Comparison of Minitrampoline- and Full-Sized Trampoline-Related Injuries in the United States, 1990–2002
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《小儿科》
Center for Injury Research and Policy, Columbus Children's Research Institute, Children's Hospital, Columbus, Ohio
Center for Biostatistics, Ohio State University, Columbus, Ohio
Department of Pediatrics, Ohio State University College of Medicine and Public Health, Columbus, Ohio
ABSTRACT
Objective. To compare mini- and full-sized trampoline–related injuries in the United States.
Methods. A retrospective analysis of data was conducted for all ages from the National Electronic Injury Surveillance System (NEISS) of the US Consumer Product Safety Commission from 1990 to 2002. We compared 137 minitrampoline-related injuries with 143 full-sized trampoline–related injuries, randomly selected from all full-sized trampoline–related injuries reported to the NEISS during the study period.
Results. Patients ranged in age from 1 to 80 years (mean [SD]: 13.9 [17.7]) and 2 to 52 years (mean [SD]: 11.0 [8.0]) for mini- and full-sized trampoline–related injuries, respectively. Most patients were younger than 18 years (82% mini, 91% full-sized). Thirty-two percent of minitrampoline- and 19% of full-sized trampoline–related injuries were to children who were younger than 6 years; girls predominated (63% mini, 51% full-sized). Children who were younger than 6 years were more likely to be injured on a minitrampoline than on a full-sized trampoline, when compared with 6- to 17-year-olds (odds ratio [OR]: 2.43; 95% confidence interval [CI]: 1.33–4.47). The majority of injuries occurred at home (87% mini, 89% full-sized). All patients who were injured on a minitrampoline were treated and released, whereas 5% of patients who were injured on a full-sized trampoline were admitted to the hospital. On minitrampolines, children who were younger than 6 years were at risk for head lacerations (OR: 4.98; 95% CI: 1.71–16.03), and children who were 6 to 17 years were at risk for lower extremity strains or sprains (OR: 6.26; 95% CI: 1.35–59.14). Children who were 6 to 17 years and injured on a full-sized trampoline were at risk for lower extremity strains or sprains (OR: 4.85; 95% CI: 1.09–44.93). Lower extremity strains or sprains were the most common injury sustained by adults (18 years and older; 33% mini, 15% full-sized).
Conclusions. Injury patterns were similar for mini- and full-sized trampolines, although minitrampoline–related injuries were less likely to require admission to the hospital and more commonly resulted in head lacerations among children who were younger than 6 years. Risk for injury could not be determined because of the lack of data regarding duration of exposure to risk. We therefore conclude that the use of full-sized trampolines by children should follow the policy recommendations of the American Academy of Pediatrics. Trampolines, including minitrampolines, should be regarded as training devices and not as toys. Until more data are available regarding exposure to risk, we caution against the use of the minitrampoline as a play device by children in the home, which is where most minitrampoline-related injuries occur.
Key Words: trampoline minitrampoline injury
Abbreviations: AAP, American Academy of Pediatrics CPSC, United States Consumer Product Safety Commission ED, emergency department NEISS, National Electronic Injury Surveillance System OR, odds ratio CI, confidence interval
George Nissen was inspired to invent the "bouncing table," later renamed the trampoline, in 1937 after watching tightrope walkers and trapeze artists perform twists, spins, and somersaults into safety nets at the circus.1 As trampoline use increased in popularity, so did the frequency of trampoline-associated injuries. The first trampoline-related injuries were reported in 1956 by Zimmerman2 and in 1960 by Ellis et al.3 Spinal cord injuries are the main severe injury associated with trampolines.4–7 Most of these injuries involve the cervical spine and result in quadriplegia.4–7 The minitrampoline is also associated with risk for spinal cord injury, most notably from poorly executed somersaults.8,9 By the late 1990s, despite the recommendation of the American Academy of Pediatrics (AAP) that trampolines not be used in home or recreational settings, recreational trampoline-related injuries reached "epidemic proportions," as reported by Furnival et al.10 Almost all of the trampolines associated with these injuries were at private homes, usually in backyards.10–13 Most of the injuries occurred on full-sized trampolines.11
Relatively few studies have focused exclusively on trampoline-related injuries in the pediatric population,13–20 and even fewer have described minitrampoline-related injuries.14,21,22 Therefore, the goal of our study was to describe and compare mini- and full-sized trampoline–related injuries among children and adults in the United States. More specific, we aimed to (1) compare the types of injuries associated with minitrampolines with those associated with full-sized trampolines, (2) compare trampoline-related injuries sustained by children (<18 years) with those sustained by adults (18 years and older) for both types of trampolines, and (3) compare trampoline-related injuries sustained by children younger than 6 years with those sustained by children 6 to 17 years for both types of trampolines.
METHODS
The US Consumer Product Safety Commission (CPSC) monitors consumer product–related injuries that are treated in US hospital emergency departments (EDs) through the National Electronic Injury Surveillance System (NEISS). The NEISS was established in 1972 with revisions made in its sampling frame in 1978, 1990, and 1997. The NEISS obtains data from a probability sample of 98 hospitals selected from the population of all hospitals with EDs in the United States and its territories.23 Projections of injuries that occur nationally are made from this probability sample. Data regarding injuries associated with consumer products and recreational activities are collected on a daily basis via computer from each participating hospital. The NEISS has been shown to be highly sensitive and accurate in identifying consumer product–related injury cases.24–27
Data were obtained from the CPSC regarding trampoline-related injuries (product code 1233) reported through the NEISS during the 13-year period 1990 through 2002. Through review of the comment fields for each case, cases were divided into 2 categories: minitrampoline-related and full-sized trampoline–related injuries. A minitrampoline was identified in the comment fields as a minitramp, small tramp, jogging tramp, or exercise tramp. During the 13-year study period, 137 minitrampoline-related injuries and 22 997 full-sized trampoline–related injuries were reported to the NEISS. These injuries represent an estimated 5400 minitrampoline-related and 915 500 full-sized trampoline–related injuries nationally. Because of the relatively small number of minitrampoline-related injury cases, we chose not to weight these cases to make national projections regarding these injuries during data analysis. The minitrampoline cases were compared with a sample of full-sized trampoline cases. Eleven full-sized trampoline–related injury cases were randomly selected from each of the 13 years of the study period (total n = 143) in the following manner. All full-sized trampoline–related injury cases were grouped by year of injury. Within each of the 13 years, each case was assigned an identification number, ranging from 1 to the total number of cases for that year. GraphPad Quickcalcs, a random-number generator program,28 was used to select randomly 11 case identification numbers from each of the 13 years. This allowed us to obtain similar sample sizes for the 2 groups while controlling for year of injury.
To evaluate whether the random sample was representative of all full-sized trampoline–related injury cases reported to the NEISS during the study period, we compared values of the major variables to be analyzed (age, gender, body part injured, type of injury, location where the injury event occurred, and disposition from the ED) between the 2 groups using 2 analyses, with and without Yates correction, and Student t test. No statistically significant differences were found for any of the variables. The same comparisons were made between the random sample of full-sized trampoline–related injuries and the national projections for all full-sized trampoline–related injuries calculated using the NEISS sample weights. In this comparison, the only significant difference found was the percentage of trampoline-related injuries that occurred at school: 4.3% for the random sample versus 1.2% for all estimated full-sized trampoline–related injuries that occurred in the United States during the study period. It was concluded that the random sample was representative of all full-sized trampoline–related injury cases reported to the NEISS during the 13-year study period.
The type of injury was grouped into 5 categories during study analyses: (1) soft tissue injury (contusion, abrasion, and hematoma), (2) fracture/dislocation, (3) laceration, (4) strain/sprain, and (5) other (concussion, crushing injury, internal organ injury, and avulsion). Likewise, the body part injured was grouped into 5 categories during study analyses: (1) head (head, face, mouth, and ear), (2) neck, (3) trunk (shoulder, upper trunk, and lower trunk), (4) lower extremity (knee, lower leg, upper leg, ankle, foot, and toe), and (5) upper extremity (elbow, lower arm, upper arm, wrist, hand, and finger). Patients were categorized into 2 main age groups for data analyses: children (younger than 18 years) and adults (18 years or older). Because the CPSC11 recommends that children younger than 6 years not use trampolines, we further divided children into 2 subgroups for analyses: children younger than 6 years and 6- to 17-year-olds.
Data were analyzed using EpiInfo software.29 Continuous data were tested for normality using the Kolmogorov-Smirnov test. Bartlett test was used to assess homogeneity of variances. Statistical analyses included 2 analysis, with and without Yates correction, Fisher's exact 2-tailed test, and the Mann-Whitney U test. The level of significance for all statistical tests was = .05. The computation of odds ratio (OR) with an exact 95% confidence interval (CI)30 was also performed.
RESULTS
Sample Description
A total of 137 minitrampoline-related injury cases were reported to the NEISS from 1990 through 2002. These patients ranged in age from 1 to 80 years (mean [SD]: 13.9 [17.7] years). A total of 113 (82.5%) patients were younger than 18 years, and 44 (32%) were younger than 6 years. Females predominated (n = 86 [62.8%]; Fig 1).
A total of 143 full-sized trampoline–related injury cases, randomly selected from all full-sized trampoline–related injury cases, were reported to the NEISS from 1990 through 2002. These patients ranged in age from 2 to 52 years (mean [SD]: 11.0 [8.0] years). Of these patients, 130 (90.9%) were younger than 18 years and 27 (18.9%) were younger than 6 years. Females accounted for slightly more than half of the cases (n = 73 [51.0%]; Fig 1).
There were no statistically significant differences between the minitrampoline and full-sized trampoline groups with respect to gender, age, or number of patients who were younger than 18 years. However, a significantly greater number of children who were younger than 6 years were injured on a minitrampoline (OR: 2.43; 95% CI: 1.33–4.47; P < .01) when compared with 6- to 17-year-olds.
The annual number of minitrampoline-related injuries during the 13-year period ranged from 6 to 18 (mean [SD]: 10.5 [3.8]), with peak numbers in 1991 (n = 16), 1995 (n = 15), and 2000 (n = 18). There was no secular trend in the number of minitrampolinerelated injuries during the study period. For full-sized trampolines, the number of cases was fixed at 11 per year by our sampling method. Overall, there were more injuries for both types of trampolines during the months of April through October, with the mode in May. Although not statistically significant, there was a greater number of minitrampoline-related injuries than full-sized trampoline–related injuries from November through February.
There was no significant difference between the 2 types of trampolines with respect to the location where the injury event occurred. Most (87.0%) minitrampoline-related injuries occurred at home, 6.5% occurred at a place of recreation or sports, 5.4% occurred at school, and the remaining 1.1% occurred on other public property. Likewise, 89.1% of full-sized trampoline–related injuries occurred at home, 4.3% occurred at a place of recreation or sports, 3.3% occurred at school, and the other 3.3% occurred on other public property.
There were 18 cases (17 mini, 1 full-sized) in which patients were not jumping on the trampoline at the time of injury. Deleting these cases from the analyses did not alter the results of the study. Therefore, they were included in all analyses. The mechanisms of injury for these 18 cases were that the trampoline was dropped or fell onto the patient (n = 7), the patient unintentionally fell from another object onto the trampoline (n = 3), the patient was underneath the trampoline and another person jumped onto the trampoline (n = 3), the patient collided with the trampoline (n = 3), the patient was injured while cutting up a minitrampoline with a knife for disposal (n = 1), and another person jumped off the trampoline and landed on the patient (n = 1). Table 1 summarizes characteristics of the study population.
Body Part Injured
The lower extremity (43.8%) was the most common body region injured on minitrampolines, followed by the head (24.8%), upper extremity (18.2%), trunk (10.2%), and neck (2.9%). The lower extremity (42.0%) was also the most common body region injured on full-sized trampolines, followed by the upper extremity (25.2%), head (14.0%), trunk (10.5%), and neck (8.4%).
There was no significant difference between children and adults with respect to body part injured on full-sized trampolines. On minitrampolines, children (younger than 18 years) were more likely to sustain a head injury (OR: 9.39; 95% CI: 1.40–402.47; P = .01), whereas adults (18 years and older) were more likely to sustain a lower extremity injury (OR: 3.11; 95% CI: 1.14–9.14; P = .02; Fig 2).
There was no significant difference in body part injured on full-sized trampolines between children who were younger than 6 years and those who were 6 to 17 years of age. However, on minitrampolines, children who were younger than 6 years were more likely to sustain a head injury (OR: 7.82; 95% CI: 2.94–22.58; P < .01), whereas children who were 6 to 17 years of age were more likely to sustain a lower extremity injury (OR: 3.95; 95% CI: 1.57–10.82; P < .01; Fig 2). Important results are summarized in Tables 2 and 3.
Type of Injury
There was a significant difference between type of injury sustained on minitrampolines compared with full-sized trampolines (P < .01). While performing analyses separately for each type of trampoline, there was no significant difference between children and adults with respect to type of injury (Fig 3); however, children who were younger than 6 years were more likely to sustain a laceration on a minitrampoline when compared with 6- to 17-year-olds (OR: 2.69; 95% CI: 1.04–7.18; P = .04). Children who were 6 to 17 years of age were more likely to sustain a strain or sprain on both minitrampolines (OR: 4.62; 95% CI: 1.40–20.00; P < .01) and full-sized trampolines (OR: 3.38; 95% CI: 1.13–12.34; P = .02) than children who were younger than 6 years (Fig 3). Important results are summarized in Tables 2 and 3.
Most Common Injuries (Body Part and Injury Type Combined)
The most common types of injuries sustained on minitrampolines for children (younger than 18 years) were head lacerations (20.3%) and for adults (18 years and older) were lower extremity strains or sprains (33.3%). Children who were younger than 6 years were most at risk for sustaining a head laceration (OR: 4.98; 95% CI: 1.71–16.03; P < .01), while children who were 6 to 17 years of age were most at risk for sustaining a lower extremity strain or sprain (OR: 6.26; 95% CI: 1.35–59.14; P = .01).
On full-sized trampolines, lower extremity strains or sprains were most common for both children (23.8%) and adults (15.4%). Furthermore, children who were younger than 6 years more frequently sustained lower extremity fractures or dislocations, whereas children who were 6 to 17 years of age were more at risk for lower extremity strains or sprains (OR: 4.85; 95% CI: 1.09–44.93; P = .03). Important results are summarized in Tables 2 and 3.
Mechanism of Injury
the comments in the narrative portion of the NEISS database, we determined that the patient was more likely to be actively using the trampoline at the time of injury when a full-sized trampoline was involved (99.3% [142 of 143]) than when a minitrampoline was involved (87.6% [120 of 137]; OR: 19.97; 95% CI: 3.04–846.49; P < .01). Only 1 (0.7%) patient was not actively using the full-sized trampoline at the time of injury, compared with 17 (12.4%) patients for the minitrampoline.
The majority of injuries were caused by a fall onto or off of the trampoline (48.8% [64 of 131] mini, 48.9% [65 of 133] full-sized). Patients who were using a minitrampoline were more likely to be injured by running into or falling/tripping over the trampoline (17.6% [23 of 131]) than those who were using a full-sized trampoline (3.0% [4 of 133]; OR: 6.82; 95% CI: 2.24–27.98; P < .01). Some of these injuries may have occurred while mounting or dismounting the minitrampoline. Patients who were using a full-sized trampoline were more likely to be injured while jumping on the trampoline or performing a stunt (35.3% [47 of 133]) than those who were using a minitrampoline (20.6% [27 of 131]; OR: 2.10; 95% CI: 1.17–3.82; P = .01). Other mechanisms of injury included colliding with another person on the trampoline and twisting an extremity on the trampoline.
Hospital Admissions
All patients who were injured on a minitrampoline were treated and released from the ED. Seven (5%) of the patients who were injured on a full-sized trampoline were admitted to the hospital. Six of the 7 had fractures; 5 of the 6 fractures were to the upper extremity, and the other was a fracture of the cervical spine. The seventh patient had a concussion. Six of the admitted patients ranged in age from 3 to 13 years, and the seventh was 34 years of age. The 34-year-old sustained the cervical spine fracture. Four of the patients were female, and 3 were male.
DISCUSSION
Minitrampoline-related injuries more commonly resulted in head lacerations among children who were younger than 6 years. Smith13 also found that younger children are more likely to sustain head, neck, and facial injuries, with head lacerations being more common among children who are younger than 6 years. The higher center of gravity of young children may make them more prone to fall head-first, and the immature strength and coordination of their arms leave them less able to protect themselves in a fall, thus resulting in an increased rate of head injury for these children.
Previous studies have demonstrated that most full-sized trampoline–related injuries to children occur on the body of the trampoline, including falls onto the mat, collisions with other trampolinists, and flips or complex maneuvers on the mat.2,10,19 In our study, patients who were using a minitrampoline were significantly more likely to be injured by running into or falling/tripping over the trampoline, whereas patients who were using a full-sized trampoline were significantly more likely to be injured while jumping on the trampoline or performing a stunt. For both types of trampoline, approximately half (49%) of injuries were caused by a fall onto or off of the trampoline.
Use of a trampoline by multiple people simultaneously occurred in 77% of the cases reported by Woodward et al14 and 83% of the cases reported in the CPSC trampoline fact sheet.11 Such group use would be expected to be more common for full-sized trampolines than for minitrampolines, because the larger mat size of a full-sized trampoline allows more room for use by multiple individuals. However, we were unable to compare group use between full-sized and minitrampolines in our study because of incomplete documentation of group use in the free-text comments reported in the NEISS database. Black and Amadeo19 found no correlation between the severity of the injury and the number of jumpers on the trampoline. Injuries associated with group use involved the youngest person of the group in 50% of cases with ages known for all trampolinists.14 In addition to being bumped or bounced off the trampoline by others, a smaller child may be injured by the elastic recoil of the mat generated by a larger person or group of people.14 The force of this recoil can result in fractures of the lower extremity,16 as well as other types of injury.
Extremity injuries, both lower and upper, have been identified as the most common trampoline-related injury in recent years.10,12,13,19,20,31 Other investigators have identified a decrease in the occurrence of fractures and dislocations with increasing age and an increase in soft tissue injuries and lower extremity strains or sprains with increasing age of the trampolinist.13,32 Likewise, in this study, the lower extremity was the most common body region injured for both types of trampoline. Lower extremity strains or sprains were more common for children who were 6 to 17 years of age and for adults. In addition, children who were younger than 6 years more frequently sustained lower extremity fractures or dislocations on full-sized trampolines than older children.
Esposito33 noted a rapid increase in the use of the trampoline as a backyard recreational activity during the past 10 years. Consistent with this observation, most mini- and full-sized trampoline–related injuries occurred at home in our study population. Others have reported similar findings,10–13, 20,31 and a change from what was previously an indoor, school-related, athletic endeavor, to a warm-weather, after school, leisure activity involving younger children at home is apparent.14
Attempts at somersaulting, both backward and forward, are the most dangerous maneuvers on the trampoline3 and have resulted in the largest number of serious injuries,7,9 especially acute injury to the cervical spinal cord.3–6 The majority of known cases of quadriplegia associated with both mini- and full-sized trampolines resulted from improper execution of a somersault.8,34 One cervical spine fracture occurred in our study, but data were unavailable regarding this patient's functional outcome.
Hospital admission rates for trampoline-related injuries reported by other investigators ranged from 1.9% to 23%.10,13,14,20,31,32 In comparison, 5% of full-sized trampoline–related injuries and none of the minitrampoline-related injuries in our study required admission to the hospital. The lack of admissions for minitrampoline-related injuries may be partly attributable to a higher proportion of injury mechanisms with lower kinetic energy involved, such as running into or falling/tripping over the trampoline.
Problems associated with recreational use of trampolines, especially at home and in backyards, are a lack of professional instruction, trained spotters, and supervision; potential degradation of the trampoline from being outdoors and unprotected from the weather; and not properly positioning the trampoline away from other objects, such as trees and fences. In addition, trampoline owners usually do not lock away the trampoline when it is not in use and do not secure minitrampolines to the floor or other stationary structure, as is recommended.9
Smith and Shields20 reported that knowledge of injury risks associated with trampolines was not an effective deterrent to trampoline use; neither could adult supervision be relied on to decrease trampoline-related injuries. They found that 73% of parents indicated that they had been aware of the potential dangers of trampolines before their child was injured, 10% reported that their child had been injured previously on a trampoline, 54.8% of children continued to use a trampoline after the injury event, and adult supervision was present at the time of injury in 56% of cases.
The literature demonstrates that neither close supervision nor advanced skill level precludes trampoline-related morbidity or mortality.14,35 For example, a 15-year-old world-ranked trampolinist died after falling from a trampoline during a gymnastics competition in Tennessee in 2004.36 Smith and Shields20 concluded that the prevention strategies of warning labels, public education, and adult supervision are inadequate to prevent trampoline-related injuries. They recommended that children not use backyard trampolines, and the sale of trampolines for private recreational use should be halted. This is in agreement with the policy position of the AAP. However, these recommendations are based on data regarding injuries that are almost entirely associated with the use of full-sized trampolines in residential backyards. Is the risk for injury similar for minitrampolines, and should these same recommendations be applied to minitrampolines The findings of our study provide a response to these questions. Injury patterns were similar for mini- and full-sized trampolines, although minitrampoline-related injuries were less likely to require admission to the hospital and more commonly resulted in head lacerations among children who were younger than 6 years. Risk for injury could not be determined because of the lack of data regarding duration of exposure to risk. We therefore conclude that the use of full-sized trampolines by children should follow the policy recommendations of the AAP. Trampolines, including minitrampolines, should be regarded as training devices and not as toys. Until more data are available regarding exposure to risk, we recommend against the use of the minitrampoline as a play device by children in the home, which is where most minitrampoline-related injuries occur.
This study has several limitations. NEISS data may not be representative of trampoline-related injuries that are treated in settings outside of EDs or injuries that do not receive medical attention. The incidence of trampoline-related injuries per hour of exposure cannot be determined from our data. Therefore, the risk for injury on minitrampolines versus full-sized trampolines cannot be determined. Although incidence rates are important in clarifying the influence of risk factors and calculating relative risks and ORs, the frequency and the relative proportion of cases provide useful measures for a comparative understanding of these sources of injury. Another limitation of this study was lack of documentation of the circumstances of injury in many cases. The small number of adults in our study precluded statistical analyses for some comparisons. Furthermore, small sample size resulted in a wide 95% CI for some ORs, when comparisons were made between children and adults. Large variability in the data may also have contributed to wide CIs.
FOOTNOTES
Accepted Oct 14, 2004.
No conflict of interest declared.
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Center for Biostatistics, Ohio State University, Columbus, Ohio
Department of Pediatrics, Ohio State University College of Medicine and Public Health, Columbus, Ohio
ABSTRACT
Objective. To compare mini- and full-sized trampoline–related injuries in the United States.
Methods. A retrospective analysis of data was conducted for all ages from the National Electronic Injury Surveillance System (NEISS) of the US Consumer Product Safety Commission from 1990 to 2002. We compared 137 minitrampoline-related injuries with 143 full-sized trampoline–related injuries, randomly selected from all full-sized trampoline–related injuries reported to the NEISS during the study period.
Results. Patients ranged in age from 1 to 80 years (mean [SD]: 13.9 [17.7]) and 2 to 52 years (mean [SD]: 11.0 [8.0]) for mini- and full-sized trampoline–related injuries, respectively. Most patients were younger than 18 years (82% mini, 91% full-sized). Thirty-two percent of minitrampoline- and 19% of full-sized trampoline–related injuries were to children who were younger than 6 years; girls predominated (63% mini, 51% full-sized). Children who were younger than 6 years were more likely to be injured on a minitrampoline than on a full-sized trampoline, when compared with 6- to 17-year-olds (odds ratio [OR]: 2.43; 95% confidence interval [CI]: 1.33–4.47). The majority of injuries occurred at home (87% mini, 89% full-sized). All patients who were injured on a minitrampoline were treated and released, whereas 5% of patients who were injured on a full-sized trampoline were admitted to the hospital. On minitrampolines, children who were younger than 6 years were at risk for head lacerations (OR: 4.98; 95% CI: 1.71–16.03), and children who were 6 to 17 years were at risk for lower extremity strains or sprains (OR: 6.26; 95% CI: 1.35–59.14). Children who were 6 to 17 years and injured on a full-sized trampoline were at risk for lower extremity strains or sprains (OR: 4.85; 95% CI: 1.09–44.93). Lower extremity strains or sprains were the most common injury sustained by adults (18 years and older; 33% mini, 15% full-sized).
Conclusions. Injury patterns were similar for mini- and full-sized trampolines, although minitrampoline–related injuries were less likely to require admission to the hospital and more commonly resulted in head lacerations among children who were younger than 6 years. Risk for injury could not be determined because of the lack of data regarding duration of exposure to risk. We therefore conclude that the use of full-sized trampolines by children should follow the policy recommendations of the American Academy of Pediatrics. Trampolines, including minitrampolines, should be regarded as training devices and not as toys. Until more data are available regarding exposure to risk, we caution against the use of the minitrampoline as a play device by children in the home, which is where most minitrampoline-related injuries occur.
Key Words: trampoline minitrampoline injury
Abbreviations: AAP, American Academy of Pediatrics CPSC, United States Consumer Product Safety Commission ED, emergency department NEISS, National Electronic Injury Surveillance System OR, odds ratio CI, confidence interval
George Nissen was inspired to invent the "bouncing table," later renamed the trampoline, in 1937 after watching tightrope walkers and trapeze artists perform twists, spins, and somersaults into safety nets at the circus.1 As trampoline use increased in popularity, so did the frequency of trampoline-associated injuries. The first trampoline-related injuries were reported in 1956 by Zimmerman2 and in 1960 by Ellis et al.3 Spinal cord injuries are the main severe injury associated with trampolines.4–7 Most of these injuries involve the cervical spine and result in quadriplegia.4–7 The minitrampoline is also associated with risk for spinal cord injury, most notably from poorly executed somersaults.8,9 By the late 1990s, despite the recommendation of the American Academy of Pediatrics (AAP) that trampolines not be used in home or recreational settings, recreational trampoline-related injuries reached "epidemic proportions," as reported by Furnival et al.10 Almost all of the trampolines associated with these injuries were at private homes, usually in backyards.10–13 Most of the injuries occurred on full-sized trampolines.11
Relatively few studies have focused exclusively on trampoline-related injuries in the pediatric population,13–20 and even fewer have described minitrampoline-related injuries.14,21,22 Therefore, the goal of our study was to describe and compare mini- and full-sized trampoline–related injuries among children and adults in the United States. More specific, we aimed to (1) compare the types of injuries associated with minitrampolines with those associated with full-sized trampolines, (2) compare trampoline-related injuries sustained by children (<18 years) with those sustained by adults (18 years and older) for both types of trampolines, and (3) compare trampoline-related injuries sustained by children younger than 6 years with those sustained by children 6 to 17 years for both types of trampolines.
METHODS
The US Consumer Product Safety Commission (CPSC) monitors consumer product–related injuries that are treated in US hospital emergency departments (EDs) through the National Electronic Injury Surveillance System (NEISS). The NEISS was established in 1972 with revisions made in its sampling frame in 1978, 1990, and 1997. The NEISS obtains data from a probability sample of 98 hospitals selected from the population of all hospitals with EDs in the United States and its territories.23 Projections of injuries that occur nationally are made from this probability sample. Data regarding injuries associated with consumer products and recreational activities are collected on a daily basis via computer from each participating hospital. The NEISS has been shown to be highly sensitive and accurate in identifying consumer product–related injury cases.24–27
Data were obtained from the CPSC regarding trampoline-related injuries (product code 1233) reported through the NEISS during the 13-year period 1990 through 2002. Through review of the comment fields for each case, cases were divided into 2 categories: minitrampoline-related and full-sized trampoline–related injuries. A minitrampoline was identified in the comment fields as a minitramp, small tramp, jogging tramp, or exercise tramp. During the 13-year study period, 137 minitrampoline-related injuries and 22 997 full-sized trampoline–related injuries were reported to the NEISS. These injuries represent an estimated 5400 minitrampoline-related and 915 500 full-sized trampoline–related injuries nationally. Because of the relatively small number of minitrampoline-related injury cases, we chose not to weight these cases to make national projections regarding these injuries during data analysis. The minitrampoline cases were compared with a sample of full-sized trampoline cases. Eleven full-sized trampoline–related injury cases were randomly selected from each of the 13 years of the study period (total n = 143) in the following manner. All full-sized trampoline–related injury cases were grouped by year of injury. Within each of the 13 years, each case was assigned an identification number, ranging from 1 to the total number of cases for that year. GraphPad Quickcalcs, a random-number generator program,28 was used to select randomly 11 case identification numbers from each of the 13 years. This allowed us to obtain similar sample sizes for the 2 groups while controlling for year of injury.
To evaluate whether the random sample was representative of all full-sized trampoline–related injury cases reported to the NEISS during the study period, we compared values of the major variables to be analyzed (age, gender, body part injured, type of injury, location where the injury event occurred, and disposition from the ED) between the 2 groups using 2 analyses, with and without Yates correction, and Student t test. No statistically significant differences were found for any of the variables. The same comparisons were made between the random sample of full-sized trampoline–related injuries and the national projections for all full-sized trampoline–related injuries calculated using the NEISS sample weights. In this comparison, the only significant difference found was the percentage of trampoline-related injuries that occurred at school: 4.3% for the random sample versus 1.2% for all estimated full-sized trampoline–related injuries that occurred in the United States during the study period. It was concluded that the random sample was representative of all full-sized trampoline–related injury cases reported to the NEISS during the 13-year study period.
The type of injury was grouped into 5 categories during study analyses: (1) soft tissue injury (contusion, abrasion, and hematoma), (2) fracture/dislocation, (3) laceration, (4) strain/sprain, and (5) other (concussion, crushing injury, internal organ injury, and avulsion). Likewise, the body part injured was grouped into 5 categories during study analyses: (1) head (head, face, mouth, and ear), (2) neck, (3) trunk (shoulder, upper trunk, and lower trunk), (4) lower extremity (knee, lower leg, upper leg, ankle, foot, and toe), and (5) upper extremity (elbow, lower arm, upper arm, wrist, hand, and finger). Patients were categorized into 2 main age groups for data analyses: children (younger than 18 years) and adults (18 years or older). Because the CPSC11 recommends that children younger than 6 years not use trampolines, we further divided children into 2 subgroups for analyses: children younger than 6 years and 6- to 17-year-olds.
Data were analyzed using EpiInfo software.29 Continuous data were tested for normality using the Kolmogorov-Smirnov test. Bartlett test was used to assess homogeneity of variances. Statistical analyses included 2 analysis, with and without Yates correction, Fisher's exact 2-tailed test, and the Mann-Whitney U test. The level of significance for all statistical tests was = .05. The computation of odds ratio (OR) with an exact 95% confidence interval (CI)30 was also performed.
RESULTS
Sample Description
A total of 137 minitrampoline-related injury cases were reported to the NEISS from 1990 through 2002. These patients ranged in age from 1 to 80 years (mean [SD]: 13.9 [17.7] years). A total of 113 (82.5%) patients were younger than 18 years, and 44 (32%) were younger than 6 years. Females predominated (n = 86 [62.8%]; Fig 1).
A total of 143 full-sized trampoline–related injury cases, randomly selected from all full-sized trampoline–related injury cases, were reported to the NEISS from 1990 through 2002. These patients ranged in age from 2 to 52 years (mean [SD]: 11.0 [8.0] years). Of these patients, 130 (90.9%) were younger than 18 years and 27 (18.9%) were younger than 6 years. Females accounted for slightly more than half of the cases (n = 73 [51.0%]; Fig 1).
There were no statistically significant differences between the minitrampoline and full-sized trampoline groups with respect to gender, age, or number of patients who were younger than 18 years. However, a significantly greater number of children who were younger than 6 years were injured on a minitrampoline (OR: 2.43; 95% CI: 1.33–4.47; P < .01) when compared with 6- to 17-year-olds.
The annual number of minitrampoline-related injuries during the 13-year period ranged from 6 to 18 (mean [SD]: 10.5 [3.8]), with peak numbers in 1991 (n = 16), 1995 (n = 15), and 2000 (n = 18). There was no secular trend in the number of minitrampolinerelated injuries during the study period. For full-sized trampolines, the number of cases was fixed at 11 per year by our sampling method. Overall, there were more injuries for both types of trampolines during the months of April through October, with the mode in May. Although not statistically significant, there was a greater number of minitrampoline-related injuries than full-sized trampoline–related injuries from November through February.
There was no significant difference between the 2 types of trampolines with respect to the location where the injury event occurred. Most (87.0%) minitrampoline-related injuries occurred at home, 6.5% occurred at a place of recreation or sports, 5.4% occurred at school, and the remaining 1.1% occurred on other public property. Likewise, 89.1% of full-sized trampoline–related injuries occurred at home, 4.3% occurred at a place of recreation or sports, 3.3% occurred at school, and the other 3.3% occurred on other public property.
There were 18 cases (17 mini, 1 full-sized) in which patients were not jumping on the trampoline at the time of injury. Deleting these cases from the analyses did not alter the results of the study. Therefore, they were included in all analyses. The mechanisms of injury for these 18 cases were that the trampoline was dropped or fell onto the patient (n = 7), the patient unintentionally fell from another object onto the trampoline (n = 3), the patient was underneath the trampoline and another person jumped onto the trampoline (n = 3), the patient collided with the trampoline (n = 3), the patient was injured while cutting up a minitrampoline with a knife for disposal (n = 1), and another person jumped off the trampoline and landed on the patient (n = 1). Table 1 summarizes characteristics of the study population.
Body Part Injured
The lower extremity (43.8%) was the most common body region injured on minitrampolines, followed by the head (24.8%), upper extremity (18.2%), trunk (10.2%), and neck (2.9%). The lower extremity (42.0%) was also the most common body region injured on full-sized trampolines, followed by the upper extremity (25.2%), head (14.0%), trunk (10.5%), and neck (8.4%).
There was no significant difference between children and adults with respect to body part injured on full-sized trampolines. On minitrampolines, children (younger than 18 years) were more likely to sustain a head injury (OR: 9.39; 95% CI: 1.40–402.47; P = .01), whereas adults (18 years and older) were more likely to sustain a lower extremity injury (OR: 3.11; 95% CI: 1.14–9.14; P = .02; Fig 2).
There was no significant difference in body part injured on full-sized trampolines between children who were younger than 6 years and those who were 6 to 17 years of age. However, on minitrampolines, children who were younger than 6 years were more likely to sustain a head injury (OR: 7.82; 95% CI: 2.94–22.58; P < .01), whereas children who were 6 to 17 years of age were more likely to sustain a lower extremity injury (OR: 3.95; 95% CI: 1.57–10.82; P < .01; Fig 2). Important results are summarized in Tables 2 and 3.
Type of Injury
There was a significant difference between type of injury sustained on minitrampolines compared with full-sized trampolines (P < .01). While performing analyses separately for each type of trampoline, there was no significant difference between children and adults with respect to type of injury (Fig 3); however, children who were younger than 6 years were more likely to sustain a laceration on a minitrampoline when compared with 6- to 17-year-olds (OR: 2.69; 95% CI: 1.04–7.18; P = .04). Children who were 6 to 17 years of age were more likely to sustain a strain or sprain on both minitrampolines (OR: 4.62; 95% CI: 1.40–20.00; P < .01) and full-sized trampolines (OR: 3.38; 95% CI: 1.13–12.34; P = .02) than children who were younger than 6 years (Fig 3). Important results are summarized in Tables 2 and 3.
Most Common Injuries (Body Part and Injury Type Combined)
The most common types of injuries sustained on minitrampolines for children (younger than 18 years) were head lacerations (20.3%) and for adults (18 years and older) were lower extremity strains or sprains (33.3%). Children who were younger than 6 years were most at risk for sustaining a head laceration (OR: 4.98; 95% CI: 1.71–16.03; P < .01), while children who were 6 to 17 years of age were most at risk for sustaining a lower extremity strain or sprain (OR: 6.26; 95% CI: 1.35–59.14; P = .01).
On full-sized trampolines, lower extremity strains or sprains were most common for both children (23.8%) and adults (15.4%). Furthermore, children who were younger than 6 years more frequently sustained lower extremity fractures or dislocations, whereas children who were 6 to 17 years of age were more at risk for lower extremity strains or sprains (OR: 4.85; 95% CI: 1.09–44.93; P = .03). Important results are summarized in Tables 2 and 3.
Mechanism of Injury
the comments in the narrative portion of the NEISS database, we determined that the patient was more likely to be actively using the trampoline at the time of injury when a full-sized trampoline was involved (99.3% [142 of 143]) than when a minitrampoline was involved (87.6% [120 of 137]; OR: 19.97; 95% CI: 3.04–846.49; P < .01). Only 1 (0.7%) patient was not actively using the full-sized trampoline at the time of injury, compared with 17 (12.4%) patients for the minitrampoline.
The majority of injuries were caused by a fall onto or off of the trampoline (48.8% [64 of 131] mini, 48.9% [65 of 133] full-sized). Patients who were using a minitrampoline were more likely to be injured by running into or falling/tripping over the trampoline (17.6% [23 of 131]) than those who were using a full-sized trampoline (3.0% [4 of 133]; OR: 6.82; 95% CI: 2.24–27.98; P < .01). Some of these injuries may have occurred while mounting or dismounting the minitrampoline. Patients who were using a full-sized trampoline were more likely to be injured while jumping on the trampoline or performing a stunt (35.3% [47 of 133]) than those who were using a minitrampoline (20.6% [27 of 131]; OR: 2.10; 95% CI: 1.17–3.82; P = .01). Other mechanisms of injury included colliding with another person on the trampoline and twisting an extremity on the trampoline.
Hospital Admissions
All patients who were injured on a minitrampoline were treated and released from the ED. Seven (5%) of the patients who were injured on a full-sized trampoline were admitted to the hospital. Six of the 7 had fractures; 5 of the 6 fractures were to the upper extremity, and the other was a fracture of the cervical spine. The seventh patient had a concussion. Six of the admitted patients ranged in age from 3 to 13 years, and the seventh was 34 years of age. The 34-year-old sustained the cervical spine fracture. Four of the patients were female, and 3 were male.
DISCUSSION
Minitrampoline-related injuries more commonly resulted in head lacerations among children who were younger than 6 years. Smith13 also found that younger children are more likely to sustain head, neck, and facial injuries, with head lacerations being more common among children who are younger than 6 years. The higher center of gravity of young children may make them more prone to fall head-first, and the immature strength and coordination of their arms leave them less able to protect themselves in a fall, thus resulting in an increased rate of head injury for these children.
Previous studies have demonstrated that most full-sized trampoline–related injuries to children occur on the body of the trampoline, including falls onto the mat, collisions with other trampolinists, and flips or complex maneuvers on the mat.2,10,19 In our study, patients who were using a minitrampoline were significantly more likely to be injured by running into or falling/tripping over the trampoline, whereas patients who were using a full-sized trampoline were significantly more likely to be injured while jumping on the trampoline or performing a stunt. For both types of trampoline, approximately half (49%) of injuries were caused by a fall onto or off of the trampoline.
Use of a trampoline by multiple people simultaneously occurred in 77% of the cases reported by Woodward et al14 and 83% of the cases reported in the CPSC trampoline fact sheet.11 Such group use would be expected to be more common for full-sized trampolines than for minitrampolines, because the larger mat size of a full-sized trampoline allows more room for use by multiple individuals. However, we were unable to compare group use between full-sized and minitrampolines in our study because of incomplete documentation of group use in the free-text comments reported in the NEISS database. Black and Amadeo19 found no correlation between the severity of the injury and the number of jumpers on the trampoline. Injuries associated with group use involved the youngest person of the group in 50% of cases with ages known for all trampolinists.14 In addition to being bumped or bounced off the trampoline by others, a smaller child may be injured by the elastic recoil of the mat generated by a larger person or group of people.14 The force of this recoil can result in fractures of the lower extremity,16 as well as other types of injury.
Extremity injuries, both lower and upper, have been identified as the most common trampoline-related injury in recent years.10,12,13,19,20,31 Other investigators have identified a decrease in the occurrence of fractures and dislocations with increasing age and an increase in soft tissue injuries and lower extremity strains or sprains with increasing age of the trampolinist.13,32 Likewise, in this study, the lower extremity was the most common body region injured for both types of trampoline. Lower extremity strains or sprains were more common for children who were 6 to 17 years of age and for adults. In addition, children who were younger than 6 years more frequently sustained lower extremity fractures or dislocations on full-sized trampolines than older children.
Esposito33 noted a rapid increase in the use of the trampoline as a backyard recreational activity during the past 10 years. Consistent with this observation, most mini- and full-sized trampoline–related injuries occurred at home in our study population. Others have reported similar findings,10–13, 20,31 and a change from what was previously an indoor, school-related, athletic endeavor, to a warm-weather, after school, leisure activity involving younger children at home is apparent.14
Attempts at somersaulting, both backward and forward, are the most dangerous maneuvers on the trampoline3 and have resulted in the largest number of serious injuries,7,9 especially acute injury to the cervical spinal cord.3–6 The majority of known cases of quadriplegia associated with both mini- and full-sized trampolines resulted from improper execution of a somersault.8,34 One cervical spine fracture occurred in our study, but data were unavailable regarding this patient's functional outcome.
Hospital admission rates for trampoline-related injuries reported by other investigators ranged from 1.9% to 23%.10,13,14,20,31,32 In comparison, 5% of full-sized trampoline–related injuries and none of the minitrampoline-related injuries in our study required admission to the hospital. The lack of admissions for minitrampoline-related injuries may be partly attributable to a higher proportion of injury mechanisms with lower kinetic energy involved, such as running into or falling/tripping over the trampoline.
Problems associated with recreational use of trampolines, especially at home and in backyards, are a lack of professional instruction, trained spotters, and supervision; potential degradation of the trampoline from being outdoors and unprotected from the weather; and not properly positioning the trampoline away from other objects, such as trees and fences. In addition, trampoline owners usually do not lock away the trampoline when it is not in use and do not secure minitrampolines to the floor or other stationary structure, as is recommended.9
Smith and Shields20 reported that knowledge of injury risks associated with trampolines was not an effective deterrent to trampoline use; neither could adult supervision be relied on to decrease trampoline-related injuries. They found that 73% of parents indicated that they had been aware of the potential dangers of trampolines before their child was injured, 10% reported that their child had been injured previously on a trampoline, 54.8% of children continued to use a trampoline after the injury event, and adult supervision was present at the time of injury in 56% of cases.
The literature demonstrates that neither close supervision nor advanced skill level precludes trampoline-related morbidity or mortality.14,35 For example, a 15-year-old world-ranked trampolinist died after falling from a trampoline during a gymnastics competition in Tennessee in 2004.36 Smith and Shields20 concluded that the prevention strategies of warning labels, public education, and adult supervision are inadequate to prevent trampoline-related injuries. They recommended that children not use backyard trampolines, and the sale of trampolines for private recreational use should be halted. This is in agreement with the policy position of the AAP. However, these recommendations are based on data regarding injuries that are almost entirely associated with the use of full-sized trampolines in residential backyards. Is the risk for injury similar for minitrampolines, and should these same recommendations be applied to minitrampolines The findings of our study provide a response to these questions. Injury patterns were similar for mini- and full-sized trampolines, although minitrampoline-related injuries were less likely to require admission to the hospital and more commonly resulted in head lacerations among children who were younger than 6 years. Risk for injury could not be determined because of the lack of data regarding duration of exposure to risk. We therefore conclude that the use of full-sized trampolines by children should follow the policy recommendations of the AAP. Trampolines, including minitrampolines, should be regarded as training devices and not as toys. Until more data are available regarding exposure to risk, we recommend against the use of the minitrampoline as a play device by children in the home, which is where most minitrampoline-related injuries occur.
This study has several limitations. NEISS data may not be representative of trampoline-related injuries that are treated in settings outside of EDs or injuries that do not receive medical attention. The incidence of trampoline-related injuries per hour of exposure cannot be determined from our data. Therefore, the risk for injury on minitrampolines versus full-sized trampolines cannot be determined. Although incidence rates are important in clarifying the influence of risk factors and calculating relative risks and ORs, the frequency and the relative proportion of cases provide useful measures for a comparative understanding of these sources of injury. Another limitation of this study was lack of documentation of the circumstances of injury in many cases. The small number of adults in our study precluded statistical analyses for some comparisons. Furthermore, small sample size resulted in a wide 95% CI for some ORs, when comparisons were made between children and adults. Large variability in the data may also have contributed to wide CIs.
FOOTNOTES
Accepted Oct 14, 2004.
No conflict of interest declared.
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