Lateral deviation of the prosthetic trochlear angle relative to the quadriceps vector in mechanically aligned total knee arthroplasty: a radiological and clinical analysis

Background: Patellofemoral alignment, particularly the relationship between the prosthetic trochlear angle (PTA) and the quadriceps vector (QV), is emerging as a new determinant of postoperative outcomes in total knee arthroplasty (TKA). Questions/Purposes: To evaluate the deviation of the PTA relative to the QV in mechanically aligned (MA) TKAs and determine its association with patient-reported outcomes. Methods: A retrospective cohort study was conducted including patients who underwent primary posterior-stabilized MA TKA between February 2019 and February 2020, with a minimum follow-up of five years. Long-leg radiographs were used to assess coronal alignment parameters and measure PTA deviation relative to the QV. The deviation angle was calculated by comparing the PTA, defined as 6–7° valgus to the distal joint line, with the QV defined from the anterior inferior iliac spine to the trochlear groove center. Results: The final cohort included 222 patients (mean age at the time of surgery: 66.0 ± 7.5 years; 81.9% female). The mean lateral deviation of the PTA relative to the QV was 5.6 ± 2.4°, with only one patient showing medial deviation. Correlation analysis revealed a significant association between PTA-QV deviation and final hip–knee–ankle (HKA) angle (r=0.672, 95% CI 0.417 – 0.559, p<0.001), but no correlation with functional scores or CPAK subtypes. Conclusion: Prosthetic trochlear angle exhibits a lateral deviation from the native quadriceps vector in total knee arthroplasty patients operated with a mechanical alignment strategy. This deviation is only associated with the final HKA angle, but not with poorer outcomes.