A 52-year-old woman with 20 years of rheumatoid arthritis has neck pain. Flexion-extension lateral radiographs show anterior subluxation of C4 on C5 measuring 4 mm with preserved atlantodental interval. This pattern of involvement is termed:

• A Atlantoaxial subluxation
• B Subaxial subluxation ✓
• C Vertical translocation (basilar invagination)
• D Cranial settling with odontoid erosion

Explanation

Subaxial subluxation refers to step-ladder subluxation below C2 caused by destruction of facet joints, discs, and ligaments, and it occurs in roughly 10 to 20 percent of rheumatoid cervical spines, often coexisting with atlantoaxial disease. Atlantoaxial subluxation is measured at C1-C2 by the atlantodental interval, and vertical translocation describes superior migration of the odontoid, neither of which is present here.

Reference: Campbell's Operative Orthopaedics, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.