Lower Trochlear Facet Asymmetry Ratio Is Associated with Objective Patellar Instability in a Retrospective MRI...

Area of Science:

• Orthopedics
• Radiology
• Biomedical Engineering

Background:

• Patella alta frequently co-occurs with patellar instability, complicating the distinction between trochlear morphology and patellar height.
• Objective patellar instability requires accurate assessment of underlying anatomical factors.

Purpose of the Study:

• To evaluate the association between the trochlear facet asymmetry ratio and patellar instability in knees with patella alta.
• To determine if trochlear morphology can be differentiated from patellar height as a predictor of instability.

Main Methods:

• Retrospective case-control study using MRI data from 123 knees.
• Comparison between knees with objective patellar instability, normal-height controls, and patella alta-positive controls without instability.
• Measurement of nine morphologic parameters, including the facet asymmetry ratio, trochlear depth, and tibial tubercle-trochlear groove (TT-TG) distance.

Main Results:

• The facet asymmetry ratio demonstrated a graded pattern across the groups (instability, patella alta-positive controls, normal-height controls).
• A lower facet asymmetry ratio was significantly associated with patellar instability, even after adjusting for the Insall-Salvati ratio and age.
• The facet asymmetry ratio showed strong diagnostic performance (AUC 0.855), outperforming the Insall-Salvati ratio (AUC 0.679).

Conclusions:

• A reduced trochlear facet asymmetry ratio is associated with objective patellar instability in knees with patella alta, independent of patellar height and age.
• The trochlear facet asymmetry ratio may serve as a valuable tool for differentiating causes of patellar instability.
• An exploratory threshold of 49% for facet asymmetry requires external validation for clinical application.