Á priori alignment of transtibial prostheses: a comparison and evaluation of three methods.

PURPOSE: The objectives of this study were to compare three á priori alignment methods and evaluate them based on initial gait quality and further alignment changes required to optimize gait. Á priori alignment is requisite for monolimbs, transtibial prostheses in which the socket and pylon are made from one piece of plastic, because monolimbs have no alignment adjustability. METHOD: The three methods investigated were traditional bench alignment (TRAD), vertical alignment axis (VAA) and anatomical based alignment (ABA). Endoskeletal components were utilized for the study, rather than monolimbs, so that alignment could be experimentally manipulated. Three endoskeletal prostheses were aligned, one according to each á priori method, for each of seven subjects. Gait and alignment data were captured, dynamic alignment was performed to optimize gait, and data were captured again. RESULTS: VAA and TRAD methods required less change compared to ABA in socket flexion angle. Looking at subjects individually, VAA produced a better alignment and better gait for the greatest number of subjects. CONCLUSIONS: A new refined method of á priori alignment is proposed based on the results of this study, and is applicable for á priori alignment of monolimbs or any type of transtibial prosthesis.

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 (Delta 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/m2 < or = BMI < 25.0 kg/m2) and obese (BMI > o= 30 kg/m2) 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 < or = 55 years), older (age >55 years), 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 + Delta m / m)(0.5). For a given stature, an obese occupant (BMI = 30-35 kg/m2) has 54-61% higher risk of injury than a normal BMI occupant (22 kg/m2). 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/m2 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.

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 < or =1 roll than 1+ roll, at 72.3% compared to 28.3%. For far-seated occupants, seatbelt effectiveness was similar in < or =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.