Pathophysiology of subacromial pain syndrome: contributions of rotator cuff-related factors and pain sensitization

Introduction: Subacromial pain syndrome (SAPS) is complex and multifactorial condition traditionally attributed to structural abnormalities such as rotator cuff tears and tendinopathy. However, pain severity in SAPS cannot be fully explained by structural changes alone. Chronic peripheral sensitization may induce neuroplastic changes within the central pain processing, suggesting that pain sensitization mechanisms could significantly contribute to SAPS-related pain. Objectives: This study aimed to investigate the relative contributions of rotator cuff-related structural abnormalities and pain sensitization to shoulder pain and disability in patients with SAPS. Methods: Fifty-three patients diagnosed with SAPS were analyzed. Data collection included demographic data, the Shoulder Pain and Disability Index (SPADI) scores, magnetic resonance imaging (MRI) findings (rotator cuff tears and tendinosis), pressure pain threshold at the shoulder, temporal summation of pain, and conditioned pain modulation. Multiple regression analysis was performed to examine the factors independently associated with SPADI scores, adjusting for covariates (age, sex, and occupational repetitive upper-extremity use). Results: Facilitated temporal summation of pain was significantly associated with higher SPADI scores after adjusting for covariates. Contrarily, MRI findings, such as the presence of rotator cuff tears and tendinosis, were not significantly associated with SPADI scores. Conclusion: Shoulder pain and disability in SAPS seem to be more strongly associated with central sensitization than with structural abnormalities detectable on MRI. These findings highlight the need to consider pain processing mechanisms in the clinical assessment and management of SAPS.