Chronic posterior atlantoaxial subluxation associated with os odontoideum: a rare condition. A case report and literature review.

Introduction: Os odontoideum is a rare cervical lesion. This unusual condition is sometimes associated with atlantoaxial subluxation, which is mostly anterior subluxation. Posterior atlantoaxial subluxation due to os odontoideum is extremely rare. Case presentation: We report an unusual case of a 60-year-old Thai female, who was diagnosed as having chronic posterior atlantoaxial subluxation associated with os odontoideum with progressive myelopathy. The patient underwent posterior arch of C1 laminectomy and an occipito-C3 fusion using an occipital plate, C2 pedicle screws, C3 lateral mass screws and autologous iliac crest strut bone graft arthrodesis. During three years of follow-up, she was clinically significantly improved and postoperative radiographs showed a solid osseous fusion without loss of correction or implant failure. Discussion: Chronic posterior atlantoaxial subluxation associated with os odontoideum is rare. This condition can cause occipital-cervical pain, myelopathy, intracranial symptoms, or death. Surgical decompression and stabilization is the treatment of choice. Principles of treatment are to prevent sudden death from neurological compromise, improve neurological status, stabilize the cervical spine, and improve quality of life. Surgical options include atlantoaxial fusion, occipito-C2 fusion, and occipito-C3 fusion. Decision making depends on the location of spinal cord compression, area for arthrodesis, and bone quality.