Aims: Free vascularized fibular graft for osteonecrosis of the femoral head is a well established procedure based on the assumption that the graft will provide mechanical support, blood supply to the osteonecrotic head and to introduce mesenchymal stem cells into the affected area of the femoral head.

Methods: We reviewed 25 cases to delineate the pathological features of femoral heads with AVN treated by vascularised fibular grafts which were retrieved at revision surgery when the construct was deemed clinically to have failed.

Results: Review of the patients’ records disclosed that 60.8% were on steroid therapy when the AVN was diagnosed. The recorded time from first symptoms of failure to conversion to total hip arthroplasty was an average of 55 months.

The length of the graft was divided into three zones : zone 3 the femoral neck; zone 2 the lower femoral head or “metaphysis”; zone 1 the more apical or epiphyseal component of the femoral head. The intention was to follow the vascularization of the pedicle and the changes in the three diverse areas of the specimen. The graft showed incorporation with the host bone. In the pedicle there was preservation of vascular patency and tissue viability.

Conclusion: However, this healing process involved a slow reparative resorptive activity which undermined the joint surface. This could suggest that non-resorbable materials in place of tissue grafts can be expected to avoid the negative effect of creeping substitution as an undermining force in the repair and revascularisation of the necrotic area in the head.

In 33 dogs we implanted femoral stems made either of carbon composite, some coated with hydroxyapatite, or of titanium alloy with a porous coating. Osseointegration was greater in the hydroxyapatite-coated than in the un-coated stems (p less than 0.001). Push-out tests, at an average of 7.2 months after implantation, showed a six-fold increase in interface shear strength and a twelve-fold increase in shear stiffness in the hydroxyapatite-coated group compared with noncoated implants. The highest shear-strength values were found in the porous-coated titanium alloy stems, around which there was also the most resorptive bone remodelling.

The purpose of this study was to determine the biological effects of the elastic modulus of the femoral stem in canine hip arthroplasty. Cementless total hip arthroplasty was performed in 12 dogs, six had a low elastic modulus polyacetal resin stem and six had a high modulus stainless steel stem. The components were otherwise similar. At six and 12 months after operation, radiographic and histomorphometric analysis showed that those with steel implants had more cortical porosity than did the other group (p less than 0.01). We suggest that the elastic modulus of the implant is an important factor in controlling cortical bone resorption. A low modulus femoral prosthesis can significantly decrease bone resorption which might otherwise eventually lead to implant failure.