Summary

PTA values measured using methods that rely on the posterior bicondylar femoral line have a high rate of false positives, reflecting more information about internal knee torsion than true patellar inclination. The torsional component within the PTA measurement is highly predominant compared to patellar inclination. These findings highlight the critical role of torsional factors, particularly KITA,

Abstract

Background

The patellar tilt angle (PTA) measured using methods that take the posterior bicondylar femoral line as a reference is composed of the inclination of two structures: the patella and the femur. In addition, posterior bicondylar femoral inclination is a reference of knee internal torsion (KITA) when compared relative to a horizontal line in ct measuring technique. When KITA exceeds patellar tilt, the PTA measurement is considered a false positive. To date, no studies in the literature have evaluated the incidence of false-positive PTA due to internal knee torsion. Differentiating between these factors is crucial for ensuring a precise approach to patellofemoral treatment.

Objective

The aim of this study is to evaluate the incidence of false-positive PTA due to KITA, and the preponderance of the two factors involved in PTA: internal knee torsion vs. patellar inclination.

Methods

This study analyzed 934 knees from 467 patients (mean age: 25.3 years; 79.4% women, 20.6% men) with patellofemoral pain and instability, all presenting with a pathological PTA >10°. KITA was subtracted from PTA to assess the influence of knee internal torsion and patellar inclination.

Results

The analysis revealed that 81.58% of cases had a resultant patellar inclination <10°, indicating that many elevated PTA values were false positives. Preponderance analysis demonstrated that knee internal torsion was the dominant factor over patellar inclination in 77% of cases. Additionally, biomechanical asymmetries were more pronounced in women, as indicated by the preponderance analysis.

Conclusion

PTA values measured using methods that rely on the posterior bicondylar femoral line have a high rate of false positives, reflecting more information about internal knee torsion than true patellar inclination. The torsional component within the PTA measurement is highly predominant compared to patellar inclination. These findings highlight the critical role of torsional factors, particularly KITA, in PTA measurement and the substantial risk of misinterpreting patellar malalignment when torsional influences are not properly accounted for.