Clinical History
A 46-year-old female patient without any significant medical history was admitted to the emergency room after having fallen from a horse. She described an axial impact on her head, without loss of consciousness, and complained about acute neck pain. She was haemodynamically stable, and her neurological status was unremarkable.
Imaging Findings
Plain radiographs of the cervical column were obtained (Fig. 1a-c), showing two fracture lines of the posterior arch of the atlas. There was no atlanto-occipital or atlanto-axial dislocation, and no evident vertebral fracture on a more caudal level.
A computed tomography (CT) examination of the head and the cervical spine was then performed (Fig. 2), showing an additional fracture line of the anterior arch of the atlas on the right with a 4 mm diastasis between the main fragments. No skull fracture or intracranial bleed was present.
Magnetic resonance imaging (MRI) was finally realized, confirming integrity of the transverse ligament of the atlas (Fig. 3).
Discussion
First described in 1920, Jefferson fracture is a rare fracture of the atlas, defined by concomitant fractures of its anterior and posterior arches, leading to a burst of the atlas ring. It generally results from axial loading upon the cervical spine, similar to occipital Anderson fracture. Different variants of Jefferson fractures have been described depending on the number of fracture lines, ranging from two to four, the latter being the most common variant [1].
Patients have a history of head or neck trauma and present with neck pain.
In general, no neurological deficits exist as the fracture entails a burst of the atlas ring and tends to enlarge the spinal canal. If present, neurological symptoms are mostly attributable to other associated cervical spine lesions, as it is the case in up to 50% of C1 fractures, and not less than 43% of them are associated with C2 fractures [1, 2].
Three-view conventional radiographs are commonly performed initially. Three main signs of a Jefferson fracture that should be remembered are: firstly, on the lateral view, an abnormal width of the retro-pharyngeal soft-tissue shadow; secondly, on the same incidence, a predental space exceeding 4 mm; thirdly, on the open-mouth view, a displacement of the lateral masses of C1 (offset), traducing the burst of the arch [2]. It has been experimentally demonstrated that, when exceeding 6.9 mm, the sum of the displacement of the two lateral masses of C1 over the upper articular surfaces of the axis is highly suspect of a disruption of the transverse atlantal ligament [3]. CT is the best technique to assess cervico-occipital junction lesions, including Jefferson fractures. Axial views may show avulsion of a tubercle on the medial surface of a lateral mass of the atlas, corresponding to the insertion site of the transverse ligament [1], indicating instability of the atlantoaxial complex even in non-displaced fractures.
Magnetic resonance imaging is irreplaceable in soft tissue analysis. It is generally performed to confirm or rule out ligamentous injury, or lesions of the spinal cord.
Non-displaced and stable Jefferson fractures are treated conservatively by hard collar immobilisation. Unstable fractures on the other hand require a more aggressive treatment including axial distraction, halo vest immobilisation, or posterior or trans-oral C1-C2 internal fixation.
In summary, Jefferson fracture is a burst-like fracture of the atlas that, if isolated, does normally not cause neurological deficits. Complete imaging workup is indispensable to search for signs of instability and other associated vertebral lesions.
Differential Diagnosis List
Jefferson fracture
Other types of atlas fractures
Congenital atlas abnormalities [4]
