Joint prosthesis with contoured pin

A joint prosthesis comprising:

• (a) a first relatively inextensible component having a first surface that is concavely arcuate in shape;
• (b) a second relatively inextensible component which is spaced from the first component along a first axis and which has a second surface that is concavely arcuate in shape;
• (c) means defining a relatively inextensible pivot member disposed between and spaced from each of the first and second components, the pivot member having a central longitudinal axis which is oriented generally perpendicular to said first axis, the first and second components being disposed entirely on opposite sides of and separated by a plane oriented generally perpendicular to said first axis and generally parallel to said central longitudinal axis of the pivot member, the pivot member also having, when viewed in section taken normal to said central longitudinal axis, two discrete, convexly arcuate surfaces spaced from one another about the circumference of the pivot member, the two spaced apart arcuate surfaces of the pivot member being disposed at greater radial distances from the central longitudinal axis of the pivot member than any other portion of the circumference of the pivot member throughout at least a majority of its length, the spaced apart convexly arcuate surfaces of the pivot member also being presented to and spaced from the first and second concavely arcuate surfaces;
• and
• (d) means for resiliently securing the pivot member to each of the first and second components, the securing means including (i) a first portion which is at least partially formed of elastomer and which secures the first concavely arcuate surface to one of the two convexly arcuate surfaces of the pivot member and (ii) a second portion which is at least partially formed of elastomer and which secures the second concavely arcuate surface to the other of the two convexly arcuate surfaces of the pivot member, each of the first and second portions of the securing means extending circumferentially about said pivot member and beyond their respective discrete arcuate portions and having at least one exposed surface that extends outwardly from adjacent the pivot member, said at least one exposed surface of the first portion of the securing means being spaced from said at least one exposed surface of the second portion of the securing means throughout at least a majority of their respective lengths measured generally radially of said central longitudinal axis of the pivot member,
• the first and second components being coupled to each other only through the pivot member and the first and second portions of the securing means, the relative inextensibility of the first and second components and the pivot member being determined in comparison to the elastomer of the securing means, the first and second portions of the securing means deflecting in torsional shear to accomodate relative rotation between the pivot member and each of the first and second components so that the first and second components can move toward and away from each other in directions generally parallel to said first axis through rotation about a second axis that is disposed at least adjacent to and at least approximately parallel to the central longitudinal axis of the pivot member.

A joint prosthesis for use in replacement of a joint in a human body comprising a first member adapted to be connected with a first portion of a human body, a second member adapted to be connected with a second portion of a human body, a pivot member disposed between the first and the second members, said pivot member having an outer periphery circumscribing a longitudinal central axis, said outer periphery comprising when viewed in section taken normal to said central axis first and second discrete arcuate surfaces and connecting surfaces disposed between said first and second arcuate surfaces, said connecting surfaces being within the generatrix of at least one of said first and second arcuate surfaces, securing means for resiliently connecting the pivot member to the first and second members for allowing said first and second members to rotate about said outer periphery of said pivot member and about axes parallel to said longitudinal central axis, said securing means including a first body of elastomeric material disposed between said first member and said first arcuate surface and a second body of elastomeric material disposed between said second member and said second arcuate surface, said first and second bodies of elastomeric material including respective extensions disposed circumferentially beyond their respective arcuate surfaces and extending toward each other, each extension disposed partially about a respective portion of connecting surface joining the first and second arcuate surfaces, said extensions of said first and second bodies of elastomeric material having respective side surfaces which are spaced from each other and which extend toward said one connecting surface to allow said first and second bodies of elastomeric material to deflect in torsional shear toward each other about said first and second arcuate surfaces while relieving stresses about the junctions of said first and second arcuate surfaces with the said one connecting surface.