The FIMPACT Trial: An excellent study with an impossible primary outcome
We read the results of the FIMPACT trial with great interest and must commend the authors for their excellent work (1). The study compared patients with shoulder impingement syndrome who were randomised to one of three groups: (1) active treatment of arthroscopic shoulder decompression (ASD), (2) a placebo operation of diagnostic arthroscopy (DA) or (3) exercise therapy. The trial demonstrated no statistically significant difference in clinical outcomes between patients undergoing ASD and DA. The results were very similar to the recently published Can Shoulder Arthroscopy Work (CSAW) study which also failed to demonstrate a benefit of ASD over a placebo operation (2).
One strength of the study was the use of a clinically relevant primary outcome. Many studies simply look for a statistically significant difference between placebo and active treatment irrespective of the effect size which can often be achieved if the sample size is large enough. For the FIMPACT trial to achieve its primary endpoint a minimally clinically important difference (MCID) of 15 units on a visual analogue scale (VAS) out of 100 was required ie the active treatment (ASD) had to produce an improvement that was at least 15 points greater than that achieved by the control groups (DA or exercise therapy). This is important as many patients would not wish to undertake an operation if they knew it would only improve their pain score by a few points on a scale of 0-100. However, in this particular trial the performance of the two control groups was so good that it meant an MCID of 15 at rest was impossible to achieve. At 24 months the mean VAS at rest was 9.9/100 in the arthroscopy group and 12.8/100 in the exercise therapy group. Even if subacromial decompression had produced perfect results and removed all pain it could not have produced a pain score that was 15 points lower than that achieved either of the control groups.
The FIMPACT trial had two primary endpoints. The second looked was pain VAS on arm activity. The mean score was unsurprisingly higher on activity than at rest and while this outcome was at least mathematically achievable it would have required an extremely well performing operation.
One of the surprising things about the FIMPACT trial is how well the patients did in the exercise therapy group. Patients in this group had a mean duration of symptoms of 22 months and had already undergone a trial of non-operative treatment which included physiotherapy and steroid injection prior to enrolment (3). One might assume that this group of patients had already “failed” exercise therapy and a different treatment strategy is needed yet 90% (95% CI: 81% to 98%) of patients allocated to this group were considered to be responders and 84.9% (95% CI: 79.9% to 89.8%) reported being satisfied with the treatment. Perhaps one reason this group did so well is the added motivation and supervision that comes with being part of a clinical trial and this is something we need to try and replicate in routine clinical practice.
1. Paavola M, Malmivaara A, Taimela S, Kanto K, Inkinen J, Kalske J, et al. Subacromial decompression versus diagnostic arthroscopy for shoulder impingement: randomised, placebo surgery controlled clinical trial. BMJ (Clinical research ed). 2018;362:k2860.
2. Beard DJ, Rees JL, Cook JA, Rombach I, Cooper C, Merritt N, et al. Arthroscopic subacromial decompression for subacromial shoulder pain (CSAW): a multicentre, pragmatic, parallel group, placebo-controlled, three-group, randomised surgical trial. Lancet (London, England). 2018;391(10118):329-38.
3. Paavola M, Malmivaara A, Taimela S, Kanto K, Jarvinen TL, Investigators F. Finnish Subacromial Impingement Arthroscopy Controlled Trial (FIMPACT): a protocol for a randomised trial comparing arthroscopic subacromial decompression and diagnostic arthroscopy (placebo control), with an exercise therapy control, in the treatment of shoulder impingement syndrome. BMJ open. 2017;7(5):e014087.
Competing interests: No competing interests