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Arthroscopic Subacromial Decompression for Subacromial Shoulder Pain (csaw): a Multicentre, Pragmatic, Parallel Group, Placebo-Controlled, Three-Group, Randomised Surgical Trial.

·Lancet·2018·463 citations·Shoulder & Elbow
Free Full Text·DOI·PubMed
SummaryAbstract on PubMed →

CSAW was a UK multicentre, placebo-controlled randomised trial testing whether arthroscopic subacromial decompression actually works. It compared decompression, placebo arthroscopy (no bone or soft tissue removal), and no treatment for chronic subacromial pain with intact rotator cuffs. The primary outcome was the Oxford Shoulder Score at 6 months.

Study Snapshot

Design
Multicenter placebo-controlled RCT
Blinding: Single-blind
Setting: 30 UK hospital sites, 38 surgeons
Funding: Arthritis Research UK
Objective
Whether subacromial decompression improves shoulder pain and function more than placebo arthroscopy or no treatment
Outcome(s)
Oxford Shoulder Score at 6 months
Subjects
313 patients (106 / 103 / 104)
  • 106Arthroscopic subacromial decompression
  • 103Investigational arthroscopy only / placebo
  • 104No treatment / monitoring
Inclusion
  • Subacromial pain at least 3 months
  • Intact rotator cuff tendons
  • Failed exercise plus steroid injection
Exclusion
  • Full-thickness rotator cuff tear
Follow-up
6 and 12 months
Statistics
Linear regressionIntention to treatMultiple imputationSensitivity analyses

Key Findings

  • Decompression and placebo arthroscopy produced essentially identical Oxford Shoulder Scores at 6 months (32.7 vs 34.2, mean difference -1.3, p=0.3141). Removing the bone spur and soft tissue, the supposed point of the operation, added nothing measurable.
  • The lack of difference held at 1 year (38.2 vs 38.4, p=0.8571). This is not a short-term washout that resolves with longer follow-up.
  • Both surgical groups edged out no treatment, but the gains were below the 4.5-point clinically important threshold (decompression +2.8, p=0.0186; arthroscopy +4.2, p=0.0014). Statistically real, clinically trivial.
  • The modified Constant-Murley functional score told the same story: no difference between surgical groups (0.3 points, p=0.8972), both modestly better than no treatment.
  • Complications were rare and equal across all arms: 6 frozen shoulders total, 2 per group (p>0.9999). Surgery carried real but uncommon harm with no offsetting mechanical benefit.
  • Treatment crossover was high, especially 42% non-compliance in the placebo arm, yet per-protocol and sensitivity analyses confirmed the same null result.
  • National context made the stakes clear: English decompression volume rose sevenfold from 2523 (2000) to 21,355 (2010) before this trial questioned the operation.
Board PearlSubacromial decompression performs no better than placebo arthroscopy for subacromial pain, so removing the bone spur confers no real benefit.

Clinical Relevance

When a patient with chronic subacromial pain and an intact cuff has already failed exercise therapy and a steroid injection, CSAW says decompression is unlikely to help beyond what a sham operation delivers.

The trial's elegance is the placebo arm. Because decompression and diagnostic-only arthroscopy gave identical results, the mechanical impingement theory that justifies removing the spur does not hold up. The small edge of surgery over no treatment is best explained by placebo effect and postoperative physiotherapy, not by anything the scalpel did to the acromion.

For the ROCK rotator cuff rehabilitation objectives, the takeaway is that structured non-operative care deserves priority, and the postoperative physio package may be doing much of the work attributed to surgery. This is the first placebo-controlled trial of shoulder surgery and a direct counseling tool: share these findings during shared decision-making before offering decompression.

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|

Arthroscopic Subacromial Decompression for Subacromial Shoulder Pain (csaw): a Multicentre, Pragmatic, Parallel Group, Placebo-Controlled, Three-Group, Randomised Surgical Trial.

·Lancet·2018·463 citations·Shoulder & Elbow
Free Full Text·DOI·PubMed
SummaryAbstract on PubMed →

CSAW was a UK multicentre, placebo-controlled randomised trial testing whether arthroscopic subacromial decompression actually works. It compared decompression, placebo arthroscopy (no bone or soft tissue removal), and no treatment for chronic subacromial pain with intact rotator cuffs. The primary outcome was the Oxford Shoulder Score at 6 months.

Study Snapshot

Design
Multicenter placebo-controlled RCT
Blinding: Single-blind
Setting: 30 UK hospital sites, 38 surgeons
Funding: Arthritis Research UK
Objective
Whether subacromial decompression improves shoulder pain and function more than placebo arthroscopy or no treatment
Outcome(s)
Oxford Shoulder Score at 6 months
Subjects
313 patients (106 / 103 / 104)
  • 106Arthroscopic subacromial decompression
  • 103Investigational arthroscopy only / placebo
  • 104No treatment / monitoring
Inclusion
  • Subacromial pain at least 3 months
  • Intact rotator cuff tendons
  • Failed exercise plus steroid injection
Exclusion
  • Full-thickness rotator cuff tear
Follow-up
6 and 12 months
Statistics
Linear regressionIntention to treatMultiple imputationSensitivity analyses

Key Findings

  • Decompression and placebo arthroscopy produced essentially identical Oxford Shoulder Scores at 6 months (32.7 vs 34.2, mean difference -1.3, p=0.3141). Removing the bone spur and soft tissue, the supposed point of the operation, added nothing measurable.
  • The lack of difference held at 1 year (38.2 vs 38.4, p=0.8571). This is not a short-term washout that resolves with longer follow-up.
  • Both surgical groups edged out no treatment, but the gains were below the 4.5-point clinically important threshold (decompression +2.8, p=0.0186; arthroscopy +4.2, p=0.0014). Statistically real, clinically trivial.
  • The modified Constant-Murley functional score told the same story: no difference between surgical groups (0.3 points, p=0.8972), both modestly better than no treatment.
  • Complications were rare and equal across all arms: 6 frozen shoulders total, 2 per group (p>0.9999). Surgery carried real but uncommon harm with no offsetting mechanical benefit.
  • Treatment crossover was high, especially 42% non-compliance in the placebo arm, yet per-protocol and sensitivity analyses confirmed the same null result.
  • National context made the stakes clear: English decompression volume rose sevenfold from 2523 (2000) to 21,355 (2010) before this trial questioned the operation.
Board PearlSubacromial decompression performs no better than placebo arthroscopy for subacromial pain, so removing the bone spur confers no real benefit.

Clinical Relevance

When a patient with chronic subacromial pain and an intact cuff has already failed exercise therapy and a steroid injection, CSAW says decompression is unlikely to help beyond what a sham operation delivers.

The trial's elegance is the placebo arm. Because decompression and diagnostic-only arthroscopy gave identical results, the mechanical impingement theory that justifies removing the spur does not hold up. The small edge of surgery over no treatment is best explained by placebo effect and postoperative physiotherapy, not by anything the scalpel did to the acromion.

For the ROCK rotator cuff rehabilitation objectives, the takeaway is that structured non-operative care deserves priority, and the postoperative physio package may be doing much of the work attributed to surgery. This is the first placebo-controlled trial of shoulder surgery and a direct counseling tool: share these findings during shared decision-making before offering decompression.

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