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Norm of the temporomandibular joint on X-rays
Last reviewed: 06.07.2025
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The temporomandibular joint is an articulation formed by the head of the condylar process and the articular surface of the mandibular fossa of the temporal bone, fully formed by the age of 15-17. The articulating surfaces are divided by a cartilaginous articular disc into upper and lower sections. Along the periphery of the head, constructed of trabecular spongy bone substance, there is a closing cortical plate. Its thickness in the anterior and posterior sections is 0.75-1.5 mm, along the upper surface 0.5-1 mm.
The compact layer covering the mandibular fossa varies in different sections. In the posterior sections, a wide strip of compact substance merges with the shadow of the pyramid of the temporal bone. The compact layer is thinnest in the central part of the glenoid cavity; anteriorly, it passes into the cortical layer of the posterior slope of the tubercle. In the middle of the posterior section of the mandibular fossa, the petrotympanic (Glaser's) fissure is visible, going towards the lumen of the external auditory canal. This fissure serves as a landmark between the extra- and intra-articular parts of the fossa.
The external auditory canal is defined as a clearly contoured, irregularly rounded clearing with a diameter of 0.8-2 cm against the background of an intense shadow of the petrous part of the pyramid of the temporal bone.
On the lateral tomogram in a state of physiological rest, the width of the X-ray joint space in all sections is the same or slightly wider between the anterior arch of the head and the posterior slope of the articular tubercle.
When opening the mouth, the head moves downward and forward along the posterior slope of the articular tubercle, reaches the top of the tubercle or even goes onto the anterior slope (in children).
In order to analyze tomograms and measure different sections of the joint, they are redrawn on tracing paper. To do this, draw a line connecting the lower edges of the articular tubercle and the external auditory canal, and drop a perpendicular from the upper point of the glenoid fossa onto it. Two more lines are drawn at an angle of 45° to the horizontal line at the point of its intersection with the perpendicular. The width of the joint space between the slope of the articular tubercle and the anterior surface of the articular head is designated as the anterior section of the space, between the bottom of the glenoid fossa and the upper surface of the articular head - as the upper section of the space, between the posterior surface of the head and the posterior section of the glenoid cavity - as the posterior section of the joint space.
Involutional changes lead to aging of the cartilage, disruption of joint function, the appearance of bone growths, and, against the background of osteoporosis, the cortical plates become clearly contoured.