The mediolateral temporomandibular joint disc position: an in vivo quantitative study

Temporomandibular joint (TMJ) discs displaced simultaneously, dorsoventrally, and mediolaterally are assumed to be rotated. However, a pilot study performed with individualized oblique-axial scans on supposedly rotated discs did not show disc rotation consistently. The aim of this study was the quantitative evaluation of disc rotation on a larger sample size, assessing the mediolateral disc geometry and position by the use of a reference system determined by the condylar long axis.

Eighty-five TMJs from 50 subjects were analyzed. One series of sagittal and 1 of 14 individualized oblique-axial magnetic resonance (MR) scans were taken for each joint. The dorsoventral disc position was diagnosed by means of the sagittal scans. The mediolateral disc width and position were then measured on every oblique-axial scan. The width and midline was computed for each disc and its deviation from the perpendicular to the condylar long axis was calculated. Finally, a statistical analysis was performed to study whether the disc width and the direction of the disc midline varied between discs normally positioned and anteriorly displaced.

The disc width varied significantly more within the anteriorly displaced discs than within the normal ones. The midline of the anteriorly displaced discs deviated more from the perpendicular to the condylar long axis than that of normally positioned discs and was mostly in a lateral direction. The disc midline also deviated more in the ventral than in the dorsal part of the disc.

Most anteriorly displaced discs were laterally displaced and showed a larger width variation than normally positioned discs. This fact seems to indicate disc deformation.