Upper Limb · 4 min read
Shoulder Impingement: Rethinking a Diagnosis That Has Outlived Its Usefulness
Subacromial impingement syndrome is one of the most common diagnoses in musculoskeletal medicine — and one of the most conceptually problematic. The mechanical model that underpinned it for decades has been substantially revised by imaging, biomechanical, and clinical outcome research. Understanding what has changed, and why it matters for how we treat patients, is one of the most important updates in shoulder practice.
The traditional model of subacromial impingement — mechanical compression of the rotator cuff against the undersurface of the acromion during arm elevation, producing pain and eventually cuff damage — was compelling in its simplicity and drove surgical practice for decades. Subacromial decompression — acromioplasty — became one of the most commonly performed operations in shoulder surgery, its rationale grounded in the assumption that removing the mechanical cause of compression would relieve symptoms and protect the cuff.
What the evidence revealed
The publication of the Finnish Subacromial Impingement Arthroscopy Controlled Trial — FIMPACT — and the UK CSAW trial represented a turning point. Both trials compared arthroscopic subacromial decompression against sham surgery (arthroscopy without decompression) and physiotherapy alone. Both found no significant difference in patient-reported outcomes at 6 and 12 months between active surgery and the control conditions. The implication — that the mechanical decompression central to the procedure's rationale may not be the operative mechanism of any benefit produced — prompted a fundamental reassessment of both the diagnosis and its surgical treatment.
Contemporary understanding has moved toward the term "rotator cuff related shoulder pain" — a broader, more mechanistically honest label that acknowledges the multifactorial nature of the condition without implying a specific structural cause that current evidence does not consistently support. Pain sensitisation, kinetic chain dysfunction, tendon pathology, psychosocial factors, and biomechanical loading patterns all contribute to the clinical picture in proportions that vary between patients — and that a diagnosis of "impingement" does not capture.
What this means for management
Structured physiotherapy — focused on rotator cuff loading, scapular control, and kinetic chain rehabilitation — remains the most well-evidenced first-line treatment and should be the default pathway for the vast majority of patients with rotator cuff related shoulder pain. Surgery, where it has a role, should be directed at specific, identifiable pathology — a defined cuff tear, a verified biceps abnormality, demonstrable AC joint pathology — rather than non-specific "decompression" of a space that the trial evidence suggests may not be the primary pain source.
The diagnosis of subacromial impingement gave us a model. The FIMPACT and CSAW trials gave us an honest assessment of that model's limitations. The best clinical response is to update practice accordingly.
💬 Has the FIMPACT and CSAW evidence changed your practice around subacromial decompression — and how do you currently frame the diagnosis of rotator cuff related shoulder pain to your patients?