2017 ISAKOS Biennial Congress ePoster #1711

 

Patella Height is Related the Tilting and the Lateralization of the Patella

Peter W. Ferlic, MD, Innsbruck AUSTRIA
Wolfgang Hackl, MD, Innsbruck AUSTRIA
Armin Runer, PD MD, Munich GERMANY
Christopher Seeber, MD, Innsbruck AUSTRIA
Michael C. Liebensteiner, MD, PhD, Innsbruck, Tyrol AUSTRIA

Medical University Innsbruck, Innsbruck, AUSTRIA

FDA Status Not Applicable

Summary

The analysis of CT scans of the knee showed that a more proximal position of the patella, i.e. patella alta, is significantly correlated to a more laterally inclined and misaligned patella, which should be considered whenever treating patients with patellofemoral disorders.

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Abstract

Introduction

Patella alta is an established risk factor for the development of PFI patello-femoral instability (PFI). Furthermore, a higher prevalence of patella alta in patients with patellar cartilage defects has been reported. The correlation between the height of the patella relative to the trochlea and the position of the patella relative to the femur however have not been studied in detail. Based on biomechanical considerations patella alta can lead to maltracking as the patella is engaged in the trochlea only in higher knee flexion. Therefore, we hypothesized that the height of the patella relative to the trochlea entrance is significantly correlated to radiologic parameters as patella tilt and lateralization.

Methods

66 CT scans of the knee were included in this retrospective study. 54,5% of the cases had a PFI. To evaluate the height of the patella relative to the trochlea, similar to the patellotrochlea index, the axial slice where the patella (P) showed its widest diameter was identified. The distance from there to the proximal entrance of the femoral trochlea (TE) where the trochlea is initially completely covered with cartilage was defined as the P-TE distance.
The following well-established patellofemoral CT scan angle measurements were determined as described by previous research: congruence angle (CA), angle between the lateral facets of the patella and the trochlea (LPFA), angles between a tangent anterior to the femoral condyles and the lateral patella facet (Laurin angle; LA) as well as the patella axis (patella tilting angle; PTA), angles between a tangent posterior to the femoral condyles and the lateral patella facet (LPCA) as well as the patella axis (PCA). Furthermore, the lateralization of the patella was determined by the distance between the deepest point of the trochlea sulcus and the patella ridge (PSO) as well as by the lateral patella offset defined by the distance from lateral border of the femur to the lateral edge of the patella (LPO).
To falsify the above mentioned hypothesis a correlation analysis was performed with Spearman correlation coefficients between the variables of the P-TE distance and patella position. Alpha was defined as 0.05.

Results

The inferential statistics (correlation analysis) confirmed our hypothesis. The P-TE distance was significantly correlated with all patellofemoral CT scan measurements evaluated (p < 0.02): CA: r = -0.56, LPFA: r = 0.43, LA: r = -0.42, PTA: r = 0.40, LPCA: r = -0.37, PCA: r = 0.37, PSO: r = 0.52, LPO: r = 0.31.

Conclusion

Based on our findings it is concluded that a more proximal position of the patella, i.e. patella alta, is associated with a more laterally inclined and misaligned patella. These findings highlight the precise association between the patella height and maltracking in patients with patella instability as well as cases without history of patellofemoral disorders. Therefore, the height of the patella relative to the femoral trochlea should be evaluated in all patients with patellofemoral disorders, especially when indicating surgical therapy in patients with PFI.