The influence of immobilization versus exercise on scar formation in the rabbit patellar tendon after excision of the central third.

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 look at two extremes (complete immobilization and vigorous, forced exercise) 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 immediately after surgery. Group II was exercised on a treadmill for 12 weeks. In Group III the limb was immobilized for 12 weeks. After 3 months, average length and cross-sectional area from Group II were greater than those of the controls and Group III tendons. Structural properties of all tests limbs were similar to each other but different from controls. Tensile modulus of Group III tendons did not decrease as much that of Group II tendons. Histology revealed a clear demarcation between the central defect and host tendon in Group III, whereas Group II tendons 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 tissue. Less aggressive exercise or delay in joint mobility may help control tissue remodeling.