OBJECTIVETo study the change and relationship among bone mineral density (BMD), collagen composition and biomechanical properties of the callus in the healing process of osteoporotic fracture.

METHODSThe osteoporotic rat model and fracture model were established through bilateral ovariectomy (OVX) and osteotomy of the middle shaft of the right hind tibiae, respectively. Ninety female SD rats were randomly divided into OVX group and sham group. With the samples of blood and callus, roentgenographic and histological observation were performed for the assessment of the healing progress of the fracture, and the serum concentration of TRAP-5b, proportion of type I collagen, BMD and biomechanical properties of the callus were measured.

RESULTSThe OVX group experienced a significant delay of fracture healing. The mean serum concentration of TRAP-5b of rats in the OVX group was much higher than that in the sham group after the operation (P less than 0.05), but the difference at the same time point after fracture was smaller than that before fracture (P less than 0.05). The BMD of the callus in both groups reached the peak value at the 6 th week after fracture while the proportion of the type I collagen and the biomechanical strength reached the peak at the 8th week.

CONCLUSIONSThe deficiency of estrogen after the ovariectomy could induce the up-regulation of the osteoclasts activities, whereas the potency of further activation after fracture was depressed. Although the synthesis of collagen together with its mineralization determines the biomechanical properties of new bone, the accumulation of collagen could be assessed as an index in the prediction of biomechanical strength of bones independent of the bone mineral deposition.