In vitro biomechanical properties of 2 compression fixation methods for midbody proximal sesamoid bone fractures in horses

Objective-To evaluate 2 methods of midbody proximal sesamoid bone repair-fi xation by a screw placed in lag fashion and circumferential wire fixation-b y comparing yield load and the adjacent soft-tissue strain during monotonic loading. Study Design-Experimental study. Sample Population-10 paired equine cadaver forelimbs from race-trained hors es. Methods-A transverse midbody osteotomy of the medial proximal sesamoid bone (PSB) was created. The osteotomy was repaired with a 4.5-mm cortex bone sc rew placed in lag fashion or a 1.25-mm circumferential wire. The limbs were instrumented with differential variable reluctance transducers placed in t he suspensory apparatus and distal sesamoidean ligaments. The limbs were te sted in axial compression in a single cycle until failure. Results-The cortex bone screw repairs had a mean yield load of 2,908.2 N; 1 limb did not fail when tested to 5,000 N. All circumferential wire repairs failed with a mean yield load of 3,406.3 N. There was no statistical diffe rence in mean yield load between the 2 repair methods. The maximum strain g enerated in the soft tissues attached to the proximal sesamoid bones was no t significantly different between repair groups. Conclusions-All repaired limbs were able to withstand loads equal to those reportedly applied to the suspensory apparatus in vivo during walking. Clinical Relevance-Each repair technique should have adequate yield strengt h for repair of midbody fractures of the PSB immediately after surgery. (C) Copyright 2000 by The American College of Veterinary Surgeons.