St Georg Sled medial unicompartmental arthroplasty: survivorship analysis and function at 20years follow up

Purpose: The peri-operative and short-term benefits of unicompartmental knee arthroplasty (UKA) are well supported in the literature. However, there remains concern regarding the higher revision rate when compared with total knee replacement. This manuscript reports the functional outcome and survivorship of a large series of fixed bearing, medial unicompartmental replacements (St Georg Sled), with a minimum of 20years follow-up. Methods: Between 1974 and 1994, 399 patients (496 knees) underwent a medial fixed-bearing UKA. Prospective data were collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan–Meier survival analysis was used to determine survivorship, with revision or need for revision as end point, and differences assessed using Mantel–Cox log rank test. Results: Functional knee scores improved post-operatively, but demonstrated a slight decline from 10years of follow-up onwards. Survivorship is estimated as 86% at 10years, 80% at 15years, and 78% at 20years. Sixty knees were revised, with progression of disease in another compartment the commonest reason. Eighty eight percent were revised using a primary prosthesis. For patients over the age of 65years at the time of index procedure, 93% died with a functioning prosthesis in situ. Conclusion: Medial UKA demonstrates good long-term function and survivorship, and represents an excellent surgical option for patients aged over 65years of age, where few patients will require a revision procedure. Level of evidence: IV