Latest research news from ISSS 2011 conference
The 2011 meeting of the International Society for Skiing Safety was held in Keystone, Colorado from May 1st - 6th 2011. As with previous ISSS meetings, researchers from ski areas worldwide came together to share knowledge and the latest research findings in the area of alpine sports injuries. Hot topics in recent years have included issues around terrain parks, helmet and wrist guard use and the biomechanics of snow sports equipment.
This page will attempt to present a summary of the main research presentations from this conference. I am also trying to integrate this new information into existing pages on this website so please bear with me. I will not be commenting on every paper from the conference but concentrating on those that present findings of interest to a general audience and trying to reach a consensus on each topic. I apologise if I offend any colleagues I don't mention who presented papers, this is in no way a reflection of the importance of your work. I have grouped the information together under specific topic sub-headings. As ever, please understand that this is my interpretation of the research presented - sometimes it can be difficult to decide what to think when even respected experts cannot agree. So if there is something here you do not agree with, please feel free to email me using the contact page.
Overall injury rates
The first thing to say about the latest epidemiology reports on snow sports injuries is confirmation of a message that I repeat frequently on this website – that is to say the overall risk of an injury from particiaptign in snow sports is pretty small – for every 1000 people spending a day on the slopes, only 2 on average will sustain an injury that requires ski patrol and/or medical attention. Looked at another way, one injury occurs approximately every 500 days spent skiing or snowboarding. The absolute figures do vary from country to country and from study to study as you might expect but these are ball park figures.
What’s more, there is a general consensus that the risk of injury is stable and in fact in many countries shows a slight decline. This is an important finding as the media likes to try and portray the opposite message – i.e. that snow sports are in fact getting “more dangerous”
Before you read any further, if you don’t understand the terms “Mean Days Between Injury” or “Injuries per 1000 skier days” (IPTSD) then I would suggest you quickly visit this page for an explanation so that the rest of what I am about to say makes sense!
Trends in snow sports injuries
Two separate studies reported on the trends seen in snow sports injuries over time.
The first came from the Sugarbush group from Vermont, USA and looked primarily at alpine ski injuries over time. This group have been studying the injury patterns at the Sugarbush ski area since 1972 and presented data relating to 38 seasons of alpine ski injury data. Their dataset, whilst not the biggest in terms of total numbers, is the longest continuous epidemiological study into the snow sports world anywhere in the world and the group are respected for the amount of work they have done over the years. The dataset used 20,015 injuries in 18,403 skiers. During this time, approx 7.5 million skier visits were recorded. Overall, the injury rate for the study over time declined by about 55% to its current level of under 1.9 IPTSD (which equates to 525 MDBI). Lower leg injuries improved the most with an 83% reduction noted. However, the improvement in lower leg injuries came mainly in the first 17 years of the study and for the last 21 seasons there has been no statistically significant improvement in this group. The incidence of severe knee sprains (ACL injuries primarily) more than tripled up to the 1990's and then plateued. In recent years, there has been a improvement in the ACL injury rate with a decline of about 30%. These observations can all be related to changing factors on the slopes such as improvements in equipment (releaseable binding in particular) and the advent of stiffer ski boots and more latterly shorter tailed carving skis.
The other trends study came from the French Medicins de Montagne (MdeM) organisation. They reported on trends in a few specific injuries in alpine skiing and snowboarding between 1999 and 2010. The French database is absolutely huge (as far as I am aware by far the largest database in the world on snow sports injuries). This particular piece of work involved 50 doctors in 37 ski resorts and included 419,809 injured people along with 21,108 uninjured controls.
Amongst alpine skiers, the incidence of ACL injuries remained relatively stable during this period – the MDBI was 3076 in 1999 and 2597 in 2010. MCL injury incidence was also stable (1781 in 1999 and 2241 in 2010). In contrast, the incidence of lower leg fractures increased from 13645 MDBI in 1999 to 9804 in 2010.
Amongst snowboarders, the incidence of the number one injury - wrist fractures - was 1454 MDBI in 1999 and 2068 MDBI in 2010 (no significant change). Knee injuries amongst snowboarders are reducing for both ACL and MCL injuries.
Finally, MdeM reported that for the first time in 2009, the risk of injury from snowboarding was less than that of alpine skiing. Every other previous injury study I have ever been aware of has consistently reported snowboarding to have the highest injury rate of all the snow sports, making this is a very interesting finding. The graph below shows the injury rates for France from 1998 to 2009. Remember that the higher the MDBI figure is, the LOWER the risk of injury.
One of the possible reasons for this observation is that there has been a decrease in the % of snowboarders who are beginners in France, and we know that this group is the most likely of anyone on the slopes to be injured. There has also been a corresponding rise in the number of alpine skiers (using twin tip skis especially) who have been pushing their limits ever harder leading to a rise in the alpine ski injury risk.
Injuries to children from alpine skiing
I presented data from Scotland specifically focussing on the patterns of injury seen amongst children (defined as those aged 16 years and under) from alpine skiing. This followed on from a previous presentation on this subject given at the 2005 meeting in Japan.
Data was available for 1959 children (1318 cases and 641 controls) and for 2034 injured adults. The injury rates amongst children and adults were 4.95 and 1.55 injuries per 1000 skier days respectively. Children using rental gear, non-carving skis and with less than one week’s total experience were more likely to be injured. Almost one in eight injured children had taken no formal instruction compared to 7.5% of the control population. Three times as many injured children had sustained a previous snow sports related injury compared to their uninjured peers. Helmet use was more common amongst the control population.
Compared to injured adult skiers, children were more likely to be injured as a consequence of a collision or using a ski lift and were more likely to sustain injury to the lower limb. Head injuries and joint disrupting injuries were less common amongst children.
We now plan to develop a specific injury prevention programme for children for Scotland hopefully in time for the 2011/12 season and will continue to monitor the injuries occuring in this very important subgroup.
Cross country (XC) skiing injuries
Up til now, very little has been known about the risks of injury from recreational cross country (nordic) skiing. Jan Rokyta presented a study from the Czech Republic reporting on 2295 XC skiing injuries occuring between 2003 and 2010. The overall injury rate was 0.1/1000 XC skiing days compared to 1.0/1000 for alpine skiing. Males and females were injured in equal proportions although injured males tended to be slightly older (average age 42.5 yrs compared to 35.5yrs). The lower extremity was the commonest area of injury and falls accounted for about 85% of all injuries. About 8% of events were due to skier exhaustion and fractures made up about 25% of all injuries.
There was a big focus at the meeting on the issue of terrain parks (TP). The presentations largely focussed on two areas - the injuries occuring in TP and the design of TP jumps.
Injuries in TPs
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.
This brings me on to the second main focus of presentations at the conference - the design of TP jumps. At present, there remain no set standards for the design of TP jumps. 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.
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.
I will be incorporating this latest information into a new page specifically relating to terrain park injuries in the near future.
Risk of serious injury
A few interesting studies focussed on helmets. Helmet sales in the US topped 1.3m in 2009/10. To date research has shown that helmets are effective at protecting against the majority of mild/moderate head injuries but hard evidence has been lacking that helmets can protect against more serious injuries such as skull fractures.
Jake Shealy from Vermont presented data from their ongoing epidemiological study that specifically focussed on this question.They defined potentially serious head injury (PSHI) as concussion, skull fracture, epidural/subdural bleed, neurological deficit or death from head injury. They found that from the 1995/6 season to the 2009/10 season, helmet use increased from 5 to 76%. Their findings were that head injuries as a % of all injuries has decreased by 20% over the time frame of the study. The incidence of PSHI (expressed as MDBI) has improved by 64% over the 15 year course of the study (from 8775 days to 24,690 days) as the rate of helmet use has increased from ~5% to ~80% (p<0.01).
Effectiveness of rental helmets
Irving Scher presented a study looking at issues relating to rental helmets. Obvious issues include rental facilities having enough helmets in appropriate sizes and that are clean. A hidden issue is the potential for helmets to be used and abused by the people who rent them and the effect this could have on the protective effect a helmet can offer. Perhaps, if a helmet is dropped or knocked repeatedly, this could reduce the effectiveness of the helmet. The situation could of course be worse if the helmet was involved in an impact on the slopes but the user does not report it to the rental store. Its not an issue if the damage is obvious to the naked eye, but this may not be the case.
So, Scher et al took 6 helmets that met current standards. Half of them were subjected to "pre-conditioning". They were dropped 30 times onto asphalt from a height of 1m. They then tested the helmets to ASTM F1446. The results showed that there was no significant difference between the preconditioned and new helmets despite the preconditioned group having visible evidence of minor damage. Based on these results, they concluded that wear and tear may not significantly reduce the effectiveness of rental helmets.
Wrist guards for snowboarders
Wrist injuries remain the number one risk for snowboarders, especially beginner snowboarders for whom the MDBI is just 100 days, the highest risk of injury for any sub group on the slopes. Many of the presentations at ISSS 2011 confirmed this ongoing risk and several focussed on the specific issue of wrist guards (WG) and the protection they may offer. Wrist guard use stil remains relatively low amongst the snowboarding population. A study from Australia for example found that whilst 44% of boarders wore a helmet, only 18% wore WG. Using methodology based on an earlier study that I have reported on they found that "don't see the need" and "uncomfortable to wear" were the main reasons given for not using WG. Thankfully, the percentage who believed that WG might actually cause injury was quite low at just 7%.
A study from the bfu in Switzerland interviewed 3827 snowboarders over 6 winter seasons. They found that the rate of WG use rose from 37% in 2002/03 to 42% in 2006/07 and then declined to 27% in 2009/10. The bfu did put alot of resources into promoting WG use initially which probably lead to the high useage rate which now seems to have dropped back after this campaign finished. This highlights one of the many problems safety campaigners face, you must keep the issues in the limelight continually otherwise it drops off people's radars! The study also found that men were more likely to wear guards than women, children wore them more than adults and advanced snowboarders have higher useage rates than beginners (who really are the main target group).
Rick Greenwald from Simbex and co-workers (including the bfu) used an instrumented glove to measure the degrees of wrist flexion and extension occuring in typical snowboarding falls along with the forces applied to the wrist and hand. A total of 128 impact events were recorded and analysed with no injuries recorded. Average maximum wrist extension for the group overall was 80.2 degrees (+/- 15.8). Backwards falls resulted in significantly higher maximum forces than forward falls.
The goal now is to move forwards with the development of an international standard for snowboarding wrist guards, just like there is currently for inline skating WG. Work presented at ISSS 2011 by Frank Michel (again from the bfu) showed that testing snowboard WG according to EN14120 (the standard for inline skating WG) revealed huge variation in WG performance. I've not been alone in arguing that the development and introduction of such a standard will be a huge help for snowboarders currently confused by the array of different guards available on the market.
Mechatronic ski bindings
Jean Francois Merino from Salomon gave two fascinating presentations on the use of an instrumented binding plate placed between ski and ski binding to measure the loads applied to a ski binding during alpine skiing. The measurements were taken over 6 years and included 8307 ski runs capturing normal skiing technique as well as situations where falls and accidents occured. All events were also videoed for analysis. 147 such incidents were available for analysis and these were classified by an expert panel as either being a situation where one would expect the binding to release or one where the release was inadvertent. These analyses potentially offer the chance to develop new algorithms for binding function so that a new mechatronic binding system can be developed with improved release-retention binding characteristics that ultimately result in a lower incidence of lower leg equipment related injuries. Fascinating stuff - watch this space!
Ski speeds in slow zones
An interesting joint presentation from Tracey Dickson (Australia) and Anne Terwiel (Canada) eaxmined the issue of skier speeds in slow zones. Previous radar work has shown that skiers frequently travel at faster speeds than they perceive. This may make it difficult for a skier to ski slowly when they're not sure what "slow" is. This study used GP modules to assess how far and how fast different skiers travelled and then compared what they felt were safe speeds with the speeds they actually travelled at. It is important to note that the participants were not told that the sensor would monitor their speed so they did not go chasing high speeds as a result. 124 sessions were logged, 61% of participants were male, their ages ranged from 9-80 yrs and 70% reported being advanced skiers. On average skiers travelled 8.9 km per hour. Whilst skiers estimated their maximum speed to be a mean of 50.3 km/hr (approx 30 mph) in fact the GPS data showed that they travelled significantly faster than this with a mean max speed of 62.0 km/hr (37 mph). The fastest mean speed recorded was 108 km/h (or 66 mph). Interestingly, those wearing helmets travelled faster than those who did not. Maximum ski speeds were more likely on intermediate (green/blue) runs rather than blacks.
Skiers were further asked to state what speeds they thought should be recommended in slow zones. A couple of examples - firstly a 39 yr old male skier thought that 30 km/hr was a sensible speed for slow zones but was in fact recorded himself travelling at 83.3 km/hr in a slow zone! Similarly, a 45 yr old female skier thought that 20 km/hr was safe but was recorded at 70.2 km/hr in a slow zone. The huges differences between perceived safe speeds and actual speeds makes it unlikely that either skier "thought" they were travelling slowly but serves to illustrate the fact that we don't always practice what we preach!
That's all for now from ISSS 2011. I will integrate this information into existing (and some new) pages on this website over the coming months so please check back and see. The next ISSS meeting will be in Bariloche, Argentina in August 2013. More details will be posted on this website in due course.
Aviemore, May 2011