Posterior stabilized knee with varus-valgus constraint

Abstract

A femoral component of a knee prosthesis has spaced condyle surfaces defining a notch therebetween. The notch defines an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the housing. The tibial component of the knee prosthesis includes a platform and a bearing supported on the platform, the bearing defining bearing surfaces configured to articulate with the condyle surfaces. The tibial component includes a spine projecting superiorly from the bearing that defines an anterior face and a posterior face. The posterior face and the posterior cam define complementary curved surfaces configured for cooperative engagement when the femoral component and the tibial component are at a predetermined flexion angle. The cam housing is configured to form a gap between the posterior cam and the spine when the knee is normally extended. In another feature, the spine includes a stiffening pin extending therethrough.

What is claimed is:  
     
         1 . A knee prosthesis comprising: 
 a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, said notch defining an elongated cam housing having a posterior cam at one end of said cam housing; and    a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on said platform, said bearing defining medial and lateral bearing surfaces configured to articulate with said medial and lateral condyle surfaces, and a spine projecting superiorly from said bearing within said cam housing when said condyle surfaces are in articulating contact with said bearing surfaces,    wherein said spine defines an anterior face and an opposite posterior face facing said posterior cam, said posterior face and said posterior cam defining complementary curved surfaces configured for cooperative engagement when said femoral component and said tibial component are rotated relative to each other to at least a predetermined flexion angle.    
     
     
         2 . The knee prosthesis according to  claim 1 , wherein said complementary curved surface of said posterior face of said spine is concave at a radius, and said complementary curved surface of said cam is curved at substantially said radius.  
     
     
         3 . The knee prosthesis according to  claim 1 , wherein: 
 said cam housing defines an anterior cam at an opposite end thereof; and    said anterior face of said spine facing said anterior cam is substantially flat.    
     
     
         4 . The knee prosthesis according to  claim 3 , wherein said anterior cam defines a substantially flat surface complementary to said anterior face of said spine.  
     
     
         5 . The knee prosthesis according to  claim 1 , wherein said cam housing defines a width sufficient to provide a clearance ranging between about 0.0 mm to about 0.13 mm on either side of said spine when said spine projects into said cam housing, whereby said spine and said cam housing interact to restrict varus-valgus pivoting between said femoral component and said tibial component.  
     
     
         6 . The knee prosthesis according to  claim 1 , wherein said cam housing each define a width sized relative each other so that said spine and said cam housing interact to restrict varus-valgus pivoting between said femoral component and said tibial component to between 0.5° and 2.5°.  
     
     
         7 . The knee prosthesis according to  claim 1 , wherein said spine has a height of about 16.0-24. mm and said cam housing includes a roof and is sized relative to said condyle surfaces so that said spine cannot contact said roof when said condyle surfaces are supported on said bearing surfaces.  
     
     
         8 . The knee prosthesis according to  claim 7 , wherein said complementary curved surface of said posterior face of said spine is concave at a radius and has a length sized so that said curved surface extends along substantially the entire height of said spine.  
     
     
         9 . The knee prosthesis according to  claim 8 , wherein said spine terminates in a rounded posterior peak.  
     
     
         10 . The knee prosthesis according to  claim 8 , wherein said posterior cam has a length from an anterior end to a posterior end that is substantially equal to the length of said curved surface of said posterior face of said spine.  
     
     
         11 . The knee prosthesis according to  claim 1 , wherein said cam housing defines an anterior-posterior distance between said curved surface of said posterior cam at said one end and an opposite end of said cam housing that is substantially greater than an anterior-posterior dimension of said spine.  
     
     
         12 . The knee prosthesis according to  claim 11 , wherein the anterior-posterior distance defined by said cam housing is about 1.5 times greater than the anterior-posterior dimension of said spine.  
     
     
         13 . The knee prosthesis according to  claim 1 , wherein said bearing is mounted on said platform to permit relative movement therebetween.  
     
     
         14 . The knee prosthesis according to  claim 13 , wherein said tibial component includes: 
 a socket defined in said platform; and    a stem extending from said bearing configured for rotating engagement within said socket.    
     
     
         15 . A knee prosthesis comprising: 
 a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, said notch defining an elongated cam housing having a posterior cam at one end of said cam housing;    a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on said platform, said bearing defining medial and lateral bearing surfaces configured to articulate with said medial and lateral condyle surfaces, and a spine projecting superiorly within said cam housing when said condyle surfaces are in articulating contact with said bearing surfaces, wherein said spine defines a posterior face facing said posterior cam and configured for cooperative engagement when said posterior cam, said spine further defining a bore therethrough; and    a pin configured to be disposed within said bore, said pin formed of a material different from the material of said spine.    
     
     
         16 . The knee prosthesis according to  claim 15 , wherein said pin is configured to be press-fit into said bore.  
     
     
         17 . The knee prosthesis according to  claim 15 , wherein tibial component includes: 
 a socket defined in said platform; and    a stem extending from said bearing configured for rotating engagement within said socket.    
     
     
         18 . The knee prosthesis according to  claim 17 , wherein said bore extends into at least a portion of said stem and said pin is configured to extend into said portion of said stem.  
     
     
         19 . The knee prosthesis according to  claim 15 , wherein said pin is formed of a mechanically stiffer material than said spine.  
     
     
         20 . The knee prosthesis according to  claim 19 , wherein said spine is formed of a plastic and said pin is formed of a metal.  
     
     
         21 . A knee prosthesis comprising: 
 a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, said notch defining an elongated cam housing having an anterior cam and a posterior cam at opposite ends of said cam housing; and    a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on said platform, said bearing defining medial and lateral bearing surfaces configured for rotating contact with said medial and lateral condyle surfaces, and a spine projecting superiorly from said bearing within said cam housing when said condyle surfaces are in articulating contact with said bearing surfaces, and said spine defining an anterior face facing said anterior cam and a posterior face adapted for articulating contact with said posterior cam,    wherein said cam housing is configured to define an anterior-posterior distance between said anterior cam and said posterior face of said spine when said femoral component and said tibial component are in a normally extended position relative to each other, whereby said posterior face of said spine is in articulating contact with said posterior cam only at a first predetermined flexion rotation angle between said femoral component and said tibial component.    
     
     
         22 . The knee prosthesis according to  claim 21 , wherein said first predetermined flexion angle is about 50°.  
     
     
         23 . The knee prosthesis according to  claim 21 , wherein said posterior cam and said posterior face define complementary curved surfaces, whereby said complementary surfaces articulate relative to each other at flexion angles between said femoral component and said tibial component greater than said first predetermined flexion angle.  
     
     
         24 . The knee prosthesis according to  claim 23 , wherein said posterior cam includes a rounded anterior end that is arranged to contact said posterior face first at said first predetermined flexion angle.  
     
     
         25 . The knee prosthesis according to  claim 23 , wherein the complementary curved surface of said posterior cam is arranged on said posterior cam so that complementary curved surface of said posterior cam is substantially nested within the complementary curved surface of said posterior face of said spine only after said femoral component and said tibial component rotate relative to each other to a second predetermined flexion angle greater than said first predetermined flexion angle.  
     
     
         26 . A knee prosthesis, comprising: 
 a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, said notch defining an elongated cam housing having a posterior cam at one end thereof; and    a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on said platform, said bearing defining medial and lateral bearing surfaces configured for rotating contact with said medial and lateral condyle surfaces, and a spine projecting superiorly from said bearing within said cam housing when said condyle surfaces are in articulating contact with said bearing surfaces, and said spine defining a posterior face adapted for articulating contact with said posterior cam,    wherein the rotating contact between said bearing and said condyle surfaces is configured to carry all of the anterior-posterior shear load of the knee prosthesis from a full extension angle to a predetermined flexion angle between said femoral component and said tibial component, and said spine is arranged relative to the rotating contact between said bearing and said condyle surfaces so that said spine contacts said posterior cam at said predetermined flexion angle to share a portion of the anterior posterior shear load of the knee at flexion angles greater than said predetermined flexion angle.