Biomechanics of Head Impacts in an Unhelmeted Sport

Concussion in sport is very common and often the injury is undetectable using CT and MRI scans. In addition, approximately 50% of concussions areunreported.The project initially investigated the suitability of a skin patch sensor and a head-band sensorfor the measurement of head impacts in unhelmeted sports. It was found that both were unsuitable due to large angular accelerationerrors. Thestudy then collaborated withCAMLab at Stanford University and 25 Mixed Martial Arts (MMA) athletes were fitted CAMLab’s validated instrumented mouthguard. 451 video confirmed impacts were recorded at 19 sparring and 11 competitive MMA events. Five concussions were diagnosed during the competitive events. The most severe impacts were simulated using the Global Human Body Model Consortium head model. The average resultant linear acceleration of the impacts that resulted in a concussion was approximately 20% lower than concussive studies of US football while the resultant average angular acceleration was 34% higher. It ishypothesised that these differences are due to the high energy frontal impacts in US football as opposed to the ‘hook’ style punches in MMA.Large strains in the mid-brain occurred from frontal impacts whereas lateralimpacts resultedin large strains in the corpus callosum. It was found that the average strain in the corpus callosum of the concussed athletes was 0.27 which was 88% higher than that in uninjured fighters. In collaboration with the Genetics department in Trinity College Dublin it was found that the maximum principal strain correlated (R2=0.84) with the volume fraction of blood brain barrierdisruptionpost-fight. In conjunction with Stanford University,it was found that the spectral density of MMA impacts was higher than that in US football.This study is the first known study to measure in vivohead impacts in unhelmeted athletes that have suffered a concussion

Impact Isolation of Training Shoes

ABSTRACT The increase in popularity of physical activities from fun runs to competitive marathons has lead to a huge industry in sports footwear, which is now worth $20bn annually. There is a resultant increase in injuries, largely due to the repeated and prolonged nature of the impact forces experienced by the leg. Clinical data indicates that the knee is the most common site of running related injury, followed by the lower leg and foot. The complexity of the ankle structure means that injuries are acute and the success rates of replacements are very low. Therefore research in this area is required; to understand both the nature and magnitude of the loads the ankle is subjected to while walking and running, and how these loads may be minimised. This paper investigates the effectiveness of four different running shoes, ranging from a low cost department store own branded shoe, to a high cost specialised running shoe. The shoes are tested on a custom built drop test rig, which can drop the shoes while fitted to a prosthetic foot and ankle. The shoes are dropped to simulate the impacts that occur while walking and running. The rig allows for a range of drop heights, and the ankle to be positioned at various angles to replicate heel strike, flat foot and toe strike. The rig is fitted with force transducers and accelerometers, to record deceleration, and ground reaction force. Also the impacts are recorded on a high speed camera for analysis; this yields the impact velocity, energy absorption and deformation

An Analysis of the Performance of Foams Used in Hurling Helmets

Abstract Head injuries can occur in most sporting activities. The seriousness of these injuries can vary greatly depending on the sport. Many sports such as American football, cricket, baseball and hurling try to reduce this risk by designing helmets that are suitable to be worn by the players. The National Standard Authority of Ireland (NSAI) has recently made great strides in this area with the introduction of the first comprehensive standard adopted for the sport I.S. 355:2006, which sets out new testing procedures that all new helmets must meet. The Gaelic Athletic Association (GAA) has also stated its intention to make the wearing of sports helmets compulsory up to minor level. The hope is that in time all the players will become comfortable with wearing helmets which has been found to be a major reason for the current low wear rates. [2] This paper covers the testing and modelling of energy absorbing materials to ascertain the optimum thickness, and density of foam within the helmet. Static tests are carried out on a compression test machine to obtain stress/strain properties. The foams are tested on a purpose built drop test rig; the displacement, impact force, velocity and acceleration are measured using LabView and a high speed camera with TEMA analysis software to gain a greater understanding of the impact mechanics of each material. The foams are modelled, both statically and dynamically, using finite element analysis. The static model uses theANSYS implicit solver, while the dynamic model uses ANSYS/LS-DYNA to create and validate an appropriate foam material model. The displacement, velocity, and energy results from the finite element model and the test results are analysed and compared so that the optimum density and thickness of foam can be obtained

The effect of impact location on brain strain

Objective: To determine the effect of impact direction on strains within the brain. Research design: Laboratory drop tests of hybrid III head-form and finite element simulation of impacts. Methods and procedures: A head-form instrumented with accelerometers and gyroscopes was dropped from 10 different heights in four orientations: front, rear, left and right hand side. Twelve impacts with constant impact energy were chosen to simulate, to determine the effect of impact location. A finite element head model was used to simulate these impacts, using 6 degrees of freedom. Following this a further set of simulations were performed, where the same acceleration profiles were applied to different head locations. Main outcome and results: The angular accelerations recorded were up to 30% higher in lateral and rear impacts when compared to frontal impacts. High strains in the mid-brain (41%) were recorded from severe frontal impacts where as high strains in the corpus callosum (44%) resulted from lateral impacts with the same energy. Conclusion: Impact direction is very significant in determining the subsequent strains developed in the brain. Lateral impacts result in the highest strains in the corpus callosum and frontal impacts result in high strains in the mid-brain

Evaluation of Skin-mounted Sensor for Head Impact Measurement

Background: The requirement to measure the number and severity of head impacts in sports has led to the development of wearable sensors. Aim: The objective of this study was to determine the reliability and accuracy of a wearable head impact sensor: xPatch, X2Biosystems Inc. Methods: The skin mounted sensor, xPatch, was fixed onto a Hybrid III headform, and dropped using an impact test rig. Four hundred impacts were performed, ranging from 20 to 200g linear acceleration, and impact velocities of 1.2m/s to 3.9m/s. During each impact, the peak linear acceleration, angular velocity and angular acceleration, were recorded and compared to reference calibrated data. Impacts were also recorded using a high-speed video camera. Results: The linear acceleration recorded by the xPatch during frontal and side impacts had errors of up to 24% when compared to the referenced data. The angular velocity and angular acceleration had substantially larger errors of up to 47.5% and 57% respectively. The location of the impact had a significant effect on the results: if the impact was to the side of the head, the device on that side may have an error of up to 71%, thus highlighting the importance of device location. All impacts were recorded using two separate xPatches and, in certain cases, the difference in angular velocity between the devices was 43%. Conclusion: The xPatch can be useful for identifying impacts and recording linear accelerations during front and side impacts, but the rotational velocity and acceleration data needs to be interpreted with caution

Strain distribution in the porcine lumbar laminae under asymmetric loading

If the articular facets of the vertebra grow in an asymmetric manner, the developed geometry causes an asymmetry of loading. When the loading environment is altered by way of increased activity, the likelihood of acquiring a stress fracture may be increased. The combination of geometric asymmetry and increased activity is hypothesised to be the precursor to the stress fracture under investigation in this study, spondylolysis. This vertebral defect is an acquired fracture with 7% prevalence in the paediatric population. This value increases to 21% among athletes who participate in hyperextension sports. Tests were carried out on porcine lumbar vertebrae, on which the effect of facet angle asymmetry was simulated by offsetting the load laterally by 7mm from the mid-point. The aim of the study is to investigate whether an increase in the coronal orientation of one facet leads to an increase in strain in the corresponding vertebral lamina. Strain in the laminae was recorded using six 3-element stacked rosette strain gauges placed bilaterally. Results show that a significant linear predictive relationship exists between load offset and average strain level in the vertebral laminae with p values of 0.006 and 0.045 for principal strains e1 and e2 on the right-hand side, and p-values of 0.009 and 0.001 for principal strains e1 and e2 on the left-hand side (R2 all .0.9). This study concludes that facet angle asymmetry does lead to a difference in strain in the vertebral laminae. Change in principal strain as a result of facet asymmetry has a linear relationship and an asymmetry threshold exists beyond which compressive strain on the more coronally oriented facet can be increased by up to 15%

Fatigue and damage of porcine pars interarticularis during asymmetric loading

If the articular facets of the vertebra grow in an asymmetric manner, the developed bone geometry causes an asymmetry of loading. When the loading environment is altered by way of increased activity, the likelihood of acquiring a stress fracture may be increased. The combination of geometric asymmetry and increased activity is hypothesised to be the precursor to the stress fracture under investigation in this study, spondylolysis. This vertebral defect is an acquired fracture with 7% prevalence in the paediatric population. This value increases to 21% among athletes who participate in hyperextension sports. Tests were carried out on porcine lumbar vertebrae, on which the effect of facet angle asymmetry was simulated by offsetting the load laterally by 7mm from the mid-point. Strain in the vertebral laminae was recorded using six 3-element stacked rosette strain gauges placed bilaterally. Specimens were loaded cyclically at a rate of 2Hz. Fatigue cycles; strain, creep, secant modulus and hysteresis were measured. The principal conclusions of this paper are that differences in facet angle lead to an asymmetry of loading in the facet joints; this in turn leads to an initial increase in strain on the side with the more coronally orientated facet. The strain amplitude, which is the driving force for crack propagation, is greater on this side at all times up to fracture, the significance of this can be observed in the increased steady state creep rate (p = 0.036) and the increase in yielding and toughening mechanisms taking place, quantified by the force-displacement hysteresis (p = 0.026)

The Implementation of a Visco-hyperelastic Numerical Material Model for Simulating the Behaviour of Polymer Foam Materials

Polyurethane foam has been in use for some time in wheelchair seating systems as it offers good pressure relieving capabilities in most cases. However, little characterisation work has gone into seating foam materials by comparison with conventional elastomeric materials. Accurate material models could allow better prediction of foam in-service behaviour, which could potentially improve seating design practises. The objective of this work was to develop an approach for the validation of hyperelastic and viscoelastic material model parameters used to simulate polyurethane foam behaviour. Material parameters were identified from relevant test procedures and implemented in a Finite Element simulation of an ISO foam indentation procedure. Physical test results were compared to results predicted using the identified material parameters. Simulations suggest a good overall agreement between test and model results

Is It Time to Give Athletes a Voice in the Dissemination Strategies of Concussion-Related Information? Exploratory Examination of 2444 Adolescent Athletes

Objective: The objective of the research was to screen male and female adolescent athletes on their concussion educational histories and preferred future methods of education in terms of educational messenger, modality, and concussion-related areas of interest. Design: Cross-sectional survey. Setting: Examination setting within the classroom. Participants: Adolescent male (n = 1854) and female (n = 590) athletes aged 12 to 18 years. Main outcome measures: To explore the concussion educational histories and preferred future methods of education in Irish male and female adolescent athletes. Results: 19.7% (n = 482) of the sample received education in the past 12 months. Male athletes had a significantly higher rate of previous education than female athletes (41% vs 17%). The methods used in previous educational interventions are failing to match the interests of the athletes. Sex played a significant role in the preferred educational methods, as male and female athletes had significant differences in their choice of educational messenger, modality, and concussion-related areas of interest. Conclusions: The current disparity in previous concussion education rates between male and female adolescent athletes should be addressed. Forthcoming research should explore the efficacy of tailoring knowledge translation strategies to match the specific needs of the recipient

An Engineering Evaluation of Ankle Prosthetics

There are a wide range of different types of ankle replacements on the market today each with adifferent mechanical design. Unfortunately the results of ankle replacements are not as good as hipand knee replacements; this is due to the complexity of the ankle joint. In the early days of anklereplacements some of the prosthetics only lasted 4 months. Recent developments have improved thelongevity of the replacements although, there are still many complications and failures of thereplacements, these include; the prosthetic components migrating into the bone, the componentsfailing due to stresses induced by the forces and the surgery itself i.e. the incision site.This paper will analyse the documented medical failures of the replacements from a mechanicalengineering perspective. Three ankle prosthetics are investigated in this paper: the Buechel-Pappas,the Scandinavian Total Ankle Replacement (STAR) and the Hintegra ankle replacement. Medicalpublications are examined to isolate the mechanical failure mechanisms of the replacements and tocategorise and quantify these failures in engineering terms. These failures will include wearcomplications and also dislocations of the prosthetic parts among other failures. The paper will conclude by comparing the mechanical reliability of the four prosthetics examined