Medial Unicompartmental Arthroplasty of the Knee

Jason M. Jennings, MD, DPT; Lindsay T. Kleeman-Forsthuber, MD; Michael P. Bolognesi, MD


J Am Acad Orthop Surg. 2019;27(5):166-176. 

In This Article

Outcomes for Conversion of Failed Unicompartmental Knee Arthroplasty to Total Knee Arthroplasty

One of the supporting arguments for UKA is that conversion to TKA is technically less challenging and morbid than TKA revision. Conflicting literature exists on the validity of this argument. Sierra et al[40] reviewed their series of failed UKAs who underwent conversion to TKA. The postconversion complication rate was 13% overall with 4.4% incidence of aseptic loosening, 3.3% of stiffness, and 1.2% of deep infection. The re-revision rate after conversion was 4.5% performed at average of 2 years from conversion surgery.[40] Complication rates after UKA conversion were similar to those after primary TKA and better compared with revision of a failed TKA.[40]

Other studies have shown worse outcomes of UKA conversion compared with those of primary TKA. Pearse et al[41] reviewed 236 failed UKAs from the New Zealand registry and found fourfold higher risk of re-revision in the failed UKA group compared with that in the primary TKA group. Furthermore, the age at re-revision of a failed UKA was 7 years younger than those who underwent revision of a primary TKA. Functional scores for converted UKAs were markedly lower than for primary TKA but were similar to scores for revised TKAs.[41] Another study by Leta et al[42] of the Norwegian database compared outcomes after conversion of 578 failed UKAs and revision of 768 failed TKAs with similar 10-year survival between groups (82% versus 81%) and found no difference in re-revision rates or patient-reported outcome scores. They found a markedly higher risk of deep infection in the revised TKA group with longer surgical duration and increased need for stems and/or augmentation than in the conversion UKA group. Collectively, these results indicate that outcomes after conversion of a UKA may not be as optimal as previously suggested but still show comparable or better outcomes than revision TKA.