The effect of variations in applied rehabilitation force on collagen concentration and maturation at the intrasynovial flexor tendon repair site

The biochemical means by which accelerated rehabilitation alters intrasynov ial flexor tendon repair site collagen synthesis and extracellular matrix m aturation are not fully understood. We hypothesized that an increased level of applied rehabilitative force in a clinically relevant animal model woul d hasten the maturation of the repair site extracellular matrix as demonstr ated by total collagen and collagen cross-link assessment. Twenty-eight fle xor digitorum profundus tendons from 14 adult dogs were transected and repa ired. The animals received either low- or high-force rehabilitation and wer e killed 10, 21, and 42 days after surgery. A 10-mm segment of tendon surro unding the repair site was obtained. Biochemical analysis showed that total collagen concentration was significantly reduced at each time point, that the reducible cross-link ratio of dihydroxylysinonorleucine to hydroxylysin onorleucine was significantly increased at each time point, and that the no nreducible pyridinoline cross-link content was significantly decreased at 1 0 days in both rehabilitative groups. Total collagen content did not vary t o a statistically significant degree with either time or as a function of r ehabilitation type. Based on these findings several clinically relevant obs ervations can be made. Increasing collagen concentration and repair site ma turation do not explain the previously demonstrated increased tensile prope rties of tendon that occur between 3 and 6 weeks after repair. Higher force rehabilitation does not alter the biochemical composition of the healing t endon through 6 weeks. Coupled with other recent data these findings sugges t that high-force rehabilitation does not stimulate accelerated healing aft er intrasynovial flexor tendon repair. Copyright (C) 2001 by the American S ociety for Surgery of the Hand.