Unilateral lateral mass compression fractures of the axis.

Lateral mass compression fractures of the axis involve compression of the pedicle and displacement of the overlying facet, with or without an accompanying fracture of the odontoid. These unilateral fractures are not rare. Correlation is made between clinical cases and cadaver material with analysis of microradiographs. Criteria for recognition of the resultant healed fracture deformity include: (1) Tilting of the odontoid; (2) Loss of the odontoid shoulder on the affected side; (3) Increased downward slope of the affected facet; (4) Lateral compression, possibly with buckling; (5) Asymmetrical apophyseal joints between axis and atlas; and (6) Tilting downward of occiput on affected side, often with evidence of rotation between the occiput and the axis. Not all criteria need be present. Clinical sequelae often include persistent neck pain, limited rotation of the head, and occipital headaches radiating anteriorly.