Unrecognized ligamentous instability due to high-energy, low-velocity mechanism of injury
J.R. Dusseldorp a,*, M. Ow-Yang b, R.J. Mobbs a
- Department of Neurosurgery, Prince of Wales Hospital, Randwick, New South Wales, Australia
- Department of Neurosurgery, St Vincent's Hospital, Sydney, New South Wales, Australia
Abstract
We report a unique mechanism of injury and illustrate the difficulties of diagnosing purely ligamentous
injuries to the cervical spine. To our knowledge, there have been no previous reports of this type of
high-energy, low-velocity mechanism of injury. The pattern of injury is also unusual, consisting of anterolisthesis
of L4 on L5 with bilateral perched facet joints, atlantoaxial instability and bilateral lower limb
fractures. We present a 49-year-old man who experienced a high-energy, low-velocity crush injury that
led to extreme hyperflexion of his spine. Standard trauma protocols were carried out, yet atlantoaxial
instability was not diagnosed until 3 days post-operatively, when the patient went into respiratory failure
due to high spinal cord compression. We fused the C1/2 vertebral bodies using Harm's technique; the
patient exhibited no long-term spinal cord dysfunction. Although uncommon, if left undiagnosed or not
considered, purely ligamentous injuries to the cervical spine can result in catastrophic complications. Such
injuries are an important subgroup to be considered at the time of initial assessment. Furthermore, when
managing the multi-trauma patient, clinicians must remember not to overlook the atlantoaxial joint, as
high-energy, low-velocity injury to the cervical spine may lead to silent, life-threatening instability that
may not be apparent on routine imaging.
© 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Purely ligamentous injuries of the cervical spine (C-spine),
while uncommon, represent a critical subgroup of C-spine injuries
and are very difficult to diagnose.1–3 As a result, there is limited
evidence available to aid clinicians in determining the high-risk
mechanisms of injury and the ''at-risk" patient groups. Furthermore,
there is no consensus on the optimal method for clearing
the C-spine to be free of injury.4–10 We report on a patient who presented
to our facility with an unusual mechanism of injury that led
to a purely ligamentous C-spine injury missed on initial screening,
and review the recent literature.
2. Case report
A 49-year-old male sustained a high-energy, low-velocity crush
injury. A hydraulic tray (500 kg) malfunctioned and lowered slowly
on top of his head and neck,which forced the patient into a sitting position.
This caused extreme hyperflexion of his entire spine and his
lower limbs were crushed (Fig. 1). On examination the patient was
alert, had marked swelling over his lumbar spine (L-spine), bilateral
compound fractures of the distal tibia and fibula, and cauda equina
syndromeasmanifested by absent sensation in the sacral region with
loose anal tone. There was no neck tenderness and no neurological
signs of a C-spine injury. A standard trauma imaging series was performed,
which consisted of a 64-slice helical CT scan of the head,
neck, chest and abdomen, as well as plain radiographs of the lower
limbs (Fig. 2). No plain radiographs of the C-spine were taken. The
major CT finding was anterolisthesis of L4 on L5 with bilateral
perched facet joints. No abnormalities of the C-spine were detected
at the time, despite specialist review. The C-spine was cleared to be
free of injury and the hard collar removed.
The patient underwent treatment for the L4/5 dislocation and was hemodynamically stable during the general anesthetic. The patient remained intubated until day 1 post-procedure. On postoperative day 2 the patient had a brief episode of non-responsiveness, and a CT scan of the head was again performed. Soon after, he became confused and his blood oxygen saturations decreased to critical levels. Rapid sequence induction, incubation and ventilation initiated and respiratory control regained. The scout-view radiograph and the low axial slices of the head CT scan obtained
earlier showed posterior displacement of the odontoid process into the vertebral canal of C1 (Fig. 3).
3. Results
The patient was transferred to a spinal unit under the care of the senior author (RM) and internal fixation performed using Harm's technique (Fig. 4). Subsequently, there were no clinical signs of brainstem or cervical spinal cord dysfunction.
4. Discussion
The respiratory compromise experienced by the patient was probably caused by the unstable atlantoaxial ligamentous injury which, in turn, resulted in high spinal cord compression by the odontoid process. This injury was clearly visualised on the second CT scan of the head; however, it was missed on the initial standard trauma series despite retrospective review of the initial C-spine CT scan suggesting abnormality. This illustrates the difficulty in diagnosing purely ligamentous injuries to the C-spine when the highrisk mechanisms of injury and the ''at-risk" patient groups remain
undefined.
To our knowledge, the mechanism of injury of high-energy, low-velocity hyperflexion of the spinal axis has not been reported previously. Likewise, there have been no reported cases of this particular pattern of injury (that is, ligamentous injury to both the Cspine with atlantoaxial instability and the L-spine with bilateral perched facet joints).
Fig. 1. Schematic of the mechanism and pattern of injury. The large arrows indicate the high-energy, low-velocity downward force causing hyperflexion of the spinal column, while the small arrow indicates L4/5 dislocation. The atlantoaxial injury and lower limb fractures are also shown.
The reported incidence of injury to the C-spine following trauma ranges from 2.0% to 4.2%, while that of significant missed Cspine injuries depends on the studied population and the duration of follow-up, although this is generally low.11,12 The incidence of missed spinal fracture after trauma is estimated to be between 0.001% and 4.6%.3,13,14 Purely ligamentous injuries represent 10% of all injuries to the C-spine.1 Despite its relatively low incidence, purely ligamentous injury to the C-spine is a well-recognized concern due to the potentially catastrophic consequences of misdiagnosis.2
There is little evidence on the injury mechanism that is likely to result in a purely soft-tissue injury. Therefore, it is difficult to identify
high-risk patients based solely on the mechanism of injury. The risk factors identified for having a C-spine injury missed on standard protocol assessment include high-energy trauma, older age and closed head injury.3 Obtunded blunt trauma patients who have high injury scores are also more likely to have positive soft-tissue findings on MRI assessment.15 However, further research is needed to identify the high-risk mechanisms of injury and the ''at-risk" patient subgroups to enable a more accurate prediction of such injuries on clinical grounds.
Although many publications describe an institution's policy for
clearing the C-spine of injury based on retrospective analyses of
individual experiences,4–10 there is no consensus on the optimal
 Unrecognized ligamentous instability due to high-energy, low-velocity mechanism of injury
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