Prosthesis with articulating surface stress reducing contact edge

In a prosthesis including a joint comprising first and second members each having a surface articulating under load and in contact with one another, the combination comprising:

• a thermoplastic first member having a substantially planar first surface;
• and
• a metallic second member having a substantially planar second surface engaging the first surface in articulating contact, the second surface having an edge, a side surface extending from said edge substantially orthogonal to said second surface, said second surface including said edge thereof being under compressive load with the first surface during said articulating contact, said second surface having a gradual tapering convex region adjacent to and extending inwardly from said edge of said second surface a distance so as to cause the first member to exhibit a gradual generally uniform rate of change of deformation in said first surface in response to said compressive load with said second surface, such that the deformation of said first surface varies uniformly from essentially zero at portions aligned with said edge to a maximum at portions of said first surface aligned with regions of said second surface spaced said distance inwardly from said edge of said second surface.

In a knee joint prosthesis comprising first and second surfaces in articulating load contact with one another, the combination comprising:

• a thermoplastic tibial bearing having a substantially planar first surface;
• and
• a metal tibial component having a substantially planar second surface for engaging the first surface in articulating contact, the second surface having an edge, a side surface extending from said edge substantially orthogonal to said second surface, said second surface, including said edge thereof, being under compressive load with the first surface during said articulating contact, said second surface having a gradual tapering region adjacent to and extending inwardly from said edge of said second surface a distance W, said compressive load causing portions of said thermoplastic tibial bearing engaged with portions of said second surface spaced inwardly from said tapering region thereof to exhibit a contact stress of generally a first value, said gradual tapering region being configured so as to cause portions of the thermoplastic tibial bearing engaged therewith to exhibit edge stress concentration of a second value of no more than about twice said first value.

In a prosthesis including a joint comprising first and second surfaces in articulating load contact with one another, the combination comprising:

• a thermoplastic bearing having a substantially planar first surface;
• and
• a metal member having a substantially planar second surface for engaging the first surface in articulating contact, the second surface having an edge, a side surface extending from said edge substantially orthogonal to said second surface, said second surface, including said edge thereof, being under compressive load with the first surface during said articulating contact, said second surface having a gradual tapering region adjacent to and extending inwardly from said edge of said second surface a distance, said compressive load causing regions of said bearing inwardly from said tapering region of said second surface of said metal member to exhibit a contact stress of generally a first value, the gradual tapering region of said second surface being configured to cause the bearing to exhibit edge stress concentration of a second value in a region of engagement of the edge of the second surface with the first surface, the second value in the first member being no more than about twice said first value.

In a knee joint prosthesis comprising first and second surfaces in articulating load contact with one another, the combination comprising:

• a thermoplastic patellar bearing having a first surface;
• and
• a metal patellar component having a second surface for engaging the first surface in articulating contact, the second surface having an edge, said second surface, including said edge thereof, being under compressive load with the first surface during said articulating contact, said second surface having a gradual tapering region adjacent to and extending inwardly from said edge of said second surface a distance W, said compressive load causing portions of said thermoplastic patellar bearing engaged with portions of said second surface spaced inwardly from said tapering region thereof to exhibit a contact stress of generally a first value, said gradual tapering region being configured so as to cause portions of the thermoplastic patellar bearing engaged therewith to exhibit edge stress concentration of a second value of no more than about twice said first value.