Healing of ligaments and tendons and the effects of hyaluronan. Morphological and biochemical studies in rabbits

Sammanfattning: The poor healing capacity of the anterior cruciate ligament and the development of postoperative adhesions, restricting tendon gliding, are two important clinical problems regarding different, although related, aspects of posttraumatic connective tissue reactions. The aim of this study was to gain more knowledge about the process of ligament and tendon healing at the cell and molecular levels and to investigate the effects of hyaluronan on the repair process. By using in situ hybridization techniques, we showed that the extrasynovial medial collateral ligament, which normally heals without any problem, expressed more procollagen mRNA than the intrasynovial anterior cruciate ligament of the rabbit knee. In both ligaments the synthesis of collagen peaked 14 days after the laceration. An injection of hyaluronan apparently increased the healing capacity of the anterior cruciate ligament at 4 and 12 weeks after surgery. Hyaluronan, added to cultured tendon segments, inhibited cell proliferation without affecting the synthesis of collagen, non-collagen proteins or proteoglycans. Combined in vivo and in vitro studies showed that proximal division of deep flexor tendons in rabbits caused a transient increase in cell proliferation and signs of matrix degradation, with a gradual decrease of tendon matrix components and tendon weight. The healing tendons and synovial sheaths differed in their ability to produce collagen and proliferate during repair. Hyaluronan, added between the repaired tendon and tendon sheath in vivo, did not affect cell proliferation or synthesis of matrix components in the healing tissues, measured in vitro 5-40 days after repair.