U.S. patent application number 10/964151 was filed with the patent office on 2005-06-30 for high flexion articular insert.
Invention is credited to Carson, Christopher P..
Application Number | 20050143832 10/964151 |
Document ID | / |
Family ID | 34465350 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050143832 |
Kind Code |
A1 |
Carson, Christopher P. |
June 30, 2005 |
High flexion articular insert
Abstract
A knee prosthesis is provided that allows for increased flexion.
The knee prosthesis includes (a) a femoral component adapted to fit
on a distal end of the femur which includes a lateral condylar
structure and a medial condylar structure and (b) an intermediate
structure configured to cooperate with a femoral component of a
knee prosthesis. The intermediate structure includes at least one
surface for contacting the femoral component and a transition of a
sagittal curvature of the at least one contact surface from a
concave surface into a convex surface at the contact interface of
the femoral component and the intermediate structure when the knee
is flexed at approximately 120.degree. to 140.degree.. The knee
prosthesis minimizes impingement on the femoral posterior cortex in
deep flexion, increases the dislocation safety factor and allows
for easier reengagement of the articular surface should the femoral
component externally rotate off of the tibial plateau.
Inventors: |
Carson, Christopher P.;
(Collierville, TN) |
Correspondence
Address: |
CHIEF PATENT COUNSEL
SMITH & NEPHEW, INC.
1450 BROOKS ROAD
MEMPHIS
TN
38116
US
|
Family ID: |
34465350 |
Appl. No.: |
10/964151 |
Filed: |
October 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60512457 |
Oct 17, 2003 |
|
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Current U.S.
Class: |
623/20.28 ;
623/20.31 |
Current CPC
Class: |
A61F 2/30942 20130101;
A61F 2/3886 20130101; A61F 2310/00029 20130101; A61F 2002/30133
20130101; A61F 2002/30604 20130101; A61F 2002/30387 20130101; A61F
2220/0025 20130101; A61F 2002/30822 20130101; A61F 2002/30884
20130101; A61F 2002/30878 20130101; A61F 2002/30616 20130101; A61F
2002/30957 20130101; A61F 2002/4631 20130101; A61F 2230/0015
20130101 |
Class at
Publication: |
623/020.28 ;
623/020.31 |
International
Class: |
A61F 002/38 |
Claims
What is claimed is:
1. A knee prosthesis comprising: a femoral component adapted to fit
on a distal end of a femur, the femoral component including a
lateral condylar structure and a medial condylar structure; and an
intermediate structure configured to cooperate with a femoral
component of a knee prosthesis, the intermediate structure
comprising a proximal surface adapted to cooperate with an outer
surface of the femoral component to allow flexion of the knee
greater than 130.degree..
2. The knee prosthesis of claim 1, wherein the intermediate
structure is a component mounted on a tibia.
3. The knee prosthesis of claim 1, wherein the intermediate
structure is part of a tibial implant.
4. The knee prosthesis of claim 1, wherein the intermediate
structure is part of an insert adapted to fit between the femoral
component and a tibial implant.
5. The knee prosthesis of claim 1, wherein the intermediate
structure comprises an articular blend at a contact interface of
the femoral component and the intermediate structure when the knee
is flexed approximately 120.degree. to 140.degree..
6. The knee prosthesis of claim 5, further comprising at least one
surface for contacting the femoral component on the proximal
surface of the intermediate structure, wherein the articular blend
comprises a transition of a sagittal curvature of the at least one
contact surface from a concave surface into a convex surface, the
transition occurring at a contact point between the femoral
component and the intermediate structure when the knee prosthesis
is flexed at approximately 120.degree. to 140.degree..
7. The knee prosthesis of claim 6, wherein the at least one contact
surface comprises a concave portion on a lateral side of the
intermediate structure and a concave portion on a medial side of
the intermediate structure, the concave portion being adapted to
cooperate with the lateral condylar structure and the medial
condylar structure of the femoral component.
8. The knee prosthesis of claim 6, wherein the intermediate
structure includes a contact surface on the lateral side of the
intermediate structure and a contact surface on the medial side of
the intermediate structure and wherein each contact surface
includes an articular blend.
9. The knee prosthesis of claim 1, further comprising a contact
interface on the intermediate structure for contacting the femoral
component, wherein the contact interface moves in an anterior
direction on the intermediate structure and in a distal direction
on the femoral component when the knee is flexed approximately
140.degree. and greater.
10. The knee prosthesis of claim 1, further comprising a post
adapted to provide support to a posterior side of the femoral
component, the post being adapted to minimize impingement on a
patellar component when the knee is flexed approximately
130.degree. or greater.
11. The knee prosthesis of claim 10, wherein the post comprises a
tapered anterior surface.
12. The knee prosthesis of claim 1, wherein the intermediate
structure further comprises a curved anterior surface adapted to
minimize impingement of an intercondylar notch of the femoral
component when the knee prosthesis is hyperextended.
13. The knee prosthesis of claim 1, wherein the intermediate
structure further comprises a curved posterior surface adapted to
minimize impingement of a posterior cortex of a femur when the knee
is flexed approximately 130.degree. or greater.
14. A knee prosthesis comprising: a femoral component adapted to
fit on a distal end of a femur, the femoral component including a
lateral condylar structure and a medial condylar structure; and an
intermediate structure configured to cooperate with a femoral
component of a knee prosthesis, the intermediate structure
comprising a proximal surface comprising an articular blend at a
contact point between the femoral component and the intermediate
structure when the knee prosthesis is flexed at approximately
120.degree. to 140.degree..
15. The knee prosthesis of claim 14, wherein the intermediate
structure is a component mounted on a tibia.
16. The knee prosthesis of claim 14, wherein the intermediate
structure is a part of a tibial implant.
17. The knee prosthesis of claim 14, wherein the intermediate
structure is a part of an insert adapted to fit between the femoral
component and a tibial implant.
18. The knee prosthesis of claim 14, further comprising at least
one surface for contacting the femoral component on the proximal
surface of the intermediate structure, wherein the articular blend
comprises a transition of a sagittal curvature of the at least one
contact surface from a concave surface into a convex surface, the
transition occurring at a contact point between the femoral
component and the intermediate structure when the knee prosthesis
is flexed at approximately 120.degree. to 140.degree..
19. The knee prosthesis of claim 18, wherein the at least one
contact surface comprises a concave portion on a lateral side of
the intermediate structure and a concave portion on a medial side
of the intermediate structure, the concave portion being adapted to
cooperate with the lateral condylar structure and the medial
condylar structure of the femoral component.
20. The knee prosthesis of claim 18, wherein the intermediate
structure includes a contact surface on the lateral side of the
intermediate structure and a contact surface on the medial side of
the intermediate structure and wherein each contact surface
includes an articular blend.
21. The knee prosthesis of claim 14, further comprising a contact
interface on the intermediate structure for contacting the femoral
component, wherein the contact interface moves in an anterior
direction on the intermediate structure and in a distal direction
on the femoral component when the knee is flexed approximately
140.degree. and greater.
22. The knee prosthesis of claim 14, further comprising a post
adapted to provide support to a posterior side of the femoral
component, the post being adapted to minimize impingement on a
patellar component when the knee is flexed approximately
130.degree. or greater.
23. The knee prosthesis of claim 22, wherein the post comprises a
tapered anterior surface.
24. The knee prosthesis of claim 14, wherein the intermediate
structure further comprises a curved anterior surface adapted to
minimize impingement of an intercondylar notch of the femoral
component when the knee prosthesis is hyperextended.
25. The knee prosthesis of claim 14, wherein the intermediate
structure further comprises a curved posterior surface adapted to
minimize impingement of a posterior cortex of femur when the knee
is flexed approximately 130.degree. or greater.
16. A knee prosthesis comprising: (a) a femoral component adapted
to fit on a distal end of a femur, the femoral component including
a lateral condylar structure and a medial condylar structure; and
(b) an intermediate structure configured to cooperate with a
femoral component of a knee prosthesis, the intermediate structure
comprising: at least one surface for contacting the femoral
component on a proximal surface of the intermediate structure
between the intermediate structure and the femoral component; and a
transition of a sagittal curvature of the at least one contact
surface from a concave surface into a convex surface, the
transition occurring at a contact point between the femoral
component and the intermediate structure when the knee prosthesis
is flexed at approximately 120.degree. to 140.degree..
27. The knee prosthesis of claim 26, wherein the intermediate
structure is a component mounted on a tibia.
28. The knee prosthesis of claim 26, wherein the intermediate
structure is part of a tibial implant.
29. The knee prosthesis of claim 26, wherein the intermediate
structure is part of an insert adapted to fit between the femoral
component and a tibial component.
30. The knee prosthesis of claim 26, wherein the at least one
contact surface comprises a concave portion on a lateral side of
the intermediate structure and a concave portion on a medial side
of the intermediate structure, the concave portions being adapted
to cooperate with the lateral condylar structure and the medial
condylar structure of the femoral component.
31. The knee prosthesis of claim 26, wherein the intermediate
structure includes a contact surface on the lateral side of the
intermediate structure and a contact surface on the medial side of
the intermediate structure and wherein each contact surface
includes an articular blend.
32. The knee prosthesis of claim 26, further comprising a contact
interface on the intermediate structure for contacting the femoral
component, wherein the contact interface moves in an anterior
direction on the intermediate structure and in a distal direction
on the femoral component when the knee is flexed approximately
140.degree. and greater.
33. The knee prosthesis of claim 26, further comprising a post
adapted to provide support to a posterior side of the femoral
component, the post being adapted to minimize impingement on a
patellar component when the knee is flexed approximately
130.degree. and greater.
34. The knee prosthesis of claim 33, wherein the post comprises a
tapered anterior surface.
35. The knee prosthesis of claim 26, wherein the intermediate
structure further comprises a curved anterior surface adapted to
minimize impingement of an intercondylar notch of the femoral
component when the knee is hyperextended.
36. The knee prosthesis of claim 26, wherein the intermediate
structure further comprises a curved posterior surface adapted to
minimize impingement of a posterior cortex of a femur when the knee
is flexed approximately 130.degree. or greater.
37. A knee prosthesis comprising: (a) a femoral component adapted
to fit on a distal end of a femur, the femoral component including
a lateral condylar structure and a medial condylar structure; and
(b) an intermediate structure configured to cooperate with a
femoral component of a knee prosthesis, the intermediate structure
comprising: at least one surface for contacting the femoral
component; a transition of a sagittal curvature of the at least one
contact surface from a concave surface into a convex surface, the
transition occurring at a contact point between the femoral
component and the intermediate structure when the knee prosthesis
is flexed at approximately 120.degree. to 140.degree.; and a post
adapted to provide posterior support to the femoral component, the
post being adapted to minimize impingement on a patellar component
when the knee is flexed approximately 130.degree. or greater.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application Ser.
No. 60/512,457, filed on Oct. 17, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to knee prostheses and, more
specifically, to knee prostheses which include the use of posterior
stabilized inserts and have an extended range of flexion.
[0004] 2. General Background of the Invention
[0005] Arthritis of the knee is a disease in which the surfaces of
the knee gradually "wear out." Osteoarthritis, characterized by
chronic degeneration of the cartilage of the joints, is the most
common form of arthritis. This may be due to either old age,
congenital deformity, or damage due to trauma. Osteoarthritis,
characterized by chronic degeneration of the cartilage of the
joints, is the most common form of arthritis. Systemic arthritis,
such as rheumatoid arthritis, or gout affects the synovium (the
membrane tissue in the joint that normally lubricates the joint),
becomes pathologic and the surface of the joint is destroyed. In
either case, when the surface of the joint is worn away, the
activities of daily living can become very difficult. Standardized
treatment such as weight loss, anti-inflammatory medication,
braces, orthotics, steroid injections, physical therapy may be
effective.
[0006] In many cases, however, despite the above non-surgical
treatments, functional limitations persist. In such cases, disease
and trauma affecting the articular surfaces of the knee joint are
commonly treated by surgically replacing the ends of the femur and
tibia with prosthetic femoral and tibial implants, referred to as
total knee replacement (TKR).
[0007] In TKR surgery, a surgeon typically affixes two prosthetic
components to the patient's bone structure; a first to the
patient's femur and a second to the patient's tibia. These
components are typically known as the femoral component and the
tibial component respectively.
[0008] The femoral component is placed on a patient's distal femur
after appropriate resection of the femur. The femoral component is
usually metallic, having a highly polished outer condylar
articulating surface, which is commonly J-shaped.
[0009] A common type of tibial component uses a tray or plateau
that generally conforms to the patient's resected proximal tibia.
The tibial component also usually includes a stem that extends at
an angle to the plateau in order to extend into a surgically formed
opening in the patient's intramedullary canal. The tibial component
and tibial stem are both usually metallic.
[0010] A plastic or polymeric (often ultra high molecular weight
polyethylene) insert or bearing fits between the tray of the tibial
component and the femoral component. This tibial insert provides a
surface against which the femoral component condylar portion
articulates, i.e., moves in gross motion corresponding generally to
the motion of the femur relative to the tibia.
[0011] In some knee prostheses, the insert also engages in motion
relative to the tibial tray. Such motion can be translational
and/or rotational sliding motion relative to the tibial plateau. In
other types of knee prostheses with tibial inserts, the tibial
inserts can engage in other types of motion relative to the tibial
plateau and/or femoral component.
[0012] Modern TKR's are tricompartmental designs; they replace
three separate articulating surfaces within the knee joint: the
patello-femoral compartment and the lateral and medial inferior
tibio-femoral compartments. Most TKR's are designed to articulate
from a position of slight hyperextension to approximately 115 to
130.degree. flexion. A tricompartmental design can meet the needs
of most TKR patients even though the healthy human knee is capable
of a range of motion (ROM) approaching 170.degree.. However, there
are some TKR patients who have a particular need to obtain high
flexion in the knee joint. For many, a TKR that permits patients to
achieve a ROM in excess of 130.degree. is desirable to allow deep
kneeling, squatting and sitting on the floor with the legs tucked
underneath.
[0013] Another problem encountered by TKR patients is unwanted
movement of the femoral component on the tibial component. This
occurs when the ligaments of the knee are "tight," or not tensioned
properly, during the TKR procedure. Ligaments located on the side
of the knee where the deformity is present become tight due to
contraction of the compartment. A tight posterior cruciate ligament
may cause the knee to move in an unnatural motion. A posterior
stabilized insert may assist in preventing the femoral component
from unnatural motion on the tibial component by providing
posterior support after the posterior cruciate ligament is removed.
However, current inserts providing posterior support are designed
to allow a ROM to only about 120.degree.. When a patient with a
standard posterior support insert demands deeper flexion, the
proximal edge of the femoral condyle edge loads into the posterior
edge of the insert. This can lead to excessive polyethylene wear.
The extreme posterior location of the contact point may also lead
to lateral condylar subluxation as the tibia internally rotates.
Deeper flexion also leads to increased femoral translation to the
posterior edge of the insert. In conforming knee designs, this can
limit range of motion because more implant material is located on
the posterior edge of the insert. As the femoral component engages
the thicker part of the insert, the lateral and medial collateral
ligaments reach their strain limit, thus preventing further
posterior translation and limiting flexion by impinging the
posterior edge of the insert against the posterior cortex of the
femur. Thus, there is a need for an insert that provides sufficient
posterior support and reduces posterior conformity. Also needed is
an insert that allows a ROM beyond 120.degree. and minimizes
polyethylene wear and accommodates condylar rotation.
BRIEF SUMMARY OF THE INVENTION
[0014] The invention provides various embodiments of improved knee
prostheses for replacing at least a portion of a knee joint between
the distal end of a femur and the proximal end of a tibia.
[0015] According to certain aspects and embodiments of the
invention, there is provided a knee prosthesis including a femoral
component adapted to fit on a distal end of a femur, the femoral
component including a lateral condylar structure and a medial
condylar structure and an intermediate structure configured to
cooperate with the femoral component. The intermediate structure
includes a proximal surface adapted to cooperate with an outer
surface of the femoral component to allow flexion of the knee
greater than 130.degree..
[0016] According to certain aspects and embodiments of the
invention, there is further provided a knee prosthesis including a
femoral component adapted to fit on a distal end of a femur, the
femoral component including a lateral condylar structure and a
medial condylar structure and an intermediate structure configured
to cooperate with the femoral component, wherein the intermediate
structure includes a proximal surface with an articular blend at
the contact interface of the femoral component and the intermediate
structure when the knee is flexed approximately 120.degree. to
140.degree..
[0017] According to certain aspects and embodiments of the
invention, there is further provided a knee prosthesis including a
femoral component adapted to fit on a distal end of a femur, the
femoral component including a lateral condylar structure and a
medial condylar structure and an intermediate structure configured
to cooperate with the femoral component. Here, the intermediate
structure includes at least one surface for contacting the femoral
component on a proximal surface of the intermediate structure
between the intermediate structure and the femoral component the
contact surface includes a curvature in the sagittal plane which
transitions, in a posterior direction, from a concave surface into
a convex surface at a contact point between the femoral component
and the intermediate structure when the knee prosthesis is flexed
at approximately 120.degree. to 140.degree..
[0018] According to certain aspects and embodiments of the
invention, there is provided a knee prosthesis having a femoral
component adapted to fit on a distal end of a femur, the femoral
component including a lateral condylar structure and a medial
condylar structure and an intermediate structure configured to
cooperate with the femoral component. The intermediate structure
includes at least one surface for contacting the femoral component,
a transition of a sagittal curvature of the contact surface from a
concave surface into a convex surface, the transition occurring at
a contact point between the femoral component and the intermediate
structure when the knee prosthesis is flexed at approximately
120.degree. to 140.degree., and a post adapted to provide posterior
support to the femoral component, the post being adapted to
minimize impingement on a patellar component when the knee is
flexed approximately 130.degree. or greater.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] FIGS. 1A-1C show an exploded front view of a knee prosthesis
according to an embodiment of the invention.
[0020] FIG. 2 is a back perspective view of a knee prosthesis
according to an embodiment of the invention.
[0021] FIG. 3 is a side elevation view of an articular insert
according to an embodiment of the invention.
[0022] FIG. 4 is a perspective view of an articular insert
according to an embodiment of the invention.
[0023] FIG. 5 is a front elevation view of an articular insert
according to an embodiment of the invention.
[0024] FIG. 6 is a bottom plan view of an articular insert
according to an embodiment of the invention.
[0025] FIG. 7 is a side cross-sectional view of a partially
assembled knee prosthesis according to an embodiment of the
invention showing full extension of the knee.
[0026] FIG. 8 is a side cross-sectional view of a partially
assembled knee prosthesis according to an embodiment of the
invention showing flexion of the knee to 90.degree..
[0027] FIG. 9 is a side cross-sectional view of a partially
assembled knee prosthesis according to an embodiment of the
invention showing flexion of the knee to 160.degree..
[0028] FIG. 10 is a side cross-sectional view of a partially
assembled knee prosthesis including a size 5 femoral component on a
size 5-6 insert according to an embodiment of the invention showing
the range of flexion from 120.degree. to 140.degree..
[0029] FIG. 11 is a side cross-sectional view of the knee
prosthesis of FIG. 10 showing flexion of the knee at
120.degree..
[0030] FIG. 12 is a side cross-sectional view of the knee
prosthesis of FIG. 10 showing flexion of the knee at
130.degree..
[0031] FIG. 13 is a side cross-sectional view of the knee
prosthesis of FIG. 10 showing flexion of the knee at
140.degree..
DETAILED DESCRIPTION OF THE INVENTION
[0032] Various embodiments of the invention provide improved knee
prostheses for replacing at least a portion of a knee joint between
the distal end of a femur and the proximal end of a tibia.
[0033] As used herein, the following directional definitions apply.
Anterior and posterior mean toward the front or toward the back of
the body, respectively. Proximal means nearer to a point of
reference, as opposed to distal which means farther from a point of
reference. For example, the distal femur is part of the knee joint,
while the proximal femur is part of the hip joint. Medial means
nearer to the middle or center of the body. Lateral means farther
from the middle or center of the body. Thus, when referring to the
knee, medial would mean the side of the knee that is closest to the
other knee and lateral would mean the side of the knee that is
farthest from the other knee.
[0034] Knee prostheses according to certain embodiments of the
invention advantageously remove material from the posterior edge of
the insert that may impinge on the femoral posterior cortex (or
corresponding portions of a femoral component) in deep flexion.
Additionally, the 160.degree. flexion contact point is moved
anteriorly on the insert and distally on the femoral component to
reduce edge loading. The anterior shift in flexion contact also
increases the dislocation safety factor in deep flexion. Finally,
should the lateral posterior condyle of the femoral component
externally rotate off of the tibial plateau, as may occur in the
normal knee in deep flexion, it will more easily engage the
articular surface as the knee returns to extension.
[0035] The invention also maintains conventional amounts of femoral
resection and utilizes existing instrumentation so that a surgeon
may decide intraoperatively whether to use a standard posterior
stabilized insert or the high flexion posterior stabilized insert
of the invention.
[0036] A preferred embodiment of a knee prosthesis according to the
invention is shown in FIGS. 1A-1C and identified by the numeral
100. The knee prosthesis 100 is designed to replace at least a
portion of a left knee joint between the distal end of a femur and
the proximal end of a tibia. A mirror image of knee prosthesis 100
(not shown) will replace at least a portion of a right knee between
the distal end of a femur and the proximal end of a tibia.
[0037] The knee prosthesis 100 includes a femoral component 200 for
mounting to a distal end of a femur, a tibial component 300 for
mounting to a proximal end of a tibia, and an intermediate
component, such as articular insert 400.
[0038] Although a knee prosthesis 100 including an asymmetrical
femoral component 200 is shown, symmetrical femoral components are
also included within the scope of the invention. The femoral
component 200 preferably includes a medial condylar portion 202, a
lateral condylar portion 204 and a patellar flange portion 206
joining the anterior portions 214, 216 ends of the medial and
lateral condylar portions 202, 204 together. The medial and lateral
condylar portions 202, 204 are substantially parallel to each other
and are spaced apart from one another to form an intercondylar
recess or notch 208. Each condylar portion 202, 204 has an outer
surface 210, 212 for engaging a portion of the tibial component 300
in an articulating fashion as will become apparent. The outer
surfaces 210, 212 of each condylar portion 202, 204 preferably have
a distal portion 218, 220 for engaging a portion of the tibial
component 300 when the knee joint is extended and partially flexed,
and a posterior portion 222, 224 (shown in FIG. 2) for engaging a
portion of the tibial component 300 when the knee joint 102 is
flexed substantially 90.degree..
[0039] The femoral component 200 may include typical attachment
aids for helping to secure the femoral component 200 to a distal
end of a femur. Such attachment aids may include one or more pegs,
fins, surface treatments, cement or other conventional or
nonconventional structure or technologies.
[0040] The tibial component 300 includes a tray or base member 302
for being secured to a proximal end of a tibia, and a stabilizing
post 316, which is insertable into the tibial medullary canal and
provides for the stabilization of the tibial component 300 on the
tibia.
[0041] The tray member 302 has a proximal or upper surface 304, a
distal or lower surface 306, a medial side 308, a lateral side 310,
an anterior or front side 312, and a posterior or rear side 314
(shown in FIG. 2). The proximal surface 304 may be substantially
flat and planar. The tray member 302 preferably includes attachment
aids for helping to secure the tray member 302 to a proximal end of
a tibia. Such attachment aids may include one or more pegs, fins,
screws, surface treatments, etc.
[0042] The femoral component 200 and tibial component 300 may be
constructed in various manners and out of various materials. For
example, the femoral component 200 and tibial component 300 may be
machined, cast, forged or otherwise constructed as a one-piece
integral unit out of a medical grade, physiologically acceptable
metal such as a cobalt chromium alloy or the like, in various sizes
to fit a range of typical patients, or may be custom-designed for a
specific patient based on data provided by a surgeon after physical
and radiography examination of the specific patient.
[0043] As shown in FIG. 4, the articular insert 400 has a proximal
or upper surface 402, a distal or lower surface 404, a medial side
406 (shown in FIG. 5), a lateral side 408, an anterior or front
side 410, and a posterior or rear side 412 (shown in FIG. 2).
Although the medial and lateral sides 406, 408 (shown in FIG. 5)
are separately identified, the insert 400 may be substantially
symmetrical so that the medial and lateral sides 406, 408 are
substantially the same or are identical.
[0044] The proximal surface 402 of the insert 400 has a medial
concave portion 414 for engaging the outer surface 210 of the
medial condylar portion 202 of the femoral component 200 in an
articulating relationship, and a lateral concave portion 416 for
engaging the outer surface 212 of the lateral condylar portion 204
of the femoral component 200 in an articulating relationship.
Lateral concavity 414 is defined by curves C1, C2 and C3. In the
front or coronal plane, curve C1 has a radius of curvature of
approximately 1.05 inches. In the sagittal plane, curves C2 and C3
have varying radii of curvature of approximately 2.88 to 3.05
inches. The radii of curvature can vary as desired. The radii may
also vary according to component size. In a preferred embodiment,
medial concavity 416 is similar to lateral concavity 414 and
includes corresponding curves C4, C5 and C6.
[0045] As shown in FIGS. 3-5, the insert includes a central post
420. The post 420 has a proximal surface 422, anterior surface 424,
posterior surface 426 and side surfaces 428, 430. In a preferred
embodiment of the invention, the proximal surface 422 of the
central post 420 preferably is parallel with distal surface 404.
The anterior surface 424 of central post 420 in this embodiment is
tapered at an angle of approximately 33.degree. with respect to the
distal surface 404 of the insert 400 to minimize impingement of the
patella or a patellar implant (not shown) in deep flexion. The base
425 is tapered 23.degree. in a posterior direction from anterior
surface 424 to minimize impingement of the intercondylar notch 208
of femoral component 200 in hyperextension.
[0046] The insert 400 may include a curved anterior surface 418, as
shown in FIG. 4. The curved anterior surface 418 has a curve C7
with central radius of curvature varying between approximately 1.5
to 2.5 inches, lateral to medial, as a general matter. Again, radii
of curvature can vary as desired. The sagittal center line of the
anterior curved surface 418 is oriented at approximately 30.degree.
to 45.degree. above the distal surface 404 of the insert 400. When
the insert 400 is attached to the tibial component 300, the curved
anterior surface 418 begins approximately 2 mm above the tray
member 302 of the tibial component 300 to allow room for the
patellar tendon (not shown).
[0047] The insert 400 preferably includes articular blends 432, 436
on the lateral and medial sides of the insert 400. Articular blends
432, 436 are similar and articular blend 432 is described in detail
below. The articular blend 432 begins at the contact interface of
the femoral component 200 and the insert 400 (the femorotibial
contact point 438) when the knee is flexed at approximately
120.degree. to 140.degree.. One result of using an articular blend
432 is that the posterior side 412 of the insert 400 is lowered and
flexion joint space is maintained. In the sagittal plane, the
articular blends 432, 436 (shown in FIG. 4) have a single sagittal
radius of approximately 1.0 inch. Thus, as shown in FIG. 3, the
articular blend 432 has a single sagittal radius of approximately
1.0 inch. However, the radius may vary and may feature any radius
or radii as circumstances dictate or suggest.
[0048] The articular blends 432, 436 increase the amount of flexion
allowed by the knee prosthesis 100 through the use of a transition
or blend of the sagittal concave curvatures of the lateral and
medial concavities, 414, 416 into a convex surface. The precise
location of the articular blends 432, 436 varies depending on the
size of the femoral component 200 and the size of the articular
insert 400. However, the articular blend will generally begin at a
point defined as the point of contact between the femoral component
and the insert (the femorotibial contact point 438) when the
femoral component is at a flexion angle of approximately
120.degree. to 140.degree.. For example, FIG. 10 illustrates the
range of flexion from 120.degree. to 140.degree. of a size 5
femoral component on a size 5-6 insert. At 120.degree. (also shown
in FIG. 11), the posterior portion 224 of outer surface 212 of
lateral condylar portion 204, has not yet engaged the articular
blend 432. However, at 130.degree. (also shown in FIG. 12), the
posterior portion 224 of outer surface 212 of lateral condylar
portion 204 directly engages the articular blend 432 at the
femorotibial contact point, as shown in FIG. 12. At 140.degree.
(also shown in FIG. 13), the posterior portion 224 of outer surface
212 of lateral condylar portion 204 is past the beginning of the
articular blend 432 at the femorotibial contact point 438 is on the
convex surface of articular blend 432. Thus, as a general matter,
as the femorotibial contact point 438 moves in a posterior
direction, the proximal surface 402 of the insert 400 transitions
from concave to convex.
[0049] As shown in FIG. 2, the insert may include a curved
posterior surface 433, which is multi-radius. The curved posterior
surface 433 has a curved surface C8 with a varying radius of
curvature, lateral to medial. The result of the curved posterior
surface 433 is the removal of material that may impinge on the
posterior cortex of the femur in deep flexion. The radius of
curvature may vary as desired to provide sufficient room for
maximal flexion.
[0050] As shown in FIG. 6, the distal surface 404 of the insert 400
may be substantially flat or planar for contacting the proximal
surface 304 of the tray member 302 of the tibial component 300. The
distal surface 404 preferably includes a dovetail locking mechanism
434 that consists of an anterior portion 440 and a posterior
portion 442, however, any conventional method for disposing the
insert relative to the tray member 302, whether constrained or
unconstrained, may be used.
[0051] In a preferred embodiment, a size 5-6 insert 400 has the
following dimensions. The overall width of the insert 400 is
approximately 2.913 inches from medial side 406 to lateral side
408. The depth of the insert 400 is approximately 1.944 inches from
anterior side 410 to posterior side 412. The thickness of the
insert 400 at the medial and lateral sides 406, 408 varies, ranging
from approximately 0.381 to 1.011 inches. The thickness of the
insert 400 at the posterior side 412 ranges from approximately
0.548 to 1.178 inches. The width of the anterior curved surface 418
ranges from approximately 1.869 to 2.421 inches. At the outermost
edges of the anterior curved surface 418, the thickness of the
insert 400 ranges from approximately 0.408 to 1.001 inches. The
central post 420 is approximately 0.560 inches wide. Its height,
from the distal surface 404 of the insert 400, ranges from
approximately 1.259 to 1.889 inches. These dimensions have a
tolerance ranging from approximately +/-0.005 to 0.020 inches.
[0052] The insert 400 may be constructed in various manners and
from various materials. For example, the insert 400 may be
machined, molded or otherwise constructed as a one-piece, integral
unit out of medical grade, physiologically acceptable plastic such
as ultra high molecular weight polyethylene or the like, in various
sizes to fit a range of typical patients, or may be custom-designed
for a specific patient based on data provided by a surgeon after
physical and radiographic examination of the specific patient. The
material can be treated, for example, by radiation, chemistry, or
other technology to alter its wear properties and/or strength or
hardness. An articular insert 400 constructed of ultra high
molecular weight polyethylene will freely slide on a polished upper
surface of the tray member 302 of the tibial component 300, thereby
reducing material wear.
[0053] As shown in FIG. 2, when the knee prosthesis 100 is
assembled, the central post 420 of the insert 400 fits within the
intercondylar recess 208. The posterior stabilized femoral
component 226 includes a horizontal connection member, or cam, 228
between the posterior portions 222, 224 of the condylar portions
202, 204. The distal portions 218, 220 of the condylar portions
222, 224 rest on the medial and lateral concavities 414, 416 of the
insert 400. Because the femoral component 226 and the insert 400
are not fastened to each other, the femoral component 226 is able
to easily move on the insert 400.
[0054] For example, the particular knee prosthesis 100 of FIG. 7 is
shown as it would appear when the knee is fully extended. Other
various maximal angles of extension are possible with various
prostheses. The distal portions 218, 220 of the medial and lateral
condylar portions 202, 204 are in contact with the medial and
lateral concavities 414, 416. When the knee is flexed to
approximately 90.degree., as shown in FIG. 8, the posterior
portions 222, 224 of the medial and lateral condylar portions 202,
204 are in contact with the medial and lateral concavities 414,
416. The cam 228 is also in contact with the posterior surface 426
of the central post 420 of femoral component 400.
[0055] At approximately 120.degree. to 140.degree. flexion, the
femoral component 200 begins to contact the articular blend 432 on
the posterior side 412 of the insert 400. However, as shown in FIG.
9, the knee can be flexed to approximately 160.degree. before the
femoral component 200 fully contacts the intersection edge of the
articular blend 432 and the curved posterior surface 433 and
additional flexion is difficult or impossible. The increased
flexion is achieved primarily by the articular blend 432 which
results in a transition on the proximal surface 402 of the insert
400 of the sagittal concave curvature of the lateral and medial
concavities 414, 416 into a convex surface that maintains the
coronal curvature of the medial and lateral condylar portions 202,
204. The articular blend 432 moves the 160.degree. femorotibial
contact point 438 anteriorly on the insert 400 and distally on the
femoral component 200. Thus, edge loading is reduced and material
that may impinge on the femoral posterior cortex (not shown) in
deep flexion has been removed. The anterior shift in the
femorotibial contact point 438 increases the dislocation safety
factor in deep flexion, making dislocation less likely. However, if
the posterior portion 224 of the lateral condylar portion 204
should rotate off the insert 400, as may occur in the normal knee
in deep flexion, it will more easily engage the lateral concavity
416 as the knee returns to extension.
[0056] The foregoing description is provided for describing various
embodiments and structures relating to the invention. Various
modifications, additions and deletions may be made to these
embodiments and/or structures without departing from the scope and
spirit of the invention.
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