Manon Pigeolet. Trampoline Injuries. HPHR. 2021;36.
The first version of the trampoline was invented by Eskimo groups in the Pacific Northwest, to help them search for game. The person launched into the air by this device could inspect a much larger area of land or ice for game than what would be possible from the ground. The recreational trampoline as we know it today was only invented in the 1930s. Four formulas are needed to understand the physics of trampolines. A person with a larger mass will as such extend the springs of the trampoline more and increase the total energy at play. However, because of that larger mass, gravity will pull this person down more compared to a person weighing less. There are several known and described mechanisms of injury for trampoline injuries, but one mechanism seems to be recurring over and over again: the failed flip or somersault. The failed flip usually leads to an impact on the cervical spine because the head reaches the trampoline first. In 1998, 6500 pediatric cervical spine injuries were reported in the United States, of which 0.5% ended in death or permanent neurological damage. The American Academy of Pediatrics (AAP) issued their first policy paper in 1977 warning for the dangers of recreational use of trampolines and its use during physical education classes. The initial policy paper came to be, after striking numbers surfacing of cervical spine injuries, quadriplegia and even death due to trampolines. Despite the success of the AAP-policy statement in 1977 to completely ban the use of trampolines, new bans are not on the radar of clinicians and public health specialists. The preferred approach for most countries in the new millennium seems to be regulation.
The trampoline initially wasn’t invented to amuse children. The first version of the trampoline was invented by Eskimo groups in the Pacific Northwest, to help them search for game. The person launched into the air by this device could inspect a much larger area of land or ice for game than what would be possible from the ground1. The modern version of the trampoline was however, only invented in more recent history. George Nissen, a high school gymnast living in 1930’s Iowa, developed the device to help him train for gymnastics competitions. He came up with the idea after seeing acrobats rebounding on a net in the circus and initially called the device a “rebound tumbler”2. After bringing his “rebound tumbler” to a YMCA summer camp in 1933 and seeing the joy it brought to children he decided to commercialize his device under the name “trampoline”3. The recreational trampoline as we know it today was born.
But how does a trampoline actually work? It all boils back to kinetic and potential energy and Newton’s law of motion. Four formulas are needed to understand the physics of trampolines. The kinetic energy (KE) is the energy produced by the person himself when he jumps on the trampoline. The potential energy (PE) in this particular case is the energy stored in the springs of the trampoline. The total energy of the person jumping is the sum of his kinetic energy and the potential energy in the springs (E = KE + PE). Another way to describe PE is through the following formulas: PE = mgh and PE = (1/2)kx^2 with m being the mass of the jumping person, g the gravity acting upon the jumping person, h the height from the ground, k the spring constant and x the length of stretching of the springs. The 4th, and final formula is Newton’s second law of motion: F = ma with F being the force of gravity. A person with a larger mass will as such extend the springs of the trampoline more and increase the total energy at play. However, because of that larger mass, gravity will pull this person down more compared to a person weighing less. Put otherwise, children will despite their lower weights and potential energy, be able to jump higher because their smaller mass is pulled down less by gravity4.
The physics above explain perfectly why games including a larger child or adults jumping together with a child on a trampoline are so much fun (and so dangerous). The combination of the extra potential energy of a larger person and the lower mass of a smaller person/child jumping together on a trampoline creates a very dangerous situation where the child will be catapulted very high into the air with a high risk of injuries if they land in a wrong position or potentially besides from the trampoline.
In 2014, an estimated 104,691 patients with trampoline related injuries presented themselves at emergency rooms across the United States according to the United States Consumer Products Safety Commission’s (CPSC) National Electronic Injury Surveillance System (NEISS).5 NEISS is an injury surveillance system that is statistically representative for the entire American population. NEISS collaborates with emergency departments across the country who collect data on injuries related to using certain consumer protducts. This representative sample of injury data is then used to calculate an estimate for the entire US.6 The number of trampoline injuries had gone up in 2014 from “only” 38,800 and 66,200 reported injuries in 1991 and 1995 respectively7. In 1998, 6500 pediatric cervical spine injuries were reported in the United States, of which 0.5% ended in death or permanent neurological damage. This means that in 1998, 325 children died or remained permanently disabled because of trampolines. Between 2000 and 2009 the CPSC received 22 reports of children dying due to trampoline use.5
More recent data from France, South Korea and the United States seem to confirm the trends of the 1990’s, the burden of trampoline injuries keeps increasing. In France, trampoline injuries in children were 9.7 times more common in 2017 compared to 2008 and the need for surgical treatment was twice as common in trampoline injuries compared to other sports injuries in the same age range8. South Korea showed a very similar image with a rapid increase in injuries between 2008 and 2017. 87.5% of the recorded trampoline injuries over this time period happened between 2013 and 20179. The United States on the other hand shows a different image. Disaggregated data on the type of trampoline used shows that injuries related to home use of trampolines decreased between 2004 and 2017, while injuries sustained on recreational sports-facility trampolines increased. Even with decreasing numbers of home trampoline-based injuries, the United States still saw over 1,3 million visits to the emergency department for trampoline-related injuries between 1998 and 201710.
The earlier described cervical spine Injuries, may be the most dramatic trampoline injuries, it is luckily not one of the most commonly sustained ones. About 36-52% of the trampoline injuries for which care is sought, are soft tissue lesions like sprains or ligament ruptures, about one third constitutes of fractures and about 10% are lacerations. Injuries to the extremities are the most common (about 75%) with the lower extremity being injured more often than the upper extremity. This list is concluded with head, trunk and finally neck injuries as the least common type11–13. For the United States this roughly equates to about 30,000 fractures per year due to trampoline injuries. See figure 1 for a complete breakdown of the different types of injuries and their relative prevalence.
Figure 1: Prevalence of fractures by body region
A, Overall distribution. B, Upper extremity. C, Lower extremity. D, Spine. E, Skull/face and rib/sternum, reproduced from Loder at al. 13.
There are several known and described mechanisms of injury for trampoline injuries, but one mechanism seems to be recurring over and over again: the failed flip or somersault1,12. The failed flip usually leads to an impact on the cervical spine because the head reaches the trampoline first. This leads to either an hyperextension or a hyperflexion trauma of the neck (figure 2)1. Other well-described mechanisms of injury are a fall directly on the mat, a collision with another jumper, a collision with the frame of the trampoline or a fall from the trampoline itself12,14. Additionally, several studies have shown that jumping with several people/children together increases the risk for any type of injuries with almost a factor 4, while the smallest child in the jumping crowd has a 14-fold increased risk of sustaining an injury14.
Figure 2: The mechanisms of cervical spine injuries, reproduced from Brown et al. 1
About 90% of injuries still happen at home1,10,13, and up to 95% of all injuries are -not surprisingly–- sustained by children (figure 3)7,12,13. Reports on the rate of supervision at time of injury range from 22% in a Norwegian study12, to 77% in an American study11. This very large difference in adult supervision rates can potentially be traced back to a difference in culture between Scandinavia and the US in how parents interact with their children and from which age onwards children are left to play by themselves. Either way, the numbers show that supervision alone will not be enough to stop the horrendous effects of trampoline use on our children.
Figure 3: Age distribution of trampoline injuries, reproduced from Loder at al. 13
For a few decades the joys and pains of trampolines were experienced freely across the United States, but then the need for regulating policies became too apparent to be ignored any longer. The American Academy of Pediatrics (AAP) issued their first policy paper in 1977 warning for the dangers of recreational use of trampolines and its use during physical education classes14. The initial policy paper came to be, after striking numbers surfacing of cervical spine injuries, quadriplegia and even death due to trampolines. No less than 59 people got a cervical spine injury resulting in quadriplegia during the 1970’s in the United States15. The AAP revised their statement again in 1981, but after that everything quieted down around trampolines until the 1990’s with a final revision of the policy in 201214. The American Association of Orthopaedic Surgery finally followed suit in 2005 and released their own policy statement speaking out against trampoline use16. In 2013, the AAP released a guidance for parents, urging to never get a mini trampoline for private use at home, but also taking the pragmatic route offering guidance on how to properly supervise your children if parents do decide to buy a mini-trampoline for the home setting.17
Public health policy can have a large and important impact on behavior and practices in society. After the publication of the first policy statement on trampoline injuries by the AAP where they advocate for a ban on trampoline use during gym classes in schools, almost all schools banned trampolines. Most likely, this ban was in part also because many insurance companies pulled out on covering schools that were still using trampolines during gym classes. But whatever the reason, the effect of the policy was clearly visible in society. Unfortunately, when the AAP loosened their position in a revised statement in 1981, trampoline made a hasty reintroduction to gym classes around the United States15. Several studies published in the new millennium emphasize the need for increased regulation and enhanced safety measures when it comes to trampoline use. Despite the success of the AAP-policy statement in 1977 to completely ban the use of trampolines, new bans are not on the radar of clinicians and public health specialists. The preferred approach for most countries in the new millennium seems to be regulation9–13.
Even though trampolines have been around for decades, we’ve reached the point where trampolines have become a true public health threat over the past few decades. Currently implemented safety regulations are not enough in protecting children and the population at large, however we can also assume that completely removing trampolines from the private and the public space will no longer be possible, or even desirable. A pragmatic approach where trampolines are used in supervised situations and for gymnastics’ use only, like the current policy of the AAP, is the most realistic and constructive way forward.
Most current and previous policies have used a primary prevention approach, calling for an overall ban on trampolines or in certain situations. This approach has proven unsuccessful given the continuing popularity of trampolines and increase of injuries over the past decades. A shift towards secondary prevention where we accept the presence of trampolines among us, while improving the quality of trampolines and addressing the major unsafe features in their construction, can become an option as well. Therefore, collaboration between clinicians, policy makers, public health specialists, schools, engineers, toy developers and market specialists, and United States Consumer Products Safety Commission will be necessary to develop new and bold regulations, policies and trampolines of improved quality and safety to alleviate the current burden of disease due to trampoline injuries.
The author(s) have no relevant financial disclosures or conflicts of interest.
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Manon Pigeolet, MD, MSc, MPH holds a research fellowship position with the Program in Global Surgery and Social Change at Harvard Medical School, while pursuing her residency in orthopedic surgery at the University of Antwerp in Belgium. She obtained her Master in Public Health with a concentration in mother and child health (MCH) at Harvard T.H. Chan School of Public Health in 2022. She has prior experience working in the Democratic Republic of Congo, Togo and Uganda where she was involved in research, clinical work and student-run public health initiatives. Her main interests lay in the management and outcome of pediatric orthopedic care provision in low- and middle-income countries. She is currently involved in studies in Pakistan, Bangladesh and Egypt. In collaboration with several Zambian and South African partners, she has been working on the development of a department-level pandemic preparedness evaluation tool for surgical departments in Southern Africa.