Chantal S. Parenteau

Biomechanical Properties of Human Cadaveric Ankle-Subtalar Joints in Quasi-Static Loading

The biomechanical properties of human ankle-subtalar joints have been determined in a quasi-static loading condition. The moving center of rotation was determined and approximated by a fixed point. The moment-angle characteristics of the ankle-subtalar joints about the fixed center of rotation have been measured under four basic movements: dorsiflexion, plantarflexion, inversion, and eversion. The method linearly increases rotation of the calcaneus until failure, and measures the moments, forces, and linear and rotational displacements. Failure was identified as the initial drop of moment on plot showing the moment representing gross injury or microfilament damage. In this study, 32 human ankle-subtalar joints have been tested to failure. The center of rotation of the ankle-subtalar joints was determined for a pure dorsiflexion (9 specimens), plantarflexion (7 specimens), inversion (8 specimens), and eversion (8 specimens). Failure in the joints occurred at an average moment of -33.1 +/- 16.5 Nm in dorsiflexion, 40.1 +/- 9.2 Nm in plantarflexion, -34.1 +/- 14.5 Nm in inversion, and 48.1 +/- 12.2 Nm in eversion. The failure angle was also determined in all four motions. Failure was best predicted by an angle of -44.0 +/- 10.9 deg in dorsiflexion, 71.6 +/- 5.7 deg in plantarflexion, -34.3 +/- 7.5 deg in inversion, and 32.4 +/- 7.3 deg in eversion. Injury was identified in every preparation tested in inversion and eversion, while it resulted in five of the nine preparations in dorsiflexion, and in three of the seven in plantarflexion. Injury occurred at -47.0 +/- 5.3 deg and -36.2 +/- 14.8 Nm in dorsiflexion, and at 68.7 +/- 5.9 deg and 36.7 +/- 2.5 Nm in plantarflexion. The results obtained in this study provide basic information of the ankle-subtalar joint kinematics, biomechanics, and injury. The data will be used to form a basis for corridors of the ankle-subtalar joint responses.

Crash Injury Risks for Obese Occupants Using a Matched-Pair Analysis

Objective. The automotive safety community is questioning the impact of obesity on the performance and assessment of occupant protection systems. This study investigates fatality and serious injury risks for front-seat occupants by body mass index (BMI) using a matched-pair analysis. It also develops a simple model for the change in injury risk with obesity. Methods. A simple model was developed for the change in injury risk with obesity. It included the normal mass (m) and stiffness (k) of the body resisting compression during a blunt impact. Stiffness is assumed constant as weight is gained (Δ m). For a given impact severity, the risk of injury was assumed proportional to compression. Energy balance was used to determine injury risks with increasing mass. NASS-CDS field data were analyzed for calendar years 1993–2004. Occupant injury was divided into normal (18.5 kg/m 2 ≤ BMI < 25.0 kg/m 2 ) and obese (BMI ≥ 30 kg/m 2 ) categories. A matched-pair analysis was carried out. Driver and front-right passenger fatalities or serious injuries (MAIS 3+) were analyzed in the same crash to determine the effect of obesity. This also allowed the determination of the relative risk of younger (age ≤ 55 years), older (age >55years), male, and female drivers that were obese compared to normal BMI. The family of Hybrid III crash test dummies was evaluated for BMI and the amount of ballast was determined so they could represent an obese or morbidly obese occupant. Results. Based on the simple model, the relative injury risk (r) for an increase in body mass is given by: r = (1 + Δ m / m) 0.5 . For a given stature, an obese occupant (BMI = 30–35 kg/m 2 ) has 54–61% higher risk of injury than a normal BMI occupant (22 kg/m 2 ). Matched pairs showed that obese drivers have a 97% higher risk of fatality and 17% higher risk of serious injury (MAIS 3+) than normal BMI drivers. Obese passengers have a 32% higher fatality risk and a 40% higher MAIS 3+ risk than normal passengers. Obese female drivers have a 119% higher MAIS 3+ risk than normal BMI female drivers and young obese drivers have a 20% higher serious injury risk than young normal drivers. This range of increased risk is consistent but broader than predicted by the simple injury model. The smallest crash test dummies need proportionately more ballast to represent an obese or morbidly obese occupant in the evaluation of safety systems. The 5% female Hybrid III has a BMI = 20.4 kg/m 2 and needs 22 kg of ballast to represent an obese and 44.8 kg to represent a morbidly obese female, while the 95% male needs only 1.7 and 36.5 kg, respectively. Conclusions. Obesity influences the risk of serious and fatal injury in motor vehicle crashes. The effect is greatest on obese female drivers and young drivers. Since some of the risk difference is related to lower seatbelt wearing rates, the comfort and use of seatbelt extenders should be examined to improve wearing rates. Also, crash testing with ballasted dummies to represent obese and morbidly obese occupants may lead to refined safety systems for this growing segment of the population.

Near and Far-Side Adult Front Passenger Kinematics in a Vehicle Rollover

In this study, U.S. accident data was analyzed to determine interior contacts and injuries for front-seated occupants in rollovers. The injury distribution for belted and unbelted, non-ejected drivers and right front passengers (RFP) was assessed for single-event accidents where the leading side of the vehicle rollover was either on the driver or passenger door. Drivers in a roll-left and RFP in roll-right rollovers were defined as near-side occupants, while drivers in roll-right and RFP in roll-left rollovers were defined as far-side occupants. Serious injuries (AIS 3+) were most common to the head and thorax for both the near and far-side occupants. However, serious spinal injuries were more frequent for the far-side occupants, where the source was most often coded as roof, windshield and interior. Based on the injury sources for both situations, head injuries seem to occur from contact with the roof, windshield (in particular for unbelted occupants) and pillars, while thoracic injuries resulted from contact with steering assembly and the interior. The field injury data was compared with the Hybrid III responses obtained from simulated mathematical rollovers to better understand occupant kinematics and injury biomechanics. These simulations were validated using laboratory tests. The laboratory tests included the FMVSS 208 dolly rollover, the ADAC corkscrew, curb and soil-trips, bounce-overs and fall-overs. Based on the mathematical simulations, the kinematics of the front far-side occupant differed from that of the near-side. For the belted far-side occupant, the torso often slipped out of the belt which allows excursion towards the near-side occupant. For the belted nearside occupant, the shoulder belt remained on the upper body during the initial roll phase. The occupant nonetheless moved up and outwards and the head could contact the roof-rail and header areas depending on the rollover condition simulated. The near-side occupants head crossed the window plane more frequently than the head of the far-side occupant. Dummy kinematics from the simulation help explain the frequency of serious head and thorax injuries reported in the field. Field data analysis and mathematical simulations are useful in understanding injury biomechanics and providing guidance for future testing.

Analysis of Head Impacts Causing Neck Compression Injury

Objective. Human cadavers have been subjected to inverted drop, linear, and pendulum impacts to the top of the head, causing neck compression injury. The data are not comparable on the basis of impact velocity because of differing impact masses and test conditions. This study analyzed the published biomechanical data and used peak head velocity to merge the datasets. Correlations were determined between biomechanical responses and serious injury (AIS 3+). Methods. Three studies were found involving 33 inverted drop tests and three others involving 42 linear or pendulum impacts to the top of a cadavers head. Various biomechanical responses were measured in the tests. The datasets could not be meaningfully merged on the basis of impact velocity. The coefficient of restitution (e) was determined and the peak head velocity calculated for tests with missing data. This allowed the datasets to be merged and statistically analyzed for relationships between head velocity, impact force, and serious injury. Power functions were fit to the biomechanical data, t-tests conducted for significant differences in injury, and logit risk functions determined. Results. The coefficient of restitution was e = 0.24 ± 0.16 (n = 19) for the drop tests and e = 0.21 ± 0.12 (n = 20) for the impact tests. Peak head velocity was 22% higher than the impact velocity for the drop tests but −20% lower in the impact tests. Head velocity averaged 6.32 ± 1.29 m/s (n = 51) causing serious injury and 3.75 ± 2.16 m/s (n = 24) without injury (t = 5.39, p = 0.00001, df = 31). Impact force was 7,382 ± 3,632 N with injury and 3,760 ± 3,528 N without (t = 3.95, p = 0.0003, df = 42). A power function fit the impact force versus head velocity data (F = 374V h 1.565 , R2 = 0.758). Conclusion. Peak head velocity was determined for inverted drop and impact tests as a means of merging and analyzing cadaver data on serious injury for impacts to the top of the head. There are relationships between head velocity, impact force, and serious injury. A 15% risk of serious injury is at 2.3 m/s (5.1 mph) head velocity and 50% risk at 4.2 m/s (9.4 mph); however, more data are needed in the 2-4 m/s head velocity range to clarify injury risks. In addition, many factors influence the risk of the neck injury, including the age and physical condition of the person; orientation of the head, neck, and torso; and location of impact and interface.

Serious Injury in Very-Low and Very-High Speed Rear Impacts

This paper analyzed rear crashes for the risk of serious injury (AIS 3+) by delta V. Rear impacts were analyzed for occupants sitting in front seats of light vehicles. Data were obtained from the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) for calendar years 1991-2004. Tow-away crashes with \mL15 mph rear delta V account for 67% of rear impacts and 15% of serious injury. Even for crashes \ml30 mph delta V, the risk for serious injury is only 0.24% (less than 1 per 420 exposed occupants). Risks increase for higher delta Vs. Individual cases in the 1997-2004 NASS-CDS electronic database were reviewed for serious injury in crashes with \mL15 mph delta V and \mG35 mph for light vehicles with calendar year \mg1996 to better understand injury mechanisms. Nine cases were available where a front-seat occupant was seriously injured in \mL15 mph rear delta V impact. Most cases involved older occupants, some of whom had stenosis of the cervical spine. These occupants experienced spinal cord injury and paralysis with or without fracture of the cervical spine. Frailty of the cervical spine was a factor in the very low speed crash injuries. There were 28 occupants in 26 crashes with serious injury at delta V \mG35 mph. In 7 of the cases, the most serious injury was to the cervical spine. Intrusion of rear structures was common leading to the front-seat occupant being supported upright or being pushed forward causing serious injury. Intrusion forces were associated with the injury. In the most severe rear crashes, rearward rotation of the seatback was not a factor in the occupants injury as the early occurrence of intrusion limited seatback rotation. This paper has identified a class of seriously injured occupants in very low speed rear crashes. Advanced age and degeneration of the cervical spinal canal can lead to spinal cord injury and paralysis in crashes otherwise not causing serious injury in normal adults. Yielding seats diminish the risk of cervical injury in frail occupants. Use of stiffer seats would increase the risk of injury in occupants with spinal stenosis. The very high speed crashes involved substantial intrusion, which occurred early in the crash and supported the seatback from rotating rearward. The collision forces and intrusion were associated with injury to front-seat occupants.

Rollover Injury: Effects of Near- and Far-Seating Position, Belt Use, and Number of Quarter Rolls

Purpose. Vehicle and occupant responses in rollovers are complex since many factors influence both. This study analyzes the following factors: 1) belt use, 2) seated position with respect to the lead side in the rollover, 3) another front occupant in the crash, and 4) number of quarter rolls. The aim was to improve our understanding of rollover injury mechanisms. Method. Rollover accidents were analyzed using 1992–2004 NASS-CDS data. The sample included adult drivers and right-front passengers. All occupants were evaluated and then a subset of non-ejected occupants was analyzed. Using roll direction and seating position, the sample was divided into near- and far-seated occupants. Injury and fatality risks were determined by seatbelt use, occupancy, rollover direction, and number of quarter rolls. Risk was defined as the number of injured (e.g., MAIS 3+) divided by the number of exposed occupants (MAIS 0-6). Significance in differences was determined. A matched-pair analysis was used to determine the risk of serious injury for near- and far-seated occupants who were either belted or unbelted in the same crash. Results. For all occupants, serious injury risks were highest for far-seated, unbelted occupants at 18.1% ± 4.8%, followed by near-seated unbelted occupants at 12.0% ± 3.5%. However, the difference was not statistically significant. Belted near- and far-seated occupants had a similar injury risk of 4.3% ± 1.2% and 4.0% ± 1.2%, respectively. For non-ejected occupants, serious injury risk was 9.5% ± 3.2% for far-seated unbelted occupants and 4.9% ± 2.1% for near-seated unbelted occupants, not a statistically significant difference. Serious injury risk was similar for belted near- and far-seated non-ejected occupants, at 3.6% ± 1.1%. Seatbelts were 64.2%–77.9% effective in preventing serious injury for all occupants and 62.1%–26.5% for far- and near-seated, non-ejected occupants, respectively. Based on the matched pairs, seatbelts were less effective for near-seated (5.0%) compared to far-seated (2.8%) occupant MAIS 3+F risks. This was similar for non-ejected occupants. An unbelted near-seated occupant increased the risk for a belted far-seated occupant by 2.2 times, whereas an unbelted far-seated occupant increased the risk for a belted near-seated occupant by 10.2 times. For all occupants, the risk of serious injury increased with the number of quarter rolls, irrespective of seated position. For near-seated occupants, seatbelt effectiveness was higher in ≤1 roll than 1+ roll, at 72.3% compared to 28.3%. For far-seated occupants, seatbelt effectiveness was similar in ≤1 and 1+ roll samples at 78.3% and 76.8%, respectively. Near-seated occupants had the lowest serious injury risk when they were the sole occupant in the vehicle. This was also true for non-ejected occupants. However, far-seated occupants had a lower injury risk when another occupant was involved in the crash. Conclusions. The effect of carrying another occupant appears to reduce the risk of serious injury to far-seated occupants. However, near-seated occupants are better off being the sole occupant in the vehicle. Seatbelt effectiveness was lowest at 28.3% for non-ejected, near-seated occupants in 1+ rolls. This finding deserves further evaluation in an effort to improve seatbelt effectiveness in rollovers. For belted drivers alone in a rollover, fatality risks are 2.24 times higher for the far- versus near-seated position. Analysis of rollovers by quarter turns indicates that occupants are both far-side and near-side in rollovers. The extent to which this confounds the relationship between roll direction, seating position, and injury risk is unknown.

Case Study of Vehicle Maneuvers Leading to Rollovers: Need for a Vehicle Test Simulating Off-Road Excursions, Recovery and Handling

Rollover crashes are an important issue in automobile safety. Currently, the safety community is not only working on advancing injury countermeasures but is also investigating technologies to help avoid rollover crashes. This chapter on a vehicle test that simulates real-world conditions is from a comprehensive textbook on occupant and vehicle responses in rollovers. The authors note that the evaluation of rollovers typically involves vehicle-handling tests that are conducted on flat road surfaces with a uniform or split coefficient of friction. They stress that it is crucial to determine the precipitating events leading to rollovers by analyzing real-world rollover crashes. The authors determined the sequence of events leading to rollovers in 63 investigated cases. The cases were divided into 3 categories defining the precipitating event leading to a rollover: negotiating a curve at usually too high a speed (47%), drifting off the road (27%), and avoiding an obstacle in the traveling lane (25%). This study prioritizes the need to carry out tests that simulate a vehicle leaving the road and having at least two wheels on the shoulder after any of these three precipitating events (90 percent of the 63 cases involved the vehicle leaving the roadway with at least 2 wheels). The authors conclude that handling tests need to include a transition from a road surface to the shoulder where there may be a drop off of approximately 50 mm and an attempt to recover back onto the road with various degrees of steering and braking.

Severe injury to near- and far-seated occupants in side impacts by crash severity and belt use.

Purpose: This study investigated the risk of severe-to-fatal injury (MAIS 4+F) to near- and far-seated front occupants in side impacts by belt use and crash severity (delta V). Methods: 1993–2007 NASS-CDS was analyzed for front-seat occupants in side impacts while they were either the near-side or far-side occupant by belt use. Light vehicles were included with model year 1994+. Injury severity was subdivided into MAIS 0–2, 3, and 4+F. The risk for MAIS 4+F injury was determined by dividing the number of MAIS 4+F by the number of exposed occupants with known injuries. Individual NASS-CDS cases were downloaded from the 1997–2007 electronic data to evaluate injury patterns causing high relative risks. Results: In 35+ mph side-impact delta Vs, the risk for MAIS 4+F injury was 75.4 ± 41.0% for unbelted near-side and 48.1 ± 14.6% for unbelted far-side occupants. The risk was 51.8 ± 14.8% for belted near-side and 30.9 ± 8.2% for far-side occupants. Seat belt use was 81.4% effective in preventing MAIS 4+F injury for near-side occupants and 93.5% for far-side occupants. The relative risk (RR) for unbelted compared to belted occupants was 35.9 for far-side occupants in 10–15 mph delta V crashes. The relative risk was 35.1 for near-side occupants in < 10 mph delta V side impacts. The high relative risks were associated with complex, high-speed multi-collision crashes often with occupant impacts on the windshield, steering wheel, or other frontal components and ejection. Conclusions: Seat belt use was more effective in preventing severe injury (MAIS 4+F) to far-side occupants than near-side occupants in < 25 mph delta V impacts. High relative risk for unbelted occupants in low-speed side impacts was explained by the fact that the accidents were high-speed, multi-impact collisions. Severe injury was caused by ejection, impact with the side interior, or impact with the frontal components where airbags sometimes deployed.

Driver Injuries in US Single-Event Rollovers

This paper will investigate occupant injuries which may be sustained during a single-event crash with known roll mechanism. The data was obtained from the weighted National Automotive Sampling System/Crashworthiness Data System (NASS-CDS) for calendar years 1992 to 1996. The effect of number of rollover turns, roll direction, ejection and belt usage on driver injury responses was analyzed in single-event trip-overs. Trip-overs were chosen for the analysis because they account for over 50% of rollover crashes. The number of rollovers was divided in 3 categories: 1/4 to 1/2 turn, 3/4 to 1 turn and above 1 turn. Roll direction was either roll-left or a roll- right along the longitudinal axis of the vehicle. Roll-left represents a roll with the driver side leading, while a roll right is with the right front passenger side leading. In the database used in this study, there were three times more belted drivers than unbelted. Ejection was more frequent when the driver was unbelted than belted. Of the 50,504 unbelted drivers, 27% were completely/partially ejected, while, of the 150,426 belted drivers, less than 1% were ejected. The rate to be seriously injured was higher when the driver was completely or partially ejected. Drivers in a roll-left trip-over were most commonly ejected through the left front area (for example, left door) of the vehicle, while drivers in a roll-right were ejected from the left front area and the roof. Of the non-ejected drivers, the rate to be seriously injured seemed higher for unbelted drivers than belted, at 2.2% and 1.1% respectively. For belted drivers in a roll-left, injuries were most frequent in the head, lower extremity (LX), thorax and upper extremities (UX), while, in a roll-right, injuries were most often to the spine, head, and thorax. Spinal injuries resulted when the vehicles rolled right, independent of the number of rolls. Unbelted drivers who rolled left, sustained serious injuries to the head, LX, thorax and UX, while those who rolled-right had serious injuries to the spine, head and thorax. Field data can be useful in the development of safety-countermeasures for rollovers as it provides insights on the significance of various parameters. The results of this study suggest the need to first prevent ejection by keeping the occupant in the vehicle. This could be accomplished by changing driver behavior through increased seat belt use and through technology by helping to obstruct ejection paths. Occupant/vehicle contacts should also be reduced to minimize the potential for injuries. In addition, a better understanding of the head, thorax, spine and lower extremity injury mechanisms is essential for the development of future safety-countermeasures.

Ejection and severe injury risks by crash type and belt use with a focus on rear impacts

Purpose: This study investigated the risk of severe-to-fatal injury (MAIS 4+F) with complete and partial ejection by crash type and belt use with a focus on ejection in rear impacts. Methods: 1993–2007 NASS-CDS was analyzed for crashes with complete and partial ejection. The effect of belt use was investigated and crashes were grouped by front, side, rear, and rollovers. Light vehicles were included with model year 1994+. Injuries of severity MAIS 4+F and AIS 3–6 by body region were determined by crash type, belt use, and ejection status. NASS-CDS electronic cases of complete ejection and serious injury were evaluated to determine the circumstances in rear impacts. Results: For unbelted occupants, the highest risk for complete ejection is in rollovers (16.4 ± 1.1%) and the risk for severe injury is 37.6 ± 2.7%. The lowest risk for complete ejection is in frontal crashes (0.97 ± 0.22%), but the risk for serious injury is 31.3 ± 6.2% when ejection occurs. The risk for ejection is 2.7 ± 1.5% in rear impacts with a 7.4 ± 3.4% risk for severe injury. For belted occupants, the highest risk for complete ejection is in rollovers (0.068 ± 0.022%) and the risk for severe injury is 25.9 ± 13.3% when ejection occurs. The relative risk for ejection is 193 times greater for unbelted compared to belted occupants in all crashes with a range of 100 times in frontal crashes up to 847 times in rear impacts. Unbelted occupants have 20 times greater risk for severe injury when completely ejected and 18 times greater risk with partial ejection compared to nonejected occupants. Belted occupants have a 77 times greater risk of severe injury when completely ejected and 37 times greater risk when partially ejected. Conclusions: Ejection involves significantly higher risks for severe injury in all crash types. The relative risk for MAIS 4+F injury is 20 times greater for unbelted and 77 times greater for belted occupants who are completely ejected compared to nonejected occupants. Ejection of occupants in rear crashes often occurs during vehicle yaw motion after the primary impact.