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

Abstract

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.