This was an experimental crossover biomechanical study which builds on previous exploratory work and compares spinal movement at both the cervical spine and lumbar spine between ‘chain cabling’ and ‘roof off’ extrication types. Roof off was chosen as it is the most frequently delivered technique by rescue services .
Participant: A single healthy volunteer was recruited to participate in this study and completed all experiments. The participant was briefed on the study, had access to a participant information sheet in advance and completed written informed consent prior to participation.
Data Collection: The participant’s height and weight were recorded prior to being fitted with the Inertial Measurement Unit (IMU) (Xsens Awinda; Xsens Technologies B.V., Enschede, Netherlands). The characteristics of IMU’s and their suitability to extrication research are described elsewhere . The IMU sensor was attached to the head using a headband. The thorax was assumed to be rigid and sensors were positioned over the clavicular notch on the sternum, and over each scapula using a tight-fitting elastic vest. A sensor was positioned on the sacrum by attaching the sensor to shorts using hook-and-loop fastening, to prevent upward travel, and securing the sensor against the body with an elastic belt. The participant was equipped with fire-retardant PPE and a helmet (with visor) to provide head and face protection. Orientation data were collected from each sensor via a wi-fi link and sampled at a rate of 40Hz. A rigid cervical collar was worn throughout this study as we have previously demonstrated that they reduce movement during extrication . A Laerdal (Laerdal Medical Corp., Stavanger, Norway) Stifneck collar was fitted by a member of the study team trained in its use and in accordance with manufacturer guidance.
Vehicle preparation: The vehicle type was pre-specified as a 5-door hatchback as this represents the commonest vehicle type on UK roads . Details of the ‘Chain Cabling’ car preparation and process can be found in Box 1. For the ‘Roof removal’ data collection, the car was pre-prepared with the A, B and C posts and the roof removed facilitating a vertical extrication technique. All sharp edges were made safe. The participant was provided with Manual In-Line Neck Stabilisation (MILNS) throughout, the back support of the driver’s seat was reclined mechanically and the Long Spinal Board (LSB) inserted to the seat base. The participant was then slid up the board until they were horizontally situated (securely) on the LSB.
Sample size: Previous work has provided mean and standard deviations for a range of volunteers undergoing ‘roof off’ extrication. Acknowledging its limitations, we used a minimally clinically important difference (MCID) derived from cadaveric work (2.7mm) . The power calculation was based on finding an anterior-posterior translational movement of 2.7mm with a significance level of 5% and a power of 80%, giving a sample size per group of 8 extrications.
Analysis: The IMU directly measures the segmental orientations from which relative motions can be calculated and reported, by assuming the relative rotations of adjacent vertebrae across the lumbar and cervical region are constant. Maximum excursions (movement from a hypothetical midline) were calculated for anterior/posterior (AP) and lateral (LR) movement of the cervical and lumbar spine, respectively. In addition to reporting maximum excursions (the single largest movement) we report “travel” - the cumulative total of all movements throughout the extrication .
Data were captured and analysed using the Biomechanics of Bodies (BoB Biomechanics Ltd, Bromsgrove, UK) software interface before being exported to Excel (Microsoft v. 16.9) and SPSS (IBM v. 25, Armonk NY) for further analysis and reporting. Maximal excursions, travel (total movement), standard deviation and confidence intervals are reported for each extrication type.
The study protocol was reviewed and approved by the University of Coventry Research Ethics Committee (reference number P88416) and the University of Cape Town, Human Research Ethics Committee (reference number 531/2021).