Factors associated with reduced early survival in the Oxford phase III medial unicompartment knee replacement

Abstract

The aim of this study was to determine the prognostic value of preoperative patellofemoral osteoarthritis, BMI and age for implant survival of unicompartmental knee arthroplasty (UKA) performed in patients meeting strict admission criteria. The data and radiographs of 437 unilateral Oxford phase III procedures (Biomet, Bridgend, UK) were analysed. All procedures were carried out or supervised by 13 specialised knee surgeons in three different hospitals. The study group comprised 437 patients with a median follow of 2.6 years (0.1–7.9). The cumulative standard case survival rate at 5 years, when there were still 101 patients at risk, was 84.7% (CI-95%: 80.1–89.3%). Young age (< 60 years) was associated with a 2.2-fold increased adjusted risk of revision (CI: 1.08–4.43; p = 0.03). The preoperative presence of radiological features of patellofemoral osteoarthritis was associated with a 0.3-fold reduced adjusted risk of revision (CI: 0.11–0.89; p = 0.03). BMI > 30 kg/m², gender, the surgeon performing the operation (either as an individual or categorised by annual surgical UKA caseload, i.e., more or less than 10 UKAs) and the hospital in which surgery took place did not predict implant survival of UKA.

We conclude that young patients (< 60 years) experience an increased early risk of revision for UKA when compared to older patients (> 60 years). Obesity (BMI > 30 kg/m²) and preoperative patellofemoral osteoarthritis are not associated with a decreased implant survival and therefore should not be considered risk factors in this context.

Introduction

The 10-year survival for medial unicompartmental knee arthroplasty (UKA) is highly variable and ranges from 80.2 to 98% [1], [2], [3]. An important condition for obtaining optimal survival of UKA is believed to be strict adherence to the indication criteria [4]. While some criteria are widely accepted, the role of patellofemoral osteoarthritis, obesity and young age remains controversial [5]. Patients with preoperative patellofemoral osteoarthritis may experience residual pain after medial UKA since only the medial compartment is replaced. The increased load in obese patients and high demanding lifestyle of young patients is believed to cause increased wear of the UKA-implant [1], [6], [7], [8]. Both situations could eventually lead to implant failure (and as a consequence to revision surgery) and for this reason are considered relative contraindications for UKA by classical guidelines [9]. More recently, the latest report of the UK National Joint Registry also raised concerns regarding implant survival for UKA in young patients [10]. In contrast, many other studies have found UKA to be a successful treatment option regardless of age, patellofemoral osteoarthritis or obesity [11], [12]. The aim of this study was to determine the prognostic value of BMI > 30 kg/m², young age (< 60 years) and the preoperative presence of patellofemoral osteoarthritis for early implant survival of UKA performed in patients meeting strict admission criteria.