Autogenous flexor tendon grafts: fibroblast activity and matrix remodeling in dogs

To investigate rates of cellular proliferation and matrix turnover in autogenous flexor tendon grafts, hindlimb intrasynovial (flexor digitorum profundus) and extrasynovial (peroneus longus) tendons were placed within the synovial sheaths of the medial and lateral forepaw digits of 18 dogs and treated with controlled early passive motion. After the dogs had been killed, short-term culture and labeling in vitro were utilized to determine rates of DNA, proteoglycan, collagen, and noncollagen protein synthesis. Schiff base covalent collagen crosslink concentrations and total collagen and protein content also were evaluated at intervals through 6 weeks. Tendon grafts of extrasynovial origin showed greater rates of DNA synthesis and significantly elevated levels of proteoglycan, collagen, and noncollagen protein synthesis and Schiff base covalent collagen crosslink concentrations (dihydroxylysinonorleucine) compared with intrasynovial tendon grafts. It was not clear to what extent the increased activity in the extrasynovial graft was due to actual differences between the intrasynovial and extrasynovial tendons or to the responses of the connective tissue surrounding the extrasynovial tendon graft. Since both types of grafts demonstrated similar unaltered levels of collagen and protein content over time, these data suggest greater rates of matrix turnover in tendon grafts of extrasynovial origin than in those of intrasynovial origin. Coupled with previous findings showing increased cellular proliferation in extrasynovial tendon grafts, these data indicate that the process of translation to an intrasynovial environment necessitates a more active process of soft-tissue repair and remodeling when extrasynovial donor tendons are used.