Paul C. Begeman

BIOMECHANICS OF THE HUMAN CHEST, ABDOMEN, AND PELVIS IN LATERAL IMPACT

Fourteen unembalmed cadavers were subjected to 44 blunt lateral impacts at velocities of approximately 4.5, 6.7, or 9.4 m/s with a 15 cm flat circular interface on a 23.4 kg pendulum accelerated to impact speed by a pneumatic impactor. Chest and abdominal injuries consisted primarily of rib fractures, with a few cases of lung or liver laceration in the highest severity impacts. There were two cases of pubic ramus fracture in the pelvic impacts. Logist analysis of the biomechanical responses and injury indicated that the maximum Viscous response had a slightly better correlation with injury than maximum compression for chest and abdominal impacts. A tolerance level of VC = 1.47 m/s for the chest and VC = 1.98 m/s for the abdomen were determined for a 25% probability of critical injury. Maximum compression was similarly set at C = 38% for the chest and at C = 44% for the abdomen. The experiments indicate that chest and abdominal injury may occur by a viscous mechanism during the rapid phase of body compression, and that the Viscous and compression responses are effective, complementary measures of injury risk in side impact. Although serious pelvic injury was infrequent, lateral public ramus fracture correlated with compression of the pelvis, not impact force or pelvic acceleration. Pelvic tolerance was set at 27% compression.

DEVELOPMENT OF A FINITE ELEMENT MODEL OF THE HUMAN NECK

A 3-dimensional finite element model of a human neck was developed to study the mechanics of cervical spine while subjected to impacts. The neck geometry was obtained from MRI scans of a 50th percentile male volunteer. This model consisting of vertebrae C1-T1 was constructed primarily of 8-node brick elements. Vertebrae were modeled using linear elastic-plastic materials and the intervertebral discs were modeled using linear viscoelastic materials. Sliding interfaces were defined to simulate the motion of synovial facet joints. A previously developed head and brain model was also incorporated. Only the passive effects of the head and neck muscles were considered. Data from head drop tests performed at Duke University and data from 3, 24 km/hr cadaver rear-end impact sled tests were used to validate the model. The validated model was integrated into a skeleton torso model previously developed to simulate a 50th percentile male driver in a 48 km/hr impact with a pre-deployed airbag. This simulation was similar to that reported by Cheng et al. In this application, the kinematics and airbag pressure predicted by the model compared with experimental data. None of the airbags used in the simulations or experiments represent any currently in production. Further research is still needed to fully validate the model before it can be used to study neck loads during head-airbag or other serious injury interactions.

Qualitative analysis of neck kinematics during low-speed rear-end impact

OBJECTIVE To analyze neck kinematics and loading patterns during rear-end impacts. DESIGN The motion of each cervical vertebra was captured using a 250 frame/s X-ray system during a whole body rear-end impact. These data were analyzed in order to understand different phases of neck loading during rear-end impact. BACKGROUND The mechanism of whiplash injury remains largely unknown. An understanding of the underlying kinematics of whiplash is crucial to the identification of possible injury mechanisms before countermeasures can be designed. METHODS Metallic markers were inserted into the vertebral bodies and spinous processes of each of the seven cervical vertebrae. Relative displacement-time traces between each pair of adjacent cervical vertebrae were calculated from X-ray data. Qualitative analyses of the kinematics of the neck at different phase of impact were performed. RESULTS The neck experiences compression, tension, shear, flexion and extension at different cervical levels and/or during different stages of the whiplash event. CONCLUSIONS Neck kinematics during whiplash is rather complicated and greatly influenced by the rotation of the thoracic spine, which occurs as a result of the straightening of the kyphotic thoracic curvature. RELEVANCE Understanding the complicated kinematics of a rear-end impact may help clinicians and researchers shed some light on potential mechanisms of whiplash neck injury.

Dynamic Axial Tolerance of the Human Foot-Ankle Complex

Dynamic axial impact tests to isolated lower legs were conducted at the Medical College of Wisconsin laboratory in the USA. The aim is to develop a more definitive and quantitative relationship between biomechanical parameters such as specimen age, axial force, and injury. Twenty-six intact adult lower legs excised from unembalmed human cadavers were tested under dynamic loading using a mini-sled pendulum device. Results from these tests were combined with the data from the studies by Wayne State University and Calspan Corporation, both in the USA. The total sample size available was 52. Statistical analysis of these data was performed using Weibull techniques. Age and dynamic axial force were the most significant discriminant variables that defined the injury risk function. Consequently, the probability of foot-ankle injury was described in terms of specimen age and force. The findings are a first step towards the quantification of the dynamic tolerance of the human foot-ankle complex under the axial impact modality.For the covering abstract of the conference see IRRD 891635.

Human ankle impact response in dorsiflexion

Although various automobile accident surveys showed between 20 to 30% of lower extremity injuries involved the foot or ankle, there is little information in the existing literature on the injury mechanisms of ankle injuries for automobile occupants involved in frontal impacts. This study addresses the injury to ankles involving dorsiflexion caused by impact loading to the bottom of the foot. Types of injuries include malleolus fractures and ligament avulsions and ruptures. For the covering abstract see IRRD 864472.

BIODYNAMIC RESPONSE OF THE MUSCULOSKELETAL SYSTEM TO IMPACT ACCELERATION

Male volunteers restrained by a lap-shoulder belt system were subjected to static and dynamic (low level impact acceleration) tests in a simulated automobile environment while electromyographic (EMG) activity of various lower extremity muscles was recorded. The seat and floor pan were supported on load cells which measured all restraining forces. Nine-accelerometer modules and high-speed photography were used to measure kinematics. Identical tests were made with an embalmed cadaver and a dummy. While reflex responses of the relaxed volunteer were found too slow to affect loads and accelerations sustained, the voluntary pre-impact contracted musculature in a subject was found to reduce certain acceleration levels and to change the restraint load distribution. Significantly more load went through the legs to the floor board, with a concomitant lowering of seat and belt loads. Although a similar load distribution was seen in cadaver and dummy tests, the response of the relaxed or tensed volunteer was substantially different from either surrogate.

Spinal Loads Resulting from -Gx Acceleration

The biodynamic response of cadaver torsos subjected to -Gdx impact acceleration is discussed in this paper, with particular emphasis on the response of the vertebral column. The existence of an axial force along the spine and its manifestation as a load on the seat pan are reported. Spinal curvature appears to be an important factor in the generation of this spine load. In anthropometric dummies, the spine load does not exist. Details of the testing and results are given, and the development of a mathematical model is shown.

A mechanism of injury to the forefoot in car crashes.

Objective:The purpose of this study was to determine a mechanism of injury of the forefoot due to impact loads and accelerations as noted in some frontal offset car crashes. Methods:The impact tests conducted simulated knee-leg-foot entrapment, floor pan intrusions, whole-body deceleration, muscle tension, and foot/pedal interaction. Specimens were impacted at speeds of up to 16 m/s. To verify this injury mechanism research was conducted in an effort to produce Lisfranc type injuries and metatarsal fractures. A total of 54 lower legs of post-mortem human subjects were tested. Two possible mechanisms of injury were investigated. For the first mechanism the driver was assumed to be braking hard with the foot on the brake pedal and at 0 deg plantar flexion (Plantar Nominal Configuration) and the brake pedal was in contact with the foot behind the ball of the foot. The second mechanism was studied by having the ball of the foot either on the brake pedal or on the floorboard with the foot plantar-flexed 35 to 50 deg (Plantar Flexed Configuration). Results:The Plantar Nominal injury mechanism yielded few injuries of the type the study set out to produce. Out of 13 specimens tested at speeds of 16 m/s, three had injuries of the metatarsal (MT) and tarsometatarsal joints. The Plantar Flexed Configuration injury mechanism yielded 65% injuries at high (12.5–16 m/s) and moderate (6–12 m/s) speeds. Conclusion:It is concluded that Lisfranc type foot injuries are the result of impacting the forefoot in the Plantar Flexed Configuration. The injuries were consistent with those reported by physicians treating accident victims and were verified by an orthopedic surgeon during post impact x-ray and autopsy. They included Lisfranc fractures, ligamentous disruptions, and metatarsal fractures.

Proposed provisional reference values for the humerus for evaluation of injury potential

Ten unembalmed cadaver arm pairs and four individual unembalmed cadaver arms were tested to fracture in three-point bending on an Instron testing machine in either the L-M or A-P direction. Two loading rates were used, 218 mm/s and 0.635 mm/s. Tests were done using an Instron servo-controlled hydraulic testing machine. After fracture, each specimen was photographed and the anterior and posterior dimensions were measured with a micrometer. Using the technique developed by Mertz, several equations were employed to calculate the normalized forces and moments. Overall, three types of fractures were observed; straight simple fractures, angled simple fractures, and spiral or irregular fractures. Language: en

Lumbar Spinal Strains Associated with Whiplash Injury: A Cadaveric Study

Fast A, Sosner J, Begeman P, Thomas MA, Chiu T: Lumbar spinal strains associated with whiplash injury: A cadaveric study. Am J Phys Med Rehabil 2002;81:645–650. Objectives To study and quantify the effects of rear-end collision on the lumbar spine. Design The lumbar spine of a cadaver was instrumented with rosette strain gauges applied on the lateral and anterior surfaces of T12, L2, and L4. Biaxial accelerometers were mounted on L1, L3, and L5. The cadaver was seated, restrained, and subjected to rear impacts of 5 g and 8 g. Results The anterior shear strains had a biphasic shape. Spinal strains peaked at the T12 at approximately 120 and 370 msec, whereas in the L4 vertebra, it peaked at 200 and 380 msec. The anterior strain pattern of the L4 and T12 vertebrae were in diametrically opposite directions. In the second set of tests (8 g experiment), the acceleration forces and strains pattern were similar to the 5 g test but of higher magnitude. The principal anterior strain was 480 &mgr;m/m for 5 g and 530 &mgr;m/m for 8 g; the lateral shear strain was 680 &mgr;m/m and 1500 &mgr;m/m in the 5 g and 8 g experiments, respectively. Conclusions Forces generated during simulated whiplash collision induce biphasic lumbar spinal motions (increased-decreased lordosis) of insufficient magnitude to cause bony injuries, but they may be sufficient to cause soft-tissue injuries.