Atraumatic odontoid fracture - rheumatoid arthritis

Case contributed by Hoe Han Guan

Presentation

Neck pain for 6 months with worsening left upper limb weakness and numbness for the past 3 weeks.

Patient Data

Age: 70 years
Gender: Male

Lateral cervical radiograph showed fracture at the base of odontoid process of axis/C2. Anterior displacement of the fractured odontoid process with grade 2 anterolisthesis over the C2 body (50% AP width).

Tip of odontoid process projects above foramen magnum in keeping with basilar invagination. It is evidenced by abnormal measurement with McRae line (the odontoid process is above this line), Chamberlain line (line connecting the posterior border of hard palate and opisthion - the tip of odontoid process is 4mm above this line (<3mm)) and McGregor line (line connecting posterior border of hard palate and most caudal point of occipital curve- the tip of odontoid process measures 6mm above this line (<5mm)).

Fracture of the odontoid process extending to both lateral masses of C2. Anterior displacement of the fractured odontoid process with narrowing of the spinal canal at cervicomedullary junction. Bony erosion at the odontoid process. The anterior atlantodental distance is narrowed.

Posterior dislocation of left greater horn from the body of hyoid bone.

Soft tissue lesion at the epitympanum and cochlear promontory extending into mastoid antrum via aditus ad antrum. Blunted right scutum and middle ear ossicular erosion.

Fracture of odontoid process with anterior displacement. Erosion of the odontoid process with periodontoid soft tissue mass. It is isointense (to spinal cord) on T1, heterogeneously hyperintense on T2/STIR and heterogeneously enhanced post-contrast.
External compression of the soft tissue mass and anterior displacement of the fractured odontoid process results in spinal canal narrowing at this level causing spinal cord myelopathy (high signal intensity within spinal cord on STIR sequence)

Loss of normal signal void on T2 sequence within the left vertebral artery from medulla oblongata (V4 segment) extending down into the left foramen transversarium(V2 segment).

Minimal C3/C4, C4/C5, C5/C6 and C6/C7 disc osteophyte complexes.

Case Discussion

This is a known case of rheumatoid arthritis (RA) on treatment. No history of significant trauma prior to complaining of neck pain.

Imaging features are suggestive of atraumatic odontoid fracture/pathological fracture secondary to rheumatoid arthritis. Soft tissue mass (seen on MRI scan) surrounding the odontoid process represents pannus (hypertrophied synovium), which is a sign of advanced rheumatoid arthritis.

Atraumatic odontoid fracture predisposes patients to spinal cord myelopathy as odontoid fractures are more likely to become non-union, especially in patients with RA. Furthermore, non-union odontoid fractures may cause progressive myelopathy1.

With severe bone erosion of the odontoid process (usually as the result of poorly controlled RA), atlantoaxial instability, and systemic bone loss, patients with long-standing RA have a high risk for the onset of fragility odontoid fractures without significant trauma. 

Atraumatic odontoid fractures should be suspected in patients with long-standing RA complaining of myelopathy and neck pain. This condition tends to be misdiagnosed as atalnto-axial subluxation or exacerbation of polyarthritis. 

Posterior spinal arthrodesis surgery is recommended treatment for atraumatic odontoid fractures in patients with RA. Osteosynthesis through the anterior approach is not recommended because fracture union is difficult to achieve.

Incidental finding of a right middle ear acquired cholesteatoma and left vertebral artery thrombosis.

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