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Efficacy and safety of the pulsed electromagnetic field in osteoarthritis: a meta-analysis
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  • Published on:
    Reply to: “Correction to meta-analysis of pulsed electromagnetic field in osteoarthritis (OA)”
    • Ziying Wu, Orthopedic Surgeon Department of Orthopaedics, Xiangya Hospital, Central South University, Changsha, Hunan Province, China, 410008
    • Other Contributors:
      • Dongxing Xie, Orthopedic Surgeon

    To the Editor:

    We appreciate the letter submitted by Dr. Mark Whelan and colleagues regarding our recently published article and very much appreciate their important suggestions. Whelan et al. pointed out that the authors have confused the standard deviation (SD) with the standard error (SE) regarding the Nelson’s trial1. After checking all the original data of included trials, admittedly, we confused the SE value with the SD value in the Nelson’s trial1. The corrected effect size is -0.92 [95% confidence interval (CI) -1.64 to -0.20] in the Nelson’s trial1. Meanwhile, the pooled effect should be corrected as -0.34 [95%CI -0.72 to 0.03] and the conclusion should be that the treatment is not effective in alleviating knee OA pain. All calculations were performed using the Review Manager 5.2. The random-effects models were built using weighted averages of the differences in means of outcomes, using the inverse variance as weights, for weighted mean differences (WMD) of outcomes reported on the same scale2.

    Secondly, Whelan et al. raised a question worth thinking about that authors should alert the reader to how atypical some very large effect sizes are3-5. We are also grateful to Dr. Whelan and colleagues for this suggestion. The extreme values indicated non-random variation in effect sizes, such that a minority of interventions might have a significantly larger effects beyond the 95% CI around the standard mean difference of meta-analysis6. Especially for cer...

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    Conflict of Interest:
    None declared.
  • Published on:
    Correction to meta-analysis of pulsed electromagnetic field in osteoarthritis (OA)
    • Mark Whelan, Researcher Institute for Musculoskeletal Health
    • Other Contributors:
      • Mamata Tamrakar, PhD Candidate
      • Chris G Maher, Director
      • Stephanie Mathieson, Post-doctoral fellow
      • Christina Abdel Shaheed, Academic Fellow

    Dear Dr Aldcroft,

    We read with interest the paper entitled “Efficacy and safety of the pulsed electromagnetic field in osteoarthritis: a meta-analysis”.1 This paper concluded that “PEMF could alleviate pain and improve physical function for patients with knee and hand [osteoarthritis] OA, but not for patients with cervical [osteoarthritis] OA.” We have a few concerns with their conclusion.

    The first concern is that the review reports very large effect sizes for some trials,2-5 but does not alert the reader to how atypical these results are. For example, Figure 3 of the manuscript1 contains three examples of effect sizes of ~3 and 4 standardised mean difference (SMD). Effect sizes this large are usually a red flag that something is amiss, either with the results of the review or the original trial. Unfortunately, both problems are present.

    The review reported a SMD for the Nelson trial5 of -3.72; but this a mistake. The authors have confused the standard deviation (SD) with the standard error (SE) and when their error is corrected the true effect size is -0.74 [95% confidence interval (CI) -1.44 to -0.04] compared with -3.72 [95% CI -4.88 to -2.56] reported in the review. The correction also changes the pooled effect to -0.33 [-0.70 to 0.04] and would support the conclusion that the treatment is not effective for knee OA.

    The other two large effect sizes are driven by outcomes in the treatment group and no change in the control group.2,3 For...

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    Conflict of Interest:
    None declared.