Load-induced Glenohumeral Translation After Rotator Cuff Tears: Protocol of an In Vivo Study (Preprint)

BACKGROUND Rotator cuff tears are a common shoulder injury, yet they sometimes remain undiagnosed as symptoms can be limited. Altered shoulder biomechanics can lead to secondary damage and degeneration. In biomechanical analyses, the shoulder (i.e., the glenohumeral joint) is normally idealised as a ball and socket joint, even though a translation is often observed clinically. To date, no conclusive changes in glenohumeral translation have been reported in patients with rotator cuff tears, and it is unknown how an additional handheld weight comparable to those during daily activities will affect glenohumeral translations in patients with rotator cuff tears. OBJECTIVE This study aims to assess the load-induced glenohumeral translation (liTr) in patients with rotator cuff tears and its association with the load-induced changes in muscle activation (liMA). METHODS Patients and asymptomatic control subjects will be recruited. Participants will fill out health questionnaires and perform 30° arm abduction and adduction trials while holding different handheld weights of max. 4kg while motion capture and electromyographic data will be collected. In addition, fluoroscopic images of the shoulders will be taken for the same movements. Isometric shoulder muscle strength for abduction and rotation will be assessed with a dynamometer. Finally, shoulder magnetic resonance images will be acquired to assess muscle status and injury presence. The dose-response relationship between additional weight, liTr, and liMA will be evaluated. RESULTS Recruitment and data collection started in May 2021 and will last until the recruitment target is achieved. Data collection is expected to be completed by the end of 2022. Data processing and analysis is currently in progress, and the first results are expected to be submitted for publication in 2023. CONCLUSIONS This study will contribute to understanding the biological variation in liTr, the influence of disease pathology on liTr, the potential compensation of rotator cuff tears by muscle activation and size, and the association of liTr and patient outcomes. The outcomes will be relevant for diagnosis, treatment and rehabilitation planning in patients with rotator cuff tears. CLINICALTRIAL Ethical approval was granted by the regional ethics board (Ethics Committee Northwest Switzerland EKNZ 2021-00182), and the study was registered at clinicaltrials.gov (Trial registration number NCT04819724) on March 29, 2021.