Office-based elastographic technique for quantifying mechanical properties of skeletal muscle.

OBJECTIVES Our objectives were to develop a new, efficient, and easy-to-administer approach to ultrasound elastography and assess its ability to provide quantitative characterization of viscoelastic properties of skeletal muscle in an outpatient clinical environment. We sought to show its validity and clinical utility in assessing myofascial trigger points, which are associated with myofascial pain syndrome. METHODS Ultrasound imaging was performed while the muscle was externally vibrated at frequencies in the range of 60 to 200 Hz using a handheld vibrator. The spatial gradient of the vibration phase yielded the shear wave speed, which is related to the viscoelastic properties of tissue. The method was validated using a calibrated experimental phantom, the biceps brachii muscle in healthy volunteers (n = 6), and the upper trapezius muscle in symptomatic patients with axial neck pain (n = 13) and asymptomatic (pain-free) control participants (n = 9). RESULTS Using the experimental phantom, our method was able to quantitatively measure the shear moduli with error rates of less than 20%. The mean shear modulus ± SD in the normal biceps brachii measured 12.5 ± 3.4 kPa, within the range of published values using more sophisticated methods. Shear wave speeds in active myofascial trigger points and the surrounding muscle tissue were significantly higher than those in normal tissue at high frequency excitations (>100 Hz; P < .05). CONCLUSIONS Off-the-shelf office-based equipment can be used to quantitatively characterize skeletal muscle viscoelastic properties with estimates comparable to those using more sophisticated methods. Our preliminary results using this method indicate that patients with spontaneous neck pain and symptomatic myofascial trigger points have increased tissue heterogeneity at the trigger point site and the surrounding muscle tissue.