A prosthetic implant (11, 61) for implantation into a resected bone at a joint, which implant comprises: a metal stem element (13, 63) which has a connector (23, 73) at one end that is shaped with a reentrant region of reduced dimension, an integral one-piece polymeric insert (15, 65) which has an interior cavity (51, 89) that receives said connector and a flange (47, 87) that circumscribes an entrance to said cavity, and a head (17, 67) having an exterior articular surface and an interior cavity (35, 77) proportioned to receive said insert, said head being formed from a graphite substrate having interior and exterior pyrocarbon surfaces, said head cavity having an entrance formed by a reentrant entrance lip (39, 79) of a lesser inner diameter and a size such that said polymeric insert must elastically deform radially inward to enter said cavity, said polymeric insert cavity having an entrance region of a size smaller than said connector and having an outer groove (45, 85) which receives said head entrance lip and leaves an annular gap (48, 88) forming a circumferential relief region that accommodates elastic deformation of said polymeric insert when said stem element is assembled with a subassembly of said head and said polymeric insert, and said integral polymeric insert being made of polymeric material having an elasticity, such that (a) it can deform radially inward sufficient to facilitate its entry into said head cavity and return to shape, (b) its entrance region can deform radially outward to facilitate assembly with said connector, and (c) once assembled with both said head and said stem connector, disassembly cannot inadvertently occur. a metal stem element (13, 63) which has a connector (23, 73) at one end that is shaped with a reentrant region of reduced dimension, an integral one-piece polymeric insert (15, 65) which has an interior cavity (51, 89) that receives said connector and a flange (47, 87) that circumscribes an entrance to said cavity, and a head (17, 67) having an exterior articular surface and an interior cavity (35, 77) proportioned to receive said insert, said head being formed from a graphite substrate having interior and exterior pyrocarbon surfaces, said head cavity having an entrance formed by a reentrant entrance lip (39, 79) of a lesser inner diameter and a size such that said polymeric insert must elastically deform radially inward to enter said cavity, said polymeric insert cavity having an entrance region of a size smaller than said connector and having an outer groove (45, 85) which receives said head entrance lip and leaves an annular gap (48, 88) forming a circumferential relief region that accommodates elastic deformation of said polymeric insert when said stem element is assembled with a subassembly of said head and said polymeric insert, and said integral polymeric insert being made of polymeric material having an elasticity, such that (a) it can deform radially inward sufficient to facilitate its entry into said head cavity and return to shape, (b) its entrance region can deform radially outward to facilitate assembly with said connector, and (c) once assembled with both said head and said stem connector, disassembly cannot inadvertently occur.