To examine the possible correlation between the stage of internal derangement and the antero-posterior length of the disk in relation to the length of the articular eminence.
Twenty asymptomatic volunteers with normal joints and 120 patients with TMJ dysfunction underwent MR imaging. The A-P length of the disk in relation to the length of the articular eminence (D/E ratio) was measured.
The D/E ratio was 0.95 in the asymptomatic volunteers, 0.83 in patients with disk displacement with reduction, 0.74 in those with disk displacement without reduction and 0.57 in the patients with disk displacement and osteoarthritis. The relationship between the D/E ratio and the stage of internal derangement was statistically significant (P<0.01).
The D/E ratio decreases with advancing internal derangement. We suggest that it is a reliable numerical method for staging the degree of the internal derangement.