Atlanto-occipital dislocation: an unusual lethal airbag injury

Initial analysis of archived non-human primate frontal and rear impact data from the biodynamics data resource

OBJECTIVE

The research objective was to conduct an initial analysis of non-human primate (NHP) data from frontal and rear impact events archived in the Biodynamics Data Resource (BDR) records of the Naval Biodynamics Laboratory (NBDL). These rare data, collected between 1973 and 1989, will inform the safety community of upper-end tolerance limits of NHP and may be related to severe crash scenarios.

METHODS

Data from frontal and rear acceleration tests to 93 macaque NHP were examined. Each NHP was fully torso restrained, whereas the head-neck complex was unrestrained. Each NHP underwent between 1 and 21 total runs; 2 total runs was most common-a low-level run and then a high-level run. Following each impact exposure, the NHP was evaluated using a series of medical examinations. Now part of the legacy collection in the BDR, these evaluations were used to assess NHP exposures to be in one of 3 categories: noninjurious, injurious, or fatal. Using reported peak sled acceleration values, data were amenable to survival analysis statistical methodology to derive injury probability curves (IPCs). IPCs were derived for injury and fatality outcomes.

RESULTS

Fatal injuries for both frontal and rear impacts were mostly at the cranio-vertebral junction. In addition to hemorrhage, fatal frontal and rear impact tests both produced predominantly atlanto-occipital dislocations, with and without spinal cord transection. After exclusions, IPCs were derived for frontal and rear impact for both (1) fatal outcome and (2) injurious outcome (any injury including fatal injury). For frontal impact, 53 NHP qualified with 5, 25, and 50% risk for fatality at 89, 105, and 114 peak sled Gs, respectively, and for injurious outcome at 70, 92, and 106 Gs, respectively. For rear impact, 34 NHP qualified with 5, 25, and 50% risk for fatality at 96, 122, 138 peak sled Gs, respectively, and for injurious outcome at 75, 99, and 115 Gs, respectively.

CONCLUSIONS

The majority of injuries were at the cranio-vertebral junction, indicating that the inertial head mass caused a tensile loading mechanism to the cervical spine. These data may be used in conjunction with finite element modeling to estimate risks to the human population. The most direct application in the automotive environment could be to the well-restrained child. The N_ij neck injury criteria, currently based on data from piglet studies, could also benefit because the NHP is a more accurate human surrogate. These types of tests are likely to never be repeated and will form an upper bound of tolerance information valuable to safety system designers.

Traumatic atlanto-occipital dislocation in children

Although once considered an invariably fatal injury, improvements in diagnosis and management have made atlanto-occipital dislocation (AOD) a survivable injury. MRI is the preferred imaging modality; occasionally, flexion/extension/distraction fluoroscopy may be required to determine craniovertebral stability. Early surgical stabilization is recommended for all children with AOD. Early occipitocervical fusion using screws in combination with a rod or plate, or sublaminar wires with a contoured rod, coupled with autograft bone, provide immediate stabilization and a high fusion rate. Halo immobilization and traction are contraindicated in the management of AOD in children because of the risk of displacement of the injured occipitocervical joint. Postoperative hydrocephalus is frequent and should be suspected when neurologic decline occurs after fixation. Nearly half of children who survive AOD will have residual neurologic deficits.

[Traumatic atlanto-occipital dislocation as part of a complex cervical spine injury. Case report in a 12-year-old girl]

Traumatic atlanto-occipital dislocation (AOD) appears to be an unusual and almost universally fatal injury. Although AOD is the cause of death in about 10% of fatal cervical spine injuries an increasing number of reports document cases of survival following this injury. Improved pre-hospital and in-hospital emergency care according to ATLS guidelines that include early cervical spine stabilization, effective diagnosis because of improved imaging after trauma including whole body multislice CT followed by expeditious reposition and adequate immobilization are reasons for this phenomenon. We report the case of a 12-year-old girl surviving an AOD accompanied by a distraction injury C6/7 with unilateral fixed spinal luxation. After a primary attempt at closed reduction and external stabilization with a halo vest, the injury was treated by a navigated dorsal spondylodesis C0-C1 using the CerviFix rod system and open reposition of the remaining subluxation C6/7 with laminar hooks. The literature was reviewed for diagnostic possibilities, management and prognosis of AOD.

Airbag-Mediated Pediatric Atlanto-Occipital Dislocation

Pediatric atlanto-occipital dislocation (AOD) most commonly occurs in victims of high-velocity motor vehicle collisions and usually results in death. The mechanical and anatomic predisposing factors for AOD in children have been well documented. With the introduction of passenger-side air bags in automobiles, reports have documented an increased incidence of pediatric cervical spine injuries, including AOD, in low-speed motor vehicle collisions. Although long-term survival in AOD is so unusual that there is no separate literature regarding its physiatric treatment, it is generally treated like any other high cervical spinal cord injury. Recent advances in adaptive technology have aided greatly in management. Despite benefits that adaptive technology affords, the best treatment for AOD is still prevention. For this reason, children under the age of 13 should be restrained backseat passengers in automobiles.

Tectorial Membrane Injuries in Children

We report three cases of tectorial membrane injury in children. An increased interspinous ratio was identified on cervical spine radiographs. The tectorial membrane injuries were diagnosed by magnetic resonance imaging. The three children were restrained passengers in high-speed motor vehicle accidents, and all sustained polytrauma. Two children with partial tears of the tectorial membrane were immobilized in a halo, and one with a longitudinal tear of the tectorial membrane had an occiput-to-C2 fusion.

Injuries caused by airbags: a review

With the number of vehicles on the road increasing, the safety aspects of motoring are becoming a progressively more important consideration in health care provision and policy. Airbags are a relatively new introduction into our vehicles. Unlike other mechanisms such as seat belts, they offer protection without the need for any action on the part of the occupant. However, the necessarily violent nature of their deployment has led to the emergence of patterns of injury as a direct result. Knowledge of the potential dangers posed by these systems is useful both for emergency department physicians in order to prevent important injuries being missed, and for car manufacturers using increas ingly modern technology to design more efficient mechanisms. We undertook a review of the current literature to ascertain the spectrum of injuries that have been attributed to the use of airbags, while putting this into the wider context of their protective contribution.

Temporomandibular joint pain following airbag deployment on the face: a case report

Varieties of injuries have been reported as a result of the deployment of the airbag/s following road traffic accidents. The purpose of this case-report is to present a physiotherapist's perspective of a patient who was diagnosed as having temporomandibular pain and dysfunction following the deployment of the airbag on the face and its implications for the dental profession. The patient was assessed using a modified Maitland assessment procedure to establish the diagnosis and the treatment consisted of Maitland mobilisation techniques, pulsed short wave diathermy and ultrasound as and when indicated directed to the upper cervical spine. The outcome of this case-report suggests that the temporomandibular symptoms presented by this patient were of cervical origin. Therefore, it is suggested that the cervical spine should be routinely examined in patients presenting with temporomandibular pain and dysfunction following trauma and early referral to physiotherapy may facilitate early recovery.

Airway management after upper cervical spine injury: what have we learned?

PURPOSE

Survival after atlanto-axial-occipital ligamentous injury is uncommon and experience with the immediate clinical management of these patients is similarly low. There has been considerable work published recently with respect to airway management in similar patients and a review of this material was undertaken.

METHODS

Medline searches were performed to seek out the English language literature using the key words and phrases: cervical spinal injury; atlanto-occipital dislocation; atlanto-occipital disarticulation; and airway management after spinal injury. The titles were culled for materials relevant particularly to upper cervical spinal injury, these were obtained and reviewed. The bibliographies of these articles were searched to ensure that the review would be complete.

RELEVANT FINDINGS

The majority of cervical spinal movement occurring during direct laryngoscopy is concentrated in the upper cervical spine. The magnitude of movement during airway management rarely exceeds the physiological limits of the spine. Movement is reduced by in-line immobilization but traction forces cause clinically important distraction and should be avoided. Indirect techniques for tracheal intubation cause less cervical movement than does the direct laryngoscope. Survival after severe upper ligamentous injury is uncommon but intact survival occurs. Missed diagnosis is common and associated with a high incidence of severe secondary injury. Failure to immobilize the spine is deemed to be the most relevant factor in secondary injury.

CONCLUSIONS

Patients who survive severe upper cervical ligamentous injury and present to hospital are uncommon. However, of those who do, both intact survival and survival with limited neurological sequelae do occur. Meticulous airway care with maintenance of alignment and provision of continuous cervical immobilization are an integral component of care in these patients.