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NDORMS coordinated this multicentre randomised controlled trial (RCT) at 32 hospitals in the UK with 51 surgeons via the Surgical Intervention Trials Unit (SITU) and in collaboration with co-chief investigators Professors David Beard and Andrew Carr. The trial was funded by Arthritis Research UK (Ref.19707)


The CSAW study was designed to determine whether a commonly used surgical procedure to treat patients with shoulder pain (impingement), arthroscopic subacromial decompression is an effective treatment.  We compared surgical, placebo surgery and non-surgical approaches to treatment. The study started in 2012, patient follow-up completed in 2016 and results were published in The Lancet November 2017.

Methods and Patients

We recruited 313 patients to this randomised controlled trial. Participants were randomly assigned (1:1:1) to receive either monitoring and assessment only, arthroscopic subacromial decompression surgery, or arthroscopy only surgery.  Patients were followed up at 6 months and 1 year after randomisation. The primary outcome was the Oxford Shoulder Score (OSS) 6 months after randomisation. The CSAW trial is registered at, number NCT01623011.


The mean OSS did not differ between the two surgical groups at 6 months (decompression mean 32·7 points [SD 11·6] vs arthroscopy mean 34·2 points [9·2]; mean difference –1·3 points (95% CI –3·9 to 1·3, p=0·3141). Both surgical groups showed a small benefit over no treatment (mean 29·4 points [SD 11·9], mean difference vs decompression 2·8 points [95% CI 0·5–5·2], p=0·0186; mean difference vs arthroscopy 4·2 [1·8–6·6], p=0·0014) but these differences were not clinically important.


Patients who had surgery (both types) did a little better than those allocated to monitoring and assessment only but this difference was not clinically important i.e. the difference in improvement is not enough to consider that surgical management is more effective than non-surgical management for this particular shoulder problem. Additionally, surgical decompression appeared to offer no extra benefit over arthroscopy only surgery.

Overall the CSAW study showed that each of the three management options led to some improvement, but no one option proved to be more effective than the others.