TMJ MRI structural features and horizontal condylar angle across a seven-type disc-condyle classification

Magnetic resonance imaging (MRI) studies of temporomandibular joint (TMJ) disc displacement have commonly examined individual or selected structural markers, whereas comprehensive evaluation of disc morphology, condylar position, condylar morphology, osseous status, and horizontal condylar angle (HCA) within a unified disc-condyle classification framework remains limited. This study aimed to characterize MRI structural features and HCA across a seven-type disc-condyle classification and to evaluate their associations and discriminatory performance for anterior disc displacement (ADD) and ADD without reduction (ADDwoR). This single-center retrospective cross-sectional study included 310 patients, contributing 568 TMJ sides. Joints were classified as normal disc position (NDP), ADD with reduction (ADDwR), or ADDwoR, with anterior, anterolateral, and anteromedial subtypes. Disc deformation, condylar position, condylar morphology, condylar osseous status, and HCA were assessed. Associations and discriminatory performance were evaluated using patient-clustered generalized estimating equation (GEE) models and receiver operating characteristic (ROC) analysis. Compared with NDP joints, joints with ADD showed greater disc deformation, more frequent condylar morphologic and osseous abnormalities, and higher HCA values. In multivariable analyses, HCA, posterior condylar position, and condylar osseous status were independently associated with ADD. For ADDwoR, disc deformation grade, condylar morphology grade, condylar osseous status, and anterior condylar position remained independently associated, whereas HCA did not. Apparent AUC values were 0.833 for the ADD model and 0.923 for the ADDwoR model; HCA alone showed only moderate discrimination for both contrasts. TMJ disc displacement is characterized by coordinated abnormalities in disc deformation, condylar position, condylar morphology, condylar osseous status, and HCA. The seven-type framework may support more refined MRI-based structural stratification, whereas HCA should be interpreted as a complementary quantitative marker rather than as a standalone diagnostic threshold.