Abstract
BackgroundMuscle atrophy caused by immobilization in the shortened position is characterized by a decrease in the size or cross-sectional area (CSA) of myofibers and decreased muscle length. Few studies have addressed the relationship between limitation of the range of motion (ROM) and the changes in CSA specifically in biarticular muscles after atrophy because of immobilization. We aimed to determine the contribution of 2 distinct muscle groups, the biarticular muscles of the post thigh (PT) and those of the post leg (PL), to the limitation of ROM as well as changes in the myofiber CSAs after joint immobilization surgery.MethodsMale Wistar rats (n = 40) were randomly divided into experimental and control groups. In the experimental group, the left knee was surgically immobilized by external fixation for 1, 2, 4, 8, or 16 weeks (n = 5 each) and sham surgery was performed on the right knee. The rats in the control groups (n = 3 per time point) did not undergo surgery. After the indicated immobilization periods, myotomy of the PT or PL biarticular muscles was performed and the ROM was measured. The hamstrings and gastrocnemius muscles from the animals operated for 1 or 16 weeks were subjected to morphological analysis.ResultsIn immobilized knees, the relative contribution of the PT biarticular myogenic components to the total restriction reached 80% throughout the first 4 weeks and decreased thereafter. The relative contribution of the PL biarticular myogenic components remained <20% throughout the immobilization period. The ratio of the myofiber CSA of the immobilized to that of the sham-operated knees was significantly lower at 16 weeks after surgery than at 1 week after surgery only in the hamstrings.ConclusionsThe relative contribution of the PT and PL components to myogenic contracture did not significantly change during the experimental period. However, the ratio of hamstrings CSAs to the sham side was larger than the ratio of medial gastrocnemius CSAs to the sham side after complete atrophy because of immobilization.
Highlights
Muscle atrophy caused by immobilization in the shortened position is characterized by a decrease in the size or cross-sectional area (CSA) of myofibers and decreased muscle length
Calculation of the arthrogenic and the post thigh (PT) and post leg (PL) biarticular myogenic components of contracture We evaluated myogenic contracture caused by the biarticular muscles of the leg, including their tendons and fascia, and arthrogenic contracture caused by the articular structures; myogenic and arthrogenic contractures were calculated with the use of the range of motion (ROM) measurements in the methods prescribed by Trudel et al [11]
The myogenic contracture in the immobilized knees was significantly lower than the arthrogenic contracture at the 8- and 16-week time points (P < 0.01; Table 1)
Summary
Muscle atrophy caused by immobilization in the shortened position is characterized by a decrease in the size or cross-sectional area (CSA) of myofibers and decreased muscle length. Few studies have addressed the relationship between limitation of the range of motion (ROM) and the changes in CSA in biarticular muscles after atrophy because of immobilization. Muscle atrophy from immobilization in shortened position is characterized by loss of muscle mass [18] and decrease in the size or cross-sectional area (CSA) of myofibers [19,20] and muscle length [5]. Few studies have addressed the relationship between muscle limitation of ROM and the changes in CSA in biarticular muscles after atrophy because of immobilization
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