Fracture across base of the odontoid process is below the transverse / cruciate ligament, and it is usually unstable. Type II odontoid fractures occur when the cervical spine is hyperflexed or hyperextended. Hyperflexion and hyperextension can be caused by trauma such as a fall or whiplash from a motor vehicle accident. They are the most common type of cervical spine fractures in patients older than 70. This is probably due to the increased risk of falls in the elderly, as well as the greater incidence of osteoporosis.