Injuries in terrain/fun parks

We now have enough detailed information on the patterns of injury seen amongst snowboarders using terrain parks (TP) and debate about TP design to justify a separate page on this website.

The history of terrain parks

Deep down inside, most of us like to jump. As kids, we were up for any challenge and "getting air" was a fun way to do so be it on a bike, skateboard whatever. Snow sports are no different. When I first started out on the slopes (don't ask me when) jumps had to be created by forming bumps in the snow but they were quickly destroyed by ski patrollers and we were moved on. Then with the advent of snowboarding, the possibilities became apparent and ski areas began to develop new features specifically to attract participants from this new sport. Freestyle skiing also got in on the act and it wasn't long before areas were competing with each other to create the "best" TP - the bigger, higher, wackier the better. Today, most ski resorts offer a TP facility. These may include rails, boxes, kickers, pipes (quarter or half) and a host of other features. Unfortunately, as the jumps got higher and higher and the participants more and more daring, it was inevitable that injuries would start to occur. Unfortunately, some of these were pretty devastating and even fatal. In some cases, law suits have followed and been successful and in recent times this has prompted a closer look at the issues of TP and jump design as well as studies relating to the injuries seen.

Early studies

The first data looking specifically at accidents occurring in TP was presented at the 2007 ISSS meeting here in Aviemore by the French MdeM organisation. They found that 2.8% of all winter sports accidents in France occurred in a TP. 64.6% of these injuries occur amongst snowboarders - this equates to 7% of all injuries seen from snowboarding.

Looking specifically at snowboarders injured in parks, their key findings comparing snowboarders injured in snow parks to all other injured snowboarders were:

* Snow park injuries were more likely to be severe in nature

- Rates of joint dislocations were higher as were rates of injury to the head, spine and chest

* Snow park injuries were less likely to affect the wrist joint (normally the number one injury

area amongst boarders)

* ACL injuries (a relatively rare injury to snowboarders outside a park) were more frequent in

snow parks

* More boarders injured in snow parks required admission to hospital

Subsequent presentations at the same meeting began the first academic discussions on TP jump design. The rather surprising bottom line was that no design standards existed for snowboard jumps - you just built a ramp that looks about right, and then let the riders get on with it.

I concluded at the time "Just remember for now that when you take off from that jump or ramp that chances are high that the person who built it probably has no idea where you are likely to land or how"

Subsequent studies

Claude Goulet and colleagues from Quebec in Canada then published data on the injuries seen from terrain park use in ski areas in Quebec between 2001 and 2005. They also found that snowboarders (and skiers) who were injured in terrain parks tended to sustain more serious injuries and were more likely to require an ambulance. They found higher rates of head and neck injuries amongst skiers and more truncal injuries amongst snowboarders. In 2009, a paper by Greve and colleagues published in Wilderness and Environmental Medicine demonstrated significantly more head injuries occuring in terrain parks, even after controlling for helmet use.

Craig Moffat et al reported on patients >12 years of age who presented to a regional trauma center in Salt Lake City, USA with an acute injury sustained at a winter resort. 72 patients were injured in a terrain park, and 263 patients were injured on nonterrain park slopes. Patients injured in terrain parks were more likely to be male [68/72 (94%) vs. 176/263 (67%), p<0.0001], younger in age [23 ± 7 vs. 36 ± 17, p<0.0001], live locally [47/72 (65%) vs. 124/263 (47%), p=0.006], use a snowboard [50/72 (69%) vs. 91/263 (35%), p<0.0001], hold a season pass [46/66 (70%) vs. 98/253 (39%), p<0.0001], and sustain an upper extremity injury [29/72 (40%) vs. 52/263 (20%), p<0.001] when compared to patients injured on non-terrain park slopes. There were no differences between the groups in terms of EMS transport to hospital, helmet use, admission rate, hospital length of stay, and patients requiring specialty consultation in the ED.

Alison Brooks from the US presented data at the World Congress on Sports Injury Prevention in Tromso, Norway (2008) from the terrain parks at two western US ski areas between 2000 and 2005. The overall rate of injury from both ski areas was 2.1 IPTSD (Explain what this means) but they were unable to calculate a specific injury rate for terrain parks as they did not have accurate data on the numbers of boarders using the parks. However, 27% of the injuries at these areas occurred in a terrain park setting. You can immediately see that this is far higher than the figure from France and I suspect that it must reflect the fact that American resorts tend to have much larger terrain park areas than France and probably a higher % of snowboarders on the slopes (although this data was not available for comparison). Of course, more snowboarders on more terrain park area will ultimately result in more injuries in total. Of those injured in a terrain park in this study, 83% were snowboarders, 82% were male and 78% were under the age of 25 years. This compares to 54%, 53% and 52% respectively amongst the other people injured elsewhere at the ski areas. Of those injured in a terrain park, more reported themselves to be experts (92% vs 56%), more owned their own gear (84% vs 58%) and more wore a helmet (27% vs 20%) compared to those injured elsewhere.

The commonest mechanism of injury in a terrain park was a fall from a significant height. Compared to those injured on the slopes, individuals injured in a terrain park were more likely to sustain head/face, back and neck injuries and interestingly less likely to sustain upper limb injuries (which as you know by now are usually far and away the commonest injury amongst snowboarders). Both fractures and concussions were commoner injury types in terrain parks compared to the slopes in general and those injured in a terrain park were 23% more likely to need transportation to hospital.

Injury data from ISSS 2011

The 2011 ISSS meeting had a big focus on TPs - both the injury patterns seen and the design of the features. Lets deal with the injury data first.

Kelly Russell from Calgary University in Canada reported on a case series of TP injuries that occured at one Alberta ski resort over two seasons (2008/09 and 2009/10). 379 injuries were reported giving an overall injury rate of 0.75 injuries per 1000 runs. This equates to one injury for every 1,333 runs attempted. Injury rates were highest on jumps and half pipes (both 2.56 injuries/1000 runs) and kickers (0.61 injuries/1000 runs). On aerial features the commonest areas to be injured were the head/neck/face (26.5% of all injuries), the wrist (18.5%) and the shoulder (11.5%). 36.2% of all injuries from aerial features were fractures. They highlighted the ongoing challenge of reducing injury risk in TPs as much as possible whilst still maintaining their appeal to thrill seekers.

Other studies came from the French Alps, Norway and Utah, USA. Whilst not being able to calculate an injury rate for TP, the French (MdeM) study looked at 386 TP injuries and concluded that TP injuries tended to be more severe and required more transfers to hospital. Interestingly, they also reported more injuries from collisions occuring in TPs than on the slopes (10% vs 7.8% for snowboarders and 21% vs 14.6% for skiers). The ongoing Norwegian study reported that of those injured in TP, 5% were beginners, 15% intermediates, 26% advanced and 45% experts. The study from Utah focused on the injuries presenting to a ski clinic during the 2007/08 and 2008/09 seasons. 561 TP injuries were recorded. The % of all injuries occuring in a TP increased between the two seasons from 20.7% to 23.6%. 36.5% of TP injuries occured in those under 17 years of age ( referred to as the "skeletally immature" group) whilst 47.6% of injuries occured in the 17-24 yr old group (labelled the "cognitively immature" group). The percentage of head and spine injuries amongst TP users was double that of non TP users. Jumps were the commonest feature to cause injury.

Not everyone believes that TPs are all doom and gloom though! Jake Shealy from the Sugarbush research group referred to on multiple pages of this website pointed out in his presentation on TP that whilst over the last 20 years we have gone from no jumping taking place to a situation where almost 100% of ski areas offer jumping, the fatality and serious injury rates (in the US at least) have not altered. He argues that it is not so much the jump per se that is the problem, but what the jumper themselves gets up to. In particular, it is landing inverted that can be associated with catastrophic injuries such as high spinal damage.

Injury mechanisms

Whilst we are now in a better position to be able to describe the injury patterns seen in terrain parks, rather less is known about the exact mechanisms and specific risk factors associated with terrain park injuries. Certainly landing inverted (onto the head/neck) and impact from a height are both likely to be factors in many catastrophic injuries.

Terrain park design and its potential influence on injuries

I have already mentioned there are currently no set standards for TP jump design. There is one school of thought (which the NSAA amongst others currently subscribes to) that says there are so many uncontrollable variables involved in the process of jumping that it is nigh on impossible to incorporate and allow for all of these in jump design. Examples of such variables include snow state, snow coefficient, aerodynamic drag and the jumper "pop". This is the extra movement the jumper makes round the time of lift off.

The other view point (not surprisingly) is that it is possible to design jumps to be "safer". Many of those who subscribe to this view are members of the US Terrain Park Council, including Professors Mont Hubbard and James McNeil, both of whom presented at ISSS 2011. They point to the ability of nordic ski jumpers to fly over 100m and yet land safely.

It all boils down to a concept known as the "effective fall height" (EFH). Nordic jumpers have an EFH of around 0.6m. Mont Hubbard in his presentation argues that given a take off angle and an arbitrary landing shape, it should be possible to calculate the EFH at every point on the landing surface and design jumps accordingly. Furthermore, Mont believes that each of the "uncontrollable variables" mentioned above is either irrelevant or has a bounded (and relatively small) upper limit.

Professor James McNeil from Colorado gave two presentations on specific issues relating to TP jumps. The first focussed on rider pops and drops and the second looked at the influence of jump take off design.

The value of dynamic analysis of TP jumps has been questioned to due to many factors, one being the variability that the rider introduces to the initiation of the jump through "popping" or "dropping". Popping involves the rider trying to augment the jump by springing upwards in some form at or around the time of take off. Dropping, as the name implies, is the opposite, where the rider tries to suppress the jump. James McNeil presented a study attempting to model these phenomena. He found that the horizontal distance travelled is weakly sensitive to the amount of pop, but the landing impact as measured in height equivalent can vary dramatically from 0.94m to 3.59m for a flat landing. The effect on landing impact is far less pronounced when the landing is parabolic.

Calculating a Effective Fall Height.....hhhmmmmm

His second presentation concerned the use of curved take offs to assist the performance of inverted manouevres. The concern is that whilst curved take offs are needed by professional riders, the use of smaller curved take offs (sometimes called "wu-tang") might pose a significant risk to the less experienced rider and result in them landing involuntarily inverted. I won't go into the maths involved in this (WAY beyond my tiny brain) but the upshot is that a small curved take off as found on many small features is sufficient to induce a large inverting angle. He concludes that curved take offs should be avoided on jumps accessible to the general (non professional) public.

A final sobering point leading on from this came in a presentation from Darrin Richards et al. They simulated a head first fall onto snow and then examined the forces applied to the neck both with and without a helmet. The results showed that helmets provided good head protection, reducing head accelerations by approx 45% but they had very little effect on neck compression loads. These compression loads were all well above the level associated with cervical spine fracture even though the EFHs used were in fact quite small. Their conclusions were that the neck is very susceptible to injury even at low drop heights (EFH of 0.78m). So, even if jumps can be made "safer" by reducing EFH to less than one metre, if you land inverted (i.e. on your head) then there remains a risk of catastrophic spinal injury.

So there you have it - the challenge of designing TP jumps that are safer or better controlled whilst still maintaining the thrill that terrain parks and their users need bearing in mind that (at least in theory) catastrophic cervical spine injury does not require a big fall or a lot of force applied to the neck.

In conclusion

Terrain parks offer exciting challenges to snow sports enthusiasts but should be treated with respect. Althought the absolute risk of an injury is relatively low, the potential for a serious or catastrophic injury is there. The key message is not to stray too far from the limits of your ability and AVOID LANDING INVERTED.

References

Goulet, C et al. Risk factors associated with serious ski patrol-reported injuries sustained by skiers and snowboarders in snow-parks and on other slopes. Canadian Journal of Public Health (2007) 98(5): 402-206
Greve, MW at al. Skiing and snowboarding head injuries in 2 areas of the United States. Wilderness and Environmental Medicine. (2009). 20(3): 234-238
Moffat, C et al. Terrain park injuries. West J Emerg Medicine (2009). 10(4): 257-262.
Brooks, MA et al. Evaluation of skiing and snowboarding injuries sustained in terrain parks versus traditional slopes. Injury Prevention (2010) 16(2): 119-122