Partial hip prosthesis

Abstract

A partial hip prosthesis for reducing friction and wear in partial hip prosthesis by combining optimized geometry of the articulation and surface treatment of the prosthetic component. In the prosthesis, 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. A 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 system comprising
 an articulation member, wherein said articulation member is aspherical in shape and after implantation, allows for free rotation in a reamed acetabulum, wherein the articulation member is shaped to be used in combination with a spherically reamed acetabulum, so as to make, after implantation, an annular, congruent band shaped contact to the spherically reamed acetabulum which, after implantation, seals fluid in a gap between the articulation member and said reamed acetabulum, wherein the annular congruent band shaped contact is centered about 30 to 55 degrees from the axis of revolution of the femoral head prosthesis, and its width is between 5 and 15 degrees of the femoral head prosthesis.   
     
     
         2 . A partial hip prosthesis system comprising
 an articulation member, wherein said articulation member is aspherical in shape and after implantation, allows for free rotation in a reamed acetabulum, wherein a convex side of the articulation member is a prosthetic femoral head, wherein the articulation member is adapted to be used with a spherical acetabulum reamer shaped to ream the bone of the acetabulum into a spherical shape so as to make, after implantation, an annular, congruent band shaped contact to the articulation member, the annular congruent band shaped contact to the articulation member having a radius of curvature which is the same as that of the reamed acetabulum, wherein the annular congruent band shaped contact is centered about 30 to 55 degrees from the axis of revolution of the femoral head prosthesis, and its width is between 5 and 15 degrees of the femoral head prosthesis.   
     
     
         3 . A partial hip prosthesis system comprising
 (a) an articulation member, wherein said articulation member is aspherical in shape and after implantation, allows for free rotation in a reamed acetabulum, and   (b) a spherical acetabulum reamer shaped to ream the bone of the acetabulum into a spherical shape so as to make, after implantation, an annular, congruent band shaped contact to the articulation member which, after implantation, seals fluid in a gap between the articulation member and said reamed acetabulum, wherein the annular congruent band shaped contact is centered about 30 to 55 degrees from the axis of revolution of the femoral head prosthesis, and its width is between 5 and 15 degrees of the femoral head prosthesis.   
     
     
         4 . A partial hip prosthesis system comprising
 (a) an articulation member, wherein said articulation member is aspherical in shape and after implantation, allows for free rotation in a reamed acetabulum, wherein a convex side of the articulation member is a prosthetic femoral head, and   (b) a spherical acetabulum reamer shaped to ream the bone of the acetabulum into a spherical shape so as to make, after implantation, an annular, congruent band shaped contact to the articulation member, the annular congruent band shaped contact to the articulation member having a radius of curvature which is the same as that of the reamed acetabulum, wherein the annular congruent band shaped contact is centered about 30 to 55 degrees from the axis of revolution of the femoral head prosthesis, and its width is between 5 and 15 degrees of the femoral head prosthesis.   
     
     
         5 . A kit comprising
 (a) a partial hip joint prosthesis, and   (b) a reamer adapted for use in a hip joint, wherein said hip joint comprises two articulation surfaces, wherein one and only one of the two articulation surfaces of the hip joint is spherical in shape allowing for free rotation of the other articulation surface, which is aspherical in shape and is shaped so as to make an annular, congruent contact to the spherical surface, wherein the annular congruent band shaped contact is centered about 30 to 55 degrees from the axis of revolution of the femoral head prosthesis, and its width is between 5 and 15 degrees of the femoral head prosthesis,   wherein the partial hip joint prosthesis is a prosthetic femoral head aspherically shaped so as to make said annular, congruent band shaped contact with a spherically reamed acetabulum over a spherically shaped band on its surface, wherein the spherically shaped band has the same radius of curvature as that of the reamed acetabulum; and wherein the reamer is spherically shaped for surgical preparation of the acetabulum and adapted to ream the subchondral bone out to a spherical shape.   
     
     
         6 . The kit according to  claim 5 , wherein the prosthetic femoral head is manufactured from metal or carbon. 
     
     
         7 . The kit according to  claim 6 , wherein the prosthetic femoral head is manufactured from metal and further comprises a diamond-like coating. 
     
     
         8 . The kit according to  claim 6 , wherein the prosthetic femoral head is manufactured from pyrolytic carbon. 
     
     
         9 . The kit according to  claim 5 , wherein the spherically shaped band on the surface of the femoral head prosthesis is centered on an axis corresponding to the orientation of a dominant load vector acting across a hip joint. 
     
     
         10 . The kit according to  claim 5 , wherein the spherically shaped band congruent to the reamed acetabulum is centered at about 45 degrees from the axis of revolution of the femoral head prosthesis and its width is about 10 degrees. 
     
     
         11 . The kit according to  claim 5 , wherein a gap in articulation is formed at the area of major load transfer. 
     
     
         12 . The kit according to  claim 9 , wherein the partial hip joint prosthesis further comprises a neck member, having a longitudinal axis running through a first end and a second end of the neck member, and
 wherein the axis of revolution of the femoral head prosthesis is offset from the neck member longitudinal axis by an offset angle when the prosthetic femoral head is coupled to the neck member.   
     
     
         13 . The kit according  claim 12 , wherein the offset angle is approximately 15 to 35 degrees. 
     
     
         14 . The kit according  claim 12 , wherein the offset angle is approximately 25 degrees. 
     
     
         15 . The kit according  claim 12 , wherein the neck member is cylindrical and threaded. 
     
     
         16 . The kit according  claim 12 , wherein the neck member includes a plurality of holes to aid in vascularization of and anchorage in the femur bone. 
     
     
         17 . A partial hip joint prosthesis
 comprising two articulation surfaces, wherein one and only one of the two articulation surfaces of the hip joint is spherical in shape allowing for free rotation of the other articulation surface, which is aspherical in shape and is shaped so as to make an annular, congruent contact to the spherical surface, wherein the annular congruent band shaped contact is centered about 30 to 55 degrees from the axis of revolution of the femoral head prosthesis, and its width is between 5 and 15 degrees of the femoral head prosthesis,   wherein the partial hip joint prosthesis is a prosthetic femoral head aspherically shaped so as to make said annular, congruent band shaped contact with a spherically reamed acetabulum over a spherically shaped band on its surface by a reamer spherically shaped for surgical preparation of the acetabulum and adapted to ream the subchondral bone out to a spherical shape, wherein the spherically shaped band has the same radius of curvature as that of the reamed acetabulum.