Femoral prosthesis with anti-rotation feature for ball

Claim 1

A hip joint prosthesis comprising in combination: (a) a femoral prosthesis having a stem extending from a distal end to a proximal end and a neck having a length extending along an axis from said proximal end to a free end, said neck, in an area adjacent said free end, having (1) an exterior surface tapering inwardly substantially along said lengths toward said axis in a direction toward said free end and (2) at least one rib outwardly from said exterior surface, said rib having an outer edge extending from said free end throughout a major portion of said neck, said outer edge tapering away from said axis in a direction away from said free end; and (b) a ball affixed to said neck free end, said ball having a cavity including (1) an inwardly facing wall and a bottom, at least a major portion of said inwardly facing wall being tapered in a direction and at an angle to provide surface to surface contact between said major portion and said exterior surface and a groove in said cavity having an inwardly facing edge outwardly from said inwardly facing wall extending throughout a length of said inwardly facing wall, said inwardly facing edge tapering at an angle similar to the angle of said rib outer edge.