The cruciate ligament of the atlas combines the transverse ligament (primary component) with superior and inferior vertical bands to form a cross-shaped restraint against the posterior dens. The transverse ligament alone has a strength of 350 N and is the primary restraint against atlantoaxial instability. In Down syndrome, rheumatoid arthritis, and trauma, transverse ligament disruption produces dangerous atlantoaxial instability.
| Origin | Transverse part: lateral masses of C1 (both sides). Vertical part: basion of the occiput (superior) to C2 body (inferior) |
|---|---|
| Insertion | Posterior dens of C2 |
| Actions | Holds the dens against the anterior C1 arch; the transverse part is the primary atlantoaxial stabiliser against anterior atlantoaxial subluxation |
|---|
Atlantoaxial instability from transverse ligament insufficiency produces the anterior atlantodental interval (AADI) greater than 3 mm in adults on lateral flexion radiograph. Posterior atlantodental interval (PADI) less than 14 mm indicates cord compression risk. Surgical C1-C2 fusion (Magerl or Harms technique) is required for instability that fails to reduce or persists with neurological risk.
Transverse ligament of the atlas disruption producing atlantoaxial instability managed with C1-C2 posterior fusion.
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