Trapezal or trapezo-metacarpal implant

Abstract

The implant comprises a stem ( 10 ) terminating in a head ( 20 ). The stem is adapted to be inserted in the metacarpus of the thumb and the head to be disposed in a space obtained particularly by removing at least a portion of the trapezium. The surface of the head is constituted by a base ( 201 ) connected to the stem and adapted to rest on the proximal end of the metacarpus, a distal surface portion ( 202 ) opposite the base and serving as a contact surface with the bone located facing the proximal end of the metacarpus, and a connecting portion ( 203 ) connecting the base and the distal surface portion of the head. The distal surface portion ( 202 ) of the head is inclined relative to a longitudinal axis ( 104 ) of the stem by a predetermined angle (α), such that, when the stem ( 10 ) is mounted straight in the metacarpus, the distal surface portion ( 202 ) of the head can be located in varus.

1 . A method for treating the trapezo-metacarpal joint, comprising the steps of: 
 providing an implant comprising a stem terminating in a head, the head comprising a contact and friction surface that is inclined relative to a longitudinal axis of the stem by an angle other than zero;    providing a space by resecting a proximal end of the metacarpus of the thumb and at least a portion of the trapezium; and    implanting the implant such that the stem is inserted substantially straight in the metacarpus of the thumb and the head is disposed in said space with said inclined contact and friction surface in varus.    
   
   
       2 . The method of  claim 1 , wherein the implant is implanted such that the inclined contact and friction surface is in direct contact with the bone located facing the proximal end of the metacarpus.  
   
   
       3 . The method of  claim 2 , wherein the bone located facing the proximal end of the metacarpus is a remaining portion of the trapezium.  
   
   
       4 . The method of  claim 1 , wherein the inclined contact and friction surface has a convex shape.  
   
   
       5 . The method of  claim 1 , wherein the inclined contact and friction surface has an axis of symmetry forming said angle with the longitudinal axis of the stem.  
   
   
       6 . The method of  claim 1 , wherein at least the inclined contact and friction surface is of pyrocarbon.  
   
   
       7 . The method of  claim 1 , wherein the inclined contact and friction surface is offset relative to the longitudinal axis of the stem to the side of the implant where the angle between the inclined contact and friction surface and the longitudinal axis of the stem is smaller.  
   
   
       8 . The method of  claim 1 , wherein said angle is at least equal to about 10°.  
   
   
       9 . A method for treating the trapezo-metacarpal joint, comprising the steps of: 
 providing an implant comprising a stem terminating in a head, the head comprising a contact and friction surface that is inclined relative to a longitudinal axis of the stem by an angle other than zero and a base surface that is opposite the contact and friction surface and inclined relative to the longitudinal axis of the stem in the same direction as the contact and friction surface and by said angle;    providing a space by resecting a proximal end of the metacarpus of the thumb and at least a portion of the trapezium; and    implanting the implant such that the stem is inserted substantially straight in the metacarpus of the thumb and the head is disposed in said space with said base surface resting on the resected proximal end of the metacarpus and said inclined contact and friction surface in varus.    
   
   
       10 . The method of  claim 9 , wherein the implant is implanted such that the inclined contact and friction surface is in direct contact with the bone located facing the proximal end of the metacarpus.  
   
   
       11 . The method of  claim 9 , wherein the inclined contact and friction surface has an axis of symmetry forming said angle with the longitudinal axis of the stem and said axis of symmetry intersects said longitudinal axis substantially at the point of intersection between a plane defined by said base surface and said longitudinal axis.  
   
   
       12 . The method of  claim 9 , wherein the inclined contact and friction surface has an axis of symmetry forming said angle with the longitudinal axis of the stem and said axis of symmetry intersects said longitudinal axis at a point located between a distal end of the stem and the point of intersection between a plane defined by said base surface and said longitudinal axis.