Morphological changes in continuously stretched skeletal muscles in sheep

Abstract

The effects of continuous elongation of skeletal muscles were studied on six sheep who underwent a lengthening osteotomy of the right tibia. Open muscle biopsies were taken from the biceps femoris muscle preoperatively (Group A), after 5 weeks of bone distraction (Group B) and after another 5 weeks without further distraction (Group C). The size and distribution of type 1 (slow-twitch) and type 2 (fast-twitch) muscle fibres were determined from sections stained for myofibrillar ATPase activity. All sections were also evaluated by light microscopy, especially with regard to myopathic changes. The type 2 fibres showed a significant decrease in size from group A to B and from group B to C. The reduction in fibre size from group A to C was 44.2%. The type 1 fibres, on the other hand, showed no significant differences in mean fibre size between the groups. However, there were considerable individual variations in type 1 fibre size between the groups. The distribution of both fibre types was similar in groups A and B (appr. 17% type 1 fibres) whereas the relative number of type 1 fibres was reduced to 12.4% in group C (P less than 0.01). Myopathic changes, i.e. muscle fibre necroses, were not seen in any of the groups. It is concluded that the type 2 fibre atrophy is mainly caused by muscular inactivity during the postoperative period, but an additional effect of continuous stretching of the muscle cannot be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)

Thigh muscle atrophy after femoral shortening

“…Furthermore, it has been demonstrated that lengthening osteotomy might lead to a reduction in the muscle fiber cross-sectional area of Type 2 fibers, but not of Type 1 fibers (Lindboe et al 1985). Our findings are, however, in contrast to those published by Lindboe et al (1985) who showed that a 10-20 percent lengthening osteotomy led to a 44 percent reduction in Type 2 fiber area. These differences may be explained by different experimental conditions.…”

“…The degree of shorteninaengthening in our experiment was similiar to that applied in previous experimental studies on limb lengthening by external distraction of the growing bone (Lindboe et al 1985) and in clinical practice in many cases.…”

“…It has been suggested that lengthening procedures may cause unphysiological stretching of skeletal muscles (Lindboe et al 1985). Furthermore, it has been demonstrated that lengthening osteotomy might lead to a reduction in the muscle fiber cross-sectional area of Type 2 fibers, but not of Type 1 fibers (Lindboe et al 1985).…”

Effect of tibial lengthening on the gastrocnemius muscle: A histopathologic and morphometric study in rabbits

“…On the other hand, Lindboe et al (1985) reported that, during 10-20 percent bone lengthening, the Type 11 fibers decreased in size, but the Type I fibers did not change in size. They suggested that atrophy of the Type 11 fibers was mainly caused by muscular inactivity during the postoperative period, but an additional effect of continuous stretching of the muscle cannot be excluded.…”

Bilaterally increased VEGF‐levels in muscles during experimental unilateral callus distraction

“…After long-term denervation, VEGF is still provable in muscles but significantly reduced [6]. Thus muscle atrophy at the distracted side might also be a factor responsible for the relatively high VEGF mRNA levels at the nondistracted side [13, 33,35].…”