Summary

Significant Impact of Knee Internal Torsion on PTA Accuracy: Incidence of False Positives . Background: Increased patellar tilt angle (PTA) is a key indicator of patellofemoral maltracking and instability. Various causes, including quadriceps dysplasia, muscle activation imbalances, patellar tendon friction syndrome, and excessive tension in the lateral patellar retinaculum. Objective: The object

Abstract

Background

Increased patellar tilt angle (PTA) is a key indicator of patellofemoral maltracking and instability. Various causes, including quadriceps dysplasia, muscle activation imbalances, patellar tendon friction syndrome, and excessive tension in the lateral patellar retinaculum, have been linked to elevated PTA. Additionally, recent studies highlight a strong association between PTA and increased femoral anteversion. The Powers and Josserand-Dejour method, commonly used to measure PTA, considers the angle formed by the patella and femur inclinations. However, the posterior bicondylar femoral line, a reference for femoral inclination, also reflects knee internal torsion, potentially complicating the assessment. This study aims to evaluate the preponderance of patellar inclination versus internal knee torsion in pathological PTA, particularly addressing the incidence of false-positive PTA due to internal torsion (KITA). The hypothesis posits that using the posterior femoral line as a reference may obscure underlying torsional disorders, risking surgical misjudgments.

Objective

The objective of this investigation is to evaluate the relative contributions of patellar inclination and internal knee torsion (KITA) to the patellar tilt angle (PTA) when using the bicondylar femoral line as a reference in measurement, and to determine the incidence of false-positive PTA results caused by internal knee torsion.

Material And Method

Between 2017 and 2024, 296 patients (592 knees) with patellofemoral pain and/or instability were evaluated using CT scans. The average age of the patients was 25.3 years, ranging from 17 to 65 years, with a gender distribution of 79.4% females and 20.6% males. Patients were positioned according to their foot progression angle footprint, and all had a patellar tilt angle (PTA) greater than 10°. The pure patellar tilt angle (PPTA) was calculated by subtracting the internal knee torsion angle (KITA) from the PTA. The study analyzed the percentage of true and false-positive PTA cases and examined the relative contributions of KITA and PPTA to the overall PTA measurement.

Results

The traditional method of measuring PTA using the posterior femoral condyles as a reference is influenced primarily by knee torsional factors rather than the actual tilt of the patella itself. The proportion of cases with PPTA < 10° was approximately 82.66% for right knees and approximately 80.51% for left knees. When analyzing the combined data for both knees, the proportion of cases with PPTA < 10° was approximately 81.58%. Thus. torsional factors, which account for 81.58% of false-positive PTA measurements, are the predominant contributors to patellar tilt angle, more so than true patellar inclination.

Conclusion

Knee internal torsion significantly affects PTA values when using the bicondylar posterior femoral line as a reference, leading to a high proportion of false-positive PTA cases and being the dominant factor compared to actual patellar tilt. To assess true lateral patellar tilt, the torsional influence should be excluded by using

Method

that measures the angle formed by the intersection of the patella's major cross-sectional axis and a horizontal line parallel to the floor.