Magnetic Resonance (MR) Abnormalities of the Lateral Pterygoid Muscle in Sideways and Rotational Disc Displacement of the Temporomandibular Joint

Objectives: The purpose of this study was to assess the magnetic resonance (MR) changes in the lateral pterygoid muscle (LPM) in cases of sideways (lateral or medial) and rotational (antero-lateral and antero-medial) disc displacement of the Temporomandibular joint (TMJ). Methods: A quantitative analysis of randomly selected MRI images of 61 patients over a period of six months was carried out who had either bilaterally normal TMJs or had rotational and/or sideways components of the disc displacement. Area and signal intensity of superior head (SLPM) and inferior head (ILPM) of lateral pterygoid muscle of normal and disc displaced muscle was noted and com- pared. Statistical analysis was carried out using Wilcoxon signed ranks test to determine difference between different muscle pairs. Results: Area of the muscle of normal subjects was higher from all the other subjects. This was followed by the muscle area of tethered discs which was then followed by sideways, rotational and an- teriorly displaced discs. Signal intensity of the SLPM of normal subjects was highest among the rest followed closely by anteromedial, anterolateral and anterior disc displacements, tethered discs, lat- eral and medially displaced discs. Relatively same pattern was seen in the ILPM. Statistical analysis showed that there were highly significant differences between different muscle pairs in their area and signal intensity. Conclusion: Abnormalities of both heads of lateral pterygoid muscle were seen in different disc place- ment individuals. Muscles associated with rotational and anterior disc displacement had higher sig- nal intensity depicting any oedematous change in the muscle.