Decreased Uncertainty of TMJ Disc Position Using MRI Intermediate Step

Objectives: Magnetic Resonance Imaging (MRI) is the accepted gold standard for temporomandibular joint (TMJ) soft tissue evaluation. Usual MRI protocols include closed and open jaw positions. While disc position in the open position is readily discernable, the location of the articular disc in the closed position is often poorly discernable. The objective of this study was to evaluate the use of an intermediate opening step in order to assess whether it reduced the uncertainty in establishing disc location.

Methods: MRI, comprised of closed and intermediate opening positions, was obtained from 41 subjects, yielding 492 images based on 3 cuts per joint and 2 joints per subject. All images were blindly evaluated by a radiologist and 2 clinicians, all calibrated. The radiologist classified the articular disc location in the closed position as either "normal" or "displaced" while the clinicians had "uncertain" as an additional choice. The clinicians also evaluated the intermediate step image. Percent agreement and kappa statistics were computed in order to evaluate the incremental diagnostic validity.

Results: Kappa statistics for intra and inter reliability were 0.95 and 0.78, respectively. Interobserver agreement for assessment of disc position was 98% for normal, 96% for disc displacements, and 88% for uncertain. The addition of the intermediate step did not change 43% of the closed position classifications. Of the remaining 57% closed position classifications, 24% changed from uncertain to normal; 2% changed from uncertain to disc displacement; 20% changed from disc displacement to normal; 7% remained uncertain; and 4% were accompanied by uncertain in the intermediate step.

Conclusion: This study demonstrates that using an intermediate step during MRI reduces the uncertainty in determining the articular disc position. This new protocol has adequate incremental validity and may help redefine normal disc status.

This research was supported by NIDCR Grant U01-DE 013331.