Biologic attachment of an allograft bone and tendon transplant to a titanium prosthesis

An Achilles tendon allograft with its bony insertion was used to bridge a T itanium implant, containing an endoprosthetic tendon anchor, and the sheep biceps muscle, Twelve sheep were operated on unilaterally and followed up c linically and histologically for 2, 4 (n = 2), 8, and 12 months (n = 4), Fu ll function of the front limb was regained after 8 to 12 weeks, There were no signs of mechanical loosening at all times. The morphologic changes at t he bone block and implant fixation site were an initial revascularization o f the allograft bone, which was observed at 2 months and enhanced at 4 mont hs but occurred without any evidence of bone remodeling, This was changed i n all specimens taken at 8 and 12 months where intensive new bone developme nt, remodeling, and bone ingrowth in the titanium implant was found. Bone m ass was shifted significantly to the tendon insertion half of the bone bloc k because of a creeping substitution of the cancellous allograft bone and b one ingrowth to the implant. Overall bone mass slightly decreased with time but resorption of allograft bone outweighed new bone development only at l esser loaded areas. Transplantation of a bone and tendon allograft to an im plant resulted in a revitalized, mechanically stable, and biologically anch ored compound.