EFFECTS OF IMMOBILIZATION ON ACHILLES-TENDON HEALING IN A RAT MODEL

The aim of this study was to evaluate the effects of immobilization an d mobilization on the functional and biomechanical recovery of injured Achilles tendons. Male Sprague-Dawley rats were allocated randomly in to four groups: (a) sham operation, (b) division only (surgical transe ction of the Achilles tendon without immobilization), (c) ''dummy'' ex ternal fixation (division of the Achilles tendon and application of Ki rschner wires), and (d) rigid external fixation (division of the Achil les tendon and immobilization with Kirschner wires connected by two tr iangular frames). All procedures were performed on the right lower lim b; the left, uninjured, lower limb served as an internal control. Kirs chner wires and external fixators were removed on day 12. Functional p erformance was determined from measurements of hind pawprints of rats walking preoperatively and on postoperative days 1, 3, 5, 7, 9, 11, 13 , and 15. On day 15, the animals were killed and biomechanical evaluat ions were performed on both the injured and the uninjured Achilles ten don constructs. No functional or mechanical deficits were observed in the sham-operation group. Animals subjected to division of the Achille s tendon had an initial functional deficit that returned to near norma l by day 15. The application of Kirschner wires was associated with an impairment of the functional performance of the rat as well as of the mechanical properties of the tendon-bone constructs. Immobilization b y connection of the Kirschner wires to an external frame had an additi onal, highly significant (p < 0.001) detrimental effect on the functio nal and mechanical recovery of Achilles tendon-calcaneal complexes.