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

Abstract

Objective - To evaluate 2 methods of midbody proximal sesamoid bone repair - fixation by a screw placed in lag fashion and circumferential wire fixation - by 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 horses. 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 screw placed in lag fashion or a 1.25-mm circumferential wire. The limbs were instrumented with differential variable reluctance transducers placed in the suspensory apparatus and distal sesamoidean ligaments. The limbs were tested 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 difference in mean yield load between the 2 repair methods. The maximum strain generated in the soft tissues attached to the proximal sesamoid bones was not 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 strength for repair of midbody fractures of the PSB immediately after surgery. © Copyright 2000 by The American College of Veterinary Surgeons.