Extensor tendon repair: an animal model which allows immediate post-operative mobilisation

In adult rabbits, an experimentally transected digital extensor tendon was repaired. The technique employed a tongue, created from the proximal tendon, folded over to bridge the transection and reattached distally. Animals were allowed immediate post-operative mobilisation. Tendon material, 14-120 days post-operatively, was examined ultrastructurally in control and experimental animals from four different zones within the repaired tendon. The operation was well tolerated and adhesion free. Associated with the repair, two types of collagen fibril populations were observed. Firstly, in areas where tendon tissue had been removed, there was a population of fibrils with a narrow range of diameters. Secondly, in areas where tendon tissue was subjected to an increased level of stress per unit cross-sectional area, a population of fibrils with a range of diameters similar to that of controls but with a marked increase in the percentage of small diameter fibrils. The relevance of these observations to human tendon repair is discussed.