Morphometric analysis of canine skeletal muscles following experimental callus distraction according to the Ilizarov method

Muscle fiber diameter and fiber-type distribution were analyzed during call us distraction. The right tibia in 24 beagles was lengthened 2.5 cm by call us distraction after osteotomy and application of a ring fixator. Distracti on was started at the fifth postoperative day, at a rate of two times for 0 .5 mm per day. Twelve dogs that underwent limb-lengthening and three dogs i n the control group that did not undergo limb-lengthening were killed at th e end of the 25-day distraction phase (group A). The remaining dogs (12 tha t underwent limb-lengthening and three that did not) were killed after an a dditional consolidation period of 25 days (group B). The tibialis anterior, extensor digitorum longus, peroneus longus, and gastrocnemius muscles were removed from the right limb (which had undergone distraction) and the left control side of each animal. Crosscut cryostat sections were stained by ad enosine triphosphatase at pH 4.3 and 9.4 to determine the size and distribu tion of types I and II fibers. Morphometric analysis of the muscle fibers w as performed by a computer-assisted two-point technique. On the lengthened side, the muscles revealed marked atrophy affecting predominantly type-II f iber in the dogs in group A and affecting both fiber types in dogs in group B. Fiber density increased in both groups. In addition, fiber-type groupin g indicative of reinnervation was obvious in group B. Fiber-type distributi on in the dogs in group B showed a shift toward type I in the tibialis ante rior (p = 0.033) and extensor digitorum longus (p = 0.034) muscles and a sh ift toward type II in the gastrocnemius (p = 0.038). The data show that ten sion-stress during tibial lengthening leads to atrophy of type-II fiber, re flecting disuse of muscle fiber in the distraction period as well as neurog enic atrophy followed by the reinnervation processes. Furthermore, the data are consistent with the occurrence of histoneogenesis during limb-lengthen ing resulting in an increase in fiber density.