Extension patellar engagement index: a new measurement of patellar height - 14/12/24

Doi : 10.1016/j.otsr.2024.104086

Vincent Chassaing ^a,⁎ , Marie-Dominique Chancelier ^b, Jean-Louis Blin ^c, Jonathan Curado ^d, Jean-Marc Zeitoun ^a
^a Ramsay Santé, Hôpital Privé d’Antony, 1 rue Velpeau, 92160 Antony, France
^b Centre d’Imagerie Médicale, 25 Avenue de la Providence, 92160 Antony, France
^c Clinique de Saint-Germain, 12 rue Baronne-Gérard, 78100 Saint-Germain-en-Laye, France
^d CHU de Rouen, Department of Orthopedic and Trauma Surgery, 1 rue de Germont, 76031 Rouen Cedex, France

^⁎Corresponding author.

Sous presse. Épreuves corrigées par l'auteur. Disponible en ligne depuis le Saturday 14 December 2024

Abstract

Introduction

Patellar instability is a multifactorial pathology requiring precise evaluation of its contributing factors, particularly patella alta. Patellotibial height measurement indexes, such as the Caton-Deschamps index, have the disadvantage of being referenced to the tibia. Patellotrochlear indexes are more appropriate but fail to account for variable knee flexion during magnetic resonance imaging (MRI).

Objective

This study aims to validate a new MRI-based patellotrochlear measurement, the extension patellar engagement (EPE) index, which is reproducible and measures patellar height relative to the trochlea independently of knee flexion during MRI.

Materials and methods

A retrospective study was conducted on 77 MRIs (37 unstable patients with a history of patellar dislocation, 40 controls with meniscal injury). The EPE index is the ratio between the patellar engagement length on the cartilaginous trochlea and the patellar cartilage length, measured on a knee virtually extended. Four measurements on multiple sagittal slices were used to calculate the EPE index.

Results

The inteobserver intraclass correlation coefficient (ICC) was excellent (0.79). The mean EPE index's value for all knees was 0.22. It was significantly higher (p = 0.034) in the instability group (0.26) compared to the control group (0.19). The average knee flexion during MRI was 11 ° (range: −8 ° to 25 °).

Discussion

The EPE index is reproducible. It is an anatomical index to classify patella alta when the patella does not reach the trochlea in knee extension (EPE index ≤0). It is also a functional index, with a mean value of 0.19 in the control group.

Conclusion

The EPE index measures the patellar engagement on the trochlea taking into account the knee flexion during MRI. It may guide surgical decision-making for patellar distalization and quantify the required correction.