Quantitative MRI analysis of the lateral pterygoid muscle in temporomandibular joint disc displacement: attachment type, volume, and signal intensity.

The role of morphological and radiological characteristics of the lateral pterygoid muscle (LPM) in the progression of temporomandibular joint (TMJ) disc displacement remains uncertain. This study was performed to investigate the association between LPM attachment type, volume, and signal intensity ratios (SIRs) and disc displacement with reduction (DDwR) and without reduction (DDwoR). A total of 188 TMJs from 94 patients were categorized into three groups: healthy controls (n = 62), DDwR (n = 62), and DDwoR (n = 64). LPM attachment type, superior and inferior LPM volumes, and SIRs were assessed using MRI. Receiver operating characteristics (ROC) analyses were applied to evaluate the discriminative ability of volumetric and SIR parameters. LPM attachment type did not differ among the groups (P = 0.36). In contrast, SIRs and superior head volume showed significant intergroup differences, reaching their highest values in the DDwoR group (all P < 0.001). ROC analyses demonstrated good discriminative performance for SIRs and superior head volume in identifying disc displacement, with stronger diagnostic accuracy for DDwoR compared with DDwR. Although a causal relationship cannot be established, the progressive increase in SIRs and superior head volume with increasing severity of disc displacement suggests that these changes reflect secondary adaptive or inflammatory responses of the LPM to altered TMJ biomechanics, associated with disc displacement. Evaluating radiological and morphological LPM characteristics alongside disc position may provide insights into the soft tissue pathophysiology accompanying disc displacement progression.