Hip joint prosthesis having a zirconia head and a ceramic cup

Abstract

This invention relates to a biojoint prosthesis comprising: a) a prosthetic comprising a first component having an outer surface comprising at least 90 mol % zirconia, and b) a second component having a surface shaped to receive the outer surface of the first component, wherein the outer surface of the first component is received on the surface of the second component, and wherein a) at least a portion of the surface of the second component receiving the first component comprises a ceramic having a surface roughness of no more than 100 nm, and b) the outer surface of the first component has a surface roughness of no more than 100 nm.

We claim:  
     
         1 . A joint prosthesis comprising: 
 a) a prosthetic comprising a first component having an outer surface comprising at least 90 mol % zirconia, and    b) a second component having a surface shaped to receive the outer surface of the first component,    wherein the outer surface of the first component is received on the surface of the second component, and    wherein a) at least a portion of the surface of the second component receiving the first component comprises a ceramic having a surface roughness of no more than 100 nm, and b) the outer surface of the first component has a surface roughness of no more than 100 nm.    
     
     
         2 . The prosthesis of  claim 1  wherein the joint is a hip joint, the first component is a substantially spherical ceramic head, the second component is an acetabular cup having a socket surface shaped to rotatably receive the outer surface of the ceramic head, wherein the outer surface of the ceramic head is received in the socket surface of the acetabular cup, and wherein a) at least a portion of the socket surface receiving the head comprises a ceramic having a surface roughness of no more than 50 nm, and b) the outer surface of the head has a surface roughness of no more than 50 nm.  
     
     
         3 . The prosthesis of  claim 2  wherein the portion of the socket surface comprising a ceramic comprises at least one oxide.  
     
     
         4 . The prosthesis of  claim 3  wherein the portion of the socket surface comprising a ceramic comprises at least about 50% alumina.  
     
     
         5 . The prosthesis of  claim 3  wherein the ceramic head consists essentially of zirconia partially stabilized by between 2 mol % and 5 mol % rare earth oxide.  
     
     
         6 . The prosthesis of  claim 5  wherein the ceramic comprising at least one oxide is selected from the group consisting of a ceramic consisting essentially of alumina having a grain size of less than one micron, YTZP zirconia having a surface roughness of no more than 15 nm, and zirconia-toughened alumina.  
     
     
         7 . The prosthesis of  claim 5  wherein the ceramic comprising at least one oxide is a ceramic consisting essentially of alumina having a surface roughness of no more than 20 nm.  
     
     
         8 . The prosthesis of  claim 7  wherein the head consists essentially of PSZ zirconia having a surface roughness Ra of no more than 10 nm and the ceramic consists essentially of alumina having a grain size of between 0.4 and 0.9 μm.  
     
     
         9 . The prosthesis of  claim 2  wherein the outer surface of the ceramic head and the socket surface each have a surface roughness Ra of no more than 15 nm.  
     
     
         10 . The prosthesis of  claim 2  wherein the outer surface of the head has a monoclinic zirconia content of less than 10%.  
     
     
         11 . The prosthesis of  claim 7  wherein the outer surface of the head and the ceramic socket surface each have a surface roughness Ra of no more than 15 nm.  
     
     
         12 . The prosthesis of  claim 2  wherein the head consists essentially of PSZ zirconia and the socket surface consists essentially of alumina, and wherein the surface roughness Ra of the outer surface of the head is at least twice the surface roughness Ra of the socket surface.  
     
     
         13 . The prosthesis of  claim 5  wherein the outer surface of the head and the ceramic socket surface each have a surface roughness Ra of no more than 10 nm.  
     
     
         14 . The prosthesis of  claim 1  wherein the articulating surfaces of the first and second components are selected such that each has a wear factor of less than 10 −7  mm 3 /Nm when subjected in tandem to ASTM G99 wherein the pin is the material of the outer surface of the first component and the plate is the material of the surface of the second component.  
     
     
         15 . The prosthesis of  claim 2  wherein the outer surface of the ceramic head and the socket surface of the acetabular cup are selected such that each has a wear factor of less than 10 −7  mm 3 /Nm when subjected in tandem to ASTM G99 wherein the pin is the material of the outer surface of the ceramic head and the plate is the material of the socket surface of the acetabular cup.  
     
     
         16 . The prosthesis of  claim 11  wherein the outer surface of the ceramic head and the socket surface of the acetabular cup are selected such that each has a wear factor of less than 10 −7  mm 3 /Nm when subjected in tandem to ASTM G99 wherein the pin is the material of the outer surface of the ceramic head and the plate is the material of the socket surface of the acetabular cup.  
     
     
         17 . An acetabular cup having a socket surface for receiving a ceramic femoral head having a surface roughness Ra of no more than 50 nm, wherein the improvement comprises at least a portion of the socket surface comprises a ceramic having a surface roughness of no more than 50 nm.  
     
     
         18 . The cup of  claim 17  wherein the ceramic socket surface has a grain size of less than one micron.  
     
     
         19 . The cup of  claim 18  wherein the ceramic consists essentially of alumina.  
     
     
         20 . A method of maintaining a low wear condition, comprising the step of: 
 a) sliding a first ceramic surface having a surface roughness of no more than 100 nm against a second ceramic surface having a surface roughness of no more than 100 nm with a force of between 5N and 25N, thereby providing a wear factor of no more than 10 −8  mm 3 /Nm.    
     
     
         21 . A hip joint prosthesis comprising: 
 a) a femoral prosthetic comprising a substantially spherical ceramic head having a diameter, and    b) an acetabular cup having a ceramic socket surface shaped to rotatably receive the ceramic head, the socket surface having a diameter,    wherein the ceramic head is received in the socket surface of the acetabular cup, and    wherein the diameter of the socket surface is larger than the diameter of the head, thereby providing rolling contact between the head and the socket surface.    
     
     
         22 . A hip joint prosthesis comprising: 
 a) a trunnion having a stem having a taper and    b) a substantially spherical ceramic head having a recess having about the same angle as the taper,    wherein the head is fitted onto the trunnion by a Morse taper lock between the stem and the recess,    wherein the recess completely traverses the head.    
     
     
         23 . A knee joint prosthesis comprising: 
 a) a femoral component having a base and a plurality of tynes extending therefrom in the same direction, and    b) a tibial plate having a surface shaped for receiving the tynes,    wherein the tynes have an outer surface comprising zirconia partially stabilized by between 2 mol % and 5 mol % rare earth oxide and a surface roughness of no more than 100 nm, and    wherein the surface of the tibial plate receiving the tynes is a ceramic having a surface roughness of no more than 100 nm.