Diverse muscle architecture adaptations in a rabbit tibial lengthening model.

BACKGROUND during limb lengthening, muscles are thought to increase the number of sarcomeres. However, this adaptation may differ among muscles with diverse architecture. PURPOSE this study wish to clarify the differences in muscle adaptation in a rabbit model of tibial lengthening. METHODS twelve rabbits underwent tibial lengthening (0.7 mm/day for 4 weeks), with the contralateral limb serving as a control, and were euthanized after either the lengthening or the consolidation period. Six muscles around the tibia were investigated in terms of muscle belly length, muscle weight, sarcomere length and serial sarcomere number. RESULTS muscle belly length increased in all the lengthened muscles. No increases in muscle mass were noted. Sarcomere length increased in the ankle plantar-flexors and was kept longer than the optimal sarcomere length after the consolidation period. Nevertheless, significant increases in sarcomere number were observed in two ankle plantar-flexors. CONCLUSION this study demonstrated that muscle belly length largely adapted to the lengthening. The increase in sarcomere number did not match the increase in muscle belly length. We estimated that elongation of the intramuscular aponeuroses is another mechanism of the adaptation in addition to the increase in sarcomere number.