COMPARISON OF SURGICALLY ATTACHED AND NON-ATTACHED REPAIR OF THE RAT ACHILLES-TENDON BONE INTERFACE - CELLULAR-ORGANIZATION AND TYPE-X COLLAGEN EXPRESSION

The effects of surgical repair versus non-repair on cell morphology an d type X collagen expression were investigated using a rat model of Ac hilles tendon avulsion. The animals mere divided into four groups. In Group I, tendon was reattached to the original attachment site by sutu ring through a drill hole in the calcaneus; in Group II, tendon was no t reattached and a drill hole was not made; in Group III, tendon was n ot reattached but a drill hole was made; and the animals in Group IV w ere sham operated. In Group I (tendon reattached), at 2 weeks postoper atively, many hypertrophic chondrocytes appeared at the reattachment s ite adjacent to bone and type X collagen was detected immunologically both in the cells and in the extracellular matrix. After 4 weeks, the cells at the original site of attachment were arranged in rows along t he newly formed tendon fibers and were stained with type X collagen an tibody. By contrast, when tendon was not reattached (Groups II and III ), a gap between the original attachment site and the tendon stump was observed through the entire postoperative period. At 8 weeks, the ori ginal attachment site was covered by fibrocartilaginous tissue and ten don became attached to the calcaneal fibrocartilage area, which is pro ximal to the original attachment site. Type X collagen was detected in the cells which were adjacent to bone. In Group IV (sham operation), there were no changes in histology or type X collagen distribution, ei ther at the attachment site or in tendon and bone, compared with the n on-operated control rats. These results suggest that surgical reattach ment of tendon to the original site is important to help reorganize ce lls during the repair process. Type X collagen was identified immunohi stochemically in the cells adjacent to bone in all the groups, suggest ing that it may play a role in maintaining distinct areas of calcified and non-calcified fibrocartilage.