Jefferson fracture
A Jefferson fracture is a bone fracture occurring at the first vertebrae.  It is classically described as a four-part break that fractures the anterior and posterior arches of the vertebra, though it may also appear as a three or two part fracture.  The fracture may result from compression of the second vertebra or hyperextension of the neck, causing a posterior break, and may be accompanied by a break in other parts of the cervical spine.
It is named after the British neurologist and neurosurgeon Sir Geoffrey Jefferson, who reported four cases of the fracture in 1920 in addition to reviewing previous cases that had been reported previously.
The differential diagnoses include: occipital condyle fractures; fractures through the superior facets of C2; odontoid fractures; ligamentous injuries; blunt vertebral artery injuries; vertebral artery dissection; and fractures through the remaining subaxial cervical spine, including vertebral body fractures, transverse process fractures, spinous process fractures, and compression fractures.

# Etiology
The most common mechanism of injury is axial compression to C1. This is seen in injuries involving direct head impact, such as head-first tackling in football or diving into shallow water. Jefferson fractures are also commonly seen in high impact motor vehicle collisions and traumatic falls. In children, Jefferson fractures may occur due to falls from playground equipment.  Less frequently, strong rotation of the head may also result in Jefferson fractures.
Jefferson fractures are extremely rare in children, but recovery is usually complete without surgery. Atlas fractures account for 1-2% of spinal column fractures and 2-13% of overall injuries to the cervical spine.   There is a bimodal distribution of atlas fractures, with most injuries seen in those in their mid-twenties and between 80-84 years of age. Approximately 57-69% of atlas fractures occur in males. The risk of cervical injury is doubled in trauma patients greater than 65 years old.

# Symptoms
Individuals with Jefferson fractures usually experience pain in the cervical spine following a traumatic axial force or hyperextension injury to the neck.  Patients may describe this as a muscle spasm or pain at the base of the occiput. On exam, they may have focal midline tenderness to palpation of the cervical spine, with limited and/or painful range of motion. As the spinal canal is relatively wide at C1 and fracture segments tend to spread outward, neurological signs/deficits are not common, but if the transverse atlantal ligament is compromised, the dens may impact the spinal cord and result in neurological deficits..  The fracture may also cause damage to the arteries in the neck, resulting in Lateral medullary syndrome, Horner's syndrome, ataxia, and the inability to sense pain or temperature.
In rare cases, congenital abnormality may cause the same symptoms as a Jefferson fracture.

# Diagnosis
If there is clinical suspicion for a Jefferson fracture, obtain lateral, anterior-posterior, and odontoid radiographs of the cervical spine, although, isolated C1 fractures can be difficult to see on plain film. Immediate CT imaging for definitive diagnosis is appropriate. Four fracture lines will be noted: two in the anterior ring and two in the posterior ring of C1. Jefferson fractures may also be associated with C2 fractures and transverse atlantal ligament injuries, so it is important to note the stability of the transverse atlantal ligament. The best imaging modality for identifying ligamentous injuries is MRI. Should this modality not be feasible, plain film findings suggestive of a transverse atlantal injury include displacement of the C1 lateral masses by more than 6.9 mm or an atlanto-dens distance of more than 3 mm.
It is highly unlikely to have a spinal cord or vertebral artery injury with an isolated Jefferson fracture; however, it is not impossible. If there is concern for blunt vertebral artery injury, obtain a CT angiogram of the neck.

# Treatment
Immediately place patients with a suspected or confirmed Jefferson fracture in spinal immobilization using a rigid cervical collar. Often times, a cervical collar is already placed by EMS in the prehospital setting. The use of surgery to treat a Jefferson fracture is somewhat controversial. A primary factor in deciding between surgical and non-surgical intervention is the degree of stability as well as the presence of damage to other cervical vertebrae. Stable, isolated Jefferson fractures, defined as having an intact transverse atlantal ligament, are treated successfully with external immobilization devices such as rigid cervical collars, a halo-thoracic braces, or a sterno-occipitomandibular braces for 8-12 weeks. The use of rigid halos can lead to intracranial infections and are often uncomfortable for individuals wearing them, and may be replaced with a more flexible alternative depending on the stability of the injured bones, but treatment of a stable injury with a halo collar can result in a full recovery. If there is a disruption of the transverse ligament (atlantal), the injury may require traction, a halo, or surgical repair such as a C1-C2 or C1-C2-C3 fusion/fixation. Discuss treatment and disposition in conjunction with Neurosurgery or Orthopedics, depending on institutional practice. Fusion may occur immediately, or later during treatment in cases where non-surgical interventions are unsuccessful.
Though a serious injury, the long-term consequences of a Jefferson's fracture are uncertain and may not impact longevity or abilities, even if untreated.  Conservative treatment with an immobilization device can produce excellent long-term recovery.
Pain, however, is a frequent complaint for patients, even beyond the first year after injury. Nearly 14-80% of patients report mild neck pain, 20% report scalp dysesthesias, and 8-20% report neck stiffness. Nearly 34% of patients with a Jefferson fracture report at least some impairment of daily living activities.