Patent ID: 7803193

Claim:
A tibial component for positioning in the knee joint, the component comprising: a body formed of a resilient polyurethane having a non-linear stress-strain relationship, the lower portion of the body defining a lower surface having a central convex portion for abuttingly engaging the head of the tibia without penetrating the head of tibia, the upper portion of the body defining an upper contact surface having at least one concave depression with a first radius of curvature, an outside portion of the body defining a maximum outside height between the lower surface and the upper surface, the upper contact surface configured for engagement with a femoral portion having a convex outer surface having a second radius of curvature, the first and second radii of curvature being different in a first bearing configuration when not exposed to loading forces to define a first contact area between the depression and the convex surface, the first contact surface being resiliently deformable to a second bearing configuration in response to bearing forces directed downward on the depression to thereby define a second contact area between the depression and the convex outer surface, the second contact area being larger than the first contact area and the first radius of curvature substantially matching the second radius of curvature; and a spine formed on said body, said spine extending upwardly toward the femur beyond the upper contact surface, the body and the spine defining an inside height, the inside height being substantially greater than the maximum outside height such that the upwardly extending spine is configured for at least partial engagement in the fossa between the femoral condyles to restrict movement, wherein the resiliency of the body allows the contact surface area configuration to change during use according to physical loading factors.