Neck Loads Research Articles

Comparison of rear seat occupant injuries in AM50 and AF05 in frontal crashes

For rear seat occupants involved in motor vehicle fatal crashes, the number of fatalities of the unbelted rear seat occupants is approximately 3.8 times higher than that of the belted rear seat occupants. In part because of this finding, the National Police Agency decided that wearing a seatbelt would be mandatory for rear seat occupants in Japan from June 2008. In addition, the Japan New Car Assessment Program (J-NCAP), beginning from 2009, considered an evaluation of rear seat occupant safety. For the evaluation test, the J-NCAP has to select from either male (Hybrid III AM50) or female (Hybrid III AF05) dummies. The purpose of the present study is to evaluate different kinematic and response characteristics of Hybrid III AM50 and AF05 dummies seated in rear seats in frontal crashes. For this study, a full-frontal rigid barrier impact test and a frontal offset deformable barrier impact test were conducted following the Japanese-type approval test procedure using a small passenger car with engine displacement of 1496 cc. For occupant restraints, three-point seatbelts were worn by both Hybrid III AM50 and Hybrid III AF05 dummies in rear seats to evaluate their different kinematics. In the full-frontal rigid barrier impact test, the measured injury criteria from AF05 dummy of HIC15, neck extension moment, Nij, and 3-ms clip chest acceleration did exceed the Injury Assessment Reference Values (IARVs) for the AM50 dummy. However, in the full-frontal rigid barrier impact test, the measured injury criteria from AM50 dummy for the 3-ms clip chest acceleration did exceed IARV. Using the measured injury criteria, the injury risks of the AF05 dummy were determined to be greater than those of the AM50 dummy in the full-frontal rigid barrier impact test. Especially, the AIS3+ neck injury risks determined from the tension force, neck extension moment and Nij of the AF05 dummy were larger by 27% to 31% when compared with the risks of the AM50 dummy. The chest deflection of the AF05 dummy (45 mm) was similar to that of the AM50 dummy (43 mm); however, the AIS3+ chest injury risk from the chest deflection of the AF05 dummy (63%) was almost twice than that of the AM50 dummy (33%). From the full-frontal rigid barrier impact test results, an ‘unconstrained ilium by the lap belt’ phenomenon (that is, the lap belt slipped up and over the ilium) was seen in the AF05 dummy, as observed from the drastic drop in chest acceleration. The test results also indicated that this phenomenon also affected head acceleration and neck load. No such phenomenon was observed in the AM50 dummy test results. In the frontal offset deformable barrier impact test, the injury criteria measured from the AM50 dummy seated on the barrier-impacted side were of higher values than those measured from the AF05 dummy seated on the nonimpacted side in the rear seat. In this offset test configuration, the left-side sill acceleration (49 G) on the impacted side was higher than the right-side sill acceleration (27 G) on the nonimpacted side. This indicates that the factor of vehicle acceleration on injury criteria is similar to the factor of dummy body size on injury criteria. The results also indicated that injury criteria from the AF05 and AM50 dummies did not exceed IARVs and that the injury risks of both dummies are very similar. The measured injury criteria and injury risks in the full-frontal rigid barrier impact test results are higher than those in the frontal offset deformable barrier impact test results.

The relationship between lower neck shear force and facet joint kinematics during automotive rear impacts

A primary goal of biomechanical safety research is the definition of localized injury thresholds in terms of quantities that are repeatable and easily measureable during experimentation. Recent biomechanical experimentation using human cadavers has highlighted the role of lower cervical facet joints in the injury mechanism resulting from low-speed automotive rear impacts. The present study was conducted to correlate lower neck forces and moments with facet joint motions during simulated rear impacts in an effort to define facet joint injury tolerance thresholds that can be used to assess automobile safety. Four male and four female intact head-neck complexes were obtained from cadaveric specimens and subjected to simulated automotive rear impacts using a pendulum-minisled device. Cervical spine segmental angulations and localized facet joint kinematics were correlated to shear and axial forces, and bending moments at the cervico-thoracic junction using linear regression. R(2) coefficients indicated that spinal kinematics correlated well with lower neck shear force and bending moment. Correlation slope was steeper in female specimens, indicating greater facet joint motions for a given loading magnitude. This study demonstrated that lower neck loads can be used to predict lower cervical facet joint kinematics during automotive rear impacts. Higher correlation slope in female specimens corresponds to higher injury susceptibility in that population. Although lower neck shear force and bending moment demonstrated adequate correlation with lower cervical facet joint motions, shear force is likely the better predictor due to similarity in the timing of peak magnitudes with regard to maximum facet joint motions.

A numerical investigation into the effect of CRS misuse on the injury potential of children in frontal and side impact crashes

This research focuses on an investigation into the head and neck injuries sustained by toddlers due to CRS misuse under frontal and side impact crashes. A fully deformable FE model incorporating a Hybrid III 3-year-old dummy was developed which has been previously validated for frontal impacts under CMVSS 208 and FMVSS 213 testing conditions. Furthermore, this model has also been validated under near-side impact conditions in accordance to crash tests carried out by NHTSA. In addition, numerical models incorporating a Q3/Q3s prototype child crash test dummies were developed. The objective of this research was to study the effect of seatbelt slack and the absence of the top tether strap on the head and neck injuries sustained by toddlers in a vehicle crash. Numerical simulations were conducted under full frontal and near side impact crash testing conditions in accordance with FMVSS 213 for the Hybrid III 3-year-old dummy and Q3/Q3s dummies in the absence and presence of slack in the seatbelt webbing, and in the absence and presence of the top tether strap. In addition, the effect of using a cross-shaped rigid ISOFIX system was also investigated. An analysis of the head and chest accelerations, neck loads and moments was completed to investigate the potential of injury due to CRS misuse. An increase in HIC 15 by approximately 30–40% for the frontal impact and 10–20% for the near-side impact respectively was observed for the Q3 child dummy due to both forms of CRS misuse. In the absence of the top tether strap the forward head excursions were observed to be increased by approximately 70% for the Hybrid III 3-year-old dummy and 40% for the Q3 dummy, respectively. Use of the cross-shaped rigid ISOFIX system illustrated a reduction in head and neck injury parameters, for both frontal and side impact conditions, in the absence and presence of CRS misuse. CRS misuse results in a significant increase in injury parameters and potential for contact related head injuries. Use of a rigid ISOFIX system to restrain a CRS provides better CRS and dummy confinement and reduced injury potential than a flexible ISOFIX system.

Understanding whiplash injury and prevention mechanisms using a human model of the neck

Objectives Various models for rear crash simulation exist and each has unique advantages and limitations. Our goals were to: determine the neck load and motion responses of a human model of the neck (HUMON) during simulated rear crashes; evaluate HUMON's biofidelity via comparisons with in vivo data; and investigate mechanisms of whiplash injury and prevention. Methods HUMON, consisting of a neck specimen ( n = 6) mounted to the torso of BioRID II and carrying a surrogate head and stabilized with muscle force replication, was subjected to simulated rear crashes in an energy-absorbing seat with fixed head restraint (HR) at peak sled accelerations of 9.9 g (Δ V 9.2 kph), 12.0 g (Δ V 11.4 kph), and 13.3 g (Δ V 13.4 kph). Physiologic spinal rotation ranges were determined from intact flexibility tests. Average time–history response corridors (±1 standard deviation) were computed for spinal motions, loads, and injury criteria. Results Neck loads generally increased caudally and consisted of shear, compression, and flexion moment caused by straightening of the kyphotic thoracic and lordotic lumbar curvatures, upward torso ramping, and head inertial and head/HR contact loads. Nonphysiologic rotation occurred in flexion at C7/T1 prior to head/HR contact and in extension at C6/7 and C7/T1 during head/HR contact. Conclusions HUMON's neck load and motion responses compared favorably with in vivo data. Lower cervical spine flexion–compression injuries prior to head/HR contact and extension–compression injuries during head/HR contact may be reduced by refinement of existing seatback, lapbelt, and HR designs and/or development of new injury prevention systems.

Neck loads and posture exposure of helicopter pilots during simulated day and night flights

This study investigated neck loads and neck postures experienced by Canadian Forces (CF) helicopter pilots during routine simulator day and night flights. During the night flights pilots’ helmets were equipped with night vision goggles (NVG) which have been implicated in the increase of neck pain amongst pilots. Pilot’s postures were determined from video recordings of their flight missions to: (1) identify the neck postures assumed during day and night flight missions, and (2) determine the amount of biomechanical cervical spine loading experienced during these flights. Neck postures and peak and cumulative cervical kinetic loading were significant different ( P < 0.05) between day and night. During night flights the percentage of work cycle spent in mildly flexed posture increased significantly from 43% during day flights to 74% during night flights. As well, cumulative reaction compression values significantly increased from 583 kN s to 694 kN s. The biomechanical results lend support to previous physiological investigations of NVG use and further justify the need for guidelines associated with NVG use. Relevance to industry The research highlights the biomechanical demands on the neck resulting from wearing a helmet with added weight from night vision equipment. The results have direct implication to military and commercial operators required to wear night vision equipment or added weight to the head.

Variations in Rear Seat Cushion Properties and the Effects on Submarining

Objective: This study aims to investigate the effects of seating posture and seat cushion properties on submarining risk for rear seated children. Methods: An instrumented 6-year-old Hybrid III dummy restrained by an inertial-reel 3-point seat belt was subjected to simulated frontal impacts (Δv = 28.8 km/h, peak acceleration = 16 g). Dummy motion was captured using high-speed digital video. Head acceleration, neck loads, chest deflection, pelvic rotation, and femur displacement were used to assess submarining. Factors investigated included pre-impact seating posture, seat cushion length, stiffness of the seat cushion foam, and the inclination of the seat cushion. Results: The most severe submarining was observed when the dummy was seated in a slouched posture where pelvic rotation was over 3 times greater than in the upright seating posture. Though the standard seat cushion with the dummy seated in the upright posture recorded the lowest values of pelvic rotation and femur displacement, it is unlikely that a child will sit in such a posture. The shortened seat cushion increased femur displacement by 19 percent compared to the standard test seat, but it offers good pre-impact belt position. Submarining occurred in cases where the front edge of the seat collapsed during interactions with the dummy's buttocks. Conclusions: These data suggest that shortening the rear seat cushion alone will not necessarily prevent submarining, but this does allow improved seated posture of the occupant, thus reducing submarining risk. This study has also shown that the collapse of the front edge of the seat cushion is a critical factor in submarining risk.

Sensitivity of THOR and Hybrid III Dummy Lower Neck Loads to Belt Systems in Frontal Impact

Objectives: To determine head–neck biomechanics with a focus on lower neck injury metrics in frontal impact. The mid- and large-size Hybrid III dummies and the mid-size Test device for Human Occupant Restraint (THOR) were positioned on a buck. Tests were conducted at low, medium, and high (3.3, 6.7, and 15.7 m/s) change in velocities using 3 restraint types: normal 3-point belt with no pretension (type A), 10-cm pretension (type B), and 200 N pretension (type C). Repeat tests were conducted. Measured vertical and shear forces and sagittal bending moments were evaluated at the upper and lower regions of the neck to different types of belt systems and at different change in velocities. Peak values normalized with respect to the belt type A were used in the comparative analysis. Metrics transformed to the occipital condyles and T1 were also evaluated. Results: All dummies showed good repeatability. Peak measured and transformed upper and lower neck moments were greatest in the large-size dummy. The mid-size Hybrid III dummy responded with greater forces and moments than the THOR. Regardless of dummy type, anthropometry, and velocity, peak lower neck moments were more sensitive to belt types than peak lower neck forces. A similar pattern was apparent for upper neck data. Moments in the THOR were more sensitive than moments in the mid-size Hybrid III dummy. Conclusions: This study offers quantitative generic restraint-based data and addresses response differences between dummies and dummies of the same family. Because of increased sensitivity to belt types at the upper and lower necks for both forces and moments, the THOR appears to be an improvement to better assess injury potential to rear seat occupants wherein frontal impact air bags do not exist.

Histological evaluation of condylar hyperplasia model of rabbit following distraction osteogenesis of the condylar neck

Condylar hyperplasia is the excessive unilateral growth of mandibular leading to facial asymmetry, occlusal disturbance, joint pain and dysfunction. The aim of this study is to evaluate the histological presence of temporomandibular joint in model of condylar hyperplasia by lengthening unilateral condylar neck of distraction osteogenesis. An extra oral distractor was employed to achieve unilateral condylar neck distraction (1·0 mm daily for 7 days). The experimental condylar necks were elongated by 7 mm compared to the contralateral. Eleven adult white rabbits were used. Eight rabbits were, respectively, sacrificed after the post-distraction period (4 or 8 weeks). All animals were evaluated clinically and histomorphometrically. The condyles radiologically showed remodelling, flattening and sclerosis. In 4-week group, thinning of the cartilage was evident, and the trabeculae were long, not multiply connected. A thin, dense fibrous layer covered all over the surface of cartilage. In 8-week group, the cartilaginous layer was similar to thickness of the normal cartilage, but still thinner than control. However, the fibrous layers covering condyle manifested slight degenerative changes, and even depressions and erosions were seen in the cartilage and subchondral bone. The trabeculae showed denser and multiply connected. In 8-week group, the cartilaginous thickness of surgical condyles was significantly thinner than the contralateral. This study indicates that unilateral distraction of condylar neck loads the condyles asymmetrically. Asymmetrical loads affect more on the surgical condyles than the contralateral, and after 8 weeks of the post-distraction, condyle could recover from asymmetrical loads in some degree.

Preservation of bone mass and biomechanical properties during winter sleep—the raccoon dog (Nyctereutes procyonoides) as a novel model species

It has been established that almost 40% of postmenopausal women in the United States have osteopenia and models to study its prevention are thus urgently needed. Bears (Ursus spp.) displaying winter sleep were previously introduced as promising models to study the treatment of disuse-induced bone loss. The present study examined the potential of another analogous model species, the raccoon dog (Nyctereutes procyonoides), in bone research. Similar to bears, raccoon dogs display prolonged passivity and catabolism in winter, but they are of a moderate body mass, easy to handle and reared on farms. Wild specimens (n=51) were hunted in winter 2007–2008. The bone mineral density of femoral diaphysis and neck was examined with peripheral quantitative computed tomography, after which their mechanical properties were tested with the three-point bending and femoral neck loading tests. A subsample of the specimens was analyzed histologically. While the body mass of the raccoon dogs decreased from 7.0±0.3 to 4.5±0.2kg (−36%) during winter, the bone mass and biomechanical properties remained unchanged despite of heavy wintertime catabolism similar to bears. Thus, the cortical mineral density remained at approximately 1400mg/cm3, the trabecular mineral density at 450mg/cm3 and the maximum load of the femoral neck at 700N. However, in histological samples, the proportion of osteoid perimeter vs. mineralized bone perimeter decreased during wintering. A possible mechanism of bone mass preservation is the endocrine status of overwintering raccoon dogs, which could participate in preventing bone loss.

A pilot study on objective quantification and anatomical modelling ofin vivohead and neck positions commonly applied in training and competition of sport horses

Head and neck positions (HNP) in sport horses are under debate in the equine community, as they could interfere with equine welfare. HNPs have not been quantified objectively and no information is available on their head and neck loading. To quantify in vivo HNPs in sport horses and develop o a model to estimate loading on the cervical vertebrae in these positions. Videos were taken of 7 Warmbloods at walk on a straight line in 5 positions, representing all HNPs during Warmblood training and competition. Markers were glued at 5 anatomical landmarks. Two-dimensional angles and distances were determined from video frames for the 5 HNPs and statistically compared (P < 0.05). A new simulation model was developed to estimate nuchal ligament cervical loading at these HNPs. The mean angles were significantly different between the 5 HNPs for the line between C1 and T6 with the horizontal and for the line connecting the facial crest (CF) and C1 with the vertical, while the vertical distance from CF to the lateral styloid process of the radius (PS) was significantly different between all 5 positions (P < 0.05). The estimated nuchal ligament loading appeared to be largest at the origin of C2 for all HNPs, except for the 'hyperextended' HNP5; the 'hyperflexed' HNP4 showed the largest loading values on the nuchal ligament origins at all locations. HNPs can be accurately quantified in the sagittal plane from angles and distances based on standard anatomical landmarks and home-video captured images. Nuchal ligament loading showed the largest estimated values at its origin on C2 in hyperflexion (HNP4). Modelling opens further perspectives to eventually estimate loading for individual horses and thus ergonomically optimise their HNP, which may improve the welfare of the sport horse during training and competition.

Head and Neck Loading in Everyday and Vigorous Activities

The purpose of this study was to document head and neck loading in a group of ordinary people engaged in non-injurious everyday and more vigorous physical activities. Twenty (20) volunteers that were representative of the general population were subjected to seven test scenarios: a soccer ball impact to the forehead, a self-imposed hand strike to the forehead, vigorous head shaking, plopping down in a chair, jumping off a step, a seated drop onto the buttocks, and a vertical drop while seated supine in a chair. Some scenarios involved prescribed and well-controlled stimuli, while others allowed the volunteers to perform common activities at a self-selected level of intensity. Head accelerations up to 31g and 2888rad/s(2) and neck loads up to 268N in posterior shear, 526N in compression, and 36 Nm in extension were recorded. Most head and neck injury criteria predicted a low risk of injury in all activities. However, rotational head accelerations and Neck Injury Criterion (NIC) values were much higher than some proposed tolerance limits in a large number of tests, all of which were non-injurious. The data from this study help us to establish an envelope of head and neck loading that is commonly encountered and presents a minimal risk of injury.

Dynamic Response of Vehicle Roof Structure and ATD Neck Loading During Dolly Rollover Tests

Dynamic Response of Vehicle Roof Structure and ATD Neck Loading During Dolly Rollover Tests

The influence of the size of the component on the outcome of resurfacing arthroplasty of the hip

The survivorship of contemporary resurfacing arthroplasty of the hip using metal-on-metal bearings is better than that of first generation designs, but short-term failures still occur. The most common reasons for failure are fracture of the femoral neck, loosening of the component, osteonecrosis of the femoral head, reaction to metal debris and malpositioning of the component. In 2008 the Australian National Joint Registry reported an inverse relationship between the size of the head component and the risk of revision in resurfacing hip arthroplasty. Hips with a femoral component size of </= 44 mm have a fivefold increased risk of revision than those with femoral components of >/= 55 mm irrespective of gender. We have reviewed the literature to explore this observation and to identify possible reasons including the design of the implant, loading of the femoral neck, the orientation of the component, the production of wear debris and the effects of metal ions, penetration of cement and vascularity of the femoral head. Our conclusion is that although multifactorial, the most important contributors to failure in resurfacing arthroplasty of the hip are likely to be the design and geometry of the component and the orientation of the acetabular component.

Physical Effects of Ejection on the Head-Neck Complex: Demonstration of a Cadaver Model

Vertebral fracture is the most common severe injury during high-speed pilot ejection. However, the loading paradigm experienced by pilots may also lead to soft-tissue spinal injuries that are more difficult to quantify and can lead to long-term deficits. This manuscript describes a new experimental protocol to simulate the effects of pilot ejection on the tissues of the head-neck complex. The model permits precise control of head-neck complex initial positioning, detailed analysis of head and spinal kinematics and upper and lower neck loads, and the ability to thoroughly investigate and identify soft-tissue injuries through upper and lower neck injury criteria, radiography, manual palpation, and cryomicrotomy. For the current test, peak acceleration of +14.8 Gz was similar to actual ejection events and duration of the acceleration pulse was approximately 100 ms. The specimen was oriented in flexion prior to initiation of inferior-to-superiorly directed acceleration. Subfailure ligamentum flavum injuries were sustained at the C4-C5 and C5-C6 cervical spinal levels and identified by increased segmental motions during the simulated ejection, increased laxity following testing, and cryomicrotomy. Upper and lower neck injury criteria did not predict these soft-tissue injuries. This experimental model can be used for detailed analysis of the effects of gender, head-neck orientation, helmet instrumentation, and acceleration pulse characteristics on cervical spine injury potential during pilot ejection events.

Vehicle and Occupant Responses in a Friction Trip Rollover Test

Objective: A friction rollover test was conducted as part of a rollover sensing project. This study evaluates vehicle and occupant responses in the test. Methods: A flat dolly carried a Saab 9-3 sedan laterally, passenger-side leading to a release point at 42 km/h (26 mph) onto a high-friction surface. The vehicle was equipped with roll, pitch and yaw gyros near the center of gravity. Accelerometers were placed at the vehicle center tunnel, A-pillar near the roof, B-pillar near the sill, suspension sub-frame and wheels. Five off-board and two on-board cameras recorded kinematics. Hybrid III dummies were instrumented for head and chest acceleration and upper neck force and moment. Belt loads were measured. Results: The vehicle release caused the tires and then wheel rims to skid on the high-friction surface. The trip involved roll angular velocities >300 deg/s at 0.5 s and a far-side impact on the driver’s side roof at 0.94 s. The driver was inverted in the far-side, ground impact. Head impact and torso deceleration resulted in 8.75 kN neck compression load with about ½” of roof deformation, 5 g vehicle deceleration. The vehicle came to rest on its roof after 1½ rolls. Conclusion: The friction rollover involved centrifugal accelerations moving the driver’s head to the roof at ground impact. The driver was inverted and the torso dove toward the ground causing high neck compression loads. This test confirms the conclusions of Malibu II and CRIS testing that belted occupants can experience neck loads before much roof deformation. This test involved a modern vehicle with a strong roof. Increasing roof strength would not reduce neck loads; reclining the head-neck-torso angle before the far-side roof impact seems a more reasonable approach to improving safety.

Letter to the Editor: Femoral Component Positioning in Hip Resurfacing with and Without Navigation

To the Editor: I read with interest the article entitled “Femoral Component Positioning in Hip Resurfacing With and Without Navigation” by Ganapathi et al. [4]. I agree with the authors that intraoperative technical errors during femoral preparation in resurfacing hip prostheses are important reasons for short-term and midterm failures of this procedure, which technically is more challenging than conventional THA [4]. In my opinion, it is possible to single out at least four procedural traps worthy of note. First, as the femoral component is provided with a central stem to aid in alignment and initial stability, it is mandatory to perform a perfect central matching drilling of the femoral head to avoid the central stem becoming load-bearing. Although these prostheses are sold together with increasingly better head-centering devices, a minimal intraoperative mistake is always possible. Error at this point concerns inclination of the bony channel, the first trap of the surgical procedure; therefore, an accurate preoperative plan is required to select the proper stem and cup sizing, while shortening surgical times. Nevertheless, a preoperative plan cannot eliminate all errors. Relatively small deviations from anatomic alignment of a resurfacing hip component, should the central stem be inserted slightly inclined, result in marked localized increases in loading of the femoral neck under conditions approximating single-limb stance [8] because the stem is not designed to be load-bearing [3]. This aspect relates to the second trap, namely, possible notching of the flanged profile of the femoral component owing to its consequent inclination. According to Anglin et al. [1], a femoral resurfacing component placement greater than 10° can lead to greater probability of notching. Shimmin and Back [7] reported fracture of the femoral neck after substantial varus placement of the femoral component and intraoperative notching of the femoral neck. In my opinion, the possible mechanism of fracture could be that the prosthetic cup flange involved in notching during weightbearing may start to angulate and eventually loosen from repeated loadings during gait or other activities. Consequent fractures of the neck are well described [2]. Even if performed perfectly, reaming of the neck and additional drilling of the channel for the central stem subtract a certain quantity of bone leading to its weakening. This aspect concerns the third trap, the bony reaming, hazardous but required by the manufacturer and completely surgeon-independent. A possible demonstration of the damaging action of bony reaming is given by the narrowing of femoral necks after resurfacing arthroplasty of the hip as described by Hing et al. [6], which may be attributable to excessive surgical dissection around the femoral neck that damages extraosseous vessels [2]. Once in place, the metal of the central stem may cause bone resorption [5] that becomes apparent only when a fracture of the bony neck occurs. This is the fourth and last trap. Therefore, the central stem, provided to improve insertion of the femoral resurfacing component, may be associated with unforeseen complications in time.

Forensic Engineering Analysis Of head Impact From Falling Picture Frame

This Paper Will Examine The Effect Of An Oak Picture Frame That Was Wall Mounted Around A Flatcreen Television. The Frame Fell From The Flat Screen Television Down 6 Inches Onto A Fireplace Mantel,Nd Then Rotated Away From The Wall, And The Upper Edge Of The Frame Struck The Plaintiff On The Head.He Plaintiff Was Sitting On An Ottoman In Front Of The Fireplace Facing Away From The Fireplace And Wasot Aware Of The Impending Impact. Plaintiff Sued The Premisesowner, Claiming Various Head, Neck Andental Injuries. An Engineering Analysis Was Performed To Assess The Magnitude Of The Force Applied Tolaintiff Neck With An Analytical Model Which Was Developed To Check The Analysis Claimed By The Opposingxpert Biomechanical Engineer. The Writer, Not A Biomechanical Engineer, Analyzed The Magnitudef The Compressive Neck Loading. The Writer Developed A Head-Neck Model That Was Utilized In Thenalysis. The Neck Was Modeled As A Spring; The Head A Sphere; The Neck-Spring Was Mounted On A Rigidlatform, I.E., The Shoulder. Based On Research, Ranges Of Spring Constants Were Estimated For The Neck.He Writer Settled On A Maximum And Minimum Neck Spring Constant With Correlating Damping. Thessue In The Case For The Writer Was The Magnitude Of The Force Applied To The Head And Neck And Whetherhat Force Was Sufficient To Cause The Injuries Claimed By The Plaintiff. The Bio-Mechanical Engineeringssues Are Addressed In The Corresponding Paper By Jon O. Jacobson, Ph.D., P.E. The Case Went Throughany Pre-Trial Discussions And Scheduling, Along With The Deposition Of The Writers Which Were Taken Bylaintiff Attorney. A Formal Written Report Was Not Prepared. Mathcad Calculations With Sidebar Explanationsere Prepared And Supplemented With An Oral Report To The Clients. As A Result Of The Analysis, Thease Settled At The Eleventh Hour Prior To Trial

Biomechanics of Cervical Facet Dislocation

Objectives: The goal of this study was to compute the dynamic neck loads during simulated high-speed bilateral facet dislocation and investigate the injury mechanism. Methods: Ten osteoligamentous functional spinal units (C3/4, n = 4; C5/6, n = 3; C7/T1, n = 3) were prepared with muscle force replication, motion tracking flags, and a 3.3-kg mass rigidly attached to the upper vertebra. Frontal impacts of increasing severity were applied to the lower vertebra until dislocation was achieved. Inverse dynamics was used to calculate the dynamic neck loads during dislocation. Average peak impact acceleration required to cause dislocation ranged between 7.6 and 11.6 g. This resulted in dynamic neck loads applied at average peak rates of 906 Nm/s for flexion moment, 8017 N/ for anterior shear, and 8100 N/s for axial compression. To determine the temporal event patterns, the average occurrence Results: Among average peak loads, axial compression of 233.6 N was first to occur followed by anterior shear force of 73.1 N and flexion moment of 30.7 Nm. Among average peak motions, axial separation of 5.3 mm was first to occur followed by flexion rotation of 63.1 degrees and anterior shear of 21.5 mm. Subsequently, average peak posterior shear force of 110.3 N was observed as the upper facet became locked in the intervertebral foramina. Average peak axial compression of 6.6 mm occurred significantly later than all preceding events. Conclusions: During bilateral facet dislocation, the main loads included flexion moment and forces of axial compression and anterior shear. These loads caused flexion rotation, facet separation, and anterior translation of the upper facet relative to the lower. The present data help elucidate the injury mechanism of cervical facet dislocation.

Position of Hip Resurfacing Component Affects Strain and Resistance to Fracture in the Femoral Neck

Retrieval studies have suggested that the cause of femoral implant failure after metal-on-metal hip resurfacing is multifactorial. Both varus positioning of the femoral component and notching of the superior part of the femoral neck have been associated with femoral component failure. The hypotheses of this study were that placement of a femoral resurfacing component alters femoral neck loading and that the cortical strain pattern reflecting this loading is directly related to the spatial orientation of the resurfacing component. An additional hypothesis was that notching of the superior part of the neck during implantation results in a decreased resistance to neck fracture under axial loading. Varus, anteverted, retroverted, and anatomic positions of the femoral component were tested in sixty-four cadaveric femora. Simulated stance-phase loading was applied, and the shear strain on the femoral neck cortex was quantified with use of a photoelastic method. Preimplantation and postimplantation strain levels were compared over the entire neck region with use of generalized estimating equations. The influence of anteversion and retroversion of the component and notching of the superior part of the neck on the neck strength were evaluated. Placement of the implant in 10 degrees of varus alignment relative to anatomic positioning increased strain on the superior aspect of the neck by 19% to 23% compared with intact femora. Anteverted and retroverted placement of the implant produced elevated strain in the anterior-inferior and posterior-inferior aspects of the neck, respectively. Placement of the component stem in alignment with the anatomic neck axis decreased neck cortical strain 6% to 19% compared with intact femora. Notching of the superior aspect of the neck decreased neck strength by 21%. Relatively small deviations from anatomic alignment of a resurfacing hip component result in marked localized increases in loading of the femoral neck under conditions approximating single-limb stance. Neutral positioning of the femoral component results in localized strain reduction. Notching of the superior aspect of the femoral neck significantly reduces the resistance to fracture (p = 0.008).

Biomechanical Analysis of Football Neck Collars

To determine the load-limiting capabilities of protective neck collars used in football through dynamic impact testing. A 50th-percentile male Hybrid III dummy was used in 48 dynamic impact tests comparing The Cowboy Collar, Bullock Collar, and Kerr Collar. A control and each collar were tested at two velocities (5 m/s and 7 m/s), three impact locations (front, top, and side of the helmet), and two shoulder pad positions (normal and raised). Research laboratory. None. None. Independent variables were the neck collars, impact velocity, and shoulder pad position. In addition to range of motion, upper and lower neck forces and moments were measured. With the top impact location, it was found that the Kerr Collar and Bullock Collar reduced head accelerations and force transmission through the neck. With the front impact location, all the collars reduced lower neck moment. The Kerr Collar was also capable of reducing the lower neck force and upper neck moment. With the side impact location, the Kerr Collar substantially reduced lower neck moment. These reductions in loads correlate with the degree to which each collar restricted the motion of the head and neck. By restricting the range of motion of the neck and redistributing load to the shoulders, neck loads can be effectively lowered.