Background: The rotator cuff muscles are subject to age-related changes, but the effect of aging on glenohumeral joint stability is poorly understood. Objectives: This study aimed to compare glenohumeral joint translation in asymptomatic young and older people. Methods: Twenty young (23.6 ± 5.3 years) and twenty older (66.5 ± 7.8 years) participants with no symptomatic shoulder pathology were recruited. Anterior and posterior glenohumeral joint translations were measured using real-time ultrasound in two positions: (1) shoulder neutral; and (2) shoulder at 90 degrees' abduction and four testing conditions: (1) rest; (2) passive accessory motion testing (PAMT) force alone; (3) PAMT with isometric internal rotation contraction; and (4) PAMT with external rotation contraction. Results: In both groups, there were significant differences between the amount of translation limited by anterior and posterior rotator cuff muscles in response to anterior and posterior PAMT force (p < 0.03), indicating rotator cuff activity-limited translation in a direction-specific manner. Young participants demonstrated increased passive posterior glenohumeral joint translation in the neutral shoulder position (p < 0.001) and their rotator cuff muscle contraction led to greater reductions in glenohumeral joint translation in the neutral shoulder position (p < 0.001), as compared with older participants. Conclusions: Rotator cuff contraction limits glenohumeral joint translation in a direction-specific manner in both young and older participants. However, younger age is associated with increased passive translation but greater ability to reduce glenohumeral joint translation with rotator cuff muscle contraction. Age-related changes should be considered when assessing and treating glenohumeral joint stability.
Keywords: Ultrasonography; aging; joint instability; rotator cuff.