THE INFLUENCE OF IMMOBILIZATION VERSUS EXERCISE ON SCAR FORMATION IN THE RABBIT PATELLAR TENDON AFTER EXCISION OF THE CENTRAL 3RD

There is much discussion about the appropriate timing and intensity of rehabilitation after reconstruction of the anterior cruciate ligament with a patellar tendon autograft. The purpose of this study was to lo ok at two extremes (complete immobilization and vigorous, forced exerc ise) on the extent of scar formation and mechanical properties of the host tendon. Three groups of six Flemish Giant rabbits had the central third patellar tendon removed in one limb. Group I was sacrificed imm ediately after surgery. Group II was exercised on a treadmill for 12 w eeks. In Group III the limb was immobilized for 12 weeks. After 3 mont hs, average length and cross-sectional area from Group II were greater than those of the controls and Group III tendons. Structural properti es of all test limbs were similar to each other but different from con trols. Tensile modulus of Group III tendons did not decrease as much t hat of Group II tendons. Histology revealed a clear demarcation betwee n the central defect and host tendon in Group III, whereas Group II te ndons remodeled throughout their cross-sections. We propose that early joint mobility produces large multiaxial stresses in original tendon leading to microdamages and repair processes within the entire host ti ssue. Less aggressive exercise or delay in joint mobility may help con trol tissue remodeling.