Morphological and histochemical analysis of a case of superficial digital flexor tendon injury in the horse.

This report compares the morphology and the concentrations of glycos-aminoglycans (GAGs) in an injured superficial digital flexor tendon (SDFT) of a horse with those of a normal tendon. An injured 6-year-old male Thoroughbred exhibited heat and swelling around the SDFT of the right forelimb. On histopathological examination, exuberant granulation was observed in the affected tendon, with activated tenocytes, angiogenesis, haemorrhage, and infiltration of small numbers of leucocytes. The collagen fibres were loosely packed and irregularly arranged. The diameter of control collagen fibrils was 20-360 nm and that of affected collagen fibrils 20-240 nm. In the analysis of GAGs in the matrix, hyaluronic acid (HA), dermatan sulphate (DS), and chondroitin sulphate (CS) were found to be major components in both control and affected tendons. Increases in DS in the affected tendon were striking. Our observations suggest that fibrillogenesis was activated by increases in DS and decreases in HA and CS. It is also assumed that absence of collagen fibrils of normal thickness and in a parallel arrangement reflected the morphological and biochemical characteristics of fibrillogenesis in the injured tendon. If the inflammatory features of an injured tendon could be altered, it might return eventually to its normal structure. Copyright 1999 W.B. Saunders Company Ltd.