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Are current back protectors suitable to prevent spinal injury in recreational snowboarders?
  1. Kai-Uwe Schmitt1,2,
  2. Bendicht Liechti1,
  3. Frank I Michel3,
  4. Rolf Stämpfli4,
  5. Paul A Brühwiler
  1. 1University and ETH Zürich, Zürich, Switzerland
  2. 2AGU Zürich, Zürich, Switzerland
  3. 3bfu—Swiss Council for Accident Prevention, Berne, Switzerland
  4. 4EMPA Swiss Federal Laboratories for Material Testing and Research, St Gallen, Switzerland
  1. Correspondence to Dr Kai-Uwe Schmitt, Institute for Biomedical Engineering, University and ETH Zürich, Gloriastrasse 35, Zürich 8092, Switzerland; schmitt{at}ethz.ch

Abstract

Objective Back protectors for snowboarders were analysed with respect to their potential to prevent spinal injury.

Design In 20 Swiss skiing resorts, athletes were interviewed on the slope. In addition, an online survey was conducted. The performance of 12 commercially available back protectors was investigated by means of mechanical testing. A currently used drop test according to standard EN1621 (motorcycle protectors), testing energy damping was supplemented by penetration tests according to standard EN1077, which reflects snowsport safety concerns.

Results 6 out of 12 back protectors fulfilled the higher safety level defined in EN1621. Protectors making use of energy-absorbing layers performed particularly well. In contrast, hard shell protectors exhibited a higher potential to withstand the penetration test. The surveys confirmed that approximately 40–50% of snowboarders use a back protector. A large majority of users expect protection from severe spinal injury such as vertebral fractures or spinal cord injury.

Conclusions The currently used test standards are fulfilled by many back protectors. Users, however, expect protectors to be efficient in impact scenarios that result in spinal injury, which are more severe than impacts as addressed in the current standards. This study highlights that there is a mismatch between the capabilities of current back protectors to prevent spinal injury in snowboarding and the expectations users have of these protectors.

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Introduction

Skiing and snowboarding are among the most popular sports in Switzerland, with more than two million participants.1 In particular, the number of snowboarders increased from about 4% of all winter sport athletes in 1990 to 25–30% today. Unfortunately, snow sports also account for a considerable number of sports injuries. Approximately 94 800 injuries are currently registered every year in Switzerland in skiing and snowboarding, that is, approximately 23% of all sports injuries.1 For people between 16 and 65 years, spinal column injuries represent 6% of the total for alpine skiing and 10% for snowboarding. More generally, the proportion of injuries to the spinal column is reported to be between 2% and 10% for these sports.2,,4

Vertebral fractures are the dominating spinal injuries in snow sports reported in the literature including anterior compression fractures (38–80%),2 3 5,,7 burst fractures (43%)8 or transverse process fractures.4 Fifty per cent of the vertebral fractures are observed in the lower thoracic and the upper lumbal spine (Th12–L1).3,,6 9 10 According to Prall et al6 and Wakahara et al,9 approximately 10% of the spinal injuries result in permanent neurological deficits. Other studies in contrast report a lower number of about 4%.7

Data related to less severe injuries of the back are sparse. Machida et al11 report a high number of (thorax) contusions and rib fractures. Swiss data show that snowboarding has a higher prevalence of general back injuries (mostly contusions) than skiing (18.3% vs 10.2%).1 According to the literature, snowboarders at highest risk are males between 20 and 25 years of age,2,,5 8,,11 who sustain 4–5.7 spinal injuries per 100 000 days of snowboarding.2 6 8 9 12

To prevent injuries to the spine and back, various back protectors are commercially available. In Switzerland, these protectors are very popular and are increasingly being used in recent years.1 There are two primary constructions found for such protectors on the market: an outer surface of hard shells, with padding underneath, or one or more layers of padding alone which can, for instance, be a visco-elastic foam. The protectors are typically held to the body with straps, with some models incorporated in clothing or backpacks.

There are currently no testing standards for such back protectors aimed at snow sports. Thus, several manufacturers perform tests according to the European standard EN1621-213 to establish the protective potential of their products. This standard relates to back protectors designed for motorcyclists; it defines the procedures and assessment of laboratory experiments to quantify the damping characteristics of a protector. To the authors' knowledge there are currently no studies that analyse whether the application of this motorcycling standard is also reasonable to assess the performance of protectors intended for snow sports. However, such knowledge—together with information about the biomechanical loading that leads to such injuries in snow sports—is needed to ensure that consumers are reasonably protected.

As a first step, we investigated the performance of a broad sample of commercially available back protectors for snowboarders, employing EN1621-2 combined with a ski helmet penetration standard. In addition, surveys were performed to analyse the expectations and experiences of recreational snowboarders.

Methods

The methods used in this study were twofold: an athlete survey was performed, and in addition experiments were conducted testing the protective potential of commercially available back protectors.

The survey was conducted in two parts. First, skiers and snowboarders were interviewed on the slopes in 20 skiing resorts of the German- and French-speaking parts of Switzerland during the winter season 2008/2009, and second, an online survey was performed.

The face-to-face interviews were performed by trained interviewers as part of an annual survey by the Swiss Council for Accident Prevention. Children younger than 8 years of age and people who did not speak German, French or English were excluded from the study. To ensure a representative sample of skiers and snowboarders, various skiing resorts were chosen according to their size, style of lifts, transport capacity, number of kilometres of ski runs as well as the types of skiers and snowboarders they attract. No skiing regions bordering a foreign country were selected.

Interviews were carried out in the mornings and afternoons on both weekdays and weekends during the most frequented winter sport holiday weeks. Interviewers were set out to get at least 75 skiers and snowboarders at one skiing resort per day to answer the questionnaire. The skiers and snowboarders were approached randomly at the top of runs just after they had got off the lifts. It took interviewers about 15 min to ask the participants all questions of the standardised questionnaire and then record their answers. Participants were asked questions about their protective equipment, on-slope conduct, personality criteria (such as willingness to take a risk or let reason prevail), personal data (such as gender, age, skill level, nationality and activity practised) as well as different control factors such as safety consciousness, number of falls experienced on average per day, previous injuries, the amount of danger subjectively perceived on the slopes, number of days spent skiing or snowboarding on average per season and the amount of experience a skier or snowboarder has. In order to answer the questions concerning on-slope conduct, personality criteria and various control factors, the participants had to mark off a number on a rating scale.

The questions of the online survey were largely similar to those of the on-slope survey. However, a focus was set on back protectors. In contrast to the on-slope survey, questions about other safety gear were omitted. Therefore, more detailed questions related to spine/back injuries, events that resulted in injury and the expectations towards back protectors were added. The online questionnaire was prepared based on the software ‘survey’ (developed by Virginia Polytechnic Institute, Blacksburg, Virginia) and the corresponding link was emailed to students of ETH and University of Zurich.

In the experimental part, 12 back protectors were tested. The samples were chosen among popular products such that all currently available designs were included (table 1). In addition, a simple backpack filled with a jumper was tested. In a first step, the protectors were impacted in a drop test according to the motorcycle standard EN 1621-2 (figure 1). A sample was placed on a defined steel cylinder, which included a sensor to measure the force transmitted through the protector. Then, a mass of 5 kg (a standardised wedge-like shape) was dropped on the sample such that the protector was impacted with an energy of 50 J. The standard requires five tests per sample at different impact points on the protector. In this study, however, only three tests per sample were performed, so that part of the protector was available for other tests. To pass safety level 1, the average of the forces determined in the test is required to be below 18 kN with no individual value exceeding 24 kN. To pass safety level 2, the average force must be below 9 kN with no individual measure exceeding 12 kN. The data for the force sensor (Kistler, Type 9091, sampling rate 100 kHz) were filtered (2 kHz low pass filter) before data processing.

Figure 1

Test set-up according to EN1621-2, comprising an impact mass which drops onto the sample, resulting in an impact energy of 50 J.

Table 1

Results of the drop tests according to EN1621 for the indicated samples and tests and results for the intrusion test according to EN1077

Second, the samples were tested according to EN 107714/EN13087-3.15 These standards describe a penetration test developed for skiing helmets. This test set-up was chosen to mimic the possible exposure of a back protector to sharp obstacles (eg, stones). The standard is based on a drop test in which a falling mass (3 kg) hits a cone (40 mm height, 60° excursion) which is placed on the surface of the protector. The required drop height is 75 cm (class A) and 37.5 cm (class B), respectively. The resulting penetration depth is determined.

Results

A total of 1550 athletes were questioned on the slope, and 1713 persons participated in the online survey. One out of 10 persons approached on the slope declined to participate. The gender distribution of both surveys was comparable. Approximately half of the participants of the on-slope interviews were younger than 30 years of age, while basically all participants of the online survey were that young. This is regarded as a result of distributing the link for the online survey primarily among students. However, as expected and intended, the online survey was thus also addressing more snowboarders (53%) than the on-slope survey (33%). In the following only some aspects with respect to back/spine protection are reported. All other details and evaluations are omitted here. Table 2 compiles the results of the two surveys.

Table 2

Results of the two surveys conducted in this study, showing a high prevalence of back protector use

The interviews on the slope revealed wearing habits with respect to various protectors in snow sports and confirmed a high protector usage rate. Regarding the reasons for wearing a back protector, 67% of the athletes questioned on the slope stated that they expect a protector to prevent injury, 17% wear a protector for a ‘safer feeling,’ and 7% use it because they had experienced a spinal/back injury in the past.

The online survey yielded 748 (44%) users of back protectors; 676 (40%) wore a protector specially designed for snow sports, while 72 (4%) wore a motorcycle protector. In addition, 502 (29%) of all responders stated that they usually wear a backpack when skiing or snowboarding. Importantly, 76% of the responders of the online survey believe that the back protector offers protection against spinal vertebral fractures, injuries to the spinal cord (49%) and contusions (42%), as well as lacerations (42%).

Table 1 summarises the results of the lab tests. The force determined according to EN1621 represents the load exerted on the spine through the protector. As can be seen, the highest safety level in those tests was achieved by protectors of different designs, including the backpack. Furthermore, it can be seen that soft shell protectors generally result in a higher energy absorption and thus a lower force transmitted through the protector.

In the penetration tests, three of the four hard shell protectors were able to withstand the impacting cone, while only one of the five soft designs was capable of doing so.

Discussion/conclusion

The surveys conducted as part of this study clearly indicate that recreational athletes want to protect their spine/back during snow sports. Therefore, back protectors are widely used and also recommended by some researchers (eg, Franz et al4). In particular, snowboarders often wear back protectors with which they hope to prevent severe injury. For Switzerland, this is a very clear trend, with the overall prevalence of back protector use rising from approximately 10% in 2004/20051 to 21% as determined now.

However, to assess the protective potential of current protectors, the only international standard available that refers to testing back protectors was developed for safety gear of motorcyclists. The use of this standard is regarded as the main limitation of this study. Lacking an alternative, the standard is used by many manufacturers of snow sports protectors, although it is questionable whether the requirements of this standard are also applicable to snow sports. The idea behind the standard is to simulate a fall on a curbside or a crash barrier on the road side (hence the use of a wedge-shaped impactor). In snow sports, similar kinds of impact might possibly occur in fun parks where snowboarders can fall on the edge of a half pipe or a ski jump. Nevertheless, the loading conditions in many falls or collisions might differ significantly from those provided by the test. To overcome this limitation, knowledge on the biomechanical loading in such impacts is needed. However, the literature on the mechanisms behind the observed spinal injuries is inconclusive. Several studies identified landing on the upper or lower back after an intentional jump as the most common mechanism.2 3 8 9 11 Donald et al5 report, in addition, that the spine of a snowboarder performing a jump is in flexion and thus loaded axially. For such axial loading of the spine, however, the benefit of a back protector seems to be very minor. Bearing in mind that mainly compression and burst fractures are reported, the preventive potential of a back protector with respect to such injury seems minor since the protector is hardly capable of damping axial loading of the spine.

Apparently, there is a mismatch between the expectations of athletes, the potential offered by the protector and the means to test this potential, that is a performance standard.

Looking at the experimental results, only three configurations failed the motorcycle standard, and half achieved safety level 2. It was found that different designs are capable of dissipating energy in case of a direct impact such that the requirements are met. Protectors using a soft shell approach did perform better with respect to dissipating energy, but also other products (including a backpack filled with a pullover) did pass the test. Hard shell designs, in contrast, offered better protection in the penetration test. From an engineering point of view, it should be possible to meet both standards. The more important question, however, is whether such standards sufficiently consider the demands of snow sports. Besides the biomechanical aspects related to an appropriate loading scenario, practical aspects such as shifting out of place (ie, the coupling of the protector to the athlete), comfort issues or resistance to further types of loading such as hyperextension or torsion might be relevant. Protection of the cervical spine, which is not covered by current back protectors, should be considered, since 6.8% of spinal injuries in snowboarding affect the cervical spine.1

What is already known on this topic

Spinal injuries such as vertebra fractures account for up to 10% of the injuries reported in skiing and snowboarding. As for the underlying injury mechanisms, different types of loading including landing on the back after a jump or axial loading of the spine are described.

What this study adds

By means of mechanical testing, it was illustrated that the protective potential of currently available back protectors does not match the expectations of athletes as determined in two surveys. Thus, a false feeling of safety may be generated in the wearer of a given protector.

In conclusion, we find a mismatch between user expectations and the abilities of current back protectors to prevent spinal injury in snowboarding. In particular, for more severe spinal injuries, the protective potential for recreational athletes is currently questionable. Despite the fact that the recent literature does not show any indications that such protectors might cause harm or represent an additional injury risk, the situation is unsatisfactory. A false feeling of safety may be generated in the wearer of a given protector. To improve the situation, basic research concerning the mechanism of spinal injuries is needed, since the biomechanical understanding of the issues appears to be rather weak to date. It remains debatable whether a special or modified standard for protectors designed for snow sports is needed.

References

Footnotes

  • Funding Each of the institutions involved funded their efforts using general resources.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.