In splitting fractures of the C1 ring (Jefferson fracture) lateral displacement of the lateral masses of C1 can stretch and disrupt the transverse ligament. Injury to this ligament results in increased mobility between C1 and C2 and instability at this level, usually requiring surgical fusion.

The transverse ligament extends from the medial portion of one lateral mass of C1 to the medial portion of the contralateral lateral mass of C1. It wraps around the odontoid process.

The carotid artery is immediately anterior to the C1 lateral masses. The vertebral artery takes two 90 degree turns at the level of C1. The first involves posterior turn just cephalad of the transverse foramina of C2. The second turn involves a turn toward the midline at the level of the posterior arch of C1.

The sagittal sinus divides into two transverse sinuses at the level of the external occipital protuberance and the nuchal ridge on the occiput. Recognizing the location of the transverse sinuses is critical to understanding occipital fixation. Violation of the transverse sinuses can lead to fatal complications of bleeding or thrombosis.

The vertebral arteries have a complex and variable course from the transverse foramen of the cervical spine to the foramen magnum. The vertebral artery has three 90 degree turns within the lateral bone of C2. The first turn involves posterior displacement, the second one cephalad angulation, and the third one angulation towards the midline. The vertebral artery is lateral to the pedicle of C2 and cephalad to the pedicle of C2. The vertebral artery is lateral to the lateral mass of C1 and cephalad to the posterior arch of C1. The carotid arteries are immediately anterior to the lateral aspect of the cervical spine in the cephalad area, within five millimeters of the anterior bony margin of C1 and C2 lateral masses.

Atlanto occipital dissociation disrupts the ligaments joining the skull to the cervical spine. This usually involves disruption of the alar ligaments, apical ligaments, and joint capsules. The bone displacement can occur between the occiput in C1 or between C1 and C2, with C1 remaining attached to the skull and displacing with the occipital condyles.

The principal ligaments of the occipital cervical joint complex are the alar ligaments joining the occiput to C2, the apical joining the basion to the dents, transverse ligament attaching to lateral aspect of C1 on both sides and wrapping around the dens, and the joint capsules extending from the occipital condyles to C1 and from lateral masses of C1 to the lateral masses of C2.

Basilar invagination refers to cephalad migration of the c-spine in relation to the foramen magnum. This is usually seen in patients with rheumatoid arthritis. The rheumatoid process destroys the articular surfaces between C1 and C2, causing the skull and C1 to settle on C2. This results in cephalad displacement of the odontoid process. In advanced stages, this process can lead to brain stem compression and potential pulmonary arrest and death.

Mandible splitting approach to the C1 C2 area requires an incision in the oral pharyngeal space and then osteotomy through the mandible. The tongue is incised along the midline to preserve hypoglossal enervation on each side. The retropharyngeal wall mucosa and muscle is split longitudinally to gain access to the anterior portion of the basion, C1, and C2. A variation of the mandible splitting approach involves a submandibular incision with access through the submandibular incision and caudal retraction of the tongue without incision within the tongue.

The transoral approach to the C1 C2 region involves an incision through the uvula and posterior pharyngeal wall. The tongue is retracted caudally. Intubation is usually through a nasal tracheal root with lateral retraction of the endotracheal tube in the region of the pharynx.