Dens fractures have accounted for 7% to 17% of all fractures of the
cervical spine in series of up to 625 cervical
fractures1-5.
In the classification system of Anderson and D'Alonzo, a type-III dens
fracture extends downward into the cancellous portion of the body of the
axis6 and typically
heals without surgical intervention. After adequate reduction with traction,
the use of a halo vest or halo cast has been associated with union rates of
80% to 100% in series ranging from twenty-one to 107
fractures1,4,5.
Although displacement and/or
dislocation2 of a
dens fracture has been described in terms of translation or angulation,
vertical displacement as a factor in determining stability or the adequacy of
reduction has received little attention. Two case reports described vertical
displacement of a type-III odontoid
fracture7,8.
Neurologic injury followed routine application of traction in both patients.
The first patient became a ventilator-dependent quadriplegic, and the second
died of complications from paralysis. The authors recommended aggressive
surgical management when faced with this fracture pattern.
We present the cases of three patients who had a type-III dens fracture
with vertical displacement to describe the clinical, radiographic, and
anatomic findings and to raise awareness of this rare but potentially
devastating injury. In addition, we evaluated the clinical effectiveness of
our treatment. Our hypothesis was that early recognition of this injury
pattern and urgent surgical management provide the potential for functional
survival. Our review of the cases was approved by our institutional review
board, which waived the need for informed consent.
We reviewed the cases of three patients with an acute traumatic type-III
dens fracture and vertical displacement treated between 1998 and 2000. All
three patients presented with vertical displacement of the dens on the initial
radiographs and/or on a computerized tomography reconstruction. Clinical
records and imaging studies were reviewed for patient demographics, mechanism
of injury, associated injuries, anatomic features of the injury, definitive
treatment, and clinical outcome. The duration of follow-up ranged from ten to
twenty-seven months.
Case 1. A sixty-five-year-old woman was involved in a
motor-vehicle accident and presented with loss of consciousness. Her injuries
included a subarachnoid hematoma, a subdural hematoma, incomplete
quadriparesis (ASIA [American Spinal Injury Association] class D, C5
level9), and
bilateral sixth cranial nerve palsy. Radiographs revealed a type-III dens
fracture with vertical distraction (Fig.
1-A). Computerized tomography demonstrated facet separation in the
coronal plane with axial distraction of the dens fracture fragment
(Fig. 1-B). A magnetic
resonance imaging scan demonstrated cerebrospinal fluid extravasation (a
pseudomeningocele) at the C1-C2 level (Fig.
1-C).
A halo vest was applied, but vertical displacement persisted despite
multiple adjustments. The patient then underwent a posterior C1-C2 arthrodesis
with sublaminar cables and iliac crest bone-grafting. During the exposure, the
pseudomeningocele was encountered and the ligamentum flavum and the C1-C2
facet capsules were noted to be disrupted. The dura mater was attenuated in
the area of the injury and was covered with Gelfoam and thrombin. Use of the
halo was continued postoperatively because of concerns of vertical instability
at the fracture site. The persistent sixth cranial nerve palsies were
attributed to traction on the nerve by the injury. At twenty-seven months
after the injury, the patient had union of the dens fracture with 5 mm of
posterior displacement but had a nonunion at the site of the C1-C2
arthrodesis. The cranial nerve palsies continued, and the incomplete
C1-C5-level quadripareses (ASIA class D) persisted.
Case 2. A thirty-nine-year-old woman was involved in a
motor-vehicle accident and was found to be unresponsive at the scene. Her
injuries included bilateral pulmonary contusions and a right temporal
subarachnoid hematoma. A lateral cervical spine radiograph demonstrated a
distracted dens fracture. Magnetic resonance imaging confirmed a type-III dens
fracture with vertical displacement (Fig.
2). The neurologic examination could not be carried out properly
because of the extremity and head injuries but was thought to reveal normal
findings. The patient had hemodynamic instability, and a halo vest was applied
for immobilization. In spite of the halo immobilization, motion at the
fracture site was noted with each ventilation viewed under fluoroscopy.
Progressive quadriparesis occurred during the first twenty-four hours after
the injury as hypotension was managed with blood and fluid replacement and
vasopressors.
Following resuscitation, at thirty-six hours after the injury the patient
underwent a posterior C1-C2 arthrodesis with sublaminar wires and iliac crest
bone graft. Transarticular screw placement was attempted, but massive bleeding
was encountered from a combination of the disrupted cavernous complex of veins
overlying the C1-C2 facet joints and epidural bleeding; the patient was
therefore maintained in the halo vest. Over the ensuing three weeks, multiple
adjustments of the vest were needed to maintain the reduction.
Because of persistent vertical instability, the patient underwent C1-C2
transarticular screw fixation twenty-five days following the initial surgical
attempt. A partially threaded screw was used as a lag screw to aid in the
reduction. Radiographs made ten months after the injury demonstrated bridging
bone from C1 to C2 and healing of the dens fracture. The patient remained an
ASIA class-A, C5 tetraplegic at the latest follow-up examination.
Case 3. A twenty-nine-year-old woman was found unconscious after
being ejected from a motor vehicle. She had sustained multiple injuries
including facial fractures, intraventricular hemorrhage, and a right brachial
plexus injury.
Cervical radiographs and computerized tomography identified a burst
fracture of C1 and a type-III dens fracture with 5 mm of distraction at the
fracture site and the C1-C2 facet joints
(Fig. 3-A). A halo vest was
immediately applied, and the patient was found to have persistent distraction
at the dens fracture site. Vertical instability, with distraction ranging from
5 to 10 mm with each ventilation, was noted on fluoroscopy at the time of
surgery. The patient underwent a C1-C2 arthrodesis with transarticular screws
and iliac crest bone graft. Partially threaded screws were used as lag screws
for reduction and fixation. The brachial plexus injury resolved at eight
months after the injury. Radiographs made at eighteen months after the
original injury demonstrated healing of the fractures and fusion
(Fig. 3-B).
Type-III dens fractures are usually relatively benign injuries associated
with few complications. Low nonunion rates with halo traction and/or
immobilization with a vest have been
reported1,4,5.
We reported three cases of vertically unstable type-III dens fractures for
which initial treatment with a halo device was associated with problems.
A review of the cases of 102 patients with atlantoaxial dislocation,
including those treated at one center and others described in the literature,
revealed a 55% prevalence of sub-arachnoid hemorrhage at the C2 level and a
15% rate of dural laceration or brainstem
injury10. All of
our patients had =5 mm of vertical displacement of the dens on the initial
imaging studies. The C1-C2 facet joints were distracted >5 mm. One of our
patients (Case 1) had a subdural hematoma and dural laceration in addition to
bilateral sixth cranial nerve palsy that was probably due to traction at the
exit of the nerves at the pontomedullary
junction8.
Postmortem studies have shown dens fractures with complete disruption of
the anterior atlantoaxial ligament, tectorial membrane, and facet joint
capsules on both sides with the dens held loosely by the alar
ligaments11. These
injuries appear to have been vertically unstable type-III dens fractures
similar to those described in this report. The circumferential injuries noted
in a distracted type-III dens fracture explain why the reductions in this
study could not be held with a halo device or sublaminar wiring alone.
The halo device, in spite of being perhaps the best external immobilizer
for cervical spine injuries, has been reported to restrict only 75% of
atlantoaxial
motion12. Patients
moving from the supine to the sitting position have been reported to
experience distraction forces of up to 9 kg when wearing a halo vest and those
of up to 13 kg when wearing a halo
cast13. Despite our
limited experience, we believe that immobilization with a halo vest is
inadequate treatment for a vertically unstable dens fracture.
We believe that type-III dens fractures with >5 mm of vertical
distraction are unstable and must be recognized and stabilized operatively as
soon as the patient's condition allows. We recommend reduction and surgical
stabilization with C1-C2 transarticular screws and posterior arthrodesis for
the treatment of these fractures. A type-III dens fracture associated with
distraction of the atlantoaxial facet joints, craniocervical sub-arachnoid
hemorrhage, or cranial nerve palsies should suggest the possibility of
vertical instability. ?