Prosthesis device for the ankle articulation

Abstract

A prosthetic ankle joint device for replacement of articular bearing surfaces of the natural joint comprises: a first component ( 2 ) for attachment to a first tibial bone segment ( 2 a ) having a first articulating bearing surface ( 5 ); a second component ( 3 ) for attachment to a second tarsal bone segment ( 3 a ) having a second articulating bearing surface ( 6 ) opposite to the first articulating bearing surface ( 5 ). The first articulating bearing surface ( 5 ) and the second articulating bearing surface ( 6 ) are substantially different in shape to the corresponding shapes of the articular bearing surfaces of the natural joint. The first surface ( 5 ) being concave, or flat, or convex. Each articulating bearing surface ( 5, 6 ) presents a respective shape designed on the basis of the shape of the opposite articulating bearing surface ( 5, 6 ) according to the common normal to their point of mutual contact at every position over the range of passive plantar and dorsi-flexion. The common normal theorem being applicable because of a four-bar linkage mechanism identified at this joint in the sagittal plane, formed by the tibio-calcaneal calcaneo-fibular ligaments.

1 . A prosthetic ankle joint device for replacement of articular bearing surfaces of the natural joint comprising: 
 a first component for attachment to a first tibial bone segment said first component having a first articulating bearing surface;    a second component for attachment to a second tarsal bone segment, said second component having a second articulating bearing surface opposite to the first articulating bearing surface; said first articulating bearing surface and said second articulating bearing surface being each substantially different in shape to the natural corresponding shapes of said articular bearing surfaces of the natural joint, the first articulating bearing surface being concave, or planar, or convex;    each articulating bearing surface presents a respective shape designed on the basis of the shape of the opposite articulating bearing surface according to the common normal theorem to their point of mutual contact at every position over the range of passive plantar and dorsi-flexion.    
   
   
       2 . A prosthetic ankle joint device according to  claim 1 , wherein the common normal to the point of mutual contact of the articulating bearing surfaces at every position over the range of passive plantar and dorsi-flexion passes close to the intersection, in the sagittal plane, of the most nearly isometric fibres in the tibio-calcaneal ligament on the medial side of the joint and calcaneo-fibular ligament on the lateral side of the joint.  
   
   
       3 . A prosthetic ankle joint device according to  claim 1 , wherein the common normal to the point of mutual contact of the articulating bearing surfaces at every position over the range of passive plantar and dorsi-flexion passes through the intersection, in the sagittal plane, of the most nearly isometric fibres in the tibio-calcaneal ligament on the medial side of the joint and calcaneo-fibular ligament on the lateral side of the joint.  
   
   
       4 . A prosthetic ankle joint device according to  claim 1 , wherein said second bearing surface ( 5 ,  6 ) presents a radius of curvature, in the sagittal plane, up to 75% longer than that of the natural talar articulating bearing surface.  
   
   
       5 . A prosthetic ankle joint device according to  claim 1 , wherein said second articulating bearing surface ( 6 ) presents a radius of curvature equivalent to a value close to the value of the radius of the corresponding natural surface of the natural ankle joint.  
   
   
       6 . A prosthetic ankle joint device according to  claim 5 , wherein the radius of curvature of said second articulating bearing ( 6 ) surface is comprised between 22 mm and 34 mm.  
   
   
       7 . A prosthetic ankle joint device according to  claim 1 , wherein said first component comprises a first portion for attachment to the first tibial bone and a second portion fastened to said first portion, said second articulating bearing surface being defined on said second portion of said first component.  
   
   
       8 . A prosthetic ankle joint device according to  claim 7 , wherein said first portion of said first component is made of a metallic material.  
   
   
       9 . A prosthetic ankle joint device according to  claim 7 , wherein said second portion of said first component is made of a plastic material, preferably ultra-high molecular weight polyethylene.  
   
   
       10 . A prosthetic ankle joint device according to  claim 1 , wherein one of the articulating bearing surfaces is substantially planar, in the sagittal plane while the other articulating bearing surface is convex.  
   
   
       11 . A prosthetic ankle joint device according to  claim 1 , wherein one of the articulating bearing surfaces is concave, in the sagittal plane, while the other articulating bearing surface is convex.  
   
   
       12 . A prosthetic ankle joint device according to  claim 11 , wherein both articulating bearing surfaces are complementary to each other, in the frontal plane.  
   
   
       13 . A prosthetic ankle joint device according to  claim 12 , wherein both articulating bearing surfaces present an undulated profile, in the frontal plane.