Histological evaluation of two designs of shoulder surface replacement implants.

Abstract

To assess the extent of osteointegration in two designs of shoulder resurfacing implants. Bony integration to the Copeland cylindrical central stem design and the Epoca RH conical-crown design were compared. Implants retrieved from six patients in each group were pair-matched. Mean time to revision surgery of Copeland implants was 37 months (standard deviation (sd) 23; 14 to 72) and Epoca RH 38 months (sd 28; 12 to 84). The mean age of patients investigated was 66 years (sd 4; 59 to 71) and 58 years (sd 17; 31 to 73) in the Copeland and Epoca RH groups respectively. None of these implants were revised for loosening. Increased osteointegration was measured under the cup in the Copeland implant group with limited bone seen in direct contact with the central stem. Bone adjacent to the Epoca RH implants was more uniform. This difference in the distribution of bone-implant contact and bone formation was attributed to the Epoca implant's conical crown, which is positioned in more dense peripheral bone. The use of a central stem may not be necessary provided there is adequate peripheral fixation within good quality humeral bone. Poor osteointegration of cementless surface replacement shoulder prosthesis may be improved by implant design.