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The indications and contraindications for unicompartmental knee arthroplasty (UKA) are controversial. The aim of the study was to determine the risk factors for re-operation in our practice. A series of 113 medial UKAs with mean follow-up of 63 months were reviewed retrospectively. Pre-operatively all knees had radiographic or arthroscopic evidence of severe cartilage damage. The re-operation rate was not related to age, gender, arthroscopic finding or body mass index. It was related to the joint space on pre-operative standing weight bearing radiographs taken in extension. The re-operation rate was 6 (95% CI 2.1-17, P<0.001) times higher when the thickness of the pre-operative medial joint space was >2 mm rather than ≤2 mm. It was 8 (95% CI 2.8-22.5, P<0.001) times higher when the thickness of the pre-operative medial space was >40% of the thickness of the lateral space. The ratio of pre-operative joint spaces has a greater influence on revision rate than the absolute measurement and is independent of radiographic magnification or the patient's normal cartilage thickness. We therefore recommend that, in medial knee osteoarthritis, UKA should only be used if the pre-operative medial joint space on standing radiographs is ≤40% of the lateral joint space, even if severe cartilage damage is seen arthroscopically.

Original publication




Journal article


The Knee

Publication Date





432 - 435


Department of Surgery, Division of Orthopaedic and Trauma Surgery, Oulu University Hospital, PL 21, 90029 OYS, Finland.


Cartilage, Articular, Knee Joint, Humans, Osteoarthritis, Knee, Prosthesis Failure, Arthroplasty, Replacement, Knee, Reoperation, Severity of Illness Index, Risk Factors, Retrospective Studies, Knee Prosthesis, Adult, Aged, Aged, 80 and over, Middle Aged, Female, Male