This is the first biomechanical analysis of different types of self-extrication published to date, reporting both cervical and lumbar movements as well as providing additional details of excursion and rotation. This is also the first study which allows direct comparison of the effect of instructions and cervical collars on spinal movement. The use of a collar and no instructions resulted in the smallest movement of the cervical and lumbar spine during self-extrication.
Instructions
Commonly people remain in cars following MVC’s as a result of concerns about movement exacerbating potential spinal injury. Delivery of instructions would require the presence of trained personnel (rescue service or clinical) on scene or a telecommunications surrogate (e.g. via mobile telephone). If instructions are not beneficial, as suggested by this study, then this would potentially release clinical and operational personnel to other tasks and empower policy that encourages potential casualties to leave their car before the arrival of clinical or operational services.
The finding of increased spinal movement with instructions was unexpected. Dixon et al. utilised instructions for all of their self-extrications, which were also adopted for Haske’s single participant study [23, 25]. Engsberg et al. did not provide instructions to their participants [33]. Gabreli et al. compared the use of instructions provided in video and verbal explanatory format prior to the subjects (all young men less than 30 years of age) attempting self-extrication – they found that instructions reduced movement in the sagittal (AP) plane (other movements were not tested / analysed) at the cervical spine [24]. No previous studies have considered movement at the lumbar spine. Within our study we attempted to maximise external validity by using participants unfamiliar with extrication and using direct verbal instruction as would be delivered by a member of a rescue team at the scene of an incident.
We suggest that the smaller movements found when no instructions were given was a result of subjects finding their own ‘route’ to leave the vehicle, resulting in a more natural, comfortable extrication. This ‘naturalness’ perhaps explains the very narrow confidence interval found for results for no-collar and no instructions across all translation movements (Figs. 2, 3, 4 and 5). If this hypothesis is correct, we would expect the difference in movement between instructions and no instructions to be larger in a patient’s own vehicle, where familiarity and well-practiced egress could lead to smaller movements. We did not investigate the effect of variations in instructions but utilised the instructions previously produced by Dixon et al. – refinement of such instructions could lead to decreased spinal movement and is a consideration in planning further research in this area.
Cervical collars
Cervical collars are carried on all FRS appliances in the UK. They are commonly applied to casualties whilst still in their car and remain in situ throughout extrication. If collars are not required in casualties suitable for self-extrication this would have significant implications for the time in their clinical course that casualties may be asked to attempt self-extrication. This could mean that some casualties could be asked to attempt self-extrication at initial call to the Emergency Services. Such a finding would also have significant implications for recommendations to bystander / buddy care at the scene of a motor vehicle collision. In our study there was a strong association between collar use and decreased cervical spinal movement (p < 0.001); this finding is in keeping with the intended purpose of such devices and is consistent with previous work [25, 33]. It is contrary to the findings of Dixon et al. who identified a small, mean increase in movement associated with collars when degrees of anterior–posterior, medial–lateral and rotational movement were combined [23]. The difference identified by Dixon was small, not present in all of the participants studied and the confidence intervals between the two groups overlapped. There has been increasing challenge to the routine use of cervical collars in prehospital care [22]. The purpose of a cervical collar is to minimise movement and as such stop an unstable fracture from causing secondary avoidable cord damage. A majority of the biomechanical analysis in this area uses healthy volunteers or cadavers and as a result it remains unclear that using a collar effectively reduces movement when an unstable cervical spine injury is present [34].
As might be expected, in our study the cervical collar did not consistently reduce movement at the lumbar spine.
Movement in the context of spinal cord injury
Significant force is required to cause unstable spinal fracture or cord injury. Such forces would normally be associated with significant movement, movement that is likely to be maximal at the point of energy transfer. Despite the potential biomechanical implausibility of small additional movements causing further cord injury, extrication strategies and rescue services approach are focused on movement minimisation and the prevention of secondary injury [18].
Limitations
This study has a number of limitations. By definition, our volunteers were healthy and without spinal pathology. They were not subjected to motor vehicle collisions, recent spinal trauma and did not have unstable (or other) spinal injuries. Our volunteers did not have distracting injuries, intoxication, confusion, pain-relief administered, or the psychological impact of a real MVC.
This limits application of our results to the significantly injured patient population. In real patients with spinal injuries, the movements may be larger in those with unstable injuries or reduced due to the pain and muscular spasm that frequently co-exists with an acute injury.
This study aimed to maximise external validity by utilising volunteers with no knowledge of the process of extrication, a mix of males and females and a range of weights, heights and BMI’s. There was no discernible association between each of these factors and spinal movement. In this context, variation of self-extrication technique by patient sex, age, weight, height or BMI cannot be recommended on the basis of this study, but could be considered in further research. The order in which participants progressed through the study arms was delivered to minimise learning, particularly in relation to the verbal instructions. Learning may, however, have occurred as the participants progressed through the study and this may affect the internal validity of the study. Likewise, the potential effect of participant fatigue on our results cannot be ruled out.
The study vehicle was the same for all volunteers and was not modified but was not one the participants were familiar with and it is possible that familiar vehicles would be associated with different extrication characteristics compared to our test vehicle. There may also be variation in results for vehicles with inherently different structural characteristics, for example, 4 × 4 type vehicles or low-riding sports vehicles.
Interpretation in a clinical context
The majority of casualties involved in MVCs are uninjured or have only minor injuries it is this subgroup in which self-extrication is the preferred route of extrication and which has the most similarities to our healthy volunteers [11]. There are several potential advantages of self-extrication over tool extrication including decreased time, decreased resource utilisation and less risk to the patient and rescuer. Within the inherent limitations of this study, this work helps us to understand self-extrication in the context of spinal movement minimisation. When a patient is suitable for self-extrication (very few casualties with unstable injuries have occult injuries [22], instructions are unnecessary, could be counter-productive and should not be delivered. In services which use collars, these may be applied to facilitate extrication and then removed once the extrication is complete to minimise any potential complications. Further work is needed in this area to understand the movements associated with application of a collar to a patient in a car and the benefits and harms of collars in this patient group at the various stages of their patient journey.
Previous researchers have concluded that self-extrication is associated with smaller movements at the cervical spine than other methods of extrication, which normally involve being physically lifted from the vehicle by rescue service personnel on to a board or a scoop [23, 24]. Trapped casualties have an excess mortality, and many of the injuries they suffer are time critical [11]. As such, the benefits and harms of current extrication techniques need to be carefully considered in the context that in all likelihood the current approach is not achieving the intended therapeutic goals in terms of movement minimisation and are potentially contributing to excess morbidity and mortality.
Future research
This should aim to answer the questions of which casualties should self-extricate, whether the principles identified here can be applied to other motor vehicles and the real-world resource, health economic and clinical benefits (or otherwise) of the adoption of self-extrication as the principle route of extrication for appropriate casualties following MVCs. Additional biomechanical studies should be designed to characterise the movement associated with in-car collar application and analysis of other commonly used extrication techniques, including those who cannot self-extricate.
Future research is needed to define which casualties may benefit from current movement minimisation techniques and furthermore engage with casualties and subject matter experts to identify a balanced solution to the problem of casualties trapped in vehicles following MVCs.