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 hydroxyapatitecoated 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 ° at 800N) and subsidence (maximal 0.036 mm at 800N). 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.