Validity and Reliability of Wearable Motion Sensors for Clinical Assessment of Shoulder Function in Brachial Plexus Birth Injury

Abstract

The modified Mallet scale (MMS) is commonly used to grade shoulder function in brachial plexus birth injury (BPBI) but has limited sensitivity and cannot grade scapulothoracic and glenohumeral mobility. This study aims to evaluate if the addition of a wearable inertial movement unit (IMU) system could improve clinical assessment based on MMS. The system validity was analyzed with simultaneous measurements with the IMU system and an optical camera system in three asymptomatic individuals. Test–retest and interrater reliability were analyzed in nine asymptomatic individuals and six BPBI patients. IMUs were placed on the upper arm, forearm, scapula, and thorax. Peak angles, range of motion, and average joint angular speed in the shoulder, scapulothoracic, glenohumeral, and elbow joints were analyzed during mobility assessments and MMS tasks. In the validity tests, clusters of reflective markers were placed on the sensors. The validity was high with an error standard deviation below 3.6°. Intraclass correlation coefficients showed that 90.3% of the 69 outcome scores showed good-to-excellent test–retest reliability, and 41% of the scores gave significant differences between BPBI patients and controls with good-to-excellent test–retest reliability. The interrater reliability was moderate to excellent, implying that standardization is important if the patient is followed-up longitudinally.

Monitoring Scapular Kinematics through Wearable Magneto-Inertial Measurement Units: State of the Art and New Frontiers

“…Details of the selected papers are summarized in Table 1 and Table 2 . Only studies reporting quantitative results on scapular kinematics are included in Table 2 [ 36 , 37 , 38 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ].…”

“…Of the included studies, ten articles used from three to five M-IMUs for unilateral upper limb monitoring [ 36 , 41 , 42 , 43 , 44 , 45 , 46 , 49 , 50 ], while only four authors used from five to seven for bilateral monitoring [ 37 , 38 , 47 , 48 ].…”

“…Moreover, in the study of Höglund et al, two different positioning techniques to track upper limb motion were evaluated and compared: a total of four M-IMUs were placed centred on the lateral and dorsal distal end of both the upper arm and forearm [ 20 ]. In all the reviewed articles, the thorax sensor was placed on the chest under the jugular notch [ 35 , 36 , 37 , 38 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]. Its role was crucial because data from scapular M-IMUs are used for tracking rotational and translational movements of the scapula with respect to the thorax M-IMUs [ 17 , 51 ].…”

“…In the literature, two different positioning techniques were described for scapular M-IMUs ( Figure 2 ). The most common M-IMU positioning to track 3D scapular kinematics was to align the x-axis of the sensor with the cranial edge of the scapular spine [ 35 , 36 , 38 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ]. In particular, the scapula M-IMU was placed over the central third between the angulus acromialis (AA) and the trigonum spinae (TS) by palpating the scapular spine from the most lateral part of the acromion to the most medial aspect of the scapula [ 35 , 36 , 38 , 42 , 43 , 44 , 45 , 46 , 47 , 49 ].…”

“…Moreover, among WS, M-IMUs are commonly used for tracking scapular kinematics [ 17 , 35 , 36 , 37 , 38 ]. M-IMUs incorporate 3D accelerometers, gyroscopes, and magnetometers to provide 3D orientation [ 3 , 17 , 39 ].…”