Visualization of Trochlear Dysplasia Using 3-Dimensional Curvature Analysis in Patients With Patellar Instability Facilitates Understanding and Improves the Reliability of the Entry Point to Trochlea Groove Angle

Abstract

Purpose

To examine a method to visualize a 3-dimensional (3D) rendered distal femur using 3D curvature analysis and to compare models of patellofemoral instability (PFI) with controls to study the reliability of the entry point to trochlear groove angle (EPTG) metric.

Methods

The 3D models of patients with recurrent patellar instability, defined by at least 2 reported patellar dislocation events, and age- and sex-matched controls were created from computed tomography scans. Curvature was calculated to highlight the proximal trochlear ridges and the trochlear groove by overlaying them on the 3D models. Anteroposterior views with and without curvature visualization were created and used for qualitative comparison and to measure the EPTG. The EPTG was measured by 2 raters with and without the aid of the curvature maps. Significant differences between patients with PFI and controls were compared with a Mann-Whitney U test. Inter-rater reliability was calculated using interclass correlation coefficients, classified according to literature and compared using a permutation test. Significance was assumed at .05.

Results

Qualitive analysis between 30 PFI patient knees (age: 23.9 ± 8.4 years, female/male: 24/6) and 30 control knees (age: 21.8 ± 5.6 years, female/male: 22/8) showed that in general, patients with PFI have a lateralized medial ridge and trochlear groove, with the trochlear groove being shorter and shallower. Qualitatively, differences between patients with PFI and controls were significant for measurements both with and without the aid of the curvature maps. Inter-rater reliability was significantly (P = .0349) better when using the curvature visualization.

Conclusions

Curvature-based visualization aids overlain on a 3D model have the power to increase the information gained from 3D imaging and corresponding 3D models, amplifying their potential value in clinical decision-making. Such visualizations facilitate both the identification of qualitative differences between patient and control morphology and improve the reliability of the EPTG trochlear dysplasia metric.

Level of Evidence

Level III, retrospective cohort study.