Prosthetic joint and method of manufacture

A method for modeling a prosthetic joint, for replacement of an anatomical joint having first and second bones wherein the second bone moves relative to the first bone by simultaneous pivoting about two non-intersecting and non-orthogonal axes of rotation, the method comprising the steps of:

• locating a first said axis of rotation of the second bone relative to the first bone;
• locating a second said axis of rotation of the second bone relative to the first bone;
• locating a curved mating surface on said second bone, said mating surface being the surface at which the second bone mates with the first bone;
• determining a first radius from said second axis to a circular arc in the curved mating surface, the center of said circular arc being a point on said second axis, said circular arc lying in a first reference plane which is perpendicular to said second axis at said center of said circular arc;
• establishing a second reference plane perpendicular to said first axis and passing through said center of said circular arc;
• defining an angle and measuring an angular variation of said angle between said first axis and said second axis at the intersection of said second axis with said second reference plane;
• determining a second radius from said first axis to said second axis, as measured in said second reference plane;
• mathematically generating a reference circle by completing said circular arc in said first reference plane;
• mathematically generating a reference toroid defining a surface by rotating said reference circle about said first axis at said second radius;
• selecting a portion of said surface of said reference toroid to substantially duplicate the mating surface;
• forming a first joint surface on a first member of said prosthetic joint, said first joint surface duplicating the topography of said selected surface portion of said toroid;
• and
• forming a second joint surface on a second member of said prosthetic joint, said second joint surface duplicating the topography of said selected surface portion of said toroid.