A new animal model of femoral head necrosis induced by intraosseous injection of ethanol.

There is no reliable animal model of the early stages of osteonecrosis of the femoral head (ONFH) for the evaluation of new therapeutic approaches. In this study, we propose a new animal model of femoral head osteonecrosis. Pure ethanol was injected into the centre of the femoral head in adult Merino sheep under fluoroscopic control. After 3, 6 and 12 weeks the animals were killed and the femoral heads were harvested. Microradiographic and histological changes were analysed and recorded. Partial necrosis was documented over a period of 12 weeks in all animals. The appearance of necrosis in combination with intact macrotexture, macrocirculation and joint cartilage is similar to the features described in early ONFH in humans. Due to its efficacy and its similarity to the early stages of ONFH in humans, this model may be suitable to evaluate new therapeutic techniques in the treatment of ONFH.

Bone morphogenetic protein-2 and growth and differentiation factor-5 enhance the healing of necrotic bone in a sheep model.

INTRODUCTION: Osteotropic growth factors enhance bone repair, but their efficacy in an area of necrotic bone is not known. The purpose of this study was to investigate the effects and potential side effects of an intraosseous application of absorbable bone morphogenetic protein-2 (BMP-2) and growth and differentiation factor-5 (GDF-5) composites in a sheep model for partial necrosis of the femoral head. MATERIALS AND METHODS: The direct injection of ethanol under fluoroscopy into the superior centre of the right femoral head produced histologically documentable necrosis of the central region of the head in a previous study of ten sheep. Another 27 sheep constituted the sample to study the effects of BMP-2 and GDF-5. Necrosis was produced in the same fashion in these animals. Four weeks later nine sheep received 300 microg recombinant BMP-2 and nine sheep 300 microg recombinant GDF-5 on an absorbable carrier by surgical implantation. Nine sheep received the carrier alone (control group). The animals were sacrificed at 3, 6, and 12 weeks after implantation and both femora were harvested. RESULTS: Bone density analysis and microscopic examination indicated that bone formation was noticeably induced as early as 3 weeks postoperatively in the growth factor treated animals. Bone regeneration was enhanced by growth factor composites. This was documented by histological scoring and histomorphometric analysis. No severe local side effects secondary to the growth factors, such as heterotopic ossification or inflammation, were observed in either group. DISCUSSION: The application of an absorbable growth factor composite in combination with established surgical techniques is a promising approach, that may enhance the healing of devitalised bone defects. Based on these results, further studies regarding biodegradation, dosage of the protein and surgical technique are required.