Angular Evaluation of the TMJ Using Axial MRI: Vector-Based Analysis of Condylar and Lateral Pterygoid Angles in Anterior Disc Displacement

This study aimed to investigate angular changes in the temporomandibular joint (TMJ) associated with anterior disc displacement (ADD) through axial magnetic resonance imaging (MRI). Specifically, the lateral pterygoid muscle (LPM) attachment angle and the condylar position angle were evaluated using a coordinate-based vector analysis method. A total of 151 patients and 302 TMJs were retrospectively evaluated. Joints were categorized into three groups: healthy, ADD with reduction (ADDwR), and ADD without reduction (ADDwoR). On axial MRI slices, angular measurements were obtained using a pixel-based coordinate system and calculated using the dot product method. Intra-observer reliability was assessed using intraclass correlation coefficients (ICCs). Measurement reliability was high (ICC = 0.965 for LPM angle, ICC = 0.969 for condylar angle). No significant differences were found in LPM angle between groups (p = 0.51). In contrast, condylar position angle was significantly lower in both ADD groups compared to healthy joints (p = 0.01). No statistically significant difference was observed between the ADDwR and ADDwoR groups. A significant decrease in condylar position angle was observed in joints affected by ADD, possibly indicating adaptive joint remodelling over time. However, no angular change was observed in the attachment angle of the lateral pterygoid muscle. The vector-based measurement method demonstrated high intra-observer reliability and may offer a reproducible approach for angular assessment of TMJ structures.