Influences of flexor sheath continuity and early motion on tendon healing in dogs

The healing response of flexor tendons treated with either sheath reconstruction or sheath excision, and early passive motion rehabilitation was investigated in a canine model. Flexor sheath repair, sheath excision, and autogenous sheath grafting were compared for biomechanical characteristics, and biochemical and ultrastructural alterations at the repair site at intervals over a 12-week period. No significant differences could be found in tendons treated with either sheath repair or sheath excision by biomechanical, biochemical, or morphologic assessments. Although ultimate load and linear slope values increased significantly in both groups at each interval (p < 0.05 for each comparison), there were no significant differences in angular rotation of the distal interphalangeal joint over time. Biochemical findings showed high levels of reducible Schiffbase crosslinks through 12 weeks, indicating a repair process undergoing active remodeling. Ultrastructural studies showed active fibrinogenesis and early evidence of longitudinal alignment of collagen fibrils in the extracellular matrix. In the sheath graft group, strength characteristics did not increase over time, and there was a high degree of disorganization of collagen fibril orientation. These findings demonstrate that reconstruction of the tendon sheath, either by suture or autogenous graft, does not improve significantly the biomechanical, biochemical, or morphologic characteristics of repaired tendons treated with early motion rehabilitation.