Anatomy & Histology · patient case question
During the initial phase of opening, what movement occurs in the upper compartment versus the lower compartment of the TMJ?
Patient case: Muscles, movement and a fractured condyle
demo: 29-year-old male
chief: Fell from a bicycle onto his chin; his bite now feels wrong.
history: No relevant medical history.
meds: None.
findings: Deviation of the mandible on opening, an anterior open bite and preauricular tenderness. Imaging confirms a fracture of the condylar neck with the condylar head displaced out of the fossa.
Show answer and explanation
Correct answer: D. Rotation occurs in the lower compartment first, followed by translation in the upper compartment
- A. This reverses the two compartments. Translation belongs to the upper joint space.
- B. The upper compartment is a gliding joint, not a rotational one.
- C. Pure hinge rotation without translation is what produces the first stage of opening, so translation is not the only movement.
- D. Correct. The TMJ is divided by the disc into two functional compartments. The lower, between condyle and disc, is the rotational or hinge compartment and accounts for roughly the first 20 to 25 mm of opening. The upper, between disc and glenoid fossa, is the translational or gliding compartment that carries the condyle-disc assembly forward down the eminence for wider opening.
Note: The recall recorded a bare choice between rotation and translation. Rotation is correct for opening about the condylar axis, but the full answer is that the two movements are sequential and occupy different joint compartments.
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