# Pathological Threshold of Patellar Tendon-Trochlear Groove Distance Using Magnetic Resonance Image in Patients with Patellar Instability

## TL;DR

This study identifies a threshold for patellar tendon-trochlear groove distance in MRI scans to help diagnose patellar instability.

## Contribution

The study establishes a new pathological threshold of 15.5 mm for PT-TG distance in MRI to assess patellar instability.

## Key findings

- The PT-TG distance was significantly higher in the instability group (20.6 mm) compared to the control group (11.8 mm).
- A PT-TG distance of 15.5 mm was identified as a pathological threshold with 81.4% accuracy.
- Higher PT-TG values correlate with lateralization forces contributing to patellar instability.

## Abstract

To evaluate and compare the values of the patellar tendon-trochlear groove (PT-TG) distance in individuals with and without patellar instability. Additionally, we aimed to define a cut-off value for the pathological limit of the PT-TG through nuclear magnetic resonance imaging (MRI) in patients with patellar instability.

The PT-TG distance of 52 knees was measured in 48 individuals with objective patellar instability (instability group) by MRI. These measurements were compared with those made in 50 knees of 44 individuals without a history of patellar instability (control group).

The PT-TG distance in the instability group (20.6 ± 5.0 mm) was greater than in the control group (11.8 ± 3.4 mm;
p
 < 0.001). A value of 15.5 mm was determined as the pathological limit, with an accuracy of 81.4%, in MRI exams.

Individuals with patellar instability have statistically higher measurements of PT-TG when compared with patients without it. Therefore, values higher than 15.5 mm for PT-TG seen in MRI exams represent a pathological lateralization force of the extensor mechanism related to patellar instability.