This study investigates the relationship between microdamage and bone adaptation in a sheep forelimb model. Based on gait analysis, a simple test rig was developed for in vitro measurement of strain on the cranial and caudal surfaces of the radius to study the effects of ulnar osteotomy and ulnar reinforcement using a Steinmann pin. Control, osteotomy and pin procedures were carried out in vivo and the adaptive response measured at intervals up to 24 weeks. Pinning proved ineffective in altering load on the radius, but ulnar osteotomy elicited an adaptive response which returned surface strains to near control levels by 24 weeks. The overloaded radius adapted by forming new bone at surfaces - renewed modelling, and by remodelling the existing cortex. The incidence of microcracks and resorption cavities increased signficantly in osteotomies at 6 weeks compared with controls and preceded the formation of secondary osteons. The timing and location of microcrack, resorption cavities and secondary osteons support the hypothesis that microdamage is a stimulus for bone remodelling.
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