Valgus subsidence of the tibial component caused by tibial component malpositioning in cementless Oxford mobile-bearing unicompartmental knee arthroplasty

Abstract Background Valgus subsidence of the tibial component is a rare complication of unicompartmental knee arthroplasty (UKA), and surgeons might consider revision surgery. The present study aimed to identify the factors related to valgus subsidence of the tibial component after cementless Oxford mobile-bearing UKA. Methods The study included 120 patients who underwent Oxford mobile-bearing UKA using a cementless tibial component in our center between September 2015 and September 2016. Six showed valgus subsidence of >2° after surgery. Patients were stratified into two groups according to the occurrence of valgus subsidence of the tibial component (valgus-subsidence [VS] group, n = 6; no-subsidence [N] group, n = 114). Postoperative radiographic evaluations were conducted to assess the varus/valgus alignment, rotation, and mediolateral position of the tibial and femoral components. The Oxford Knee Score (OKS) was assessed at 3, 6, and 12 months postoperatively. Positional parameters and sequential change in OKS were compared between the two groups using unpaired t-test (P Results At 3 months postoperatively, an average valgus subsidence of 3.4° in the VS group was observed, with a significant decrease in OKS. Valgus subsidence was associated with a significantly more medial position and external rotation of the tibial component. After 3 months, valgus subsidence stopped and the OKS gradually improved without revision surgery. Conclusions Valgus subsidence might be caused by the malpositioning of the tibial component. Valgus subsidence of the tibial component after UKA appears to stop, with simultaneous pain relief, even without revision after 3 months postoperatively.