Degenerative partial and complete rupture of the rotator cuff is a common injury among elder patients. However, the clinical manifestation varies largely with some patients having severe pain and limiting range of motion and others having no complaints. The basic functions of the rotator cuff are to facilitate shoulder motion and stabilization and centering of the glenohumeral joint. The objective of this study is to quantify the difference in superior glenohumeral translation in patients with degenerative rotator cuff tear compared to healthy control subjects and to determine the effect of isolated complete supraspinatus tear and combined complete supraspinatus and either partial infraspinatus or partial subscapularis tear.

The study will examine a cohort of 10 patients with isolated complete supraspinatus muscle tear and 10 patients with complete supraspinatus muscle tear and either partial infraspinatus muscle tear or partial subscapularis muscle tear, and a cohort of 10 age-matched healthy control persons. The participants will be recruited from the Clinic of Orthopaedics and Traumatology at the University Hospital Basel. Inclusion criteria: 45 years < age < 65 years; degenerative complete supraspinatus muscle tear or complete supraspinatus muscle tear and either partial infraspinatus muscle tear or partial subscapularis muscle tear; unilateral rotator cuff tear. Exclusion criteria: traumatic tendon ruptures; prior treatment of the ipsilateral upper extremity; clinical history of the contralateral glenohumeral joint; no complete supraspinatus muscle tear; tears in more than two rotator cuff muscles; neuromuscular disorders affecting upper limb movement; additional pathologies that influence the mobility of the shoulder joint; inability to provide informed consent.

Patients will complete the health questionnaire and reflective markers and electromyographic sensors will be placed on anatomical landmarks and shoulder muscles, respectively, before loaded and unloaded abduction and flexion arm movements will be performed. Centre of rotation of both shoulders will be calculated to determine glenohumeral translation. This parameter will be compared between patient groups and control subjects using linear mixed models with group membership and load as fixed factor and subject as random factor. The critical shoulder angle will be included as covariate into the model to detect a potential modulating role of this factor on glenohumeral translation.

Inclusion criteria patients

• 45 years ≤ age ≤ 65 years
• Degenerative complete supraspinatus muscle tear or complete supraspinatus muscle tear and either partial infraspinatus muscle tear or partial subscapularis muscle tear
• Unilateral rotator cuff tear

Exclusion criteria patients

• Traumatic tendon ruptures
• Incomplete supraspinatus muscle tear
• Tears in more than two rotator cuff muscles
• Prior conservative treatment or surgery of the ipsilateral upper extremity
• Clinical history of the contralateral glenohumeral joint
• Range of motion < 90° in abduction and flexion
• Neuromuscular disorders affecting upper limb movement
• Additional pathologies that influence the mobility of the shoulder joints
• Inability to provide informed consent

Inclusion criteria healthy control subjects

• 45 years ≤ age ≤ 65 years

• 10 patients with isolated complete supraspinatus muscle tear
• 10 patients with complete supraspinatus muscle tear and either partial infraspinatus muscle tear or partial subscapularis muscle tear
• 10 healthy control subjects