Cross-sectional area of condylar head and TMJ internal derangement

Objective: The aim of this study was to evaluate the inter-observer agreement on assessing the area of condylar head on serial MRIs; and to assess its relationship with the severity of TMJ internal derangement (ID). Methods: TMJ serial MR images of 156 young females (mean age 22.5 ± 2.9, 113 TMJ ID patients, 43 normal subjects) were analyzed in this study. The staging of TMJ ID of each joint was diagnosed by using both static and dynamic TMJ MRIs. The static serial MRIs were also used to measure the cross-sectional area of condylar head (ACH). While viewed from lateral to medial, the first sagtittal TMJ MRI showing complete ascending ramus plus two consecutive images more medially were chosen for assessing the ACH. Area bounded by the contour of condyle head from the superior attachment of lateral pterygoid muscle anteriorly to the inferior attachment of inferior lamina of the bilaminar zone posteriorly was measured as the cross-sectional area of a single slice. The ACH was defined as the mean of the cross-sectional area measure on the 3 consecutive sagittal images. All measurements were performed by 2 dentists familiar with MRI interpretation. Intra-class correlation coefficient and one way ANOVA were used to perform the statistical analyses. Results: The inter-observer agreement between both rankers was high (intra-class correlation coefficient, 0.96 for assessing right TMJ, 0.93 for left TMJ). The mean ACH(0.56 ± 0.18,0.75 ± 0.15,0.82 ± 0.16 cm2)was smallest in disc displacement without reduction group, followed by disc displacement with reduction group, and normal group. The difference between each group was significant (p< 0.01). Conclusions: The method used to assess the cross-sectional area yield high inter-observer agreement. The size of condylar head seems to be negatively associated with the severity of TMJ internal derangement.