The Oxford medial unicompartmental knee replacement using a minimally-invasive approach
The Journal of Bone and Joint Surgery. British volumeVol. 88-B, No. 8 CorrespondenceFree AccessThe Oxford medial unicompartmental knee replacement using a minimally-invasive approachE. S. B. SAWEERESE. S. B. SAWEERESSearch for more papers by this authorPublished Online:1 Aug 2006https://doi.org/10.1302/0301-620X.88B8.18225AboutSectionsPDF/EPUB ToolsDownload CitationsTrack CitationsPermissionsAdd to Favourites ShareShare onFacebookTwitterLinked InRedditEmail Sir,I read with great interest the paper by Pandit et al1 in the January 2006 issue entitled ‘The Oxford medial unicompartmental knee replacement using a minimally-invasive approach’. I wish to congratulate the authors on such a large series of Oxford unicompartmental knee replacements, followed up for a good period of time, with excellent survivorship and clinical results.Although it may not be very obvious in the manuscript (it occupies only one sentence), the way in which the authors reported the Oxford knee score (OKS) deserves careful consideration. The long story of the OKS lies behind that sentence.Since its first description, the OKS has been the subject of rigorous validation, which demonstrated the score to be a short, practical, reliable and valid outcome measure for knee arthroplasty that is also sensitive to clinically-important changes over time. The layout remained essentially the same; 12 questions with five possible answers for each, covering aspects of knee pain and function. The scoring system, however, has kept changing over the past two decades. In its original version as described by the Oxford group, the responses to each question were marked on a scale of 1 to 5. Adding up the marks yields a score of 60 for the worst possible knee, and a score of 12 for the normal, or best possible knee.My first encounter with the OKS was during my work and research at Oswestry, where the scoring system was different. Each question was marked on a scale of 0 to 4, and the total score ranged from 0 to 48. The worst knee therefore attracted a score of 0, and the best score of 48, was achieved by the normal or best possible knee. In their reply to a letter to the editor of the Journal of Bone and Joint Surgery [Br] about this specific scoring method, authors White, Jones and Harcourt commented that they preferred to use the scoring system along a conventional scale, and that this format of scoring the OKS was widely used. They also stressed that authors using the OKS should clearly describe how they use this instrument to avoid any confusion. By reading only the abstract, it was not possible to tell which scale was used in 16 of 24 references which studied or used the OKS. Four papers obviously used the score in its original form, and another four papers, including this one by Pandit et al,1 used it along the conventional scale. It was interesting to see two papers from Oxford, again including this paper, using the OKS in its ‘Oswestry’ form.In an annotation published in this journal, Pynsent stated that once an outcome measure is chosen, its scoring system should not be changed as attempts at change or modification will make comparison with other studies valueless. However, four years later Pynsent himself was one of the authors of a ‘Birmingham’ initiative to modify the Oxford knee score. Nevertheless, to give the Birmingham group the credit they deserve, they repeated the process of validation and testing of reliability, a prerequisite for any modification of outcome measures according to Pynsent’s annotation. In their recent paper they suggested changes in the layout, enabling patients to record pain and function for each knee separately. They described techniques for dealing with and recording scores for incomplete questionnaires. They also suggested an alternative scoring system, in which each question was scored between four and zero and the final index was expressed as a percentage. Only one other paper followed the same lines and reported normalised medians for the OKS, expressing it as a percentage.Despite the definite improvements suggested by the Birmingham group, which were welcomed but not adopted by the originators of the score, they still retained the inverted scale of the original score. The worst possible joint thus scored 100% and a healthy joint scored nought. The difficulty with this scale became obvious when the authors tried to categorise results, thus designating a knee with a score above 90% as poor and below 10% as excellent. Most of the other general health questionnaires (Short Form (SF) 12 and SF 36) and disease/site specific scores (Harris hip score and American Knee Society score) use a conventional scale with a higher score indicating a better and more normal knee.It is therefore clear that we have at least three versions of the OKS and that simply quoting a mean ‘Oxford score’ does not tell the reader if results were good or bad, unless the specific scale is indicated. Furthermore, this complicates any attempt at comparing different studies. It is time that a single method is agreed on by the originators and users’ groups together. If I may suggest an ‘Egyptian’ initiative to reconcile Oxford, Oswestry and Birmingham, I think that a score expressed as a percentile, which follows a conventional scale, from 0 to 100, would be most appropriate. Thus the worst knee would score a 0 and the normal knee would achieve a 100% score. This is easily understandable and would bring the OKS in line with other commonly-used scores. Finally, a modification of the OKS name would indicate to the reader that it was the final modification/version of the score which was used.A fully referenced version of this letter is available on our website at www.jbjs.org.uk References 1 Pandit H, Jenkins C, Barker K, Dodd CAF, Murray DW. The Oxford medial uni-compartmental knee replacement using a minimally-invasive approach. J Bone Joint Surg [Br] 2006;88-B:54–60. Link, Google ScholarFiguresReferencesRelatedDetails Vol. 88-B, No. 8 Metrics History Published online 1 August 2006 Published in print 1 August 2006 InformationCopyright © 2006, The British Editorial Society of Bone and Joint Surgery: All rights reservedPDF download
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