "D" Figure)
shows components 12, 14 in 90 degrees offlexion, and the fifth
figure (the "E" figure) shows components 12, 14 in 135 degrees
offlexion. FIGS. 6A-6E are perspective views, FIGS. 7A-7E are
medial side views, FIGS. 8A-8E are posterior views, and FIGS. 9A-9E
are front views.
[0074] With the knee in 4 degrees of extension (i.e., maximal or
hyper extension) (FIGS. 6A, 7A, 8A, 9A), protrusions 34a, 34b on
meniscal component 14 mate with grooves 26a, 26b on femoral
component 12 to provide stability to the joint by limiting rotation
and anterior translation of femoral component 12 relative to
meniscal component 14. Preventing such translation makes the
patient's knee feel more stable and thus more natural.
Additionally, the anterior side of protrusions 34a and 34b
restricts posterior translation of the femoral component 12
relative to meniscal component 14, which prevents blunt impact and
excessive forces and wear on the anterior cam surface 28a.
Protrusions 34a, 34b may alternatively be referred to as a "wave."
In alternative embodiments, protrusions 34a, 34b may be replaced
with one protrusion that extends all the way across meniscal
component 14 and/or grooves 26a, 26b may be replaced with one
groove that extends all the way across femoral component 12.
[0075] Referring to FIGS. 6B, 7B, 8B and 9B, when the knee is in 0
degrees of flexion, protrusions 34a, 34b and grooves 26a, 26b still
provide stability to the knee. At this point anterior cam surface
28a of intercondylar opening 28 contacts anterior surface 66a of
post 32. This contact provides additional anterior-posterior
stability and positions components 12, 14 relative to one
another.
[0076] FIGS. 6C, 7C, 8C and 9C show components 12, 14 as if
attached to a knee in 45 degrees of flexion. At this stage, which
might be referred to as "mid-flexion," the tibia (and meniscal
component 14) rotates internally relative to the femur (and femoral
component 12). In other words, in the left knee (as in the
figures), the tibia rotates clockwise in a top view relative to the
femur as the knee flexes. In the right knee, the tibia rotates
counterclockwise in top view in flexion. Also at this stage,
posterior cam surface 28b of intercondylar opening 28 contacts
posterior surface 66b of post 32. This contact begins to turn
rotary motion of the two components 12, 14 into posterior
translation of the lateral condyle 25b of femoral component 12
relative to meniscal component 14.
[0077] With the knee in 90 degrees of flexion, as in FIGS. 6D, 7D,
8D and 9D, posterior cam surface 28b slides down posterior surface
66b of post 32 and creates posterior translation and internal
rotation of meniscal component 12 relative to femoral component 14.
This rotation is illustrated well by FIG. 7D. Contact of posterior
cam surface 28b with posterior surface 66b drives both condyles
25a, 25b in the posterior direction, but lateral condyle 25b
translate posteriorly farther than medial condyle 25a.
[0078] In deep flexion (135 degrees), as in FIGS. 6E, 7E, 8E and
9E, the rotation of femoral component 12 relative to meniscal
component 14 is even more pronounced. This is shown best in FIG.
7E. The reverse of these motions of components 12, 14 occurs when
the knee is moved from flexion to extension.
* * * * *