Cone beam computed tomography in the assessment of TMJ deformity in children with JIA: repeatability of a novel scoring system

Abstract

Background: The temporomandibular joint (TMJ) is frequently involved in juvenile idiopathic arthritis (JIA). Diagnostic imaging is necessary to correctly diagnose and evaluate TMJ involvement, however, hitherto little has been published on the accuracy of the applied scoring systems and measurements. The present study aims to investigate the precision of 20 imaging features and five measurements based on cone beam computed tomography (CBCT).

Methods: Imaging and clinical data from 84 participants in the Norwegian study on juvenile idiopathic arthritis, the NorJIA study, were collected. Altogether 20 imaging features and five measurements were evaluated independently by three experienced radiologists for intra- and interobserver agreement. Agreement of categorical variables was assessed by Fleiss', Cohen's simple or weighted Kappa as appropriate. Agreement of continuous variables was assessed with 95% limits of agreement as advised by Bland and Altman.

Results: "Overall impression of TMJ deformity" showed almost perfect intraobserver agreement with a kappa coefficient of 0.81 (95% CI 0.69-0.92), and substantial interobserver agreement (Fleiss' kappa 0.70 (0.61-0.78)). Moreover, both "flattening" and "irregularities" of the eminence/fossa and condyle performed well, with intra- and interobserver agreements of 0.66-0.82 and 0.55-0.76, respectively. "Reduced condylar volume" and "continuity" of the fossa/eminence had moderate intra- and interobserver Kappa values, whereas continuity of the condyle had Kappa values above 0.55. Measurements of distances and angles had limits of agreement of more than 15% of the sample mean.

Conclusions: We propose a CBCT-based scoring system of nine precise imaging features suggestive of TMJ deformity in JIA. Their clinical validity must be tested.

Trial registration: ClinicalTrials.gov NCT03904459.

Keywords: Arthritis juvenile; Observer variation; Precision; Scoring system; Temporomandibular joint.

Fig. 1

Image volume orientation models. Coronal (a, d), sagittal (b, e) and axial (c, f) view of the TMJ. a–c Condyle-corrected. In an axial view through the centre of the condyle, the sagittal plane is aligned perpendicular to the long axis (mesiolateral diameter) of the condyle. d–f Ramus-corrected. The sagittal plane is aligned from the coronoid process through the centre of the condyle in the axial view, and approximated to the longitudinal axis of the ramus in the coronal view. Arrowheads in a and b indicate the ‘equator’ in the variable ‘reduced condylar volume’

Fig. 2

Linear and angular measurements of the glenoid fossa and condyle. Sagittal view of the glenoid fossa (a, b) and axial view of the condyle (c). a Method A. A reference line was drawn between the postglenoid process (A) and the apex of the articular eminence (B). Fossa depth (CD, orange) was measured from the deepest point of the fossa (D) to the reference line. Fossa length (AB, red) was measured along the reference line. The fossa-eminence inclination angle (ABD, red) was measured between the reference line and the deepest point of the fossa. b Method B. The depth of the glenoid fossa (BE, green) was measured from the apex of the articular eminence (B) to a horizontal line through the upper border of the external auditory canal (F) and the deepest point of the fossa (D). A fossa-eminence inclination angle (EDB, yellow) between the horizontal line and a line from the deepest point of the glenoid fossa to the apex of the articular eminence was constructed (according to reference [37]). c Anteroposterior (GH, violet) and mesiolateral (IJ, blue) diameter of the condyle

Fig. 3

Distribution of findings, right side, 1st reading. The x-axis denotes number of participants

Fig. 4

Grading of continuity of the articular surface. Coronal (a) and sagittal (b) view of the TMJ. a Grade 0, continuous outline of the glenoid fossa and condyle, the discrete condylar irregularity is continuous. b Grade 1, a discontinuity (arrow) posteriorly in the condyle

Fig. 5

Grading of irregularities. Coronal views of the TMJ. a Grade 0, smooth outline of the glenoid fossa and the condyle. b Grade 1, mild irregularity. Depressions (arrows) in the central part of the glenoid fossa. c Grade 2, moderate/severe irregularity. Deep brake (arrowhead) in the condyle

Fig. 6

Flattening of the condyle in the coronal view. a Grade 0, absent, i.e. convex throughout. b Grade 1, mild or partial flattening. c Grade 2, moderately or severely flattened, or flattened throughout

Fig. 7

Flattening of the articular eminence and glenoid fossa and condyle in the sagittal view. a Both Grade 0. b Fossa grade 0. Condyle grade 1, subtle anterior flattening. c Fossa grade 1, mild widening or flattening. Condyle grade 2, mild flattening, involves part of the surface of the condyle. d Fossa grade 1 mild to moderate widening or flattening. Condyle grade 3, moderate flattening, loss of height of the condyle. e Fossa grade 1, moderate widening or flattening. Condyle grade 3, moderate flattening and loss of height of the condyle. f Fossa grade 2, severely flattened fossa/eminence. Condyle grade 3, severe flattening, involves the entire surface of the condyle and loss of height of the condyle. Note also the irregularities (asterisk) in the articular eminence/glenoid fossa in (d) and (e), the osteophyte at the anterior part of the condyle in (d) and the thickened, sclerotic appearance of the condyle in (e)

Fig. 8

Variability of TMJ measurements. Each line represents the mean difference in percentage of the mean value (mean difference/mean × 100%) with the corresponding 95% limits of agreement in percent [(mean difference/mean × 100%) ± (1.96 SD/mean × 100%)]. Abbreviations: CC, condyle-corrected; L, left; R, right; RC, ramus-corrected