# The Orientation of the Prosthetic Trochlear Angle Is Predictable in Kinematically Aligned Total Knee Arthroplasty

## TL;DR

This study developed a formula to predict the orientation of the prosthetic trochlear angle in knee replacement surgery using preoperative measurements, improving implant alignment and patient outcomes.

## Contribution

A novel formula was developed to accurately predict prosthetic trochlear angle orientation in kinematically aligned total knee arthroplasty.

## Key findings

- The formula predicted PTA orientation with 100% accuracy in all cases.
- A difference of less than 0.5° between predicted and actual PTA was observed in 75% of cases.
- Patients with lower LDFA and QLF^FMA values were at risk for medial PTA orientation.

## Abstract

Abstract: Objective: This study aimed to predict the orientation of the prosthetic trochlear angle (PTA) relative to the quadriceps line of force (QLF) in kinematically aligned total knee arthroplasty (KA-TKA) by using preoperative radiographic parameters. Methods: This study included 144 patients who underwent KA-TKA with a femoral component designed for mechanical alignment (MADFC), with a PTA of 6°. Radiographic parameters, including the lateral distal femoral angle (LDFA) and the QLF^FMA (quadriceps line of force–femoral mechanical axis angle), were measured pre- and postoperatively. We developed and validated a formula to predict PTA orientation based on these values: “X = QLF^FMA−(PTA−(90°−LDFA))”, where values of x > 0° predict a lateral PTA orientation, while x < 0° predicts a medial PTA. Results: The formula accurately predicted PTA orientation in 100% of the cases, with a difference between the predicted and actual PTA values of <0.5° in 75% of the cases. Patients with an LDFA < 86° and lower QLF^FMA values were identified as at risk for medial PTA orientation, which can affect patellar tracking. Conclusions: Our formula offers a reliable preoperative tool for predicting PTA orientation in KA-TKA, aiding in component selection and alignment strategies to improve patellofemoral function and patient outcomes.