9 This scheme classifies odontoid fractures by anatomic location. Many classification schemes for odontoid fractures have been proposed, but the most commonly used is that described by Anderson and D’Alonzo in 1974. They are the most common and potentially most devastating of all axis fractures. The treatment of odontoid fractures has long been a topic of debate. All these adaptations combine to make a highly mobile yet stable connection between the skull and the spine. There is also close apposition of the spinal cord to the axis of rotation, which minimizes the torsional forces on the spinal cord that would be present if the cord were located more posteriorly. 13 The odontoid process is held tightly to the anterior portion of the C1 ring by the strong transverse ligament, which prevents subluxation in the sagittal plane. Other noteworthy features of the C1-2 joint include the absence of a true intervertebral disk and relatively loose capsular ligaments, 12 evolution of the ligamentum flavum into a weaker atlantoaxial membrane, a rich blood supply from branches of the vertebral and carotid arteries, and an increased spinal canal diameter. The atlantoaxial joints also allow about 50 degrees of axial rotation and 10 degrees of flexion-extension.
Approximately 50% of the rotational movement of the entire spine takes place at C1-2 fusion of this segment would cause this motion to be lost. The atlantoaxial complex is configured to allow much more rotational movement than in any other segment. 11 Because the weight of the cranium is transmitted from a relatively lateral and posterior position to a medial and anterior position at C2, the axis is referred to as a transitional vertebra. This anatomy consists of the axis, atlas, odontoid process, occipital condyles, C2-3 disk, C1-2 facet joints, synovium of the occipital condyles, and the ligaments that attach to C1, C2, and the skull. The anatomy of the axis is unique in that it forms a connection with the mobile upper cervical spine and cranium and the lower cervical spine. Os odontoideum and fractured calcified pannus may mimic acute C2 fractures. These injuries may be missed clinically because of the lack of clinical signs except for neck pain.
2, 9, 10 C2 fractures are classified as odontoid fractures involving the dens Hangman’s fractures, a traumatic spondylolisthesis through the pars interarticularis and miscellaneous fractures, including facet fractures or injury through the foramen transversarium. 1Īpproximately 9% to 20% of all cervical fractures are dens fractures, 2, 6 – 10 with most (65% to 74%) being type II fractures.
Since 2000, the incidence of persons older than 60 years at time of injury has increased to 11.5%, as opposed to 4.7% before 1980. 4, 5 In the elderly, falls are the most common cause of cervical spine injury. 4 The mortality rate for these injuries ranges from 25% to 50%. 2 Cervical spine injury occurs in 1.5% of injured children, 3 and 53% of these injuries are related to motor vehicles: motor vehicle crashes, 31% pedestrian versus motor vehicle, 16% and bicycle versus motor vehicle, 6%. 1 The cervical spine is affected in more than 60% of spinal injuries. The estimated annual incidence of spinal cord injury in the United States, not including those who die at the scene, is approximately 12,000 new cases each year.
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