Unfavorable effect of knee immobilization on Achilles tendon healing in rabbits.

This study was undertaken to assess the effect of knee immobilization on the treatment of Achilles tendon rupture. After their Achilles tendons were severed, rabbits were divided into 2 groups. In Group A, only the ankle joint was immobilized. In Group B, both the knee and ankle joints were immobilized. At 4 weeks after surgery, both the ultimate tensile force and stiffness of the severed tendons were significantly greater in Group A than in Group B. In Group A, dense collagen fibers were seen in the repaired tendons, and the bundles of collagen fibers were parallel to one another along the axis of the tendons. In contrast, in Group B, dilated veins and capillaries were seen in the repaired tendons, and the proliferation of connective tissue containing collagen fibers was severely reduced around these veins and capillaries and was in general irregular and uneven. These results suggest that knee immobilization retards the healing of a ruptured Achilles tendon without suture, due to congestion and tension deprivation produced by keeping the tendon static.