The biomechanical environment of a bone fracture and its influence upon the morphology of healing.

The mechanism by which mechanical stimulus of reparative tissues directs the pattern of healing of a bone fracture is not understood. Several hypotheses have been developed that predict the ossification pattern during healing for a given ambient mechanical environment. These have remained unproved because of the absence of data on stress fields in the reparative tissue of real fractures. The present study examines the predictive performance of the most recent hypothesis that was proposed by Claes and Heigele (J. Biomech. 32 (1999) 255), against measured and calculated data from the clinical fracture reported by Gardner et al. (J. Biomech. 33 (2000) 415). The hypothesis was used to predict ossification from the preceding stress and strain fields present in the FEM of Gardner et al. at four temporal stages during healing. Predictions were then compared with the observed differentiation and maturation. During early healing of the interfragmentary gap region, the hypothesis correctly predicted the formation of connective tissue and fibrocartilage, and during later healing it correctly predicted the beginning of endochondral ossification. At the periphery of the periosteal callus, the hypothesis correctly predicted intramembraneous ossification during early healing, and also its thickening by endochondral ossification during later healing. However, the hypothesis incorrectly predicted intramembraneous ossification during early healing of the main periosteal callus, although in later healing it correctly predicted endochondral ossification.