The isolated evaluation of changes in muscle following immobilization and disuse is a challenge in living subjects. The purpose of this study was to determine whether magnetic resonance elastography is capable of detecting these changes.
An animal model was created to produce a mild joint contracture following 42 days of one forelimb immobilization in a maximally flexed position with twice-daily passive exercise. Eight pairs of dog forelimbs were harvested. Magnetic resonance elastography scans were performed on the experimental limb in an extended elbow position with a torque of 0.6 Nm. Scans of the contralateral limb were performed in two conditions, position matching and torque matching. Furthermore, wet weight, cross sectional area, resting muscle length, and range of elbow joint motion were measured.
The muscle from the experimental limb showed significant reduction in muscle mass, cross sectional area, slack length, and range of elbow motion. When comparing limbs in position matching condition, the muscle lengths were similar, and the experimental muscle had a significantly higher shear modulus (79.1 (SD 12.0) kPa) than the contralateral muscle (31.9 (SD 24.4) kPa). When comparing limbs in torque matching conditions, the muscle strains were similar, and the experimental muscle had a significantly lower shear modulus than the contralateral muscle (113.0 (SD 24.8) kPa).
These findings suggest that following immobilization, magnetic resonance elastography has the potential to be used as a clinical tool to guide rehabilitation and as a research tool to study the loss of passive elastic components of muscle.