Failures of metal-backed unicompartmental arthroplasty

Thirty-one failed metal-backed unicompartmental arthroplasties (MBUKAs) werereviewed with respect to their etiology of failure. In 11 cases (35.5%), the failure mode was ‘medial-lateral mismatch’ (medial-lateral subluxation in the coronal plane). Six cases (19%) failed secondary to lack of ingrowth in uncemented prostheses; four of which were as a result of failed femoral component ingrowth, and two of which were as a result of failed tibial component ingrowth. Five cases (16%) failed secondary to tilting of the tibial component in the coronal or sagittal plane. Three cases (9.7%) were revised secondary to failure of fixation of the cemented femoral component. Three cases (9.7%) failed as a result of articular surface wear of the tibial component. The remaining three cases (9.7%) failed due to progressive degenerative arthritis of the contralateral compartment. The mean time to failure requiring revision to tricompartmental total knee arthroplasty was 2.6 years. Failures of metal-backed unicompartmental arthroplasty can be prevented with usage of appropriate instrumentation, improved surgical technique, and properly designed components to avoid the most common causes of failure which appeared in this series to be secondary to instrumentation failure, surgical errors and failure of fixation.