Database Review of 514 Patients with Os Odontoideum. Detailed Analysis of 258 Surgically Treated (1978-2019).

Objective: Database review (1978-2019) is to identify the cause of os odontoideum, its presentation, associated abnormalities, and management recommendations.

Methods and materials: Review of referral database of 514 patients and 258 surgically treated patients ages 4-64 years. Detailed history of early childhood trauma and initial encounter record retrieval were made. Patients had dynamic motion radiographs, dynamic motion MRI and also CT to identify pathology and reducibility of craniocervical instability. Preoperative crown halo traction was made before the year 2000 except in children. Intraoperative traction with O-arm/CT documentation was made since 2001. Reducible and partially reducible cases underwent halo traction under general anesthesia distraction, dorsal stabilization, and rib graft augmentation for fusion. Later semi-rigid instrumentation and subsequently rigid instrumentation was made. Irreducible compression of cervicomedullary junction was treated with ventral decompression. The follow up was 3-20 years.

Results: Database; acute worsening after trauma 262, insidious neurological deficit 252. Minimal/normal motion with neurological deficit was present in 18, previous C1-C2 fusion with worsening in 18. 28 patients of 64 without treatment worsened in 4 years. An intact odontoid process was seen in 52 children of 156 who had early craniovertebral junction trauma and later developed os odontoideum.

Surgical experience: There were 174 patients with reducible lesions and partially reducible were 22. Irreducible lesions were 62. Of the reducible, 50 underwent transarticular C1-C2 fusion, 26 C1 lateral mass, and C2 pars screw fixation. 182 had occipitocervical fusion (19 had extension of previous C1-C2 fusion and 43 after transoral decompression). 62 with irreducible ventral compression of the cervicomedullary junction underwent transoral decompression; 43 had a trapped transverse ligament between the os and C2 body and 19 previous C1-C2 fusions. Compression was by the axis body, os odontoideum, and the posterior C2 arch. Syndromic and skeletal/connective tissue abnormalities were found in 86 (36%).

Complications: 2 patients worsened, age 10 and 62, due to failure of semi-rigid construct.

Conclusions: The etiology of os odontoideum is multifactorial considering the associated abnormalities, reports of congenital-familiar occurrence, and early childhood craniovertebral trauma which also plays a role in the etiology. Patients with reducible lesions require stabilization. Asymptomatic patients are at risk for later instability. Patients who underwent childhood C1-C2 fusion must be followed for later problems. The irreducibility was seen due to trapped transverse ligament, pannus, or previous dorsal C1-C2 fusion.