ABSTRACT
<p>Objective：To investigate the lower limb skeletal muscle stiffness in healthy individuals.</p><p>Methods：Using ultrasonographic elastography, we measured the degree of stiffness of the rectus femoris and medial head of the gastrocnemius in healthy individuals and investigated the relationships between muscle stiffness and thickness, a quantitative measure of muscles, and between muscle stiffness and brightness, a qualitative measure of muscles. Furthermore, relationships between muscle stiffness and age, body weight, and body mass index (BMI) were also studied.</p><p>Results：Rectus femoris stiffness was positively correlated with muscle thickness. Rectus femoris stiffness had a weak negative correlation with muscle brightness and a weak positive correlation with body weight and BMI. Stiffness of the medial head of the gastrocnemius showed no correlation with any of the study variables. Muscle stiffness did not correlate with age in either of the muscles. No sex-related difference was found in the degree of muscle stiffness.</p><p>Conclusion：Although rectus femoris stiffness was associated with muscle thickness and brightness, these relationships were not observed for muscle stiffness of the medial head of the gastrocnemius. The data suggested that rectus femoris stiffness reflects the quantitative and qualitative states of the muscle, and the presence of such relationships may depend on the location of the muscle.</p>
ABSTRACT
Skeletal muscles are overstretched following limb lengthening procedures. Muscles can adapt to this lengthening by adding new sarcomeres in series. Recent developments in limb lengthening provide adult patients more opportunities to undergo limb lengthening procedures. The purpose of this study was to clarify the difference in muscle adaptation between adult and young groups using a rabbit model of limb lengthening. Five mature (10-43 month old) and 6 immature (3-4 month old) white rabbits underwent tibial osteotomy. After a 1-week lag phase, tibial lengthening was applied at a rate of 1.4 mm/day for 2 weeks. Animals were euthanized after the completion of lengthening. Both hindlimbs were immersed in buffered formalin with the ankle and knee at a right angle. Muscle belly length, muscle fiber bundle length and sarcomere length were measured, and sarcomere number and internal tendon length were calculated in five representative muscles around the lengthened segment. Muscle belly length increased in all the lengthened muscles compared with the corresponding contralateral muscles regardless the group. Aponeurosis length increased significantly in one muscle for the adult group and three muscles for the young group. Sarcomere length tended to be longer or was significantly longer in the lengthened muscles. Serial sarcomere number significantly increased in 3 lengthened muscles in the adult group with a more conspicuous increase in the amount, while this occurred in 2 muscles in the young group with only a tiny increase. The predominant processes of skeletal muscle adaptation to the limb lengthening are sarcomere number addition in muscle fibers for the adult group and elongation of internal tendon for the young group.
ABSTRACT
Skeletal muscle is known to be set at an over-stretched length in clinical tendon transfer. Such chronic stretching of skeletal muscle increases the serial sarcomere number required for muscle adaptation. Passive tension of the muscle must be affected during the adaptation. Thus, the objective of this study was to clarify the origin of increased passive tension after stretched tendon transfer in an animal model. The distal tendon of the extensor digitorum of the second toe was transposed to the extensor retinaculum at 3.7 mm of muscle sarcomere length. The contralateral muscle served as control. Muscle passive length-tension curves were measured at 1 week and 4 weeks after the transfer to the bilateral muscles. After functional measurements were taken, the muscles were dissected into fiber bundles and single muscle fibers to measure their passive mechanical properties with a micro force transducer. Passive tension was increased in the transferred muscle with a steeper inclination and leftward shift of muscle length-tension curve. Elastic modulus of the transferred fiber bundle increased at both time points, while those of the transferred single fibers increased only at 1 week. Results of the study suggest that the transferred muscle increased passive tension mainly due to proliferation of extracellular connective tissue within the muscle. Increased passive tension was a characteristic feature for the transferred muscle, which may ultimately represent a target for therapeutic intervention to optimize muscle function.