Os odontoideum: presentation, diagnosis, and treatment in a series of 78 patients

Clinical article

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Object

The most contentious issue in the management of os odontoideum surrounds the decision to attempt atlantoaxial fusion in patients with asymptomatic lesions. The authors examined the clinical presentation and outcome in patients with os odontoideum who underwent surgical stabilization, with an emphasis on 3 patients who initially received conservative treatment and suffered delayed neurological injury.

Methods

Seventy-eight patients (mean age 20.5 years; median 15 years) were identified in a 17-year retrospective review. The median follow-up period was 14 months (range 1–115 months). Neck pain was the most common symptom (64%), and 56% of patients presented after traumatic injury. Eighteen patients had neurological signs or symptoms at presentation, and an additional 15 had a history of intermittent or prior neurological symptoms. Fifteen patients had undergone ≥ 1 attempt at atlantoaxial fusion elsewhere.

Results

Seventy-seven patients underwent posterior fusion and rigid screw fixation combined with a graft/wire construct: 75 had C1–2 fusion and 2 had occipitocervical fusion. One patient had an odontoid screw placed. Fusion was achieved in all patients at a median of 4.8 months (range 2–17 months). Approximately 90% of patients had resolution or improvement of their neck pain or neurological symptoms.

Conclusions

The authors believe that patients with os odontoideum are at risk for future spinal cord compromise. Forty-four percent of our patients had myelopathic symptoms at referral, and 3 had significant neurological deterioration when a known os odontoideum was left untreated. This risk of late neurological deterioration should be considered when counseling patients. Stabilization using internal screw fixation techniques resulted in 100% fusion, whereas 15% of patients had previously undergone unsuccessful wire and external bracing attempts.

Abbreviation used in this paper: SCI = spinal cord injury.

Article Information

Address correspondence to: Douglas Brockmeyer, M.D., Department of Neurosurgery, University of Utah, 175 North Medical Drive, Salt Lake City, Utah 84132. email: douglas.brockmeyer@hsc.utah.edu.

© AANS, except where prohibited by US copyright law.

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Figures

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    Diagrams depicting an os odontoideum in neutral (A), flexed (B), and extended (C) positions. The ossicle and the ring of C-1 move as a unit. The spinal cord may be injured anteriorly by the ossicle if there is excessive movement on extension or posteriorly by the posterior ring of C-1 if there is too much movement on flexion. The amount of movement (C-1 translation) was calculated as the distance between the posterior cortical margin of the anterior tubercle of C-1 and the anterior margin of the C-2 vertebral body as indicated by the dotted lines and “a” or “b” in panels B and C. With either anterior or posterior instability, this distance increases.

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    Bar graph showing the number of patients within different age groups.

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    Sagittal T2-weighted MR image in a patient with os odontoideum showing the typical appearance and location of spinal cord change thought to be indicative of injury.

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    Case 1. Plain radiograph obtained when the child was 2 years old at the time of the original injury. An abnormal odontoid apex (arrowhead) discontinuous from the rest of C-2 (arrow) is demonstrated.

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    Case 1. Plain radiographs demonstrating a highly unstable C1–2 region with 8 mm of movement on flexion (A) from a neutral position (B) associated with discontinuity between the odontoid and the body of C-2.

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    Case 2. Sagittal T1-weighted MR image (A) and CT reconstruction (B) showing the position of the os (arrows) fused to the anterior arch of C-1 and its close proximity to the spinal cord (*). The C1–os complex is retrolisthesed with the patient's head in a neutral position, reducing the space available for the spinal cord.

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    Case 3. Computed tomography images showing typical os odontoideum. The odontoid process is separated from the body of C-2 and has a smooth corticated margin.

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    Case 3. Plain films showing significant motion between extension (left) and flexion (right). The anterior arch of C-1 (white arrow, extension view) is posteriorly displaced over the body of C-2. The space available for the cord (black double-headed arrow, both views) is substantially reduced in flexion because of the anterior translation of C-2, indicated by the position of the posterior arch of C-1 (white arrow, flexion view).

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    Case 3. Plain film showing neck stabilization with bilateral transarticular screws in normal alignment with bicortical iliac crest allograft placed with posterior cabling.

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    Case 3. Photographs obtained 3 months after surgery demonstrating that the patient has retained an excellent range of motion.

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