Revision of failed unicompartmental knee replacement to total knee replacement

Recent reports suggest good outcome results following unicompartmental knee replacement (UKR). However, a number of authors have commented on the problem of osseous defects requiring technically difficult revision surgery. We reviewed clinical outcomes following revision total knee replacement (TKR) for failed UKR and analysed the reasons for failure and the technical aspects of the revision surgery. Between 2001 and 2010 our institute performed 132 UKR's out of which 33 required revision to TKR during a period 6 years. Demographics, details and indications for primary and revision surgery, the revised prosthesis including augments, technical difficulties and complications were noted. Patient outcome assessment was based on the Oxford knee score (OKS). Survival analysis for the UKR prosthesis was calculated using Kaplan-Meier Survival curves. Reasons for revision included aseptic loosening, persistent pain, dislocated meniscus, mal-alignment and other compartment osteoarthritis. Median time to revision was 19 months (range 2-159). Using revision as the end-point the survival proportion at 5-years was 69%. 18 revisions required additional intra-operative constructs including stemmed implants, wedge augmentation or bone graft. The mean 1 year post-operative OKS was 29 compared to 39 for primary TKR during the same period (p<0.001). Aseptic loosening was the commonest mode of failure. UKR survivorship at a non-specialist institute is considerably lower than at originating centres. Two thirds of the revisions were technically difficult and required additional constructs. The clinical outcome after revision surgery was inferior to that of primary TKR. The role of UKR needs to be more clearly defined.