Elastography and tactile imaging for mechanical characterization of superficial muscles

Quantification of the mechanical properties of muscle is of significant clinical interest. Local changes in the mechanical properties of muscle are often associated with clinical symptoms. In particular, myofascial trigger points (MTrPs) are a very common, yet poorly understood and overlooked, cause of nonarticular musculoskeletal pain. MTrPs are localized, stiff, hyperirritable tender nodules, palpated in taut bands of skeletal muscle. Objective validated measures of the mechanical properties of MTrPs could potentially be a clinical outcome measure. We are investigating ultrasound shear wave elastography and tactile imaging as complementary objective methods to assess the mechanical properties of MTrPs. In an ongoing clinical study, we recruited 50 subjects (27 healthy controls and 23 with symptomatic chronic neck pain and active MTrPs). The upper trapezius muscles in these subjects were imaged using shear wave elastography using an external vibration source with varying frequency in the range [50–200] Hz to measure shear wave speed and dispersion in tissue, and tactile imaging using an array of pressure sensors allowing 3D reconstruction of mechanical structure of tissue. Preliminary analysis demonstrates that symptomatic muscle tissue in subjects with neck pain is mechanically more heterogeneous and stiffer compared to normal muscle in control subjects (p < 0.05).