Instability between C1 and C2 usually has a result of disruption of the transverse ligament and can lead to anterior translation of C1 on C2. This results in compression of the brain stem between the posterior arch of C1 and the odontoid process.

The pharynx and the esophagus are immediately anterior to C1 and C2.

The transverse ligament wraps around the odontoid process and attaches to C1 on both sides. The apical ligament inserts on the apex of the dens. The alar ligaments insert immediately lateral to the apical ligament insertion.

The vertebral artery has a complex course through the occipital cervical junction. In this region, it has four 90 degree turns between C1 and C2 prior to entering the foramen magnum. The carotid artery is immediately anterior to the occipital cervical junction.

Hangman’s fracture refers to a fracture in the posterior arch of C2. Since this injury occurs between the superior articular surface and the inferior articular surface of C2, it is also referred to as pars interarticularis fracture of C2.

A Type II fracture of the odontoid process involves at the junction between the odontoid process and the C2 vertebral body. These fractures frequently fail to unite. The bone in this region is primarily cortical. Even minor displacements of the fracture can lead to marked reduction in the surface area available for healing. Additionally, the articulation between the transverse ligament and the odontoid process contains a synovial capsule. Fracture in this region disrupts the synovial capsule, leading to an interarticular fracture. Presence of the synovial fluid in the fracture site can further impair bone healing.

The pharynx and esophagus are immediately anterior to C2. Pathologic processes in the C2 vertebral body can require surgical approach through the mouth (transoral approach) or through the tongue (mandiblesplitting approach).

The transverse ligament wraps around the odontoid process and attaches to C1 on both sides.

The vertebral artery has two 90 degree turns in the bone in the lateral region of C2. The first involves a lateral 90 degree turn and the second a cephalad ninety degree turn at the level of the lateral edge of C2 vertebral body. Injury to the vertebral artery is a potential complication of screw fixation into C2. The vertebral artery is caudal to the pedicle of C2 and lateral to the pedicle of C2. The carotid artery is immediately anterior to the lateral masses of C2.