Submitted to: Journal of Orthopaedic Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/16/2000
Publication Date: N/A
Citation: Interpretive Summary: Distraction Osteogenesis (DO) is one of the most dramatic procedures ever developed in orthopedics. It is a procedure that can be used to lengthen and straighten human bones. In addition, however, because new bone grows so fast, it provides an excellent opportunity to study in a very short period of time how bone cells really behave and to learn the mechanisms by which new bone is formed. This is important in learning how to develop new ways to strengthen bone and to prevent bone loss under conditions such as aging. In this study, we have developed another method to test the strength and integrity of the new bone formed using the DO technique in an animal model. This technique will allow us to determine the effects of various diets and stresses on bone development and repair.
Technical Abstract: These studies were designed to determine the reliability of in vitro tensile testing to measure the temporal development of regenerate bone strength in rats during limb lengthening (distraction osteogenesis, DO). External fixators were placed on the right tibiae of 36 virus-free, 400-450 g male Sprague Dawley rats, and osteotomies (n=33) were performed. Distraction was initiated the following morning (0 day latency) at 0.4 mm/day and continued to day 20 and the 8 mm gap was allowed to consolidate for up to 50 days (day 70 postop). Contralateral unoperated and operated (fixator only) controls were included. On days 20, 30, 50 and 70 postop, the rats were anestheized, and their tibia were radiographed prior to undergoing sacrifice for histological or tensile analysis. On day 70, an additional group was tested by three-point bending. Radiodensity measurements demonstrated progressive mineralization of the DO gap, and histology confirmed typical intramembranous ossification of collagen bundles oriented parallel to the distraction force. Tensile stiffness increased significantly between days 20 and 30 postop, this increase correlated with initial radiographic and histologic bridging of the DO gap. Energy to failure and ultimate tensile strength increased progressively to day 70. At day 70, the force failure for three-point bending was 65% of control tibiae. In conclusion, in vitro tensile testing provides a reliable method to test the development of structural integrity during the early stages of DO. Therefore, the biomechanical effects of postulated modulators of bone repair can be measured during early stages (bone formation, bridging, early consolidation) of DO in a rat model.