TKA design-integrated trochlea groove rotation reduces patellofemoral pressure.

Purpose: Total knee arthroplasty (TKA) leaves 11-25% of the patients unsatisfied, and patellofemoral joint pain is one cause. This study aimed to compare the differences between kinematics and load transfer in the same knee with axial internal/external rotation of the femoral component (CoRo) versus a separate axial internal/external trochlear groove rotation (TrRo) which is included in the TKA trochlea design.
Methods: A validated weight-bearing finite element model with modifications of the TKA axial femoral component rotation (CoRo) and a modified trochlear rotation (TrRo) was calculated and analysed.
Results: Compared to the neutrally implanted TKA at 105° of flexion, a 6° external rotation of the trochlear groove reduced the retropatellar stress by 7%, whereas a 3° internal trochlear groove rotation increased the retropatellar stress by 7%. With femoral component rotation, the tibia inlay stress of 6.7 MPa at 60° of flexion was two times higher both with a 3° internal component rotation and a 6° external rotation.
Conclusion: These results demonstrate in the tested TKA design that a trochlear groove rotation can reduce retropatellar stress. Additionally, during the TKA operation, the surgeon should be aware of the significant influence of axial femoral component rotation on mechanical inlay stress during flexion and of the fact that even small changes in the patellofemoral joint may influence the tibiofemoral joint. These results support that an external rotation of the femoral component should be preferred in TKA to avoid anterior knee pain. Furthermore, new developed TKA designs should integrate an externally rotated trochlea groove.