Letter to the Editor
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LETTER TO THE EDITOR
Letter to the Editor Lennard Funk1 · Chris Littlewood2 Received: 24 August 2020 / Accepted: 31 August 2020 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2020
Dear Professor Karlsson, We would like to share our views on a paper recently published in Knee Surgery, Sports Traumatology, Arthroscopy. Feichtinger et al. [1] conclude that conservative treatment should be recommended for patients with Rockwood (RW) type III acromioclavicular joint (ACJ) dislocations and that surgery should be recommended in patients with RW type IV ACJ dislocations. Although we applaud the authors for their hard work on this in an attempt to tackle some still unanswered and important questions on ACJ injuries, we are concerned that these conclusions are potentially misleading due to a high risk of selection and attrition bias, as well as measurement and classification concerns that essentially render the study fundamentally flawed. When comparing conservative and surgical approaches within the RW type III and IV classifications, patients are selected according to the treatment received rather than through a process of random allocation. Such non-random selection risks selection bias meaning that the groups being compared differ systematically in important ways that might influence their response to treatment. So, any attempt to compare the effectiveness of treatments is not valid because if the groups are different to begin with, they will be different at the end of treatment for reasons other than the treatment received. An example validating our concern regarding selection bias is the difference in age of patients in the This comment refers to the article available online at https://doi. org/10.1007/s00167-020-06193-0. * Lennard Funk [email protected] Chris Littlewood [email protected] 1
Wrightington, Wigan and Leigh NHS Foundation Trust, Wigan, UK
Department of Health Professions, Faculty of Health, Psychology and Social Care, Manchester Metropolitan University, Manchester, UK
2
conservatively and surgically treated patients. For RW type III ACJ dislocations, those treated surgically were on average 39.8 years old, whereas those treated conservatively were on average 49.1 years old. This is almost a 10-year difference and any clinician will reflect the clinical importance of this age gap in this condition and how it might influence treatment selection. Feichtinger et al. [1] report this difference as not significant, inferring this is not a concern, but this reflects a misuse of significance testing. In declaring no significant difference in age between the two groups, data from 19 patients treated conservatively were analysed and 10 patients undergoing surgery. Hence, a lack of significant difference is due to a lack of data to detect a difference and it is certainly not safe to assume the groups are comparable. In patients with RW type IV ACJ dislocations, the age difference between the conservatively managed and surgical groups was 20 years. Clearly, any c
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