Table A1.

The scoring system tested in the exercise is referred to as the Juvenile Idiopathic Arthritis Magnetic Resonance Scoring System for Temporomandibular Joints (JAMRIS-TMJ). The semiquantitative grades are weighted per domain to yield domain scores which are scaled from 0–100% [17]. The two temporomandibular joints are graded separately.

INFLAMMATORY DOMAIN
Definition	Bone Marrow Edema	Bone Marrow Enhancement	Effusion	Synovial Thickening	Joint Enhancement
	Compared to the mandibular ramus, hyperintense marrow signaling within the condyle on T2w FS or STIR images, and/or hypointense signaling on pre-contrast T1w images without FS.	Compared to the mandibular ramus, hyperintense marrow signaling within the condyle on post-contrast T1w FS images.	Increased joint fluid with isointense signaling of joint space compared to that of cerebrospinal fluid on T2w FS or STIR images.	Thickened synovial lining of the TMJ with intermediate signal on T2w images.	Signal intensity of the synovium, capsule, and joint fluid higher than that of muscle on post-contrast T1w FS images.
Grading	Absent	Absent	Normal: ≤1mm fluid in joint recess	Absent: No synovium visible (joint space ≤1 mm width)	Normal: High signal intensity confined to signal perimeter of normal amount of joint fluid on corresponding fluid-sensitive image
	Present	Present	Small: >1 and ≤2mm fluid in recess or involving entire joint compartment	Mild: >1 and ≤2mm thickness at the point of maximum synovial thickening	Mild: High signal intensity focally exceeding signal perimeter of physiologic amount of joint fluid on corresponding fluid-sensitive image
			Large: >2mm fluid in recess or involving entire joint compartment	Moderate/Severe: >2mm thickness at the point of maximum synovial thickening	Moderate/Severe: High signal intensity diffusely involving one or both joint compartments
DAMAGE DOMAIN
Definition	Condylar Flattening		Erosions		Disk Abnormalities
	Loss of the round or slightly rectangular shape of the condylar head, viewed in the sagittal-oblique plane.		Any irregularity or breaks of the bony joint surfaces leading to the loss of the smooth continuous surface of the bone, seen in both sagittal and coronal planes		Any abnormality of the articular disk, including flattening, displacement, or destruction.
Grading	Normal round/slightly rectangular shape		No irregularities or deep breaks		Absent
	Mild: Extent of flattening involves part of the surface of the condyle		Mild: Presence of irregularities involving only part of the articular surface of the condyle		Present
	Moderate/Severe: Extent of flattening involves the entire surface of the condyle, or loss of height in the condyle.		Moderate/Severe: Presence of deep breaks in the subchondral bone seen in two planes, or irregularities involving the entire articular surface of the condyle