A 24-year-old sustains an axial load injury to the head in a diving accident. Open mouth odontoid views show bilateral outward displacement of the lateral masses of C1 relative to C2. Combined displacement measures 8 mm. Which statement best reflects the significance of this finding?

• A Displacement under 10 mm confirms an intact transverse atlantal ligament and conservative care suffices
• B Any measurable displacement requires urgent skull traction for 6 weeks
• C Lateral mass displacement is irrelevant because stability depends only on the odontoid
• D Combined displacement greater than 7 mm suggests rupture of the transverse atlantal ligament, making the injury unstable ✓

Explanation

This is a Jefferson burst fracture of the atlas ring caused by axial loading. By Spence's rule, combined lateral mass displacement exceeding 7 mm on the open mouth view implies rupture of the transverse atlantal ligament, rendering C1-C2 mechanically unstable; definitive stabilisation is then advised. Smaller displacements suggest the ligament is intact and can be treated with rigid immobilisation. Stability depends on ligamentous integrity, not merely the bony ring.

Reference: Apley's System of Orthopaedics and Fractures, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.