To evaluate the potential of quantitative ultrasound (QUS) and electrical impedance myography (EIM) to assess subtle disuse atrophy (DA).

DA accompanies many neurological conditions. However, technologies to assess DA are limited. One very common non-neurological cause of DA that can serve as an excellent testing ground for assessing technologies potentially sensitive to DA is rotator cuff injury. Magnetic resonance imaging (MRI) has been used for this purpose, but is generally only useful in severe rotator cuff tears when fatty muscle atrophy is present. Here we sought to evaluate the potential value of two alternative technologies, QUS and EIM, since they are easily applied, convenient, and cost-effective.

Twenty-six patients (9 men and 17 women, median age 54 years) were identified in the orthopedic clinic with unilateral shoulder pathology, ranging from mild tendonitis to full thickness rotator cuff tears. Patients underwent bilateral multifrequency EIM measurements and QUS imaging of supraspinatus, infraspinatus, teres minor, and deltoid (a non-rotator cuff muscle). In addition, standard questionnaires were given. Recent MRIs were also reviewed. Paired analyses were utilized to compare the two sides in each individual.

There were no adverse events and all participants tolerated both procedures well. Whereas several patients showed asymmetries between the two sides in specific muscles, no significant difference was observed across the entire group of subjects for basic QUS and EIM measures (average echointensity and 50 kHz impedance values, respectively). However, in patients who did have MRIs completed, the muscles generally appeared entirely normal.

This study supports that QUS and EIM are easily performed and well-tolerated in this group of orthopedic patients. Further study of these technologies, including more advanced metrics, such as multifrequency EIM values and ultrasound elastographic or texture parameters, may be needed to identify subtle DA.