A 40-year-old patient with rheumatoid arthritis develops atlantoaxial instability. The transverse ligament of the atlas holds the dens of C2 against the anterior arch of C1. An atlanto-dental interval (ADI) greater than what measurement in adults on lateral radiograph indicates transverse ligament disruption requiring surgical stabilization?
- A 2 mm
- B 3 mm ✓
- C 5 mm
- D 7 mm
Correct answer: B. 3 mm
Explanation
In adults, an atlanto-dental interval (ADI) greater than 3 mm on lateral flexion radiograph indicates transverse ligament disruption and atlantoaxial instability. In children, the upper limit of normal is 5 mm. The ADI is measured from the posterior aspect of the anterior arch of C1 to the anterior surface of the dens. Values of 3-6 mm suggest partial ligament rupture; greater than 6 mm suggests complete rupture with risk of spinal cord compression.
Reference: Rockwood and Green's Fractures in Adults, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.