Accuracy and reliability of inertial measurement units to estimate shoulder joint kinematics for clinical application: a systematic review

Inertial measurement units (IMUs) are low-cost, wearable sensors that can estimate body segment orientation by tracking relative sensor orientations. This review aimed to synthesize and evaluate studies investigating the accuracy and reliability of IMUs in measuring shoulder kinematics for clinical application in patients with musculoskeletal injuries. Shoulder kinematics were chosen due to their importance in assessing upper extremity function, performing overhead activities, and the increasing demand for objective, accessible motion-tracking tools in clinical settings. Studies within PubMed/MEDLINE, Scopus, Cochrane Central Register of Controlled Trials, IEEE Xplore, and Google Scholar were screened for eligibility. They were selected based on the following inclusion criteria: (1) application of inertial sensors to assess motions, (2) sensors used accelerometers and gyroscopes or similarly functioning technologies, (3) sensors applied to shoulders, (4) studies published from 2011 to 2024, (5) studies written in English, (6) studies found in peer reviewed, original research articles, (7) studies with full text available. Of 1900 articles identified in our initial literature search, 49 were included. Articles were excluded based on these criteria: (1) Reviews, systematic reviews, or meta-analyses, (2) Studies without ethical approval, (3) Animal or cadaveric studies, (4) Studies prior to 2011. A data extraction was included with key findings of each article. The Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) quality assessment tool was used to assess each article's risk of bias. We compared outcome metrics across studies quantifying IMU accuracy and reliability, including root mean square error (RMSE) and intraclass correlation coefficient (ICC), respectively. IMU-based shoulder kinematics exhibited a wide-range of RMSEs (<1° - 12°) and ICCs (0.32 - 0.98) depending on the motion and number of sensors used. Overall, there was a tolerable RMSE (between 5-10°; mean = 7.10 ± 3.97) and good ICC (>0.75; mean = 0.810 ± 0.145) across studies for 6.77 IMUs on average. The goal of this review was to assess the current IMU use in upper extremities, identify factors preventing clinical use, and inform future research. More IMU-based clinical studies are needed to understand shoulder pathology motor deficits. Additional validation studies are needed to demonstrate IMU efficacy when paired with other technologies.