In Vitro Biomechanical Properties of 2 Compression Fixation Methods for Midbody Proximal Sesamoid Bone Fractures in Horses

Abstract

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. Experimental study. 10 paired equine cadaver forelimbs from race-trained horses. 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. 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. All repaired limbs were able to withstand loads equal to those reportedly applied to the suspensory apparatus in vivo during walking. Each repair technique should have adequate yield strength for repair of midbody fractures of the PSB immediately after surgery.