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

Abstract

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 degrees 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 degrees, 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.