Download PDFPDF

Efficacy and safety of the pulsed electromagnetic field in osteoarthritis: a meta-analysis
Compose Response

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Author Information
First or given name, e.g. 'Peter'.
Your last, or family, name, e.g. 'MacMoody'.
Your email address, e.g.
Your role and/or occupation, e.g. 'Orthopedic Surgeon'.
Your organization or institution (if applicable), e.g. 'Royal Free Hospital'.
Statement of Competing Interests


  • A rapid response is a moderated but not peer reviewed online response to a published article in a BMJ journal; it will not receive a DOI and will not be indexed unless it is also republished as a Letter, Correspondence or as other content. Find out more about rapid responses.
  • We intend to post all responses which are approved by the Editor, within 14 days (BMJ Journals) or 24 hours (The BMJ), however timeframes cannot be guaranteed. Responses must comply with our requirements and should contribute substantially to the topic, but it is at our absolute discretion whether we publish a response, and we reserve the right to edit or remove responses before and after publication and also republish some or all in other BMJ publications, including third party local editions in other countries and languages
  • Our requirements are stated in our rapid response terms and conditions and must be read. These include ensuring that: i) you do not include any illustrative content including tables and graphs, ii) you do not include any information that includes specifics about any patients,iii) you do not include any original data, unless it has already been published in a peer reviewed journal and you have included a reference, iv) your response is lawful, not defamatory, original and accurate, v) you declare any competing interests, vi) you understand that your name and other personal details set out in our rapid response terms and conditions will be published with any responses we publish and vii) you understand that once a response is published, we may continue to publish your response and/or edit or remove it in the future.
  • By submitting this rapid response you are agreeing to our terms and conditions for rapid responses and understand that your personal data will be processed in accordance with those terms and our privacy notice.
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

Vertical Tabs

Other responses

Jump to comment:

  • 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...

    Show More
    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...

    Show More
    Conflict of Interest:
    None declared.