CLINICAL
PROBLEMS AND CORRELATIONS OF CRANIOVERTEBRAL JUNCTION
Among pathologic entities at the craniocervical junction, one of the most common is the dens fracture, which may constitute nearly 20% of all fractures of the cervical spine. It is the most common cervical fracture in the elderly patient. The mean age at onset of odontoid fractures is 47, with a bimodal distribution. Younger patients tend to present with dens fractures as a com- ponent of a constellation of severe injuries that result from a high-speed, high-energy injury. Elderly patients comprise the second, larger peak group of those affected. These fractures are typically the result of a low-speed trauma such as falls from the standing position. A high proportion of the dens volume is cancellous bone, and osteopenia and osteoporosis predispose older people to these types of fractures. The latter deserve special consideration in the elderly, in whom mortality rates have been reported as high as 40%.
Dens fractures are
generally classified as types I, II, and III. Type I fractures involve just the
tip of the dens and are the least common. Type II fractures involve the base of
the odontoid process and do not extend into the C2 vertebral body. They are
considered the most common and the least stable. Type III fractures extend into
the body of C2. Differentiating the type of dens fracture is of significant clinical
importance. Dens fractures in younger patients tend to be discovered during
imaging after high-energy trauma such as motor vehicle accidents or falls and
are most clearly evident on sagittal and coronal reconstructions of axial
computed tomography (CT). In these patients it is important to rule out
atlantooccipital dislocation, which is associated with type I dens fractures. A
more common clinical scenario is an elderly patient presenting after a fall
with upper cervical neck pain and reduced range of motion. On arrival, these
patients often undergo CT of the head and neck, and the practitioner should
scrutinize both coronal and sagittal reconstructions to evaluate for a dens
fracture. If CT is unavailable or the patient presents in an ambulatory setting,
three plain radiographs with anteroposterior, open-mouth odontoid, and cross-table lateral views should be obtained.
Isolated type I
fractures that have occurred from low-energy injuries can generally be treated
with application of a hard cervical collar and are associated with a high
healing rate without surgical intervention. Type I fractures in younger
patients or after high-impact injury should be evaluated with magnetic
resonance imaging (MRI) to rule out atlantooccipital dislocation, because these
fractures involve the alar ligament.
Type II fractures are
considered unstable fractures and have a low healing rate, which is due to
disruption of cancellous bone blood supply. The vascular supply to C2 runs from
caudal to cranial, making the dens a watershed area, and this underscores the
reason for the high nonunion rate observed in this fracture pattern.
Historically, intervention of some sort has been advocated, whether it be
surgical stabilization or nonsurgical immobilization (e.g., use of a halo-vest
orthosis). The treatment of type II fractures has become an area of
considerable clinical controversy. The benefit of surgical fixation is that it
may greatly decrease the risk of nonunion, avoid cord compression that may
occur as a sequelae of nonunion, and
possibly obviate the need for immobilization with an orthosis. However,
surgical intervention must be
weighed against the patient’s comorbidities and the risks of surgical
intervention. The alternative to surgery is a halo-vest orthosis, which immobilizes
the cervical spine to promote fracture healing. A well-described danger of halo
vest immobilization is a high mortality rate observed with its use in elderly
patients. These patients are at high risk for falls, and use of this device
confers an even more morbid scenario should they fall and re-injure themselves.
This has caused many
surgeons to avoid the use of these devices in elderly patients. An alternative
treatment regimen is a period of rigid collar immobilization followed by
flexion and extension radiographs. A pain-free, radiographically stable fibrous
union is an acceptable outcome in an elderly patient with substantial
comorbidities. In patients deemed to be acceptable surgical candidates, type II
dens fractures can be treated anteriorly with an odontoid screw or posteriorly
with wiring techniques, transarticular screws, or segmental screw fixation
across C1-2. The type of surgical treatment is dependent on both fracture
morphology and surgeon expertise.
Type III fractures
extend into the cancellous, well-vascularized portion of the C2 body and
portend a good prognosis. They tend to heal well with a cervical collar owing
to the large contact area between the fracture surfaces.
JEFFERSON
FRACTURE
A Jefferson fracture
refers to a specific injury pattern of the atlas. A complete Jefferson fracture
requires that the atlas be fractured at both the anterior and posterior arches
bilaterally, disrupting the atlantooccipital and atlantoaxial articulations.
The classic definition of a Jefferson fracture results in four distinct bone
fragments, but variations with any number of fragments are common. This
fracture type is a result of severe axial loading, which transmits stress from
the skull to the lateral masses of the atlas. The lateral masses undergo some
element of lateral distraction, and the axial forces are transmitted to the
thin anterior and posterior arches of the atlas.
This fracture type is
often seen in patients presenting after a dive into a shallow pool or who have
been launched upward in a motor vehicle accident, striking their head on the
car’s roof. Patients are usually neurologically intact but may complain of
neck pain. All patients should receive a CT scan on arrival in the emergency
department after this type of trauma. Stable fractures generally have minimal
displacement and can be treated in a brace. Unstable fractures are associated
with greater displacement, and a halovest orthosis or surgical intervention
may be required.
HANGMAN’S
FRACTURE AND FRACTURES OF THE AXIS
Classic hangman’s
fracture consists of bilateral fractures through the pars interarticularis of
C2. Its namesake is a reference to the type of fractures once thought to
contribute to the cause of death during judicial hangings. This type of
fracture is now most commonly seen in motor vehicle accidents, where the head
lurches forward past a restrained torso and then snaps abruptly backward when
motion ceases. This hyperextension is likely the cause of the observed fracture
pattern. Patients with this injury may complain of pain but most often are
neurologically intact because this fracture effectively expands the spinal
canal. The vast majority of these patients can be treated with halo
immobilization, although highly displaced or angulated fractures may require
operative treatment. The fracture is generally associated with good long-term
outcome and recovery.
ATLANTOOCCIPITAL
DISLOCATION
Sometimes morbidly
referred to as “internal decapitation,” atlantooccipital dislocation is a rare
clinical entity remarkable for its change in reporting over the past several
years. It does not have a strict, universally accepted definition, but it
generally indicates that there is instability
at the craniocervical junction that allows for an inappropriate amount of
displacement or mobility of the occiput relative to the atlas. Atlantooccipital
dislocation is a result of extremely high-energy trauma. These patients
frequently present with serious trauma to other organ systems, including the
chest and abdomen, and are often clinically unstable. Owing to the severity of
the associated injuries, atlantooccipital dislocation was once thought to be unsurvivable and usually found only
at autopsy. With the advent of on-site intubation and maturation of support
systems outside the hospital, atlantooccipital dislocation has become a much
more recognized and treatable pathologic process. This is a highly unstable
injury and requires prompt surgical treatment with instrumented occipital-cervical
fusion.
