Diagnosing Muscle Atrophy by Use of a Comprehensive Method of Assessing the Elastic Properties of Muscle During Passive Stretching

OBJECTIVE. The purpose of this study was to apply a new method for quantitatively assessing atrophied muscles by use of sonoelastography. SUBJECTS AND METHODS. B-mode sonography and shear-wave elastography of the gastrocnemius muscle (GM) were performed on 12 patients and 32 healthy control volunteers during passive stretching induced by ankle rotation from 40° plantar flexion to 30° dorsiflexion. The GM length and corresponding elastic moduli were measured consecutively per frame. The elastic modulus-length curve was created by plotting the elastic modulus against the GM length during passive stretching. Three physiologically significant parameters-slack elasticity modulus (E0), slack length (l0), and passive elastic coefficient (k)-were estimated from the measured elasticity modulus-length curve to quantify the elastic properties of the GM. RESULTS. All results showed a smooth exponential curve. In the state of relaxation, atrophied GM was softer than GM of healthy control subjects. However, when the muscles were passively stretched from a state of slack to tension, k was significantly greater for the patients with atrophied GMs than for the control subjects. Furthermore, the diagnostic accuracy of k for muscle atrophy was greater than that of E0. CONCLUSION. Increased elastic stiffness may be considered a positive finding for the characterization of muscle atrophy. Because of its high diagnostic accuracy and reproducibility, the elastic modulus-length curve can provide new insights into the diagnosis of muscle disease and allows monitoring of muscle function in rehabilitation.