Response of rabbit skeletal muscle to tibial lengthening.

Background: Experimental and clinical studies have provided knowledge regarding osteogenesis during limb lengthening. However, response of skeletal muscle to limb lengthening is not fully understood, especially as concerns histogenesis. We studied the morphological response of rabbit skeletal muscle to limb lengthening. In this study, we investigated proliferation of satellite cells, responsible for generation of new myonuclei, during limb lengthening.

Methods: Tibialis anterior muscles of young and adult rabbits were subjected to lengthening at a rate of 0.5 mm twice per day for 20 days. After lengthening, muscle wet weight was measured to assess skeletal muscle growth, then proliferating cell nuclear antigen was measured. Immunostaining was performed to analyze proliferating cells in the proximal, middle, and distal portions of the muscle belly and the musculotendinous junction.

Results: Muscle wet weight increased significantly after lengthening both in adult (0.4 g) and young (0.1 g) rabbits. Satellite cells showed proliferation in response to lengthening. In adult rabbits, satellite cell proliferation increased along the entire lengthened muscle to a similar degree (from 7.1% in the middle portion to 8.6% in the musculotendinous junction). In young rabbits, proliferation was greater in the musculotendinous junction (4.8%) than that in other muscle portions (2.3% in the middle and distal portions, and 2.4% in the proximal portion). In adult rabbits, the rate of increase in satellite cell proliferation was 1780% in the middle portion to 2860% in the musculotendinous junction, whereas the rate was between 210% in the middle portion and 290% in the distal portion in young rabbit. The rate of increase in cell proliferation by lengthening was higher in adult muscle than that in young muscles as well as satellite cell proliferation.

Conclusion: These findings indicate that limb lengthening promotes muscle growth in both young and adult rabbits.