Osteochondral glenoid allograft for biologic resurfacing of the glenoid: biomechanical comparison of novel design concepts

IntroductionBiologic resurfacing of the glenoid has hitherto failed to adequately restore the geometry and biology of the glenoid. We hypothesised that a new concept for a press-fit osteochondral allograft glenoid replacement would restore the anatomic geometry of the glenoid, with primary stability guaranteed by the construct through press-fit fixation alone.Material and methodsFive sawbone models of human scapulae and 5 models using sheep scapulae were prepared for testing of 3 different interface designs (cross, rectangle, and dovetail). Micromotion at the graft interface was assessed in response to 1000 cycles of 30 N shear and 100 N compressive load, and maximal craniocaudal force was determined under 500 N compressive load.ResultsIn sawbones, mean (range) micromotion ranged from 38 (13-88) μm for cross to 208 (89-335) μm for rectangle, and decreased to 29 (21-57) μm for cross to 104 (34-127) μm for rectangle after 1000 cycles of applied shear force. In sheep bone, the mean (range) of micromotion was 15 (9-22) μm for dovetail to 51 (10-503) μm for cross and decreased to 15 (10-20) μm for dovetail to 44 (24-199) μm for cross; after 1000 cycles with the rectangle design, it decreased from 32 (25-217) μm to 16 (9-143) μm.DiscussionDespite biomechanical differences, in vitro allograft stability was generally adequate for all tested designs, particularly after the graft was allowed to “seat” by repetitive loading. While various geometries are potentially candidates for press-fitting a glenoid allograft to a host scapula, a rectangular interface between graft and host provided a favorable combination of both technical feasibility and biomechanical reliability.ConclusionThe concept of an osteochondral glenoid allograft for glenoid reconstruction is technically feasible and demonstrates adequate primary stability in vitro.