The Effect of Lateral Eccentricity on Failure Loads, Kinematics, and Canal Occlusions of the Cervical Spine in Axial Loading

Current neck injury criteria do not include limits for lateral bending combined with axial compression and this has been observed as a clinically relevant mechanism, particularly for rollover motor vehicle crashes. The primary objectives of this study were to evaluate the effects of lateral eccentricity (the perpendicular distance from the axial force to the centre of the spine) on peak loads, kinematics, and spinal canal occlusions of subaxial cervical spine specimens tested in dynamic axial compression (0.5 m/s). Twelve 3-vertebra human cadaver cervical spine specimens were tested in two groups: low and high eccentricity with initial eccentricities of 1% and 150% of the lateral diameter of the vertebral body. Six-axis loads inferior to the specimen, kinematics of the superior-most vertebra, and spinal canal occlusions were measured. High speed video was collected and acoustic emission (AE) sensors were used to define the time of injury. The effects of eccentricity on peak loads, kinematics, and canal occlusions were evaluated using unpaired Student t-tests. The high eccentricity group had lower peak axial forces (1544 ±629 vs. 4296 ±1693 N), inferior displacements (0.2 ±1.0 vs. 6.6 ±2.0 mm), and canal occlusions (27 ±5 vs. 53 ±15%) and higher peak ipsilateral bending moments (53 ±17 vs. 3 ±18 Nm), ipsilateral bending rotations (22 ±3 vs. 1 ±2o), and ipsilateral displacements (4.5 ±1.4 vs. -1.0 ±1.3 mm, p<0.05 for all comparisons). These results provide new insights to develop prevention, recognition, and treatment strategies for compressive cervical spine injuries with lateral eccentricities.Applied Science, Faculty ofMedicine, Faculty ofMechanical Engineering, Department ofOrthopaedic Surgery, Department ofUnreviewedFacult

Acoustic Emission Signals Can Discriminate Between Compressive Bone Fractures and Tensile Ligament Injuries in the Spine during Dynamic Loading

Acoustic emission (AE) sensors are a reliable tool in detecting fracture, however they have not been used to differentiate between compressive osseous and tensile ligamentous failures in the spine. This study evaluated the effectiveness of AE data in detecting the time of injury of ligamentum flavum (LF) and vertebral body (VB) specimens tested in tension and compression, respectively, and in differentiating between these failures. AE signals were collected while LF (n=7) and VB (n=7) specimens from human cadavers were tested in tension and compression (0.4 m/s), respectively. Times of injury (time of peak AE amplitude) were compared to those using traditional methods (VB: time of peak force, LF: visual evidence in high speed video). Peak AE signal amplitudes and frequencies (using Fourier and wavelet transformations) for the LF and VB specimens were compared. In each group, six specimens failed (VB, fracture; LF, periosteal stripping or attenuation) and one did not. Time of injury using AE signals for VB and LF specimens produced average absolute differences to traditional methods of 0.7 (SD 0.2) ms and 2.4 (SD 1.5) ms (representing 14% and 20% of the average loading time), respectively. AE signals from VB fractures had higher amplitudes and frequencies than those from LF failures (average peak amplitude 87.7 (SD 6.9) dB vs. 71.8 (SD 9.8) dB for the inferior sensor, p<0.05; median characteristic frequency from the inferior sensor 97 (interquartile range, IQR, 41) kHz vs. 31 (IQR 2) kHz, p<0.05). These findings demonstrate that AE signals could be used to delineate complex failures of the spine.Applied Science, Faculty ofMedicine, Faculty ofMechanical Engineering, Department ofOrthopaedic Surgery, Department ofReviewedFacult

Moment Measurements in Spine Segment Dynamic Tolerance Testing using Eccentric Compression are Susceptible to Artifacts Based on Loading Configuration

The tolerance of the spine to bending moments, used for evaluation of injury prevention devices, is often determined through eccentric axial compression experiments using segments of the cadaver spine. Preliminary experiments in our laboratory demonstrated that eccentric axial compression resulted in ‘unexpected’ (artifact) moments. The aim of this study was to evaluate the static and dynamic effects of test configuration on bending moments during eccentric axial compression typical in injurious cadaver spine segment testing. Specific objectives were to create dynamic equilibrium equations for the loads measured inferior to the specimen, experimentally verify these equations, and compare moments from various test configurations using synthetic (rubber) and human cadaver specimens. Dynamic equilibrium equations were developed based on a generic spine testing apparatus. The equations were verified by performing quasistatic and dynamic experiments on a rubber specimen and comparing calculated shear forces and bending moments to those measured using a six-axis load cell. Additional quasistatic and dynamic experiments with various test configurations were performed on rubber and human cadaver cervical spine specimens (consisting of three vertebrae and the interconnecting ligaments and intervertebral discs). Calculated shear force and bending moment curves had similar shapes to those measured and the values in the first local minima differed from those measured by 3% and 15%, respectively, in the dynamic test, and these occurred within 1.5 ms of those measured. In the rubber specimen experiments, for the hinge joint (translation constrained), quasistatic and dynamic posterior eccentric compression resulted in flexion (‘unexpected’) moments. For the slider and hinge joints and the roller joints (translation unconstrained), extension (‘expected’) moments were measured quasistatically and initial flexion (‘unexpected’) moments were measured dynamically. In the human cadaver experiments with roller joints, anterior and posterior eccentric compression resulted in extension moments, which were ‘unexpected’ and ‘expected’, for those configurations respectively. The ‘unexpected’ moments were due to the inertia of the superior mounting structures. This study has shown that eccentric axial compression produces ‘unexpected’ moments due to translation constraints at all loading rates and due to the inertia of the superior mounting structures in dynamic experiments. It may be incorrect to assume that bending moments are equal to the product of compression force and eccentricity, particularly where the test configuration involves translational constraints and where the experiments are dynamic. In order to reduce inertial moment artifacts, the mass, and moment of inertia, of any loading jig structures that rotate with the specimen should be minimized to the extent possible. Also, the distance between these structures and the load cell should be reduced.Applied Science, Faculty ofMedicine, Faculty ofNon UBCMechanical Engineering, Department ofOrthopaedic Surgery, Department ofReviewedFacultyResearche

The impact of transportation infrastructure on bicycling injuries and crashes: a review of the literature

Background. Bicycling has the potential to improve fitness, diminish obesity, and reduce noise, air pollution, and greenhouse gases associated with travel. However, bicyclists incur a higher risk of injuries requiring hospitalization than motor vehicle occupants. Therefore, understanding ways of making bicycling safer and increasing rates of bicycling are important to improving population health. There is a growing body of research examining transportation infrastructure and the risk of injury to bicyclists. Methods We reviewed studies of the impact of transportation infrastructure on bicyclist safety. The results were tabulated within two categories of infrastructure, namely that at intersections (e.g. roundabouts, traffic lights) or between intersections on "straightaways" (e.g. bike lanes or paths). To assess safety, studies examining the following outcomes were included: injuries; injury severity; and crashes (collisions and/or falls). Results The literature to date on transportation infrastructure and cyclist safety is limited by the incomplete range of facilities studied and difficulties in controlling for exposure to risk. However, evidence from the 23 papers reviewed (eight that examined intersections and 15 that examined straightaways) suggests that infrastructure influences injury and crash risk. Intersection studies focused mainly on roundabouts. They found that multi-lane roundabouts can significantly increase risk to bicyclists unless a separated cycle track is included in the design. Studies of straightaways grouped facilities into few categories, such that facilities with potentially different risks may have been classified within a single category. Results to date suggest that sidewalks and multi-use trails pose the highest risk, major roads are more hazardous than minor roads, and the presence of bicycle facilities (e.g. on-road bike routes, on-road marked bike lanes, and off-road bike paths) was associated with the lowest risk. Conclusion Evidence is beginning to accumulate that purpose-built bicycle-specific facilities reduce crashes and injuries among cyclists, providing the basis for initial transportation engineering guidelines for cyclist safety. Street lighting, paved surfaces, and low-angled grades are additional factors that appear to improve cyclist safety. Future research examining a greater variety of infrastructure would allow development of more detailed guidelines.Applied Science, Faculty ofEnvironmental Health (SOEH), School ofMechanical Engineering, Department ofPopulation and Public Health (SPPH), School ofScience, Faculty ofMedicine, Faculty ofResources, Environment and Sustainability (IRES), Institute forReviewedFacult

Shear deformation and fracture of human cortical bone

Bone can be viewed as a nano-fibrous composite with complex hierarchical structures. Its deformation and fracture behavior depend on both the local structure and the type of stress applied. In contrast to the extensive studies on bone fracture under compression and tension, there is a lack of knowledge on the fracture process under shear, a stress state often exists in hip fracture. This study investigated the mechanical behavior of human cortical bone under shear, with the focus on the relation between the fracture pattern and the microstructure. Iosipescu shear tests were performed on notched rectangular bar specimens made from human cortical bone. They were prepared at different angles (i.e. 0º, 30º, 60º and 90º) with respect to the long axis of the femoral shaft. The results showed that human cortical bone behaved as an anisotropic material under shear with the highest shear strength (~50 MPa) obtained when shearing perpendicular to the Haversian systems or secondary osteons. Digital image correlation (DIC) analysis found that shear strain concentration bands had a close association with long bone axis with an average deviation of 11.8º to 18.5º. The fracture pattern was also greatly affected by the structure with the crack path generally following the direction of the long axes of osteons. More importantly, we observed unique peripheral arc-shaped microcracks within osteons, using laser scanning confocal microscopy (LSCM). They were generally long cracks that developed within a lamella without crossing the boundaries. This microcracking pattern clearly differed from that created under either compressive or tensile stress: these arc-shaped microcracks tended to be located away from the Haversian canal in early-stage damaged osteons, with ~70% developing in the outer third osteonal wall. Further study by second harmonic generation (SHG) and twophoton excitation fluorescence (TPEF) microscopy revealed a strong influence of the organization of collagen fibrils on shear microcracking. This study concluded that shear-induced microcracking of human cortical bone follows a unique pattern that is governed by the lamellar structure of the osteons.Applied Science, Faculty ofMedicine, Faculty ofOther UBCMaterials Engineering, Department ofMechanical Engineering, Department ofOrthopaedic Surgery, Department ofReviewedFacultyGraduateUnknow

A scoping review of the proximal humerus fracture literature

Background: Proximal humerus fractures are a common fragility fracture that significantly affects the independence of older adults. The outcomes of these fractures are frequently disappointing and previous systematic reviews are unable to guide clinical practice. Through an integrated knowledge user collaboration, we sought to map the breadth of literature available to guide the management of proximal humerus fractures. Methods: We utilized a scoping review technique because of its novel ability to map research activity and identify knowledge gaps in fields with diverse treatments. Through multiple electronic database searches, we identified a comprehensive body of proximal humerus fracture literature that was classified into eight research themes. Meta-data from each study were abstracted and descriptive statistics were used to summarize the results. Results: 1,051 studies met our inclusion criteria with the majority of research being performed in Europe (64%). The included literature consists primarily of surgical treatment studies (67%) and biomechanical fracture models (10%). Nearly half of all clinical studies are uncontrolled case series of a single treatment (48%). Non-randomized comparative studies represented 12% of the literature and only 3% of the studies were randomized controlled trials. Finally, studies with a primary outcome examining the effectiveness of non-operative treatment or using a prognostic study design were also uncommon (4% and 6%, respectively). Conclusions: The current study provides a comprehensive summary of the existing proximal humerus fracture literature using a thematic framework developed by a multi-disciplinary collaboration. Several knowledge gaps have been identified and have generated a roadmap for future research priorities.Applied Science, Faculty ofMechanical Engineering, Department ofMedicine, Faculty ofOrthopaedics, Department ofNon UBCReviewedFacult

Severity of urban cycling injuries and the relationship with personal, trip, route and crash characteristics : analyses using four severity metrics

Objective: To examine the relationship between cycling injury severity and personal, trip, route and crash characteristics. Results: Older age and collision with a motor vehicle were consistently associated with increased severity in all four metrics and statistically significant in three each (both variables with ambulance transport and CTAS; age with hospital admission; and motor vehicle collision with did not continue by bike). Other factors were consistently associated with more severe injuries, but statistically significant in one metric each: downhill grades; higher motor vehicle speeds; sidewalks (these significant for ambulance transport); multiuse paths and local streets (both significant for hospital admission). Conclusions: In two of Canada's largest cities, about one-third of the bicycle crashes were collisions with motor vehicles and the resulting injuries were more severe than in other crash circumstances, underscoring the importance of separating cyclists from motor vehicle traffic. Our results also suggest that bicycling injury severity and injury risk would be reduced on facilities that minimise slopes, have lower vehicle speeds, and that are designed for bicycling rather than shared with pedestrians.Applied Science, Faculty ofMedicine, Faculty ofNon UBCExperimental Medicine, Division ofMechanical Engineering, Department ofPediatrics, Department ofPopulation and Public Health (SPPH), School ofResources, Environment and Sustainability (IRES), Institute forReviewedFacultyResearche

A scoping review of biomechanical testing for proximal humerus fracture implants

Background: Fixation failure is a relatively common sequela of surgical management of proximal humerus fractures (PHF). The purpose of this study is to understand the current state of the literature with regard to the biomechanical testing of proximal humerus fracture implants. Methods A scoping review of the proximal humerus fracture literature was performed, and studies testing the mechanical properties of a PHF treatment were included in this review. Descriptive statistics were used to summarize the characteristics and methods of the included studies. Results 1,051 proximal humerus fracture studies were reviewed; 67 studies met our inclusion criteria. The most common specimen used was cadaver bone (87 %), followed by sawbones (7 %) and animal bones (4 %). A two-part fracture pattern was tested most frequently (68 %), followed by three-part (23 %), and four-part (8 %). Implants tested included locking plates (52 %), intramedullary devices (25 %), and non-locking plates (25 %). Hemi-arthroplasty was tested in 5 studies (7 %), with no studies using reverse total shoulder arthroplasty (RTSA) implants. Torque was the most common mode of force applied (51 %), followed by axial loading (45 %), and cantilever bending (34 %). Substantial testing diversity was observed across all studies. Conclusions The biomechanical literature was found to be both diverse and heterogeneous. More complex fracture patterns and RTSA implants have not been adequately tested. These gaps in the current literature will need to be addressed to ensure that future biomechanical research is clinically relevant and capable of improving the outcomes of challenging proximal humerus fracture patterns.Applied Science, Faculty ofMechanical Engineering, Department ofMedicine, Faculty ofOrthopaedics, Department ofNon UBCReviewedFacult

Merging pathology with biomechanics using CHIMERA (Closed-Head Impact Model of Engineered Rotational Acceleration): a novel, surgery-free model of traumatic brain injury

Background: Traumatic brain injury (TBI) is a major health care concern that currently lacks any effective treatment. Despite promising outcomes from many preclinical studies, clinical evaluations have failed to identify effective pharmacological therapies, suggesting that the translational potential of preclinical models may require improvement. Rodents continue to be the most widely used species for preclinical TBI research. As most human TBIs result from impact to an intact skull, closed head injury (CHI) models are highly relevant, however, traditional CHI models suffer from extensive experimental variability that may be due to poor control over biomechanical inputs. Here we describe a novel CHI model called CHIMERA (Closed-Head Impact Model of Engineered Rotational Acceleration) that fully integrates biomechanical, behavioral, and neuropathological analyses. CHIMERA is distinct from existing neurotrauma model systems in that it uses a completely non-surgical procedure to precisely deliver impacts of prescribed dynamic characteristics to a closed skull while enabling kinematic analysis of unconstrained head movement. In this study, we characterized head kinematics as well as functional, neuropathological, and biochemical outcomes up to 14d following repeated TBI (rTBI) in adult C57BL/6 mice using CHIMERA. Results Head kinematic analysis showed excellent repeatability over two closed head impacts separated at 24h. Injured mice showed significantly prolonged loss of righting reflex and displayed neurological, motor, and cognitive deficits along with anxiety-like behavior. Repeated TBI led to diffuse axonal injury with extensive microgliosis in white matter from 2-14d post-rTBI. Injured mouse brains also showed significantly increased levels of TNF-α and IL-1β and increased endogenous tau phosphorylation. Conclusions Repeated TBI using CHIMERA mimics many of the functional and pathological characteristics of human TBI with a reliable biomechanical response of the head. This makes CHIMERA well suited to investigate the pathophysiology of TBI and for drug development programs.Applied Science, Faculty ofMechanical Engineering, Department ofOrthopaedics, Department ofPathology and Laboratory Medicine, Department ofMedicine, Faculty ofReviewedFacult

Altered Tau Kinase Activity in rTg4510 Mice after a Single Interfaced CHIMERA Traumatic Brain Injury

Traumatic brain injury (TBI) is an established risk factor for neurodegenerative diseases. In this study, we used the Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA) to investigate the effects of a single high-energy TBI in rTg4510 mice, a mouse model of tauopathy. Fifteen male rTg4510 mice (4 mo) were impacted at 4.0 J using interfaced CHIMERA and were compared to sham controls. Immediately after injury, the TBI mice showed significant mortality (7/15; 47%) and a prolonged duration of loss of the righting reflex. At 2 mo post-injury, surviving mice displayed significant microgliosis (Iba1) and axonal injury (Neurosilver). Western blotting indicated a reduced p-GSK-3β (S9):GSK-3β ratio in TBI mice, suggesting chronic activation of tau kinase. Although longitudinal analysis of plasma total tau suggested that TBI accelerates the appearance of tau in the circulation, there were no significant differences in brain total or p-tau levels, nor did we observe evidence of enhanced neurodegeneration in TBI mice compared to sham mice. In summary, we showed that a single high-energy head impact induces chronic white matter injury and altered GSK-3β activity without an apparent change in post-injury tauopathy in rTg4510 mice.Applied Science, Faculty ofMedicine, Faculty ofOther UBCNon UBCBiomedical Engineering, School ofPathology and Laboratory Medicine, Department ofReviewedFacultyResearcherPostdoctoralGraduat