Torsional performance of canine femoral osteotomy union.

This study allows the establishment of a protocol for standardizing the technical methodology of canine surgery for mechanical testing. Twenty mongrels were divided into 4 groups of 5 dogs each. All dogs had one femur selected as the test bone and the contralateral as paired control. The test femur was osteotomized and plated. The dogs were sacrificed at 7, 10, 13 and 16 weeks according to their group designation to determine healing of the osteotomy. Both test and control femora were tested to fracture in torsion using a computerized torsion machine. Various mechanical parameters were studied with the age of osteotomy union. The study found that all bones sustained spiral fractures through the osteotomy site. The maximum torque capacity and stiffness increased with age of union. There is an apparent biphasic pattern in the remodelling process. Up till the 13th week there was a decline in the polar moment of inertia and a rise in the torsional stress with an increase in strength. We postulate that this was due to a reduction of the outer diameter of the external bridging callus. After the 13th week, there was a reversal in the process and the outer diameter of the callus increased. The findings provide a baseline reference for future studies involving osteotomy healing as is necessary in bone allograft reconstruction and bone transport.