Kannus, P., Jozsa, L., Kvist, M., Lehto, M. & Järvinen, M. 1992. The effect of immobilization on myotendinous junction: an ultrastructural, histochemical and immunohistochemical study. Acta Physiol Scand144, 387–394. Received 28 April 1991, accepted 13 October 1991. ISSN 0001–6772. Tampere Research Station of Sports Medicine, UKK-Institute, and Department of Surgery, Tampere University Central Hospital, Tampere, Finland; Department of Morphology, National Institute of Traumatology, Budapest, Hungary; and Sports Medical Research Unit, Paavo Nurmi Center, University of Turku, Turku, Finland.
The effect of immobilization on the myotendinous junction of the calf muscles in the rat was studied histochemically, immunohistochemically and morphometrically with a transmission electron microscope.
After 3 weeks of immobilization, the contact area between the muscle cells and tendineal collagen fibres was reduced by almost 50% in both type I (slow-twitch) and type II (fast-twitch) muscle fibres. The terminal finger-like processes of the muscle cells became shallow and cylindrical or were completely atrophied. Their basal membranes were slightly thickened. Histochemically, the most remarkable alteration in the myotendinous junction was the marked decrease in the sulphate containing glyco-saminoglycans. In the basal lamina of the muscle fibres, the glycosaminoglycan and proteoglycan content was also reduced. Immunohistochemical analyses revealed that the amount of type III collagen was markedly increased on the myotendinous interface, but the amount and distribution of type I collagen was not affected by immobilization.
These findings suggest that immobilization causes degenerative changes at the myotendinous junction, which, in turn, most likely decrease its tensile strength and may predispose it to rupture during activity.