Risk factors and patterns of injury in snowmobile crashes

Wilderness and Environmental Medicine, 10,226-232 (1999)

ORIGINAL RESEARCH

Risk factors and patterns of injury in snowmobile crashes GREGORY J. BEILMAN, MD, KAREN J. BRASEL, MD, KARL DITTRICH, MD, SUSAN SEATIER, MD, DONALD M. JACOBS, MD, J. KEVIN CROSTON, MD From North Memorial Health Care. Robbinsdale. MN (Drs Beilman. Seatter. and Croston); Regions Medical Center (formerly St PaulRamsey Medical Center), St Paul, MN (Dr Brasel); Hennepin County Medical Center. Minneapolis. MN (Dr Dittrich and Dr Jacobs); and the University of Minnesota. Minneapolis, MN (Drs Beilman, Brasel. and Seatter).

Objective.-To evaluate risk factors for snowmobile injury and patterns of injury. Methods.-We performed a retrospective analysis of patients with snowmobile injury at three trauma centers. Data were collected from trauma databases and patient charts from January 1988 through April 1996; we obtained statistics from the Minnesota Department of Natural Resources for comparison purposes. Results.-There were 274 patients identified. The average age was 29 years (SD 12, range 1.677). The male:female ratio was 6.6: 1. Helmets were used in 35%, not used in 10%, and not reported in 55%. Ethanol consumption was reported in 44% of patients. The average speed of the snowmobile at the time of the accident, when reported, was 47 mph/75 kph (n = 103, range 10-100 mph/I6-166 kph). Of these patients, 26% (n = 27) reported a speed in excess of the legal limit (55 mph/88 kph). Accidents were more common in the afternoon and evening hours, and most accidents were caused by the snowmobile striking terrain or man-made objects. Mortality rate was 3.6% for this patient group (10 of 274). The average injury severity score (ISS) was 15 (SD 11). The average Glasgow Coma Score (GCS) was 14. The 'average number of patients who went to the intensive care unit and the total lengths of stay were 2 ± 5 and 8 ± 9 days, respectively. Neither GCS nor ISS correlated with reported speed. The frequencies of different types of injuries are as follows: fractures of upper and lower extremities (n = 184), serious head injury (n = 92), facial fractures or soft tissue injury to head or neck (n = 88), thoracic injury (n = 80), spine injuries (n = 50), intraabdominal injuries (n = 41), and pelvic fractures (n = 31). Conclusions.-Snowmobile injuries are related to ethanol use and the high speed attained by the newer generation of snowmobiles. Extremity fractures were a common component of snowmobile injury in this series, and rates of such injuries are similar to rates of these injuries in motorcycle accidents in states with helmet laws. Efforts at prevention of snowmobile injuries should be targeted at rider education and enforcement of alcohol restrictions. Key words: snowmobile, blunt trauma, recreational injury, head injury, pelvic fractures, extremity

injury

Introduction Snowmobiling is an increasingly popular winter recreational activity in the upper Midwest. Worldwide snowmobile sales have increased over 50% in the last 5 years; the most popular engine size (500 cm3) and thus potential speed have increased as well. l In the state of MinDirect correspondence to North Trauma Institute, North Memorial Health Care. 3300 Oakdale Avenue North. Robbinsdale. MN 554222900 (e-mail: [email protected]) (Dr Beilman).

nesota. registered vehicles now number over 250000. The Minnesota Department of Natural Resources maintains an extensive system of marked and groomed trails and is actively involved in snowmobile education and safety training using volunteer instructors to teach classes for youth, young adult, and adult snowmobilers. Despite these efforts, the number of snowmobile-related injuries and deaths continues to rise in this state, with an almost threefold increase in fatal and nonfatal accidents over the last 10 years. Reasons for this increase are un-

227

Injury in Snowmobile Crashes Table 1. Demographic data from patients suffering injury related to snowmobile use Total patients (n) North Memorial St. Paul-Ramsey Hennepin County Average age (years [standard deviation]) Range Males: Females Ethanol use reported Helmet uSe Yes No Not reported Position Driver Passenger Unknown Pedestrian

274 140 74

60 29 (12)

l.6-n 238:36 121/274 (44%) 95 (35%) 29 (10%) 150 (55%) 239 (87%) 26 (10%) 8 (3%)

1

clear, though the new high-powered machines, burgeoning numbers of riders, and a larger percentage of inexperienced riders are all possible factors. In 1972, Gross 2 reported on the causes of snowmobile deaths in Minnesota, finding that half (8 of 16) succumbed with head and neck trauma. In 1994, a case report of a complex pelvic fracture implicated the high speed attained by the newer machines as contributing to the increased severity of injury.3 Overall, however, little has been published detailing the demographics, circumstances of injury, or outcomes in this group of trauma patients. We reviewed admissions to three busy trauma centers over an 8-year period in an attempt to characterize the risk factors and patterns of injury in these snowmobile crashes.

Methods This study was performed at three trauma centers in the Twin Cities area (Minneapolis-St Paul) of Minnesota. These included North Memorial Health Care, a level II trauma center in Robbinsdale, MN; St Paul-Ramsey Medical Center (now Regions Medical Center), a level I trauma center in St Paul, MN; and Hennepin County Medical Center, a level I trauma center in Minneapolis, MN. Patients were identified from trauma databases at each institution and charts abstracted for data not present in the trauma databases. Patient data from January 1988 through April 1996 were included. This study was approved by the institutional review

Table 2. Month of ocurrence of injury Month

n

April-October November December January February March

13 71 101 64 19

3

boards at each institution and at the University of Minnesota. Data captured included age of patient, time of accident, intensive care unit and hospital lengths of stay, injury severity score (ISS), Glasgow Coma Score (GCS), ethanol use, and type of injury. Ethanol use was determined by the self-report of the patients and by measured blood alcohol levels. Types of injury were classified as spine injuries (including cervical, thoracic, and lumbar spine injuries), head injury, intraabdominal injury, thoracic injury (including rib fractures, pulmonary contusion, and hemothorax), pelvic fracture, facial injury (facial bone fractures and soft tissue injury requiring operative closure), and extremity fractures (including upper and lower extremities). An area was counted once only for each patient, with multiple injuries involving the area (such as both femoral and radial fractures) counting as one for analysis. Additional data were obtained from the Minnesota Department of Natural Resources for the inclusive years (number of snowmobiles registered, total number of reported accidents, and number of deaths).

Results A total of 274 patients were identified and included in this analysis. There were 238 boys or men and 36 girls or women. The average age was 29 years (range, 1.677 years). The average speed at the time of injury when reported (n = 103) was 47 mph/75 kph with a range of 10 to 100 mph/16 to 160 kph. An additional 24 patients described the speed as high, fast, racing, or other word denoting a high rate of speed. Most injuries were to the driver of the snowmobile (87%). Ethanol use was reported in 44% of patients. Demographic data are summarized in Table 1. Most injuries resulted from the snowmobile striking a man-made or natural object (78%). An additional 19% of injuries resulted from a passenger or driver falling off or being thrown off the snowmobile. Unusual causes of injury included one injury from backfire from the snow-

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Beilman et al

Table 3. Hospital statistics in all patients after snowmobile injury and in those with an average injury severity score (ISS) of greater than 15

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All Patients

274 10 (3.6%)

ISS> 15

95 7 (7.4%)

2

5

8

14

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11

Time of Injury

Fig 1. Frequency plot illustrating number of injuries occurring at I-hour intervals throughout a 24-hour day. I

mobile, one pedestrian struck by a snowmobile, and six patients who fell through the ice. As one would expect, peak months for snowmobile injury occurrence were December through February. Only three injuries were seen in the months of April through October (Table 2). The peak times of injury were between the hours of 3 and 5 PM. A high number of injuries occurred between the hours of midnight and 1 AM before tapering off (Fig 1). There were no significant variations in reported alcohol use by time of day. Both patients with crashes occurring between 4 AM and 6 AM reported alcohol use. The one patient with a crash occurring between 6 AM and 8 AM did not report alcohol use. Reported alcohol use at other times ranged from 31% to 66%. Mortality in this group of patients was 3.6% (10 of 274). There were 136 fatalities reported to the Minnesota Department of Natural Resou;ces due to snowmobile use during this same time. The average ISS was 15 (SD = 11), and the average GCS was 14. There were 95 patients with an ISS of more than 15. As expected, a majority of deaths occurred in this group (7 of 10). Table 3 outlines hospital data for these two groups of patients. Of patients that died, the average ISS was 30. Three patients died within the first 24 hours of hospitalization, five died between 2 and 10 days after injury, and two died on days 12 and 37 after injury, respectively. Average GCS for patients that died was 5, with five patients of the 10 deaths having a GCS of 3. Hypothermia (an emergency department temperature of less than 35.0°C [95°F]) was present in 17 patients (6%). Three of these patients had severe hypothermia, with temperatures of 27.7°C (81.9°F), 28.1°C (82.5°F), and 31.8°C (89.2°F) on presentation to the emergency department. The patient presenting at the emergency department with a temperature of 27.7°C (81.9°F) was an immersion injury and died within 24 hours of hospital-

ization. Of the remaining 14 patients with temperatures between 32.2°C (90°F) and 35.0°C (95°F), there were two mortalities. Only one case of frostbite was reported. Figure 2 shows the types of injuries. Extremity fracture was the most common injury, occurring in 67% of patients. Head fracture (34%), facial injuries (32%), and thoracic injuries (29%) were each present in about one third of patients, followed by spine injury (18%), intraabdominal injury (15%), and pelvic fracture (11 %). There was no correlation between speed and either ISS (,-2 = 0.06) or GCS (,-2 = 0.08). In addition, there was no increase in ISS or decrease in GCS in those patients who reported only an unspecified high rate of speed. Discussion

According to the Minnesota Department of Natural Resources, both snowmobile-related injuries and deaths have increased between 1987 and 1998; the raw numbers of total and fatal accidents over this time present an alarming trend (Fig 3; data compiled from Minnesota Department of Natural Resources statistics). Minnesota law requires registration of all snowmobiles used on public land; accidents involving injury, death, or property damage greater than $500 must be reported. The number of registered machines has increased from 175000 in 1987 to 278 000 in 1997. Interestingly, over this time, the death rate per 100 000 machines has actually decreased from 9.5 over the 1987-88 season to 6.8 over the 1997-98 season (data not shown). The percentage of fatalities per total number of accidents has remained relatively constant, however, with a mean and median of 4.6% (Fig 4). This percentage is slightly greater than the 3.4% deaths found in our series; the difference likely represents those patients who never made it to the hospital. Although the 274 patients examined in this paper represent only a fraction of the thousands involved in snow-

229

Injury in Snowmobile Crashes

Extremity Fractures

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Pelvic Fx

Thoracic

Intraabdomin~1

Head

C,T, L Spine

o

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20

30

40

50

60

70

80

90

100 110 120 130 140 150 160 170 180 190

Total Patients with Injury Fig 2. Number of injuries reported in each category: extremity fractures (67%), head injury (34%), facial fractures or soft tissue injury (32%), thoracic injury (29%), spine injury (18%), intraabdominal injury (15%), and pelvic fracture (11 %).

mobile-related injuries in Minnesota from 1988 to 1996, their requirement for transfer and admission to a level I or level II trauma center suggests they are the most severely injured, at greatest risk for poor outcomes, and large consumers of health care dollars. Thus this is the population to which prevention must be targeted.

The demographics of injured patients in this study parallel the findings of other reported series of recreational snowmobile trauma in North America. 4 - 7 In all these series, young men who average in age from 25 to 30 years are most at risk for injury, and drivers are involved 50% to 90% of the time. In Minnesota, the av-

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230

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Fig 4.

erage age of registered snowmobile owners is 40 years, suggesting that those who crash may not be representative of the snowmobiling population as a whole. This was also the conclusion of a Swedish study examining snowmobile-related deaths and finding "deviant driver behavior"; those who died were more likely to have had other vehicle-related violations. 8 The demographics of fatal crashes are even more heavily skewed toward young male drivers who have ingested alcohol. In the New Hampshire series, 67% of fatal accidents involved alcohol vs 16% of nonfatal crashes.? In the North Dakota series, all fatalities involved alcoho1. 6 A case-control study of snowmobile deaths in Ontario using sexmatched drivers from fatal motor vehicle and motorcycle crashes found that the snowmobilers were four times more likely than control subjects to have used alcohol. 9 With a reported use of 44%, alcohol clearly played a role in our study population; however, we did not do a breakdown of alcohol use between fatal and nonfatal crashes. This rate of alcohol use was actually very similar to that reported for a group of injured motorcycle drivers in California (44% in our patients vs 42% in motorcycle crashes). 10 Interestingly, the high speed, lack of helmet use, and single vehicle involvement that characterized the crashes of intoxicated motorcyclists mimics a typical pattern seen in snowmobilers. Like driving while intoxicated, excessive speed intuitively seems to be a risk factor for snowmobile-related injury. Unfortunately, data regarding actual speed at the time of a crash are often qualitative rather than quanti-

tative or not recorded at all. However, review of our data allows some speculation about the potential role of excessive speed. In Minnesota, the snowmobile speed limit is 50 mph/80 kph. Thus the average speed in this series (47 mph/75 kph) is very close to the legal limit, with 26% reporting excessive rates of speed at the time of the crash. Although speed did not independently correlate with severity of injury as measured by ISS or GCS, the circumstances of these crashes suggest that a high rate of speed is a contributing factor. Striking a fixed object was the most common cause of accident in our series. Additionally, the majority of crashes occurred during the twilight and early evening hours, times of difficult or decreased visibility. Excessive speed decreases necessary reaction time: even if the driver sees an object in his or her path, it may be too late to avoid it. Subtle changes in terrain may likewise not be appreciated at high speeds and in poor light. Our findings regarding the circumstances of snowmobile crashes are very similar to those reported in a series of fatal accidents in Ontario where the majority collided with a fixed object at excessive speed in suboptimal light. 4 In both Ontario and New Hampshire, a common scenario preceding fatal crashes was snowmobilers speeding over the unobstructed expanse of a frozen lake and encountering unexpected uneven terrain or thin ice; in these series, head injury and submersion were almost equally common causes of death. 4 ,7 In our series, submersion is an uncommon form of snowmobile injury, with only 6 of 274 subjects falling

231

Injury in Snowmobile Crashes

through the ice. Interestingly, drowning was reported as the most common cause of snowmobile death in Sweden, and the majority of crashes there occurred late in the season (March and April), presumably when the ice is more likely to be unsafe. s In North American series, deaths after submersion are more likely secondary to hypothermia. 4 ,5,7 This was true in our study series as well, with the single death in the submersion group presenting with profound hypothermia (27.7°C [81.9°F]). Another key area targeted for snowmobile injury prevention is helmet use. In Miimesota, helmets are recommended for everyone but are only required for those under age 18. Our study population had an average GCS of 14, and head injury was the second most common injury, occurring in 34% (Fig 2). Although only 35% in this series wore a helmet, the data are not known for the majority. Thus direct relationships between helmet use and the risk or severity of head injury cannot be made. Also, the average GCS for those presenting with head injury was not determined. However, in the 95 patients with ISS of more than 15, the average GCS declined to 11. In this group, mortality almost doubled compared with the study population as a whole (Table 2), Not surprisingly, the ISS was higher (an average score of 30) and GCS lower (an average score of 5) in those who died; 50% had a GCS of 3. These figures suggest a direct correlation between the severity of head injury and the risk of death. Head injuries are common in other series as well, as are low or unknown rates of helmet use. 5.6 More data are needed to determine the effect of helmet use on head injury and outcome in snowmobile crashes. Severe head injuries (GCS of less than 7) may not be typical of most snowmobile crashes, particularly if the victim is not thrown from the vehicle. However, the significant association between low GCS and fatal outcome may be enough to advocate mandatory helmet use. An argument against mandatory helmet use can be found in data from New Hampshire, where 4 of 6 patients with fatal head injuries wore helmets. 7 However, this statistic must be countered with the high rate of helmet use (57%) among those with nonfatal head injuries in the same series. Extremity injuries were the most common in this series (67%, Fig 3). Because we did not distinguish upper from lower extremity injuries, this distribution is unknown in our patients. Spine injuries (18%) and pelvic fractures (11 %) were much less common. Orthopedic injuries are common in other off-road vehicle crashes, but a higher incidence of multiple injuries is noted in patients involved in snowmobile crashes vs other offroad vehicle crashes. 11 ,12 Although we did not define multiple injury as a separate category in our patients, 35% had ISS of more than 15, In this group, intensive

care unit and hospital lengths of stay, as well as mortality, were increased compared with the patient population as a whole, In conclusion, we have identified a number of risk factors for snowmobile-related trauma. As in other series, we found young male drivers are involved in the majority of crashes and that alcohol likely plays a significant role. Most crashes occur after collision with a fixed object, with a peak occurrence in late afternoon. Though the evidence is indirect, these circumstances suggest high speed in combination with decreased visibility contribute to crashes. The injury pattern in nonfatal snowmobile trauma is somewhat predictable. The extremities by far appear to be the most vulnerable, followed by the head, face, and thorax. Multiple injuries are less common, but not surprisingly, an ISS of more than 15 increases the length of a hospital stay and more than doubles mortality. Despite the marked prevalence of head injury and the significant increased risk of death with severe head injury, helmet use was poorly reported among our patients. Effective in October 2002, Minnesota law will require adults to complete a snowmobile safety course, and efforts are already well underway to provide this service. Though this has not been a popular policy with some snowmobilers, it is apparent from this study that snowmobile-related injury is largely avoidable, as most of the risks are not inherent to the sport but result from how it is practiced. Though the injured may not represent the snowmobile population as a whole, prevention should target snowmobile drivers. However, it is also clear that current safety equipment is inadequate to prevent the most common injuries. Finally, the use of alcohol among snowmobilers, like that among automobile drivers, is a serious public health issue. Although better law enforcement may be necessary, this behavior is unlikely to change until driving while intoxicated is deemed unacceptable by the snowmobiling population as a whole. Acknowledgment

Support was provided by North Trauma Institute. References 1. Snowmobile Safety Training. St Paul, MN: Minnesota De-

partment of Natural Resources Newsletter; Fall 1998. 2. Gross HP. Snowmobile fatalities in Minnesota. Minn Med. 1972;55:983-985. 3. Veverka TJ. Snowmobiles in the 90s: The impact of speed. Skylines. January 1994:8-9. 4. Rowe B, Milner R, Johnson C, Bota G. Snowmobile-related deaths in Ontario: A 5-year review. Can Med Assoc J. 1992;146:147-152.

232 5. Hamdy CR, Dhir A, Cameron B, Jones H, Fitzgerald GWN. Snowmobile injuries in Northern Newfoundland and Labrador: An 18-year review. J Trauma. 1988;28: 1232-1237. 6. James EC, Lenz JO, Swenson WM, Cooley AM, Gomez YL, Antonenko DR. Snowmobile trauma: An eleven year experience. Am Surgeon. 1991;57:349-353. 7. Hewitt A, Solet D, Kiely M. Injuries associated with use of snowmobiles, New Hampshire, 1989-1992. JAMA. 1995;273:448-449. 8. Eriksson A, Bjornstig U. Fatal snowmobile accidents in Northern Sweden. J Trauma. 1982;22:977-982. 9. Rowe B, Milner R, Johnson C, Bota G. The association

Beilman et al of alcohol and night driving with fatal snowmobile trauma: A case-control study. Ann Emerg Med. 1994;24:842848. 10. Peek-Asa C, Kraus JE Alcohol use, driver, and crash characteristics among injured motorcycle drivers. J Trauma. 1996;41:989-993. 11.· Pyper JA, Black GB. Orthopaedic injuries in children associated with the use of off-road vehicles. J Bone Joint Surg. 1988;70A:275-284. 12. Postl BD, Moffatt MEK, Black GB, Cameron CB. Injuries and deaths associated with off-road recreational vehicles among children in Manitoba. Can Med Assoc J. 1987;137: 297-300.