Biomechanical and histological evaluation of a hydroxyapatite-coated titanium femoral stem fixed with an intramedullary morsellized bone grafting technique: an animal experiment on goats

To reconstruct femoral intramedullary bone-stock loss in revision surgery of failed total hip arthroplasties, morsellized trabecular bone grafts can be used. In 14 goats a noncemented hydroxyapatite-coated titanium stem was fixed within a circumferential construction of bone allografts. After 6 or 12 wk, four goats were used for mechanical tests and three for histology. The stability of the stems relative to the bone was determined in a loading experiment with Roentgenstereo-Photogrammatic Analysis (RSA). Owing to two loosenings and two fractures, only one 6-wk specimen and three 12-wk specimens were available for mechanical testing. The prostheses were very stable at 12 wk. The most important movements were axial rotation (maximal 0.17 degrees at 800 N) and subsidence (maximal 0.036 mm at 800 N). After unloading, there was 40-60% elastic recovery. Histological examination showed revascularization and remodelling of the graft in all the specimens investigated. At the graft site, bone apposition and bone resorption had resulted in a mixture of graft and new bone. Bone incorporation was mainly seen in the proximal areas. Graft lysis was evident in the midshaft region and at distal levels around the prostheses