Analysis of burn injuries in frontal automobile crashes.

The purpose of this study was to investigate burn injuries resulting from frontal automobile crashes and to determine the effects of frontal airbags on the incidence of burn injuries. The study included 25,464 individual cases from the National Automotive Sampling System database files for the years 1993 to 2000. Occupants were at a significantly higher risk to sustain a burn injury when exposed to an airbag deployment (1.54%) compared with those who received a burn injury when not exposed to an airbag deployment (0.02%; P = 0.02). In contrast to previous publications, this study found that 1.53% of front seat occupants exposed to an airbag deployment sustained an airbag-induced burn injury. The vast majority of airbag-induced burn injuries were minor (98.7%); however, in cases with no airbag deployment, the burns were often much more serious, including fatal burns (29.6%). Occupant weight, height, sex, seatbelt use, and seat position were all found not to be significant in predicting the risk of airbag induced burn injury, whereas age and crash velocity were found to be significant.

Prediction of severe eye injuries in automobile accidents: static and dynamic rupture pressure of the eye.

The purpose of this paper is to determine the static and dynamic rupture pressures of 20 human and 20 porcine eyes. This study found the static test results show an average rupture pressure for porcine eyes of 1.00 +/- 0.18 MPa while the average rupture pressure for human eyes was 0.36 +/- 0.20 MPa. For dynamic loading, the average porcine rupture pressure was 1.64 +/- 0.32 MPa, and the average rupture pressure for human eyes was 0.91 +/- 0.29 MPa. Significant differences are found between average rupture pressures from all four groups of tests (p = 0.01). A risk function has been developed and predicts a 50% risk of globe rupture at 1.02 MPa, 1.66 MPa, 0.35 MPa, and 0.90 MPa internal pressure for porcine static, porcine dynamic, human static, and human dynamic loading conditions, respectively.

Correlation of cell strain in single osteocytes with intracellular calcium, but not intracellular nitric oxide, in response to fluid flow.

Osteocytes compose 90-95% of all bone cells and are the mechanosensors of bone. In this study, the strain experienced by individual osteocytes resulting from an applied fluid flow shear stress was quantified and correlated to two biological responses measured in real-time within the same individual osteocytes: (1) the upregulation of intracellular calcium and (2) changes in intracellular nitric oxide. Osteocyte-like MLO-Y4 cells were loaded with Fluo-4 AM and DAR-4M and exposed to uniform laminar fluid flow shear stresses of 2, 8, or 16 dyn/cm(2). Intracellular calcium and nitric oxide changes were determined by measuring the difference in fluorescence intensity from the cell's basal level prior to fluid flow and the level immediately following exposure. Individual cell strains were calculated using digital image correlation. MLO-Y4 cells showed a linear increase in cell strain, intracellular calcium concentration, and nitric oxide concentration with an increase in applied fluid flow rate. The increase in intracellular calcium was well correlated to the strain that each cell experienced. This study shows that osteocytes exposed to the same fluid flow experienced a range of individual strains and changes in intracellular calcium and nitric oxide concentrations, and the changes in intracellular calcium were correlated with cell strain. These results are among the first to establish a relationship between the strain experienced by osteocytes in response to fluid flow shear and a biological response at the single cell level. Mechanosensing and chemical signaling in osteocytes has been hypothesized to occur at the single cell level, making it imperative to understand the biological response of the individual cell.

Severe upper extremity injuries in frontal automobile crashes: the effects of depowered airbags.

BACKGROUND: The purpose of this study was to determine the effects of depowered frontal airbags on the incidence of severe upper extremity injuries. METHODS: The National Automotive Sampling System database files from 1993 to 2000 were examined in a study that included 2,413,347 occupants who were exposed to an airbag deployment in the United States. RESULTS: Occupants exposed to a depowered airbag deployment were significantly more likely to sustain a severe upper extremity injury (3.9%) than those occupants exposed to a full-powered airbag deployment (2.5%) (P=.01). Full-powered systems resulted in an injury distribution of 89.2% fractures and 7.9% dislocations compared with depowered systems with 55.3% fractures and 44.3% dislocations. CONCLUSIONS: Although depowered airbags were designed to reduce the risk of injuries, they appear to have increased the overall incidence of severe upper extremity injuries through a shift from long bone fractures to joint dislocations.

The effects of depowered airbags on skin injuries in frontal automobile crashes.

The purpose of this study was to determine the effects of depowered frontal airbags on the incidence of skin injuries. The National Automotive Sampling System database files from 1993 to 2000 were examined in a study including 2,246,524 occupants exposed to airbag deployment in the United States. There was no significant difference between full-powered and depowered airbags, with 60.2 percent of those exposed to a full-powered deployment sustaining a skin injury versus 59.5 percent of occupants exposed to a depowered airbag (p = 0.19). Whether occupants were exposed to a full-powered airbag (1,936,485 occupants) or a depowered airbay (310,039 occupants), the majority of skin injuries were to the upper extremity and the face. Regardless of airbag power, the overwhelming majority of the skin injuries were minor (99.8 percent). There was not a significantly greater risk of injury from any source for occupants exposed to a depowered airbag or a full-powered airbag (p = 0.87). The data suggest that the implementation of depowered airbags did not affect the number, seriousness, location, or source of skin injuries.

The effects of depowered airbags on eye injuries in frontal automobile crashes.

The purpose of this study was to investigate eye injuries resulting from frontal automobile crashes and to determine the effects of depowered airbags. The National Automotive Sampling System database files from 1993 to 2000 were examined in a 3-part investigation of 22 236 individual crashes. Of the 2 103 308 occupants exposed to a full powered deployment, 3.7% sustained an eye injury compared to 1.7% of the 310 039 occupants exposed to a depowered airbag deployment. Occupants were at a significantly higher risk to sustain an airbag-induced eye injury when exposed to a full powered airbag compared with occupants exposed to a depowered airbag deployment ( P = .04). Approximately, 90% of the eye injuries in full powered airbag deployments were caused by the airbag, compared to only 35% of the depowered airbag eye injuries.

Material properties of human rib cortical bone from dynamic tension coupon testing.

The purpose of this study was to develop material properties of human rib cortical bone using dynamic tension coupon testing. This study presents 117 human rib cortical bone coupon tests from six cadavers, three male and three female, ranging in age from 18 to 67 years old. The rib sections were taken from the anterior, lateral, and posterior regions on ribs 1 through 12 of each cadaver's rib cage. The cortical bone was isolated from each rib section with a low speed diamond saw, and milled into dog bone shaped tension coupons using a small computer numerical control machine. A high-rate servo-hydraulic Material Testing System equipped with a custom slack adaptor, to provide constant strain rates, was used to apply tension loads to failure at an average rate of 0.5 strains/sec. The elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, and strain energy density were determined from the resulting stress versus strain curves. The overall average of all cadaver data gives an elastic modulus of 13.9 GPa, a yield stress of 93.9 MPa, a yield strain of 0.88 %, an ultimate stress of 124.2 MPa, an ultimate strain of 2.7 %, and a strain energy density of 250.1 MPa-microstrain. For all cadavers, the plastic region of the stress versus strain curves was substantial and contributed approximately 60 % to the strain energy and over 80 % in the tests with the 18 year old cadaver. The rib cortical bone becomes more brittle with increasing age, shown by an increase in the modulus (p < 0.01) and a decrease in peak strain (p < 0.01). In contrast to previous three-bending tests on whole rib and rib cortical bone coupons, there were no significant differences in material properties with respect to rib region or rib level. When these results are considered in conjunction with the previous three-point bending tests, there is regional variation in the structural response of the human rib cage, but this variation appears to be primarily a result of changes in the local geometry of each rib while the material properties remain nearly constant within an individual.

Defining regional variation in the material properties of human rib cortical bone and its effect on fracture prediction.

This paper presents the results of dynamic material tests and computational modeling that elucidate the effects of regional rib mechanical properties on thoracic fracture patterns. First, a total of 80 experiments were performed using small cortical bone samples from 23 separate locations on the rib cages of four cadavers (2 male, 2 female). Each specimen was subjected to dynamic three-point bending resulting in an average strain rate of 5 +/- 1.5 strain/s. Test coupon modeling was used to verify the test setup. Regional variation was defined by location as anterior, lateral, or posterior as well as by rib level 1 through 12. The specimen stiffness and ultimate stress and strain were analyzed by location and rib level. Second, these material properties were incorporated into a human body computational model. The rib cage was partitioned into anterior, lateral, and posterior segments and the material properties were varied by location using an elastic-plastic material model. A total of 12 simulations with a rigid impactor were performed including 2 separate material assumptions, original and modified rib properties for regional variations, 3 separate impactor velocities, and 2 directions, anterior and lateral. The data from the material tests for all subjects indicate a statistically significant increase in the average stiffness and average ultimate stress for the cortical bone specimens located in the lateral (11.9 GPa modulus, 153.5 MPa ultimate stress) portion of the ribs versus the anterior (7.51 GPa, 116.7 MPa) and posterior (10.7 GPa, 127.7 MPa) rib locations. In addition, the stiffness, ultimate stress, and ultimate strain for all subjects are significantly different by rib level with each variable generally increasing with increasing rib number. The results from the computational modeling for both frontal and lateral impacts illustrate that the location and number of rib fractures are altered by the inclusion of rib material properties that vary by region.

Upper extremity interaction with a helicopter side airbag: injury criteria for dynamic hyperextension of the female elbow joint.

This paper describes a three part analysis to characterize the interaction between the female upper extremity and a helicopter cockpit side airbag system and to develop dynamic hyperextension injury criteria for the female elbow joint. Part I involved a series of 10 experiments with an original Army Black Hawk helicopter side airbag. A 5(th) percentile female Hybrid III instrumented upper extremity was used to demonstrate side airbag upper extremity loading. Two out of the 10 tests resulted in high elbow bending moments of 128 Nm and 144 Nm. Part II included dynamic hyperextension tests on 24 female cadaver elbow joints. The energy source was a drop tower utilizing a three-point bending configuration to apply elbow bending moments matching the previously conducted side airbag tests. Post-test necropsy showed that 16 of the 24 elbow joint tests resulted in injuries. Injury severity ranged from minor cartilage damage to more moderate joint dislocations and severe transverse fractures of the distal humerus. Peak elbow bending moments ranged from 42.4 Nm to 146.3 Nm. Peak bending moment proved to be a significant indicator of any elbow injury (p = 0.02) as well as elbow joint dislocation (p = 0.01). Logistic regression analyses were used to develop single and multiple variate injury risk functions. Using peak moment data for the entire test population, a 50% risk of obtaining any elbow injury was found at 56 Nm while a 50% risk of sustaining an elbow joint dislocation was found at 93 Nm for the female population. These results indicate that the peak elbow bending moments achieved in Part I are associated with a greater than 90% risk for elbow injury. Subsequently, the airbag was re-designed in an effort to mitigate this as well as the other upper extremity injury risks. Part III assessed the redesigned side airbag module to ensure injury risks had been reduced prior to implementing the new system. To facilitate this, 12 redesigned side airbag deployments were conducted using the same procedures as Part I. Results indicate that the re-designed side airbag has effectively mitigated elbow injury risks induced by the original side airbag design. It is anticipated that this study will provide researchers with additional injury criteria for assessing upper extremity injury risk caused by both military and automotive side airbag deployments.