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The potential advantages of unicompartmental knee arthroplasty (UKA) include lower morbidity and mortality, quicker recovery, good range of motion, good medium and long-term survival results, potential bone conservation and perceived easier revision. Converting a UKA to a total knee arthroplasty (TKA) may be challenging due to issues of bone loss, need for augmentation, restoring joint line and rotation. We present the intraoperative findings of 201 cases of failed UKA's from the Trent Wales arthroplasty audit group (TWAAG) register. The objectives of the study were to determine the modes of failure, number of cases requiring augments and bone grafting, types of augments and implants used in revision surgery. This study does not include the clinical outcomes after revision knee surgery. The average age of the cohort at revision surgery was 67 years. There were 111 females and 90 males. The commonest modes of failure in young patients were unexplained pain/instability and aseptic loosening and in older patients they were aseptic loosening and progression of the disease. The survivorship of the implant was higher in the less than 55 years age group in comparison to the older patients. A total of 49 patients (25.9%) required bone grafting commonest in the 60 years and above age group (79.6%). Fifty patients (26.4%) required some form of augmentation, with the commonest site being tibia and commonest augment being tibial stem (35 cases). Only 8% of the cohort required revision knee implants whereas 78% of the cases received a cruciate retaining primary knee implant. To the author's knowledge, this is one of the largest studies in the literature which signifies the technical difficulties that might be experienced in revising the UKA's which will require appropriate pre-operative planning.