Motion quality in rotator cuff tear using an inertial measurement unit: new parameters for dynamic motion assessment

Purpose: This study aimed to (1) figure out the difference in motion smoothness between a nonpathologic shoulder and the other with a rotator cuff tear by measuring the angular velocity using an inertial measurement unit (IMU) sensor and (2) propose the parameters to describe the difference because there is no literature on this topic. Material and Methods: We enrolled patients with rotator cuff disease diagnosed by magnetic resonance imaging. The intact shoulder of participants was compared with the shoulder with rotator cuff tear by using IMU on the basis of the parameters that establish motion smoothness: the number of peaks, the peak velocity-to-mean velocity ratio (PV/MV), and the number of sign reversals. In addition, subgroup analysis was performed with respect to tear size (small to medium vs. large to massive). In addition, correlations with the American Shoulder and Elbow Surgeons score and symptom duration (months) were evaluated. Results: Among 24 patients (15 males, 9 females), all 3 parameters for the motion quality of patients with a rotator cuff tear exhibited significant difference. The parameters showed a significant difference between the small to medium tear group and the large to massive tear group. A negative correlation was found between symptom duration and parameters of motion quality, except for PV/MV. Conclusions: Motion quality assessment using IMU showed a marked difference in the shoulder with a rotator cuff tear compared with the intact shoulder. Hence, IMU-based parameters for dynamic motion quality could be considered as an option for assessing the function of the shoulder. (C) 2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.