Ideal alignment for UKA: are we any closer?

Abstract

The recently published article by Petterson et al 1Petterson SC Blood TD Plancher KD Role of alignment in successful clinical outcomes following medial unicompartmental knee arthroplasty: current concepts.J Isakos. 2020; 5: 224-22810.1136/jisakos-2019-000401Abstract Full Text Full Text PDF Scopus (3) Google Scholar questions the role of alignment in outcomes after medial unicompartmental knee arthroplasty (UKA). In this review the authors select a series of articles to review, in order to provide improved clarity around guidelines for the ideal alignment to aim for when performing UKA. The authors also have the additional related aim of providing clearer guidelines for the degree of preoperative deformity that can be accepted when performing UKA. There is a disparity of opinion within the orthopaedic community as to the indications for UKA, with some authors advocating that up to 50% of arthroplasty patients are suitable,2Willis-Owen CA Brust K Alsop H et al.Unicondylar knee arthroplasty in the UK National health service: an analysis of candidacy, outcome and cost efficacy.Knee. 2009; 16: 473-47810.1016/j.knee.2009.04.006http://www.ncbi.nlm.nih.gov/pubmed/19464898Abstract Full Text Full Text PDF PubMed Scopus (195) Google Scholar while others advocate almost exclusive use of total knee replacement (TKR). Given this disparity, a review can be helpful in clarifying indications and utilisation of this procedure. The authors quote the rates of UKA being 8%–15% of all arthroplasty. This figure is quoted from a UK paper from 2009,2Willis-Owen CA Brust K Alsop H et al.Unicondylar knee arthroplasty in the UK National health service: an analysis of candidacy, outcome and cost efficacy.Knee. 2009; 16: 473-47810.1016/j.knee.2009.04.006http://www.ncbi.nlm.nih.gov/pubmed/19464898Abstract Full Text Full Text PDF PubMed Scopus (195) Google Scholar and this figure has fluctuated since that time, varying widely around the world and also between centres within the same country. UKA ‘enthusiasts’ will see broader indications, and for example in some regions in Europe higher rates of utilisation are seen. In Australia, the 2019 National Joint Registry Report3Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR)Hip, Knee & Shoulder Arthroplasty: 2019 Annual Report. AOA, Adelaide2019https://aoanjrr.sahmri.com/annual-reports-2019Google Scholar reported a partial knee replacement rate of 7.8%, about half of the rate reported when the registry first reported this in 2003. The 2019 Swedish Registry4The Swedish knee arthroplasty register – annual report.978-91-88017-29-1 The Swedish Knee Arthroplasty Register, Lund2019http://www.myknee.se/pdf/SVK_2019_1.0_Eng.pdfGoogle Scholar reported a similar rate of 8.9%. Over this same time period the revision rate for unicompartmental knee replacement in the Australian Registry was three times that for TKR. There is no doubt that the presence of independent registry surveillance within a country has an impact on surgeons' choices, as risk of revision is a major criterion impacting decisions. The oft-present disparity between results reported by individual authors and that reported in registries suggests that the excellent outcomes and high survival rates reported by specialist centres may not be reproducible across the wider orthopaedic community. For this reason it is likely that many surgeons view TKR as the ‘lower risk’ option. In reviewing the literature the authors find some general concepts that are universally accepted. Overcorrection into valgus is clearly to be avoided, as it results in higher failure rates. This is somewhat intuitive, as it will realign patients to an alignment they have never experienced: an ‘unnatural’ alignment that can result in poorer functional outcomes, and excessive lateral compartment loads leading to premature wear and failure. What also seems clear is that for patients who have a deformity that is correctable to neutral or slight varus, restoring pat