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It was pleasing to read the BMJ-reprinted article of Buchbinder et al1 in the BJSM. Key recommendations from the article1 which are consistent with systematic review (SR) evidence include that knee arthroscopy is not superior to less invasive treatment for knee osteoarthritis (OA) (or degenerative meniscal tear); that degenerative meniscal tears are common in asymptomatic knees in the middle-aged and elderly; and that moderate level exercise is an effective treatment for knee OA.
Based on expert society guidelines only2 (not SRs), the authors make recommendations that corticosteroid injections are a ‘first line’ treatment for knee OA, while they caution that hyaluronan (HA) gel injections have ‘inconsistent evidence’ and that platelet-rich plasma (PRP) injections have ‘insufficient evidence’.
A recent Cochrane review3 found the quality of evidence in favour of corticosteroid injection for knee OA to be poor even in the short term and absent for the medium to long term. Although hard to study in humans, there is a good theoretical basis to suggest that corticosteroid injections may lead to long-term damage to knee joint cartilage, so there should be good evidence of efficacy before rating them ‘first line’ treatment, which the recent Cochrane review3 did not find.
There is variation in the SR conclusions for HA injections for knee OA, although a consistent finding is a statistically significant improvement in outcomes from HA injections over placebo injections in the medium term. A recent review of SRs found that the highest quality SR published to date (also a Cochrane review) revealed that HA injections were beneficial for knee OA.4 Furthermore, in a direct head-to-head comparison between HA and corticosteroid, in any time duration beyond a month, HA leads to superior outcomes.5
A 2015 high-quality SR on PRP injections for knee OA6 found evidence supporting the use of PRP based on the six randomised controlled trials (RCTs) that had been published by that date. This was prior to another 2016 placebo-controlled RCT also supporting PRP.7 While it is a reasonable position that further research on PRP injections in knee OA is desirable, it is not reasonable to set a higher bar for what would constitute ‘sufficient’ evidence for PRP injections than cortisone injections.
The authors correctly and courageously argue that SR evidence should take precedence over expert opinion with respect to knee arthroscopy. This level of scientific rigour should also be applied when making recommendations regarding knee injections as well. Expert society recommendations should not be considered the highest level of evidence, particularly when they are contradicted by high level SR evidence.