Explanatory Limitations of the Subacromial Impingement Theory for Rotator Cuff Injury: A Critical Review of Lesion Location, Acromial Morphology, and Evidence for Subacromial Decompression

Background/Objective: The subacromial impingement theory proposes that repetitive compression of the rotator cuff beneath the acromion causes pain and structural damage.However, evidence regarding lesion location, acromial morphology, and the clinical effectiveness of subacromial decompression has challenged the theory's explanatory adequacy.This narrative review evaluated the validity and scope of the traditional subacromial impingement theory across these three domains.Design: Narrative review Methods: PubMed was searched for studies addressing subacromial pain, partial-thickness rotator cuff tears, acromial morphology, and subacromial decompression.Reference lists of relevant studies and reviews were also screened, and arthroscopic, imaging, comparative, randomized controlled, and placebo surgery-controlled studies were included in the review.Results:Partial-thickness rotator cuff tears were more frequently observed on the articular surface facing the humeral head than on the bursal surface facing the acromion.Associations between acromial morphology, including a hooked acromion, and rotator cuff pathology were inconsistent.In patients aged ≥50 years, acromial morphology was not significantly associated with rotator cuff pathology, whereas age showed a stronger association.Acromial morphology also failed to consistently explain tendon healing after rotator cuff repair.Furthermore, the FIMPACT trial found no superiority of subacromial decompression over diagnostic arthroscopy or exercise therapy, whereas the CSAW trial found no superiority over arthroscopy-only placebo surgery.Conclusions: External subacromial compression may contribute to rotator cuff pathology in some patients, but it should not be considered a universal explanation for rotator cuff injury.Rotator cuff pathology may be better understood within a multifactorial framework that considers lesion location, age-related degeneration, repetitive loading, tensile and shear stresses, and tendon biomechanics.