Extra Attention Should Be Paid to Patellar Resurfacing to Obtain Good Postoperative Patellar Tracking in Bicruciate Substituting Total Knee Arthroplasty.

Bicruciate-substituting total knee arthroplasty (BCS-TKA) mimicking normal knee anatomy contributes to the physiological knee kinematics of the tibiofemoral joint; however, potential disadvantages have been predicted regarding the patellofemoral joint environment. This study aimed to compare the postoperative patellar tracking of BCS-TKA with that of posterior stabilized (PS)-TKA and explore the surgical factors necessary for achieving good postoperative patellar tracking. The patellar tilt angle (PTA) of the resurfaced patella 1 month and 1 year after surgery was retrospectively compared in 160 knees (80 BCS-TKA and 80 PS-TKA). The factors influencing patellar tracking, postoperative coronal limb alignment, femoral and tibial component position and axial rotation, patellar resection angle, patellar component position, and change in patellar thickness after resurfacing were evaluated. Then, the correlation between the postoperative PTA and each surgical factor was analyzed. The mean postoperative PTA significantly increased from 1 month to 1 year after surgery in BCS-TKA (6.3 ± 4.9 degrees [standard deviation] to 7.9 ± 5.8 degrees, p < 0.001) but not in PS-TKA. The 1-year postoperative lateral patellar tilt was significantly greater in BCS-TKA than in PS-TKA (7.9 ± 5.8 degrees vs. 4.4 ± 5.0 degrees, p < 0.001). The patellar resection angle positively correlated with the 1-year postoperative PTA in both groups (r = 0.46 and 0.40). Medial patellar component positioning showed a strong negative correlation with the 1-year postoperative PTA in BCS-TKA and a moderate correlation with PS-TKA (r = -0.63 and -0.38). Multivariate regression analysis showed that the patellar resection angle and patellar component position influenced 1-year postoperative patellar tilt in BCS-TKA and PS-TKA. Postoperative patellar tracking in BCS-TKA, in which the femur is positioned more anteriorly relative to the tibia, tended to be more prone to lateral inclination than in PS-TKA. For better patellar tracking, extra attention should be paid to parallel patellar resection and central patellar component positioning during patellar resurfacing in BCS-TKA.