OBJECTIVETo explore the deep-frozen allograft strut in the rabbits for the sake of finding some evidence to support the clinical practice of cortical strut allograft.

METHODSFifty deep-frozen allograft struts were implanted on the lateral side of the femur in 50 male New Zealand white rabbits. These rabbits were randomly divided into 5 groups. The specimen were retrieved at 2, 4, 8, 16, 24 weeks after surgeries. In each group histomorphology and biomechanic properties were studied.

RESULTSFrom the X ray photography the edge of the strut would turn blunt at the 4th week, union could be found at the 8th week, the inner side of the strut could be absorbed at the 24th week. In the early stage when the strut was implanted in the rabbit, the capillary would be found to grow into the cortical strut from the interior side of it. Then the capillaries were found to converge at the 16th week. This phenomenon is correspondent with the resorption of the dead bone and formation of the new bone. There are few neoformated capillaries on the lateral side of the strut. From the decalcificied section, allograft struts were found to unit to the host at 4 to 8th week. Osteoclast and the new bone formation could be seen at the 8th week, and 3% of the total area of what had been the allograft was replaced by the new bone at that time, 12% was replaced at the 16th week, 21% at the 24th week. There are few resorption or neoformated bone at the lateral side of the strut. The biomechanical property indicated that the strength of the strut decreased at the early time, and only 38% of its original strength remained at 16 weeks.

CONCLUSIONSThe cortical allograft strut can unit to the host by the callus. The capillaries invading into the allograft from the interior side, new bone is formed from the interior side. The biomechanical strength of the strut decreased at early stage.