Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-08-05
2001-05-29
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S020230, C623S033000
Reexamination Certificate
active
06238434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject invention relates to orthopedic prosthetic components, and particularly to a knee joint prosthesis.
2. Description of the Related Art
A natural knee joint includes the distal end of the femur, the proximal end of the tibia and a meniscus bearing therebetween. The femur and the tibia are held in proper relationship to one another and to the bearing by a plurality of ligaments, including the posterior cruciate ligament, the anterior cruciate ligament and collateral ligaments. Flexion of the knee joint causes the tibia to rotate relative to the femur about an axis extending generally in a medial-to-lateral direction. Flexion also generates rotation of the tibia about its own axis.
Damage or disease can affect the ability of the natural knee to function properly. The damage or disease can deteriorate the bones, the articular cartilage, the ligaments or some combination thereof. A damaged or diseased natural knee can be replaced by a prosthetic knee joint. A prior art knee joint prosthesis includes a femoral component securely mounted to the distal end of a resected femur, a tibial component securely mounted to the proximal end of a resected tibia and a bearing disposed between the femoral and tibial components. The inferior face of the femoral component includes a pair of condyles. The condyles have a convexly arcuate shape, and the superior surface of the bearing has a pair of arcuate concave regions for articular bearing engagement with the condyles of the femoral component. The superior face of the tibial component may be substantially planar and is in bearing engagement with the inferior face of the bearing.
Currently available prosthetic knee joints take many different forms depending upon the preferences of the orthopedic surgeon, the condition of the natural knee and the health, age and mobility of the patient. Some prior art knee joint prostheses fixedly mount the inferior surface of the bearing to the superior surface of the tibial component. Other knee joint prostheses permit rotary movement and/or sliding movement between the bearing and the tibial component. Movement of the bearing against the tibial component achieves many functional advantages described in the prior art. These functional advantages include an avoidance of dislocation in response to normal walking movement without reliance upon a fixed hinged connection. Very effective prior art knee joint prostheses that incorporate certain of the structural features referred to herein are disclosed in U.S. Pat. No. 4,470,158 and U.S. Pat. No. 4,309,778.
A prior art knee joint that permits rotational movement of the bearing on the tibial component is shown in
FIGS. 1-6
, and is identified generally by the numeral
100
. The prior art prosthesis
100
includes a femoral component
102
for mounting to the distal end
104
of the natural femur
106
. The femoral component
102
includes an inferior articular bearing face having medial and lateral condyles
108
and
110
as shown in FIG.
2
.
The prior art prosthesis
100
further includes a tibial component
112
that is mounted to the resected proximal end
114
of a tibia
116
. The tibial component
112
includes an inferior surface having a generally conical projection
118
configured to be engaged in a cavity prepared in the resected distal end
114
of the tibia
116
. The tibial component
112
further include a general planar superior bearing surface
120
. The bearing surface
120
is formed with a generally conical central recess.
The prior art knee prosthesis
100
further includes a bearing
122
disposed between the femoral component
102
and the tibial component
112
. The prior art bearing includes a superior articular bearing surface
124
configured for articular bearing engagement with the condyles
108
and
110
of the femoral component
102
. The bearing
122
further includes an inferior surface for engagement with the tibial component. More particularly, the inferior surface of the prior art bearing
122
includes a central projection (not shown) that is rotatably engaged in the recess that extends into the superior surface
120
of the tibial component
112
. The inferior surface of the bearing further includes a generally planar bearing surface
126
that is in rotational bearing engagement on the superior planar bearing surface
120
of the tibial component
112
.
The components of a knee joint undergo complex movement relative to one another during walking and other activities. In particular, natural movement of the knee joint causes rotation of the tibia about a generally medial to lateral axis. Simultaneously, the natural movement of the leg will generate some pivotal movement between the tibia and femur about an axis extending generally along the load bearing direction. This pivoting movement will cause some rotation of the prior art bearing
122
on the femoral and tibial components
102
and
112
. Rotation of the bearing
122
relative to the femoral component
102
causes the condyles
108
and
110
of the femoral component
102
to climb upwardly toward the lips at the anterior and posterior ends of the bearing
122
. This creates the potential for a spinout dislocation. The spinout can be controlled by proper attention to maintenance of collateral ligament tension during implantation. However, the cruciate ligaments are the principle anterior-posterior and medial-lateral stabilizers of the knee. These cruciate ligaments often are removed as part of the surgery to implant the prosthetic knee. Thus, the potential for dislocation exists with prior art knee joint prostheses that employ a rotating bearing.
The instability of the prior art rotating bearing prosthetic knee joint is illustrated most clearly in
FIGS. 1-6
. In particular, the prior art rotating bearing
122
can be forced to rotate to a dislocated position under the action of combined effects of an anterior-posterior shearing load, distraction of one of the condylar components
108
and
110
of the femoral prosthetic component
102
and a lax collateral ligament associated with the distracted component. Only ligament tension sufficient to prevent the femoral condyle on the distracted side from climbing over the lip of the bearing can prevent such dislocation. There is no other sufficient soft or hard tissue in the knee to prevent such dislocation. The dislocation mode is stable under compressive load. Both anterior-posterior and medial-lateral shift of the prior art femoral component
102
relative to the tibial component
112
, as illustrated in
FIGS. 5 and 6
, must accompany such dislocation. The shearing force and the effect of the vertical rotational axis of the bearing accentuate conditions that can lead to the illustrated spinout. Spinout does not occur in the prior art prosthetic joints where there is an allowance for anterior-posterior translation of the bearing. Thus, the illustrated spinout is a unique disadvantage of a fixed axis rotating platform tibial bearing knee prosthesis as illustrated in
FIGS. 1-6
.
One prior art technique for minimizing spinout dislocation involves the use of a bearing with increased engagement between the bearing and the femoral component. Such a bearing requires a greater degree of distraction to allow spinout. Although prosthetic knee joints of this type reduce spinout, they do not completely eliminate the occurrence of spinout.
The prior art also includes a rotational stop on the patellar component of the prosthetic knee joint marketed under the name New Jersey LCS. The rotational stop, however, has not prevented spinout of the rotating patella bearing.
In view of the above, it is an object of the subject invention to provide a successful anti-spinout stop joint that will not adversely affect the function of the prosthetic joint.
It is also an object of the subject invention to provide a prosthetic knee joint that can provide enough rotary motion for the needed functions, while still preventing spinout.
SUMMARY OF THE INVENTION
The subject invention is directed
Biomedical Engineering Trust I
Casella Anthony J.
Hespos Gerald E.
Porco Michael J.
Snow Bruce
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