Abstract
Fracture healing is influenced by fixation stability and experimental evidence suggests that the initial mechanical conditions may determine the healing outcome.
We hypothesised that mechanical conditions influence not only the healing outcome, but also the early phase of fracture healing. Additionally, it was hypothesised that decreased fixation stability characterised by an increased shear interfragmentary movement results in a delay in healing. Sixtyβfour sheep underwent a midβshaft tibial osteotomy which was treated with either a rigid or a semirigid external fixator. Animals were sacrificed at 2, 3, 6 and 9 weeks postoperatively and the fracture callus was analysed using radiological, biomechanical and histological techniques.
The tibia treated with semiβrigid fixation showed inferior callus stiffness and quality after 6 weeks. At 9 weeks, the calluses were no longer distinguishable in their mechanical competence. The calluses at 9 weeks produced under rigid fixation were smaller and consisted of a reduced fibrous tissue component. These results demonstrate that the callus formation over the course of healing differed both morphologically and in the rate of development.
In this study, we provide evidence that the course of healing is influenced by the initial fixation stability. The semiβrigid fixator did not result in delayed healing, but a less optimal healing path was taken. An upper limit of stability required for successful healing remains unknown, however a limit by which healing is less optimal has been determined. Β© 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.