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.
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° 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.
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).
Rotational malalignment of tibial vertical cuts can affect tibial coverage in Oxford mobile-bearing unicompartmental knee arthroplasty.