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Platelet-Rich Plasma Injections vs Placebo for Patients With Ankle Osteoarthritis
To the Editor A recent study provided evidence that intra-articular PRP injections did not significantly improve ankle symptoms and function over 26 weeks compared with placebo saline injections among patients with ankle osteoarthritis. However, I am concerned about some methodological issues. Because this was a multicenter, stratified, block-randomized, double-blind, placebo-controlled study, the baseline characteristics should have been well balanced between the PRP and placebo groups. The authors performed a multivariable analysis with stepwise backward elimination to make adjustments for baseline variables that were associated with the primary outcome. However, imbalances that may have led to confounding bias were seen in Table 1 in the article for several baseline characteristics of the 2 study groups. First, compared with patients in the placebo group, those in the PRP group had a higher body mass index, which is significantly associated with ankle osteoarthritis and worsening ankle symptoms. Second, a higher proportion of patients in the PRP group had more advanced stages of ankle osteoarthritis using several different radiological classification systems. Third, because ankle osteoarthritis leads to poorer mental and physical quality of life, it is understandable that patients in the PRP group with higher body mass index and more advanced stages of ankle osteoarthritis had lower frequency of playing sports than those in the placebo group. Therefore, I believe the authors should have included variables with significant between-group differences as covariates in the analyses of both primary and secondary outcomes.
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