Richard L. Stalnaker

Impact Injury Mechanisms in Abdominal Organs

Blunt abdominal trauma is a major cause of death in the United States. However, little experimental work has been done to clarify the mechanism of blunt abdominal injury and to quantify tolerance parameters for the abdominal organs. This paper describes a joint study by the Highway Safety Research Institute and the Section of General Surgery of The University of Michigan in which direct impacts were applied to livers and kidneys. The tests were performed in a high-speed testing machine at a controlled ram velocity and stroke limit. The organ was surgically mobilized in anesthesized Rhesus monkeys and then placed on a load cell while still being perfused in the living animal. Tests were performed at ram speeds of 120, 6000, and 12000 in/min (5, 250, and 500 cm/s). The resulting load-deflection data were normalized and average stress-strain curves plotted for each test. In addition, the resulting injury severity was estimated immediately after impact using an injury scale of 1 to 5. A discussion of the injury mechanisms observed in the tests is given, and correlation between injury severity and the mechanical parameters of stress, strain, and strain energy produced in the tissue of the organ is presented.

Impact Response and Tolerance of the Lower Extremities

This paper presents the results of direct impact tests and driving point impedance tests on the legs of seated unembalmed human cadavers. Variables studied in the program included impactor energy and impact direction (axial and oblique). Multiple strain gage rosettes were applied to the bone to determine the strain distribution in the bone. The test results indicate that the unembalmed skeletal system of the lower extremities is capable of carrying significantly greater loads than those determined in tests with embalmed subjects (the only similar data reported in the present literature). The strain analysis indicated that significant bending moments are generated in the femur with axial knee impact. The results of the impedance tests are used to characterize the load transmission behavior of the knee-femur-pelvis complex, and the impact test results are combined with this information to produce suggested response characteristics for dummy simulation of knee impact response.

Biomechanical Aspects of Head Injury

With the advent of high speed air and land transportation, engineers have become increasingly aware of the mechanical frangibility of the human body. Thus, we have seen the evolution of various isolating and load distributing devices ranging from seat belts and padded sun visors, to ejection seats, crash helmets, and acceleration couches. While there is a large amount of information available regarding the response of inanimate systems to vibration and impact, there is a comparable dearth of knowledge pertaining to the mechanical responses of biological systems. Therefore, the design of much supporting and protective equipment is often based on intuition because of the lack of information available about the mechanical behavior of the human body. In addition, such knowledge would be helpful in the treatment of injury by serving to identify the mechanism of trauma. Thus, both a rational design procedure for impact protection and a rational therapy for treatment of trauma cannot be developed until a quantitive description of the mechanical responses of the human body is obtained.

Mechanisms of femoral fracture

Abstract Mechanisms of femoral fracture of the condyles and shaft were experimentally investigated through controlled knee impact of denuded femurs in six human cadavers. High-speed movies recorded knee joint compression, femoral displacements and deformation, and fracture initiation. Fracture initiated at 10.6 ± 2.7 kN knee load after 1.3 ± 0.1 cm of knee joint compression for a 10.1 kg rigid impact at 13.2 ± 1.4 m/s. Interestingly, fracture occurred 0.5 ms–1.5 ms after the peak in applied knee load of 18.3 ± 6.9 kN, probably because a significant portion of the load is developed by inertial accelerations displacing the femur and coupled masses. Axial strain measurements at the femoral midshaft showed increasing anteroposterior bending and compressional deformations until the initiation of observed fracture. The kinematics of the observed fracture and the midshaft deformational strains indicate that fracture is predominantly due to tensile strain from anteroposterior bending of the femoral shaft or patellar wedging of the condyles.

Human Torso Response to Blunt Trauma

The most frequent causes of blunt abdominal injury are the steering wheel and the lap belt. The organs most often injured are the liver, pancreas, spleen and intestines. Based on this information, a series of animal abdominal impacts were designed to study the relationship between shape and type of impactor, velocity and direction of impact, body region impacted and injury level. The results of this study are given in the form of an experimental scaling factor which relates the sensitivity to impacts of the various body regions. This scaling factor was found to be dependent of body weight, making it applicable for evaluating human tolerances to abdominal impacts.

Side impact tolerance to blunt trauma

The object of this research program has been to extend the scope of earlier work to include long-duration head impacts and to develop new scaling relationships to allow extrapolation of impact data from infrahuman primates to living humans. A series of living primate side impacts to the head and torso was conducted in parallel with a series of impacts to human cadavers. Dimensional analysis techniques were employed to estimate in vivo human tolerance to side injury. The threshold of closed brain injury to humans was found to be 76 g for a pulse duration of 20 ms and an impact velocity of 43 ft/s (13.2 m/s). The maximum tolerable penetration to the chest was found to be 2.65 in (6.72 cm) for both the left and right sides. Scaling of abdominal injuries to humans was accomplished by employing a factor that relates impact contact area, animal mass, impact force, and pulse duration to injury severity. The maximum tolerable contact pressure to the upper abdomen of a human was found to be 32 lbf/inu2 (220 kPa).

DOOR CRASHWORTHINESS CRITERIA

The object of the program was to make long duration head impacts and to develop scaling relationships to allow extrapolation of impact data for infra-human primates to living humans. A series of primate side impacts, to the head and body was conducted in parallel with a series of impacts to human cadavers. Dimensional analysis techniques were employed to estimate in vivo human tolerance to side impacts. The threshold of closed brain injury to humans was found to be 76Gs for a pulse duration of 20 msec and an impact velocity of 29.5 mph. The maximum tolerable penetration to the chest was found to be 2.65 inches for both the left and right sides. Scaling of abdominal injuries to humans was accomplished by employing a factor which relates impact contact area, animal mass, impact force, and pulse duration, to injury severity. The maximum tolerable contact pressure to the upper abdomen of a human was found to be 32 psi.

PROTECTION OF CHILD OCCUPANTS IN AUTOMOBILE CRASHES

Detailed investigations of automobile crashes in which children under 10 years old were passengers were carried out. The purpose of this study was to investigate the injury patterns of restrained and unrestrained children and to assess performance of child restraint systems in real world crashes. Crashes which occurred mainly in Washtenaw and Oakland counties of the state of Michigan were surveyed. 37% of the children in the investigated cases were restrained by an adult lap belt or a child restraint. It was found that only 4. 7% of the children in the overall sample were restrained. Both adult seat belts and child restraints (when used) were found to be effective in reducing injuries in crashes. Head and facial injuries were found to be the most common form of injury to children. The vehicle interior contact points which produced some of these injuries were not covered by Federal Motor Vehicle Safety Standard 201 on occupant protection in interior impact, which specifies requirements for padded instrument panels and some other interior components. Language: en

Occupant Injury Assessment Criteria

This paper is a brief review of the complex subject of human injury mechanisms and impact tolerance. Authomotive accident-related injury patterns are briefly described and the status of knowledge in the biomechanics of trauman of the head, neck, chest, abdomen and extremites is discussed. /Author/

A High-Speed Cineradiographic Technique for Biomechanical Impact

The paper discusses the techniques which have been developed for application to human injury and tolerance and coolant protection research. This system consists of a high-speed motion picture camera which views a 2-inch diameter output phosphor of a high gain 4-stage, magnetically focussed image intensifer tube, gated on an off synchronously with shutter pulses from the motion picture camera. A fast lens optically couples the input photocathode of the image intensifier tube to x-ray images produced on a fluorescent screen by a d. c. x-ray generator. The system is adaptable to a wide variety of experimental configurations. Examples of x-ray penetration of targeted human cadaver head, neck, knee, and lateral thorax views obtained with the system are shown and discussed. Language: en