In Vivo Evaluation of a Naturally Derived Cytocompatibile and Architecturally Optimized Tendon Allograft in the Horse

Abstract

In horses, debilitating tendon injuries can result from external trauma. Currently, the repair of tendon defects arising from trauma relies heavily upon de novo tissue regeneration. Endogenous repair and subsequent remodeling can take as long as 18 months. The biomechanical properties of healed tendon are considered inferior those of uninjured tendon. In this study, cadaveric equine tendon was processed using two variations of a previously published physico-chemical method of allograft processing. The resultant biomaterials were then implanted into the FDS tendons of eight normal horses. Sham operated and autograft implanted tendons served as controls. All tendons were examined ultrasonographically every 2 weeks post operatively. After sacrifice at 12 weeks, tendon tissue was harvested and assessed grossly and histologically. In tendons receiving type-1 allografts, ultrasonographic cross-sectional area (CSA) was observed to increase at every time-point. The type-1 allografts remained well demarcated and surrounded by a hypoechoic zone of variable width. While remaining visible in situ, type-2 allografts exhibited incorporation into host tendon. CSA measurements for the type-2 allograft treated tendons stabilized by 6 weeks post-operatively. Histologically, type-1 allografts elicited a significantly larger width of reaction and greater amount of fibrosis. A predominantly lymphocytic infiltration was observed at the graft-host interface. The graft itself remained largely acellular. The width of reaction surrounding type-2 allografts was significantly less than that surrounding the type-1 allografts. Type-2 allografts were also infiltrated with small numbers of cells exhibiting tenocytic morphology.