Posterior Stabilized Knee With Varus-Valgus Constraint

Abstract

A knee prosthesis in one embodiment includes a femoral component having a notch defined between spaced apart medial and a lateral condyle surfaces, the notch defining an elongated cam housing having a posterior cam at one end of the cam housing, and a tibial component including (i) a platform, (ii) a bearing supported on and rotatable in relation to the platform, the bearing defining medial and lateral bearing surfaces, and (iii) a spine projecting superiorly from the bearing within the cam housing, wherein the spine includes an anterior face and an opposite posterior face facing the posterior cam when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces, wherein the posterior face of the spine is concave along substantially the entire height of the spine, and wherein the spine terminates in a convex rounded posterior peak.

What is claimed is: 
     
         1 . A knee prosthesis comprising:
 a femoral component configured to be attached to a distal end of a femur and having a notch defined between spaced apart medial and a lateral condyle surfaces, the notch defining an elongated cam housing having a posterior cam at one end of the cam housing; and   a tibial component including (i) a platform configured for attachment to a proximal end of a tibia, (ii) a bearing supported on and rotatable in relation to the platform, the bearing defining medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and (iii) a spine projecting superiorly from the bearing within the cam housing when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces,   wherein the spine includes an anterior face and an opposite posterior face facing the posterior cam when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces,   wherein the posterior face of the spine is concave along substantially the entire height of the spine, and   wherein the spine terminates in a convex rounded posterior peak.   
     
     
         2 . The knee prosthesis of  claim 1 , wherein:
 the cam housing is configured to define an anterior-posterior distance between the anterior cam and the posterior face of the spine when the femoral component and the tibial component are in a normally extended position relative to each other, whereby the posterior face of the spine is in articulating contact with the posterior cam only at a first predetermined flexion rotation angle between the femoral component and the tibial component.   
     
     
         3 . The knee prosthesis of  claim 2 , wherein the first predetermined flexion angle is about 50°. 
     
     
         4 . The knee prosthesis of  claim 3 , wherein a complementary curved surface of the posterior cam is arranged on the posterior cam so that the complementary curved surface is substantially nested within the concave posterior face of the spine only after the femoral component and the tibial component rotate relative to each other to a second predetermined flexion angle greater than the first predetermined flexion angle. 
     
     
         5 . The knee prosthesis of  claim 4 , wherein the complementary curved surface of the posterior cam is substantially completely nested within the concave posterior face of the spine at about 120° of flexion. 
     
     
         6 . The knee prosthesis of  claim 5 , wherein the complementary curved surface is curved at a first radius, and the concave surface of the posterior face of the spine is curved at substantially the first radius. 
     
     
         7 . The knee prosthesis of  claim 6 , wherein:
 the cam housing defines a width sufficient to provide a clearance ranging between about 0.12 mm to about 0.50 mm on each side of the spine when the spine projects into the cam housing.   
     
     
         8 . The knee prosthesis of  claim 2 , wherein:
 the cam housing defines an anterior cam at an opposite end thereof;   the anterior face of the spine facing the anterior cam is substantially flat; and   the anterior cam defines a substantially flat surface complementary to the anterior face of the spine.   
     
     
         9 . The knee prosthesis of  claim 2 , further comprising:
 a bore extending through the spine, the spine formed of a first material; and   a pin configured to be disposed within the bore, the pin being formed of a second material which is different from the first material.   
     
     
         10 . The knee prosthesis of  claim 1 , wherein the spine has a height of about 16.0-24.0 mm and the cam housing includes a roof and is sized relative to the condyle surfaces so that the spine cannot contact the roof when the condyle surfaces are supported on the bearing surfaces. 
     
     
         11 . The knee prosthesis of  claim 1 , wherein the spine and the cam housing interact with each other to allow X degrees of pivoting between the femoral component and the bearing of said tibial component, and
   0.5 degrees≦ X ≦2.5 degrees.
   
     
     
         12 . The knee prosthesis of  claim 11 , wherein the cam housing defines an anterior-posterior distance between the posterior cam of the cam housing and an opposite end of the cam housing that is substantially greater than the maximum anterior-posterior dimension of the spine. 
     
     
         13 . The knee prosthesis of  claim 12 , wherein the anterior-posterior distance defined by the cam housing is about  1 . 5  times greater than the maximum anterior-posterior dimension of the spine. 
     
     
         14 . The knee prosthesis of  claim 13 , wherein the cam housing defines a width sufficient to provide a clearance ranging between about 0.12 mm to about 0.50 mm on each side of the spine when the spine projects into the cam housing. 
     
     
         15 . The knee prosthesis of  claim 1 , wherein:
 the cam housing defines an anterior cam at an opposite end thereof;   the anterior face of the spine facing the anterior cam is substantially flat; and   the anterior cam defines a substantially flat surface complementary to the anterior face of the spine.   
     
     
         16 . The knee prosthesis of  claim 1 , further comprising:
 a bore extending through the spine, the spine formed of a first material; and   a pin configured to be disposed within the bore, the pin being formed of a second material which is different from the first material.