BME 598/698 Seminar
Friday January 14th 8-9am
Blusson Spinal Cord Centre Lecture Hall
Speaker: Carolyn Van Toen
Supervisors: Peter Cripton, Tom Oxland
Title: Lateral Bending in Head-First Impacts: Acoustic Emission Monitoring of Spine Injuries
Axial compression is a common injury mechanism for the cervical spine resulting from head-first impacts. Neck injury criteria used to evaluate safety devices define limits for cervical spine forces and moments in the sagittal plane (flexion and extension) but the influence of moments in the coronal plane (lateral bending) is unknown. In addition, neck injury criteria are based on mechanical tolerances that are often subjectively determined. Acoustic emission (AE) sensors could provide more objective data on the timing of injury; these have been used to detect the time of injury of facial and ankle bones but AE signals have not been reported for spinal ligaments tested at any loading rate or for any component of the spine in dynamic loading. The aims of my thesis are to 1) examine the ability of AE signals to detect injury in the spine and differentiate between failures of different spine components (Study 1) and 2) examine the effect of lateral bending on failure of the cervical spine and neurologic injury potential in dynamic axial compression using cadaveric spine specimens (Study 2). It is hoped that the AE methods developed in Study 1 will assist in the definition of failure forces and moments in Study 2. This research will generate crucial guidelines for the development of injury prevention devices and may assist in reducing incidence rates of spinal cord injury. This presentation will focus on Study 1.
In Study 1, isolated cadaveric vertebral bodies and ligamentum flavum specimens were tested in compression and tension, respectively, using a servohydraulic material testing machine while collecting AE signals and high speed video at 33,000 fps. Time of injury was determined using the peak amplitude of the AE signals and this was compared to that determined using traditional methods (time of peak force and time of first visual evidence of injury). AE signals from vertebral bodies and ligament specimens were also compared in terms of peak amplitudes and frequency contents. Vertebral body specimens fractured and ligament specimens failed by midsubstance attenuation and periosteal stripping. Time of injury determined using AE signals produced average differences (from those defined using traditional methods) of less than 2 ms. Vertebral body fractures were associated with higher amplitude and higher frequency AE signals than those associated with ligament failures. Using AE signals, identification of the time of injury and differentiation between failures of different spine components was possible. Using these sensors it may become possible to decode complex failures of the spine that involve combinations of osseous and ligamentous failure that occur at different times.