The transverse ligament of the atlas (atlantoaxial joint) primarily restrains which movement, and its rupture (as in Down syndrome or rheumatoid arthritis) most endangers which structure?

• A Restrains lateral rotation; rupture endangers the vertebral artery
• B Restrains flexion; rupture endangers the hypoglossal nerve
• C Restrains anterior translation of atlas on axis; rupture endangers the spinal cord by posterior displacement of the dens into the spinal canal ✓
• D Restrains posterior translation; rupture endangers the brainstem

Explanation

The transverse ligament of the atlas holds the dens of the axis (C2) against the anterior arch of the atlas, preventing the dens from moving posteriorly into the spinal canal during flexion. Rupture or laxity allows atlantoaxial instability: during neck flexion the atlas slides forward (anterior atlantoaxial subluxation) and the dens is driven posteriorly into the spinal canal, compressing the cervical spinal cord between the dens and the posterior arch of the atlas. This is why Down syndrome (ligamentous laxity due to trisomy 21) and rheumatoid arthritis require flexion-extension cervical radiographs before general anaesthesia to exclude atlantoaxial instability.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.