ULTRASTRUCTURAL STUDIES ON MYOFIBRILLOGENESIS AND NEOGENESIS OF SKELETAL-MUSCLES AFTER PROLONGED TRACTION IN RABBITS

Little is known about the morphological response of muscle after long term traction. The purpose of this study was to investigate the morpho logical changes of skeletal muscle during limb lengthening. After appl ication of mini-extraskeletal fixator, the hindlimb of New Zealand whi te rabbit was osteotomized and then slowly lengthened at the rate of 1 mm/day up to a 20 mm gain in length. The muscles of hindlimbs were pe rfused and dissected. Morphological studies were performed at electron microscopic level. Transmission electron microscopy revealed foci of microtrauma at the myotendinous junction. The distance between the mus cle fibers and tendon parenchyma increased, with numerous primitive me senchyme-like cells interposed within this gap. The cytoplasmic space of these cells was devoid of myofibril formation at the ends of stretc hed fibers. Within the satellite near the myotendinous junction myofil ament production was observed in various gradations of maturation. It is concluded that myofibrillogenesis with traction neogenesis of skele tal muscle during limb lengthening does exist and occurs mainly near t he myotendinous junction. The myotendinous junction in mature skeletal muscle actively participated in the process of limb lengthening.