Developing a Rabbit Model of the Femoral Head Osteonecrosis Induced by Microwave Heating: Optimum Temperature and Time Screening

BACKGROUND: An ideal model of osteonecrosis of the femoral head in beneficial to the study on the cause of disease. pathogenesy and treatment. So far there has not been a coherent method to prepare this model. OBJECTIVE: To establish a rabbit model of Osteonecrosis of femoral head induced by microwave heating, and to decide optimum microwave temperature and heating time. DESIGN: Randomized controlled animal trial. SETTING: Animal Experimental Center of Kunming Medical College. MATERIALS: The experiment was performed at the Animal Experimental Center of Kunming Medical College between September 2004 and November 2005. Forty-eight healthy adult New Zealand rabbits, either male or female, were provided by the Animal Experimental Center Kunming Medical College. The animal procedure was accorded with the ethical standards GW-92C multi-functional microwave therapy apparatus was the product of Grand World Medical Apparatus (Tianjin) Co. Ltd. METHOS: The microwave antenna was inserted into the rabbit femoral head. Ninety-six femoral heads in forty-eight rabbits were randomly divided into tour groups (n=24) according to the microwave temperature and heating time: microwave heating at 50℃ for 10 minutes group: 55℃ for 10 minutes group: 50℃ for 20 minutes group and 60℃ for 10 minutes group The models of osteonecrosis of femoral head were induced by microwave heating using multi-functional microwave therapy apparatus according to the temperature and heating lime of grouping. MAIN OUTCOME MEASURES: In each group, two rabbits (four femoral heads) were killed immediately, one, two, four, eight and twelve weeks after operation, respectively. A series of examinations were carried out, including gross observation, X-ray to observe bone trahecular arrangement. cystis degeneration, head collapse or hip joint destruction, MRI to observe the necrotic area, and HE staining to observe the osteonecrosis arid bone repair. RESULTS: Marrow tissues partially coagulated in the microwave heating at 50℃ for 10 minutes group at the end of the 1(superscript st) week, and the osteonecrtisis returned to normality at the end of the 8(superscript th) week. In 55℃ for 10 minutes group, marrow tissues were completely coagulated at the end of the (superscript st) week, and decreased signal on T1 weighted images arid increased signal on T2 images were identified at the end of the 2(superscript nd) week. In the 4(superscript th) week, bone repair was found simultaneously when osieonecrosis occurred. At the end of the l2(superscript th) week, the osieonecrosis continued and the repair stopped, and the femoral head collapse occurred. All femoral heads collapsed at the and 8(superscript th) week in 50℃, for 20 minutes group and 60℃ for 10 minutes group. CONCLUSION: Microwave heating at 55℃ for 10 minutes is the optimal choice to develop a rabbit model of osteonecrosis of the femoral head.