Which of the following organs is least likely to be damaged in an automobile accident?

Annu Proc Assoc Adv Automot Med. 2000; 44: 17–36.

Abstract

Public awareness for safety and vehicle improvements has contributed to significant reduction in injuries secondary to motor vehicle crashes. The spectrum of trauma has shifted from one region of the body to another with varying consequences. For example, airbags have minimized head and neck injuries for adults while emphasizing the lower regions of the human body. Studies have concentrated on the changing patterns of these injuries in frontal impacts. However, there is almost a paucity of data with regard to the characterization of abdominal injuries. Consequently, this study was conducted to determine the patterns of abdominal injuries in frontal and side impacts with an emphasis on more recent crashes. In particular, the frequency and severity of trauma were investigated with a focus on the various abdominal organs (e.g., spleen and liver). Results indicate that side crashes contribute to a large percentage of injuries to the abdomen. The liver and spleen organs are most vulnerable; therefore, it may be beneficial to apply concerted efforts to focus on injury biomechanics research and prioritization activities in these areas of the abdomen. These data may be of benefit to develop anthropomorphic dummies with improved biofidelity.

EPIDEMIOLOGICAL DATA FROM VEHICULAR crashes have been gathered since 1977 in a systematic manner to provide insights into numerous collision-related variables (Ricci 1980). For example, the effects of the weight of the vehicle(s) in a particular crash mode have been investigated on the resulting injuries to the occupants. Similarly, the effects of restraint systems in frontal crashes have been determined to evaluate the efficacy of airbags in reducing the potential for serious to fatal injuries (DOT 1996). With changes in vehicle designs and public awareness for safety and use of restraint systems, injuries appear to have shifted from the head-torso structures to the more distal locations of the human body in frontal impacts (Burgess et al., 1995). International studies and CIREN centers have begun to analyze data gathered from recent epidemiological studies (Hill et al., 1992; Augenstein et al., 1995; Augenstein et al., 1999; Hassan et al., 1999). Despite these efforts, abdominal injury analysis appears to have received little attention. In fact, the widely used and US regulated anthropomorphic Hybrid III dummy has no proven biofidelity in the abdominal region (Schneider 1989; Backaitis and Mertz 1994). Anatomically, the abdomen consists of components with widely varying biomechanical responses and injury mechanisms; in order to design and develop a biofidelic abdomen, the first task would be to identify and prioritize the specific abdominal components susceptible to trauma secondary to impact. To achieve this objective, it is important to obtain and analyze data applicable to the current motor vehicle environment. Consequently, the present study was designed to analyze the most recent epidemiological data from a US database to determine the frequency and severity of injury in frontal and side impacts. Results are presented as a function of frontal, left side, right side, near side and far side impacts. Abdominal injury severities are grouped into Abbreviated Injury Scale AIS ≥ 2 and ≥ 3 categories (AIS 1990). Delta-v distributions are presented under each impact in each AIS group.

METHODS

DATABASE

The National Crash Severity Study (NCSS) was a major vehicular crash data collection program of the National Center for Statistics and Analysis (NCSA) of the National Highway Traffic Safety Administration at the Department of Transportation in the United States (Ricci 1980). Data collection, which began in January 1977, was terminated in March 1979. The National Automotive Sampling System (NASS), formerly called the National Accident Sampling System, followed the National Crash Severity Study and has been collecting data since 1979.

The NASS was created to produce a national traffic collision database for the evaluation of old and the development of new highway vehicle safety standards, and to identify highway safety needs. The system consists of 24 teams of vehicular crash researchers throughout the United States. At each primary sampling unit (PSU) site, the research team investigates a probability sample of police-reported crashes involving passenger cars, light trucks and vans which are towed, according to the police report, from the scene secondary to damage. This system is termed the Crashworthiness Data System (CDS).

Zone centers have been established to ensure quality control of CDS data and technical management of the teams within their zone. Quality control is carried out through zone center site visits to the PSUs and through the review of case report materials received at the zone centers. The zone centers provide quality control in the areas of sampling, completeness, reliability, and validity of data. They also provide annual team evaluations, training, and act as a communication link between PSU teams and NCSA staff.

The database meets the following criteria. The vehicular collision is reported on state or local crash forms signed by the police officer and available through the police agency files. The incident is reported to the state crash statistics. It involves a harmful event that is defined as property damage and/or personal injury due to collision of a motor vehicle in transport on a traffic way. Crashes in parking lots and driveways are excluded.

A consistent set of data elements was incorporated into the database from 1979 to 1984. Information regarding occupant compartment details was added in 1985. The General Estimates System was introduced in 1988 as part of a major restructuring of the NASS program. In 1993, the database was refined to include additional variables such as contacts with vehicular components.

NATIONAL ESTIMATES

The NASS/CDS is a probability sample of all police reported crashes in the United States involving at least one passenger vehicle (passenger cars, pickup trucks, vans, and sport utility vehicles) towed from the crash scene due to damage from the crash (NASS 1993–1999). The selection of crashes is accomplished in three stages. The first stage is the selection of the Primary Sampling Units (PSUs). The country is divided into 1,195 PSUs grouped into 12 categories described by geographic region and degree of urbanization. Two PSUs were selected from each strata with probability proportional to the number of fatal and injury crashes listed in each PSU. The second stage is the selection of the police jurisdictions based on the number of fatal and injury crashes listed in each. The more fatal and injury crashes listed, the higher the probability of its selection. Those jurisdictions that are selected are called sample jurisdictions.

The third stage is the selection of the crashes from all crashes in all of the sample jurisdictions. The procedure used to obtain the desired sample by type and severity of crashes is an unequal probability selection. This requires listing police crash reports in categories defined by the most severe police-reported injury to an occupant of a towed passenger vehicle, disposition of the injured (transported to a medical facility, hospitalized), and model year of the passenger vehicle. A weighting factor was assigned to crashes in each category to increase or decrease the probability of selection. A random selection was made from the total crashes listed in all categories. Other factors affecting the selection probabilities of selection include the number of crashes listed, the date and time of the crash, and the police agencies from which the crash was listed. The result is that each sampled crash from a PSU has a unique selection probability.

If each sampled crash in a PSU is multiplied by its second- and third-stage expansion factors, an unbiased estimate of the total number of crashes in the PSU is obtained. To produce the national estimates, the PSU level estimates are inflated by the first-stage expansion factor. Thus, the national expansion factor is the product of the first-, second-, and third-stage expansion factors.

The national estimates equal the inverse of the probability of the PSUs being selected, the probability of the police jurisdictions being selected, and the probability of the crash being selected for that day. Since the number of crashes in the sample is predetermined, the national estimate for each crash within a stratum is different. To account for this bias, a ratio weight was developed. The ratio weight is the national estimate multiplied by a ratio factor. For each stratum, the ratio factor is equal to the total number of crashes listed in all of the police jurisdictions (sampled and non-sampled) divided by the number of crashes selected.

SELECTION CRITERIA

The database groups information into six different areas; collision/crash, vehicle exterior, vehicle interior, general vehicle, occupant assessment and occupant injury files. In order to conduct an epidemiological analysis using the database, it is important to relate certain key variables that include the PSU, case number, vehicle number, and occupant number on an annual basis. In the present study, for the years 1993 to 1998, key variables were merged. Data were limited to passenger cars and light trucks. The selection criteria excluded occupants less than 16 years of age. However, drivers and front seat passengers were included. Rear seat occupants were excluded from the database. In addition, rollovers and ejected occupants were excluded.

ANALYSIS

Frontal (11 to 1 o’clock), near side (driver for left side and passenger for right side), far side (driver for right side and passenger for left side), left side (8 to 10 o’clock), and right side (2 to 4 o’clock) impacts were analyzed in the study. The weighted frequency of abdominal injuries was obtained as a function of AIS rating and contact with vehicular interior systems. In addition, the delta-v distribution for these impacts was extracted. Since unknown variables were ignored, the total number of injuries and associated contact points do not represent the actual total weighted frequencies. Therefore, relative percentages instead of the absolute numbers are presented in the Results Section (below) and the data set forms the focus of this paper. Injury classification was determined based on AIS rating for various systems/organs of the human abdomen. Appendix A provides some additional details on the topic of abdominal anatomy.

STUDY MATRIX

• ♦ Time frame: NASS/CDS years 1993 to 1998

• ♦ AIS rating: 2 – 6

• ♦ Impact: left and right side, near and far side, and frontal

• ♦ Occupants: drivers and passengers

• ♦ Restraint system: lap and shoulder belt with and without airbag, lap belt only, shoulder belt only, and none

• ♦ Change in velocity: zero to 90 kph (kilometers per hour)

• ♦ Component/region of abdomen: liver, spleen, kidney, pancreas, arteries, urogenital, digestive and diaphragm

RESULTS

In the NASS/CDS years 1993 to 1998, out of 7.4 million occupants exposed to vehicular crashes, 5.8 million were drivers and 1.6 million were right front seat passengers. Abdominal injuries were not uniformly distributed on an annual basis. In this period, 129,269 abdominal injuries were found for the frontal, left side and right side impacts (Figure 1). Approximately one-half of these injuries occurred in frontal crashes. Left side and right side collisions contributed to approximately one-third and one-fifth of abdominal injuries. In this combined data set, spleen, liver, kidney and digestive system trauma was most frequent (Figure 2). A significant majority of trauma (two-thirds to four-fifths) occurred in the AIS=2 category. Injuries at the AIS=6 level occurred only in frontal and right side impacts (Figure 3).

Distribution of abdominal injuries as a function of impact direction for the years 1993 to 1998.

Distribution of the four most frequent abdominal injuries in the combined data set for the years 1993 to 1998.

Distribution of abdominal injuries as a function of AIS rating for the years 1993 to 1998.

In the AIS ≥ 2 category, for the combined data set, the liver, spleen, digestive and kidney sustained the four most frequent number of injuries in frontal impact. In contrast, the spleen, kidney, liver and digestive or diaphragm trauma was most prevalent in left and near side crashes. Kidney and liver injuries followed by digestive/spleen trauma were most common in right and far side collisions. These data are summarized in table 1. In the AIS ≥ 3 category, the liver was the most frequently injured organ in frontal, right side and far side crashes; this was followed by spleen trauma. In contrast, the spleen sustained the maximum number of injuries in left and near side impacts. Digestive and diaphragm trauma was the second most common abdominal injury in these collisions, respectively (Table 1).

Table 1

Frequency of injuries (%) as a function of abdominal organ/system for the years 1993 to 1998. Data are grouped into AIS ≥ 2 and AIS ≥ 3 under each impact direction.

When abdominal injuries were attributed to vehicular interior contact (restraints not included), in the AIS ≥ 2 category, the spleen, liver, kidney, digestive, arteries and urogenital systems sustained the most frequent injuries. In contrast, the spleen, liver, kidney, diaphragm, arteries and urogenital systems were commonly involved under the AIS ≥ 3 category. The spleen sustained the maximum number of injuries in frontal, left side, and near side crashes under the AIS ≥ 2 category. However, the kidney and liver sustained injuries most frequently in far side and right side collisions, respectively. The spleen was most frequently injured in all impacts under the AIS ≥ 3 category except far side crashes wherein the liver accounted for the highest share. The pancreas organ sustained little or no injuries in all AIS categories. Table 2 provides a summary of these data. In general, abdominal injuries were most common to the lap and shoulder-belted driver in frontal, left side and near side collisions; in contrast, the unrestrained passenger was identified in right side and far side crashes. Table 3 provides a detailed summary of abdominal injuries as a function of the restraint system for driver and passenger occupants in all modes.

Table 2

Frequency of abdominal injuries (%) associated with vehicular interior contact for the years 1993 to 1998. Data are grouped into AIS ≥ 2 and AIS ≥ 3 under each impact direction.

Table 3

Frequency of abdominal injuries (%) secondary to vehicular interior contact for the years 1993 to 1998. Data are grouped into AIS ≥ 2 and AIS ≥ 3 under each impact direction.

The plots of cumulative frequency versus change in velocity distribution for frontal, near side, far side, left side and right side impacts are shown in figures 4–8, respectively. In the AIS ≥ 2 category, the 50th percentile level for abdominal injury occurred at the lowest change in velocity (23 kph) for left side crashes. This was followed by near side (27 kph), far side (30 kph), right side (32 kph) and frontal (41 kph) collisions. The change in velocities was higher under each impact mode when the AIS = 2 category was excluded from the data set (Figures 4–8).

Injury frequency (%) distribution as a function of delta-V (kph) in frontal impact.

Injury frequency (%) distribution as a function of delta-V (kph) in right side impact.

DISCUSSION

The objective of the study was to determine the frequency of abdominal injury to organs/tissues. Therefore, injuries were given predominant importance. Although numerous variables were analyzed, in the interest of brevity and to comply with the page limitations in this presentation, injuries associated with occupant type (driver versus passenger), impact modality (e.g., frontal versus side), and occupant restraint (lap and shoulder belt only versus airbag only) were grouped. In other words, if an occupant sustained abdominal injuries to the liver and kidney, both organs were included in the data analysis. In effect, the present analysis does not provide human occupant-based abdominal injury epidemiology. This type of approach is followed because it is appropriate to determine the frequency of injuries to the tissues in order to focus on the prioritization of abdominal injury (mitigation) research. As indicated in the Introduction, once the frequency of injury is associated with the type of abdominal organ/tissue, it will then be possible to concentrate on issues such as improving the biofidelity of an anthropomorphic test device and specification of metric(s) for injury quantification.

This study was not intended to compare the efficacy of various restraint systems under different crash modes (e.g., frontal versus left side). This can be done when one takes into consideration variables such as the rates of exposure. This exercise is considered as a future extension. Furthermore, only data from 1993 to 1998 were selected because of the significant under-use of restraint systems in early years in the NASS database. Any comparison with previous years, in addition, would have included insignificant availability of airbag restraints to both occupants. From this point of view, although not exhaustive, the present study is a more appropriate epidemiological analysis of data applicable to the current population. It should be noted that although the NASS database provides information about specific abdominal injuries, it was not originally designed as a full clinical analysis. Another limitation is the applicability and interpretation of data when the sample size becomes small which can happen with data parsed. In these instances, caution should be exercised to fully generalize all conclusions. As indicated later, it may be appropriate to include statistical procedures to determine the significance of these data. This is considered as a future extension of this study.

The present analysis has certain similarities and differences with previous data. Using NCSS data for frontal impacts, Bondy identified the liver (39.5%), spleen (25%), digestive (16.4%) and kidney (14.1%) to be the four most frequently injured organs (Bondy 1980). Using the NASS database for the years 1988 to 1994, the following order for abdominal injury was reported: liver (37.8%), spleen (22.6%), digestive (16.81%), arteries (11.6%), kidney (3.6%) and urogenital (3.2%) systems (Elhagediab and Rouhana 1998). The present analysis for the years 1993 to 1998 indicated the order of injuries to be liver (34.8%), spleen (28.3%), arteries (14.2%) and digestive (8.7%) systems. While the liver and spleen organs sustained injuries most frequently in all these studies, the two earlier reports found the digestive system to be next in the order of importance. In contrast, the present study identified arteries to be the third most commonly involved. Similarly, while kidney injuries were the fourth-most common in the Bondy study, the frequency of renal trauma appears to have diminished in the two recent NASS studies. These differences may be attributed to the availability and use of restraint systems in later model vehicles; confirmation of this issue requires further investigation. All the above analyses considered the frequency of all AIS ≥ 3 abdominal injuries.

With regard to right side impact, the present NASS data indicates the liver, spleen and kidney to be most frequently injured. Under this impact condition, the asymmetrical location of the liver, together with the partial protection by the rib cage, renders the solid organ most vulnerable to injury. Direct compressive forces have been attributed to be a major mechanism of serious (AIS ≥ 3) injury to the liver in clinical and biomechanical studies (Pringle 1908; Baxter and Williams 1961; Glenn et al., 1966; Longmire et al., 1966; Mays 1966; Melvin et al., 1973; Defore et al., 1976; Aldrete et al., 1979). Oblique pendulum impacts to intact human cadavers at the infra-thoracic cage level have produced serious hepatic trauma with forces ranging from 1.9 to 2.1 kN at displacements of 60 to 85 mm (Yoganandan et al., 1996). Splenic trauma under this modality may be attributed to the deceleration-induced mechanism.

Rouhana and Foster identified the kidney, spleen and liver as the most frequently injured organs in left side impact (Rouhana and Foster 1985). In contrast, the present study determined the spleen, diaphragm and liver to be the order of injury occurrence. Direct impact to the left upper abdomen is a common mechanism of injury to the spleen. Kidneys, on the other hand, have more anatomical protection in the human body and may have a higher tolerance threshold in terms of direct impact (Schneider et al., 1992). In fact, as can be appreciated from table 1, kidney injuries are significantly higher in the AIS ≥ 2 category compared to the AIS ≥ 3 category under all impact modes, indicating that most renal trauma is relatively less severe in vehicular crashes. In direct contrast, injuries to the diaphragm tend to be more serious under all impact modes (Table 1). These injuries are particularly preponderant in left side and near side impacts. Contact-induced deformations lead to membrane shearing and/or avulsion of the diaphragm (Magee 1935; Desforges et al., 1957; Sutton et al., 1967; Ward et al., 1981; Voeller et al., 1990; Roberts and Compton 1993). From an experimental standpoint, these injuries are difficult to reproduce in a laboratory.

In both AIS categories, when injuries were attributed to vehicular interior contact, the spleen was more frequently injured than the liver in left side, frontal and near side impacts. This finding suggests that abdominal injury is dependent on the type of organ/tissue and impact direction. In order to establish the actual levels of significance, statistical analyses needs to be done on the entire ensemble. The appearance of diaphragmatic injuries in the higher AIS grouping may have been secondary to distributed loading to the membranous tissue. With regard to the restraint system effects on injury secondary to interior contacts, in general, lap and shoulder belted occupants sustained the maximum number of injuries in all impact modes. As expected, the driver was involved in left side, frontal and near side impacts. Although restraint usage has enhanced in recent years, unrestrained occupants still accounted for a considerable share of abdominal trauma in the ensemble. An analysis of the effectiveness of restraint systems is possible in future years as the sample size and exposure rate advances. It will also be possible to determine the relative effects of airbag deployment on abdominal injuries.

The frequency distribution with respect to delta-v indicated changes with impact mode (Figures 4–8). Although not as detailed, similar velocity changes were reported using 1980 to 1987 NASS files (Roberts and Compton 1993). It should be noted that the 1987 NASS data do not have the weighting factors needed to make national estimates. As expected, the cumulative distribution of injuries as a function of delta-v indicated a higher change in velocity at the 50 percent injury level for frontal than lateral impacts (Figures 4–8). This was true for both AIS groupings. The lower change in velocity (Table 4) for all types of lateral impacts indicates the severity and importance of focusing injury research activities (e.g., dummy evaluations and injury criteria) in this impact mode. In particular, left and near side impacts which were more sensitive to speed with respect to injury underscore their role in the prioritization process.

Table 4

Delta-v at 50% Frequency Level

A comparison of the injuries by different body regions as a function of AIS indicates the prevalence of abdominal injuries to increase with increasing AIS. In fact, abdominal injuries constituted approximately four percent of all AIS ≥ 3 injuries while at the more serious levels of injury (4 and 5) the contribution was considerably higher. Table 5 includes the comparison of injuries with the combined data set (frontal and side). This finding underscores the importance of abdominal trauma in vehicular crashes.

Table 5

Injuries for the combined data set as a function of AIS and body region

Based on the present analysis of abdominal injuries, it can be concluded that side impacts account for more abdominal injuries than frontal impacts and occur at fairly lower changes in velocity. It can also be concluded that the spleen and liver organs need to be considered to prioritize injury research. The current FMVSS 214, the side impact standard, has no specific abdominal injury criteria. However, the thoracic trauma index was originally developed included injuries to organs within the hard thorax (Eppinger, 1984). In addition, since the federally regulated Hybrid III dummy has no proven biofidelity in the abdomen region, the findings reported herein (applicable to the current environment) may assist in the following activities. Prioritize abdominal injury research for its assessment, quantification, derivation of corridors, appropriate instrumentation areas for the abdomen, evaluation of current and future dummies, and mitigation.

(Presenter: Narayan Yoganandan)

Don Huelke: Number one, I looked at one of your early slides and you had a lot of AIS 6 injuries. There is no AIS 6 abdominal injury, only if you are transected. AIS 6 is an indicator of death and I think a lot of the AIS 6 injuries have to be at the AIS 3, 4 or 5 level rather than at AIS 6. Number two, were these people who were restrained or unrestrained airbagged as well?

N. Yoganandan: In the NASS database the weighted frequency of all the data included people with and without airbags for both drivers and passengers. However, the number of people who had airbags were less because we started the data from 1993 onwards, so as the years progressed, the number of airbag exposures or the number of injuries due to airbags increased, but still not to a significant level. And that’s one of the reasons, when it was split into driver and passenger in the different modes, all the airbag cases were grouped into “other” categories because they were all still small.

Joe Marsh: Fascinating insights. Methodologically there are some issues. One concern in using the NASS data is that the weight factors are a weight of accidents, not of vehicles, not of occupants and certainly not a weight of injuries. So a lot of people question the use of weight factors especially when you get down to the injury levels that you’re looking at. This becomes particularly acute when you get to the AIS 4, 5 and 6 because there are very few of them anyway. Often we find it’s easier just to combine AIS 4, 5 and 6 so you don’t get that sort of clutter but there’s no easy answer to that. Putting up an N as if you’ve got hundreds of thousands of cases when maybe there’s only a couple of AIS 4, 5 and 6 bears some thinking about using the weight factors, although I don’t have any good answers.

The other observation I have is that you are showing these mixes of injuries always adding to 100%, and your comment about how some injuries as shown in your bar charts are coming down and some are going up. They’re not normalized so if one bar chart goes down, say kidneys go down, then spleens go up just because they all have to add to 100%. It’s not that the spleen injuries actually went up. My concern is that the words you used all through the slides about those bars describe them as if they were risk or as if they were normalized. If you want to see if spleens are going up or down or kidneys are going up or down across these different AIS levels, then you really ought to normalize them and divide by the number of people involved rather than doing percentages. What you were trying to do – talk about the risk of these injuries -- wasn’t reflected in these slides because they were all done on per cent to a hundred.

You also mentioned that the kidneys went down at higher AIS levels in the bar chart and that may be a definition of how the AIS dictionary is set up in the first place. That may have nothing to do with the field experience. You may be giving us an AIS coding lecture on how kidney injuries should be properly coded but that is not reflecting what is actually happening in the field. There’s a mix there of what are the definitions in the AIS levels for these different injuries versus what’s happening in the field. I’m not sure whether that comes out. But you’re more familiar with those codings than I am and there may be a way to tally it up on another round.

N. Yoganandan: I can speak to two issues. I fully agree with you that this is not the end of the research. I do not think I used the word “normalized” in any of my slides except once when I said that if you were to normalize for the passenger portions then you’ll probably see a higher percentage. With regard to the spleen injuries going up because the kidney injuries went down, I was just looking at one angle. Obviously, there are other angles. In other words, the issues we are looking at is how many injuries are caused by one particular variable or due to one particular variable and that’s what we are pursuing. And you will have a little more confidence in what I showed you now because you have a larger sample size. Once you start analyzing the data as you look at AIS 4 and 5 injuries, then your confidence becomes lower and lower because you have less data. Now we are married to the NASS database because we don’t have any other database in the world. We can criticize the NASS database for not being what we want it to be, but we don’t have anything else. Until we develop another one that meets all our demands, I think it is worth looking at this one and see if we can draw any sensible and logical conclusions and see whether there is any reason to look into the abdominal injury criteria for the motor vehicle environment. I agree with your comments that this is not the best database in the world, but it’s what we’ve got.

J. Marsh: I wasn’t intending to criticize the NASS database. I wanted to commend you for digging into the NASS data at this level and trying to look at specific injuries. In fact, this is not done enough. I used the word “normalize” because you had used it toward the end of your presentation to acknowledge the fact that really there is a difference between doing percentages to a hundred and normalizing. My comment about normalization might have helped in the earlier charts to help tell the story in the direction you’re taking.

N. Yoganandan: I agree it has to be normalized.

Urs Maag: You presented all the tables with AIS > 2 and the next one to AIS > 3. Now AIS > 3 is a subset of > 2. Why did you not present separately AIS = 2 compared with more serious ones, AIS > 3? I find it somewhat difficult when you compare things where the second set is a subset of the first one.

N. Yoganandan: As I said, there are several ways of looking at it. You can look at AIS 2 separately, AIS 3 separately, AIS 4 or AIS 5 and that was done in the first few slides where you had stacked bar charts of looking at AIS 2, 3, 4, 5 but when I started putting the data together for this talk, I thought in the 20 minutes of time for this presentation instead of doing just AIS 2 or AIS 3, I thought I would put all the AIS > 3 together so that we would look at all the more serious injuries. When relatively minor injuries are included in the sample, it would be interesting to see whether the type of organs that are injured will change. And it so happened to our surprise spleen and liver turned out to be the players in the ballgame. So that was one of the reasons it was done. Yes, we do have the data and we can analyze it in any different way we want.

​

Injury frequency (%) distribution as a function of delta-V (kph) in near side impact.

Injury frequency (%) distribution as a function of delta-V (kph) in far side impact.

Injury frequency (%) distribution as a function of delta-V (kph) in left side impact.

Acknowledgment

This study was supported in part by DOT NHTSA DTNH22-93-Y-17028 and VA Medical Research.

Appendix A

Abdominal Anatomy: The abdomen lies between the thorax and pelvis and is enclosed by muscles. The upper border is defined by the boundaries of the zyphoid process, cartilage of ribs 7–10, and ends of ribs 11 and 12. The solid organs include the liver, spleen, kidneys and pancreas. The hollow organs include the stomach, intestines, urinary bladder and uterus. The liver lies in the upper part of the abdominal cavity and occupies most of the right hypochondrium and epigastrium. It extends into the left of the hypochondrium. The antero-lateral portion of the right lobe is covered by six through tenth ribs and their cartilaginous connections to the sternum. The liver lies more inferiorly under erect body position due to gravity. The spleen is located in the left hypochondrium with cranial extension into the epigastric region. It lies between the diaphragm and fundus of the stomach along the left posterior wall of the upper abdomen at the level of the seventh and ninth ribs. The pancreas is a retroperitoneal organ that extends nearly transversely across the posterior abdominal wall from the duodenum to the spleen behind the stomach. This organ ascends slightly to the left in the epigastric and left hypochondriac regions. The head of the pancreas is in the curve of the duodenum. The anterior surface of the neck is covered with peritoneum and is adjacent to the pylorus of the stomach. The body of the pancreas extends left across the aorta and L2. The kidneys lie on each side of the spinal column spanning from lower thoracic to mid lumbar levels. The right kidney lies at a slightly lower level than the left because of the liver. Superiorly, each kidney is related to the diaphragm that separates from the pleural cavity and the 12th rib. The stomach is situated within the esophagus and small intestine. It lies in the epigastric, umbilical, and left hypochondriac areas. It is bounded by the diaphragm and anterior abdominal wall between the liver and spleen. Its general shape approximates the letter ‘J.’ The small intestine is a coiled tube that extends from the stomach to the ileocecal valve leading into the large intestine. The small intestine occupies the central and lower parts of the abdominal cavity. It is related in front to the greater omentum and abdominal wall. The three principal parts of the small intestine are the duodenum, jejunum and ileum. The large intestine extends from the distal end of the ileum of the small intestine to the anus. The large intestine consists of the cecum, vermiform appendix, colon, rectum, and anal canal. The reader is referred to standard textbooks on anatomy for further details on the abdomen. Recently, Yoganandan et al (2000 In Press) has conducted an exhaustive review on the biomechanics of abdominal injuries which includes clinical, epidemiological and laboratory-driven investigations. In addition, the NASS injury-coding manual also provides illustrative information on abdominal organs.

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