Rotational position of the tibial component can decrease bony coverage of the tibial component in Oxford mobile-bearing unicompartmental knee arthroplasty

Background: This study examined how coverage of the tibial component changes when the tibia vertical cut is externally or internally rotated in Oxford mobile-bearing unicompartmental knee arthroplasty. Materials and methods: Fifty patients scheduled for primary Oxford medial unicompartmental knee arthroplasty (UKA) at the current hospital were included in this study. This study was a computed tomography (CT) simulation study. The anteroposterior (AP) and mediolateral (ML) length as well as the ML/AP ratio of the tibial cut surfaces were calculated when the vertical cut was performed parallel (base line), five degrees externally rotated (ER5), 10 degrees externally rotated (ER10), five degrees internally rotated (IR5), or 10 internally rotated (IR10) relative to the tibial AP line using pre-operative CT. The tibial AP line connecting the middle of the posterior collateral ligament to the medial border of the patellar tendon attachment is a reproducible and reliable line because it is perpendicular to the SEA. These parameters among three lines were compared using a repeated measures ANOVA. Results: The mean ML/AP ratios were statistically significantly lower in ER5 (0.53 +/- 0.04) than base line (0.56 +/- 0.04) (P < 0.01). The ER10 (0.48 +/- 0.03) also exhibited lower mean ML/AP ratios than ER5 (0.53 +/- 0.04) (P < 0.01). The mean ML/AP ratios were higher in IR5 (0.59 +/- 0.04) than base line (0.56 +/- 0.04) (P < 0.01). The IR10 (0.63 +/- 0.06) also showed a higher mean ML/AP ratio than IR5 (0.59 0.04) (P < 0.01). Conclusion: Rotational malalignment of tibial vertical cuts can affect tibial coverage in Oxford mobile-bearing unicompartmental knee arthroplasty. (C) 2019 Elsevier B.V. All rights reserved.