The alar ligaments are paired strong cords connecting the odontoid process to the occipital condyles, limiting the range of atlantoaxial rotation and lateral flexion. Together with the transverse ligament they are the primary stabilisers of the atlantoaxial joint. Their disruption in high-energy cervical trauma produces rotational instability that is distinct from the anteroposterior instability of transverse ligament rupture.
| Origin | Lateral aspects of the odontoid process (dens) of C2 |
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| Insertion | Medial surfaces of the occipital condyles (check ligaments) and lateral mass of C1 |
| Actions | Limit rotation and lateral flexion at the atlantoaxial joint, acting as the second line of defence against C1 on C2 subluxation after the transverse ligament |
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Alar ligament tears are increasingly identified on high-resolution MRI following whiplash injuries but their clinical significance is controversial. Isolated alar ligament disruption rarely causes significant instability given the intact transverse ligament. In rheumatoid arthritis, both the transverse and alar ligaments are destroyed progressively, producing multiplanar atlantoaxial instability that is more complex than the anterior instability of isolated transverse ligament failure.
Rotational instability at the atlantoaxial joint from alar ligament tears in high-energy trauma, usually occurring alongside transverse ligament injury and managed with C1-C2 fusion for significant instability.
