Shoulder Impingement: The Diagnosis That Explains Too Much

"Shoulder impingement" is one of the most common diagnoses in physiotherapy and orthopaedics — applied to somewhere between 44% and 70% of people who present with shoulder pain that isn't from a specific injury. It's also one of the least specific.

An umbrella term, not a diagnosis

"Impingement" describes a mechanism, not a condition: the idea that rotator cuff tendons get physically pinched between the head of the humerus and the acromion above it during arm movement. In practice, the label gets applied across a range of distinct underlying issues — rotator cuff tendinopathy, subacromial bursitis, and partial-thickness rotator cuff tears all get grouped under it.

That's the core problem with the term: two people both diagnosed with "shoulder impingement" may have meaningfully different underlying tissue problems, different prognoses, and different things that actually help.

Why the mechanical theory matters

The mechanical impingement theory isn't just an academic detail — it's the stated rationale behind a specific, commonly performed surgery: subacromial decompression, where the underside of the acromion is smoothed to create more space for the tendons to move through.

The CSAW trial in the UK and the FIMPACT trial in Finland both compared decompression surgery against placebo surgery — a genuine operation that omitted only the specific decompression step — and found no clinically meaningful difference in outcomes, including at 10-year follow-up in the case of FIMPACT.

A Cochrane review and a BMJ Rapid Recommendation, both informed by these and earlier trials, concluded with high-certainty evidence that subacromial decompression does not improve pain, function, or quality of life compared with placebo surgery or physiotherapy. That's about as strong as evidence gets in this field — and it led to a formal recommendation against the surgery for chronic shoulder pain.

Despite that, subacromial decompression remains one of the most frequently performed orthopaedic surgeries worldwide. The gap between the evidence and common practice is exactly why the diagnosis behind it deserves scrutiny.

Why terminology is shifting

Because the evidence doesn't support tendons being mechanically "impinged" as the primary driver of symptoms, many clinicians now use "subacromial pain syndrome" or "rotator cuff-related shoulder pain" instead. These terms describe the location and presentation of pain without asserting a mechanical cause that hasn't held up under scrutiny.

This isn't universal — "impingement" is still widely used in both clinical practice and research literature — but the shift reflects a genuine correction in how the condition is understood, not just a preference for new jargon.

What the evidence actually supports

If decompression surgery isn't the answer for most people, the good news is that the alternative is well-supported and non-surgical. Structured, progressive loading of the rotator cuff and surrounding shoulder muscles, combined with scapular control training, is the evidence-based first-line approach for the range of conditions this diagnosis covers.

Surgery still has a role for a smaller subset of cases — particularly full-thickness rotator cuff tears — but for the broad "impingement" presentation this diagnosis usually covers, exercise-based rehabilitation is the first and best-evidenced option, not a fallback after surgery fails.