Foot & Ankle
Recently colleagues have been saying things like; ‘looks like we are out of a job there then!’ referring to two recent papers claiming equivalence between operative and non-operative treatment of acute Achilles tendon rupture.1,2 You may accuse me of just trying to protect my mortgage repayments but there is a serious statistical point to be made here.
Whilst it does appear that, with an accelerated rehabilitation programme, outcomes in terms of strength, power and range of movement may be similar in the short to medium term, neither of these papers had sufficient statistical power to validate the claim that there is no significant difference in re-rupture rate.
Strength, power and range of movement are continuous variables and, depending on various factors, require relatively small numbers of patients to attain sufficient statistical power.3 Re-rupture, however, is a binary consideration – it either re-ruptures or it doesn’t - and you need far more patients for a sufficiently powerful study in this situation.
In the Willits paper,2 the power analysis was conducted to detect a greater than 5-fold increase in re-rupture rate (from 2.5 to 13%). The study was actually underpowered even to detect this as their own analysis required 77 patients in each group but they only recruited 72 and then 17 dropped out! If one conducts a power analysis using the authors' data, it shows that the numbers needed to detect a doubling of re-rupture rate, which many would consider clinically significant, with 80% power, is 966 patients per group (a tripling would require 331 patients in each). Infection is another binary consideration; there was no statistically significant difference in the infection rates either. If you run your own Chi squared test using their data you will see that p=0.24. Surely no one in their right mind would claim that there is an equivalent risk of infection between operative and non-operative treatment so why claim it for re-rupture?
In order to practice an ‘evidence-based’ approach, we should tell the patient that the functional outcome may well be the same whether we operate or not but the risk of re-rupture is between 2 and 5 times higher without surgery. Until a randomised controlled trial of around 2000 patients is conducted, I cannot see that we can say anything else.
Mr Chris Pearce, Consultant Orthopaedic Surgeon, Jurong Healthcare, Singapore
References
1. Keating JF, Will EM. Operative versus non-operative treatment of acute rupture of tendo Achillis: a prospective randomised evaluation of functional outcome. J Bone Joint Surg [Br] 2011;93-B:1071-8.
2. Willits K, Amendola A, Bryant D, Mohtadi NG, Giffin JR, Fowler P, Kean CO, Kirkley A. Operative versus nonoperative treatment of acute Achilles tendon ruptures: a multicenter randomized trial using accelerated functional rehabilitation. J Bone Joint Surg [Am] 2010;92-A:2767-75.
3. Sexton SA, Ferguson N, Pearce C, Ricketts DM. The misuse of 'no significant difference' in British orthopaedic literature. Ann R Coll Surg Engl 2008;90:58-61.
