Management of C1-C2 instability with distorted cranio-vertebral anatomy by using 3D CT angiography model: A rare case report

Atlantoaxial instability is between C1/atlas and C2/axis, and it can be caused by different conditions such as congenital anomalies (Down syndrome, Morquio syndrome, and other skeletal dysplasias), inflammatory diseases, traumatic fractures, tumors, and infections. This necessitates the need for surgical occipito-cervical fusion (OCF) to prevent further injury to the spinal cord and subsequent myelopathy. Atlantoaxial instability is a rare condition and is commonly seen in 30% of patients with Down syndrome and in 30–80% of patients with rheumatoid arthritis; however, very few are symptomatic. Here, we present a rare case of a 17-year-old male with atlantoaxial instability due to occipitalized atlas and congenital fusion of C2-C3. The patient was operated by occipitoaxial fixation using C2 pedicle screws and an occipital plate with a rod construct with onlay bone allograft for bony fusion. Occipitoaxial fixation with a significant decrease in atlantodental interval (ADI) can be obtained by the use of C2 pedicle screws, and an occipital plate with a rod construct provides a rigid fixation and stability in the management of atlantoaxial joint instability with C1-C2 fusion due to an onlay bone allograft. Unnecessary C1 instrumentation and donor site morbidity for bone autografts can be avoided. Use of the 3D CT model helps to delineate the altered occipitocervical and vertebral artery anatomy intraoperatively, which aids in appropriate reduction and fixation.