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Case study: CSAW - investigating the effectiveness of surgery for shoulder impingement

The CSAW Study was conducted in 31 sites across the UK, all of which were supported by the NIHR Clinical Research Network through the musculoskeletal specialty. 

Find out more

CSAW impact case study: What is the Clinical and Cost Effectiveness of Arthroscopic Sub-acromial Decompression Surgery?

Shoulder problems causing pain and decreased function are very common. One of the causes of this is shoulder impingement, where the bone at the top of the shoulder rubs against the tendons in the shoulder when a patient’s arm is raised. Surgery is very widely used to treat shoulder impingement, despite limited evidence of its effectiveness. The CSAW study aimed to investigate the effectiveness of surgery by comparing it with a placebo surgery and no treatment interventions.

The CSAW study recruited 313 patients in total. They were randomly allocated to one of the three possible treatments and were followed up at six months and one year afterwards. They reported on shoulder pain and function which was assessed against the Oxford Shoulder Score (Dawson, Fitzpatrick and Carr, 1996), a questionnaire that aimed to determine the extent of their shoulder problem.

The surgery used to treat shoulder impingement is decompression surgery, a keyhole procedure in which an instrument called an arthroscope is inserted into a patient’s shoulder and used by a surgeon to examine the shoulder and reshape part of the shoulder blade. In the placebo procedure, a keyhole incision was made and the arthroscope inserted but the surgeon did not then reshape the shoulder. Patients in the surgical groups were not told which procedure they had undergone. Treatment for the third group of patients was active monitoring for three months followed by a clinical assessment. From an ethical point of view, it is normal practice to have a period of active monitoring and researchers were confident that patients in this group would not be disadvantaged as a result of this.

Outcomes and findings

Patients who had surgery (both treatment and placebo) did a little better than those allocated to monitoring and assessment only but this difference was not large enough to show that the surgery was more effective. The surgical decompression did not appear to offer any additional benefit over the placebo 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.

Natalie Carter, Head of Research Liaison and Evaluation at Arthritis Research UK, said of the CSAW study:

Painful shoulders account for 2.4% of all GP consultations in the UK and can make it difficult to work, drive, or get dressed.... This study suggests that treatments such as physiotherapy can be just as effective as shoulder surgery... and could influence the decisions made by health providers.

Value to the NHS

Following the publication of the CSAW trial, NHS England has put the surgical treatment for this particular shoulder pain on a list of ‘procedures of limited value’, meaning that it will now only be performed when specific criteria are met. NHS England intend that rates of surgery will halve as a result of this, which will result in savings of £75 million per year.

In the 10 years before the CSAW trial, rates of surgery had increased by 750%. During the seven-year period of the trial these rates plateaued. This is likely to be attributable to the widespread publicity of the trial which raised the issue of treatment uncertainty within the clinical community. 

The results of the CSAW trial performed in 30 NHS hospitals show no benefit of subacromial decompression surgery over placebo surgery. We anticipate that the number of these operations being performed will reduce significantly with avoidance of risk for patients and major cost savings for the NHS.
Professor Andrew Carr and Professor David Beard, University of Oxford, Co-Chief Investigators for the CSAW Trial

Key publications

Arthroscopic subacromial decompression for subacromial shoulder pain (CSAW): a multicentre, pragmatic, parallel group, placebo-controlled, three-group, randomised surgical trial, Beard DJ, Rees JL, Cook JA, Rombach I, Cooper C, Merritt N, Shirkey BA, Donovan JL, Gwilym S, Savulescu J, Moser J, Gray A, Jepson M, Tracey I, Judge A, Wartolowska K, Carr AJ, The Lancet, 2018 391 (10118), 329-338

More power to their elbow, Godlee F, BMJ 2019, 364: l792

Questionnaire on the perceptions of patients about shoulder surgery, Dawson J, Fitzpatrick R, Carr, J Bone Joint Surg Br. 1996 Jul;78(4):593-600

An independent trial from Finland published in 2018 has confirmed the findings of the CSAW trial: Paavola M, Malmivaara A, Taimela S, et al. Finnish Subacromial Impingement Arthroscopy Controlled Trial (FIMPACT) Investigators. Subacromial decompression versus diagnostic arthroscopy for shoulder impingement: randomised, placebo surgery controlled clinical trial. BMJ 2018;362:k2860. 10.1136/bmjk2860 pmid:30026230