Partial hip prosthesis

Abstract

The invention reduces friction and wear in partial hip prosthesis by combining optimized geometry of the articulation and surface treatment of the prosthetic component. The acetabulum is reamed to the bone. One of the articulating surfaces—either that of the reamed acetabulum, or that of the femoral head prosthesis is a-spherical so that a fluid-filled gap is formed at the area of major load transfer. The fluid-filled gap is sealed by an annular area of contact, over which the concave and the convex components are congruent. The preferred surface treatment is by diamond-like coating, which results in very low coefficient of friction and high abrasion resistance against the bone. The prosthetic head is fixed to the femur by either a conventional stem, a perforated shell, or a femoral neck prosthesis screwed onto the femur so that it is partially covered by bone and partially exposed on the medial-inferior aspect, where it abuts the reamed cortex of the calcar region.

1 . A partial hip prosthesis, wherein one and only one of the articulation members is spherical in shape allowing for free rotation of the other articulation member, which is aspherical in shape and is shaped so as to make an annular, congruent contact to the spherical member. 
     
     
         2 . The partial hip prosthesis according to  claim 1 , wherein the concave side of the articulation is a spherical cavity ( 100 ) reamed out in the acetabulum. 
     
     
         3 . The partial hip prosthesis according to  claim 1 , wherein the convex side of the articulation is a prosthetic femoral head ( 40 ), shaped so as to make an annular, congruent contact with the reamed acetabulum over a spherically shaped band ( 51 ) on its surface of the same radius of curvature ( 41 ) as that of the reamed acetabulum ( 102 ). 
     
     
         4 . The partial hip prosthesis according to  claim 3 , wherein the prosthetic femoral head ( 40 ) is manufactured from metal, and preferably comprises a diamond-like coating or is manufactured from carbon, e.g. pyrolytic carbon. 
     
     
         5 . The partial hip prosthesis according to  claim 3 , wherein the spherically shaped band ( 51 ) on the surface of the femoral head prosthesis ( 40 ) is centered on an axis ( 73 ) corresponding to the orientation of the dominant load vector ( 72 ) acting across the hip joint. 
     
     
         6 . The partial hip prosthesis according to  claim 3 , wherein the spherically shaped band ( 51 ), congruent to the reamed acetabulum ( 100 ) is centered at 30 to 55 degrees, preferably at about 45 degrees, from the axis of revolution of the head, and its width is between 5 and 15 degrees, preferably about 10 degrees. 
     
     
         7 . The partial hip prosthesis according to  claim 1 , wherein the concave side of the articulation is an aspherical cavity ( 201 ) reamed out in the acetabulum, with the radius ( 202 ) over a spherical band ( 203 ) equal to the radius ( 205 ) of the spherical prosthetic femoral head. 
     
     
         8 . The partial hip prosthesis according to  claim 7 , wherein the prosthetic femoral head ( 300 ) is manufactured from metal, and preferably comprises a diamond-like coating or is manufactured from carbon, e.g. pyrolytic carbon. 
     
     
         9 . The partial hip prosthesis according to  claim 1 , whereby a gap ( 110 ,  301 ) in articulation is formed at the area of major load transfer. 
     
     
         10 . A partial hip prosthesis wherein the prosthetic head of the femur is affixed to the neck of the femur via a cylindrical prosthetic neck ( 30 ) abutting the reamed femoral neck from outside the medial-inferior cortex ( 60 ), while crossing the anterior and the posterior cortices of the femoral neck to engage the lateral-superior area of the femoral neck from within ( 61 ). 
     
     
         11 . The partial hip prosthesis according to  claim 10 , wherein the prosthesis of the neck is threaded on outside ( 36 ) and inside ( 37 ). 
     
     
         12 . The partial hip prosthesis according to  claim 10 , wherein the prosthesis of the neck is provided by a multitude of holes ( 38 ) to aid in vascularization of and anchorage in the bone of the femoral neck. 
     
     
         13 . A method of surgical treatment of the hip joint with a partial hip prosthesis, wherein one and only one of the articulation members is spherical in shape allowing for free rotation of the other articulation member, which is aspherical in shape and is shaped so as to make an annular, congruent contact to the spherical member. 
     
     
         14 . An aspherical acetabulum reamer ( 200 ) shaped so as to ream the bone with a spherical band ( 203 ), a recess at the polar region ( 301 ) and an equatorial region wider than the diameter of the sphere corresponding to the spherical band ( 203 ).