Working Diagnosis:
Os odontoideum

Treatment:
The athlete was referred to neurosurgery for further recommendations on management of the os odontoideum. Initial neurosurgical evaluation determined medical disqualification. The athlete subsequently pursued a second opinion and medical disqualification was reaffirmed. After an in-depth discussion about risks and benefits, surgery was not recommended because he was asymptomatic and only had minimal instability. It was ultimately felt that the recurrent stingers were unrelated to the os odontoideum.

Outcome:
The student athlete remained on scholarship and was able to act as a manager. He was counseled against any future participation in contact sports. He will require ongoing clinical and radiographic follow-up exams to monitor for future instability.

Author's Comments:
An os odontoideum is an anatomic anomaly in which the odontoid process is separated from the body of the axis. It appears as an ossicle with smooth circumferential cortical margins. There is considerable debate regarding the etiology of os odontoideum. The congenital theory suggests the os is a result of failure of fusion between the dens and the body of the axis. The traumatic hypothesis suggests an unrecognized fracture at the odontoid synchondrosis occurring prior to ossification. Emerging evidence favors trauma as the underlying etiology. An os odontoideum may be asymptomatic, but can also present with neck pain, myelopathy, or intracranial manifestations related to vertebrobasilar ischemia after C1-C2 instability. (1-4)

Editor's Comments:
The incidence of os odontoideum is not known because the lesion is usually asymptomatic. The clinical presentation can vary from an incidental radiographic finding to severe symptoms of myelopathy, vertebral artery compression, and intracranial manifestations. Diagnosis can be made with routine cervical spine radiographs with an open-mouth odontoid view. Assess for instability with lateral flexion and extension radiography. Instability in an adult is defined as greater than 3 mm of anterior and posterior displacement of the atlas on the axis. For children, the displacement requirement is greater than 4 to 5 mm. CT and MRI can confirm the diagnosis and provide helpful detail. Operative stabilization should be considered in patients with symptomatic neurologic involvement, including transient symptoms; instability of >5 mm posteriorly or anteriorly; progressive instability, and persistent neck complaints. (5-7)

References:
1. Concannon LG, Harrast MA, Herring SA. Radiating upper limb pain in the contact sport athlete: an update on transient quadriparesis and stingers. Curr Sports Med Rep. 2012;11:28-34.
2. Hadley M. Os odontoideum. Neurosurgery. 2002;50(3 Suppl):S148–55.
3. Kelly JD, Aliquo D, Stiler MR, et al. Association of burners with cervical canal and foraminal stenosis. Am J Sports Med. 2000 Mar-Apr;28(2):214-7.
4. Zhao D, Wang S, Passias PG, Wang C. Craniocervical Instability in the Setting of Os Odontoideum: Assessment of Cause, Presentation, and Surgical Outcomes in a Series of 279 Cases. Neurosurgery. 2015;0:1-8.
5. Robson K. Os Odontoideum: Rare Cervical Lesion. West J Emerg Med. 2011;4:520-522
6. Arvin B, Fournier-Gosselin MP, Fehlings M. Os odontoideum: etiology and surgical management. Neurosurgery. 2010;66:A22–A31.
7. Warner W. Pediatric cervical spine. In: Canale ST, Beaty JH, editors. Campbell's Operative Orthopaedics. 11th ed. Philadelphia, PA: Mosby; 2007. pp. 1879–1898.

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