E-letter: Are there risk factors in alpine skiing?

This E-letter is in response to Are there risk factors in alpine skiing? A controlled multicentre survey of 1278 skiers. Abstract | Full article

We read with interest the article from Hasler et al. (2009) “Are there risk factors in alpine skiing? A controlled multicentre survey of 1278 skiers”.

In general, the answer is: ‘yes, there are internal (e.g. gender, age, fitness, skill level, risk taking) and external (equipment, environment) risk factors’ according to comprehensive model for injury causation by Bahr and Krosshaug (1). However, we would like to comment on the presented data and methods used because some results seem contrary to other studies in this research field.

Firstly, Hasler et al. reported that skiers with new equipment have a higher risk of being injured. However, there seems a mistake in the presented data because in the abstract the Odds Ratio (OR) was 59 with a 95% confidence interval of 0.37-0.93 while in Table 1 the OR was 0.59. If the OR of 0.59 was correct, new equipment would decrease injury risk. In addition, what means new equipment? Did the authors compare carving skiers with traditional skiers as done by Burtscher et al. (2) showing a reduced injury rate since the introduction of carving ski? Where is the cut off between new and old equipment? In the discussion section, Hasler et al. stated that the results might be explained by a mismatch between the abilities of the skier and the equipment. Unfortunately, they did not include skill levels in their questionnaire. Several studies showed higher injury rates in less skilled skiers and snowboarders (3, 4) while more skilled skiers had a higher risk to sustain a more severe injury (5).

Secondly, there seem mistakes concerning the presented data about snow conditions. In Figure 3, artificial snow versus old snow and fresh snow versus powder snow show OR <1 while in Table 1 the same OR are presented vice versa (OR 0.21 for old snow vs. artificial snow and OR 0.31 for old snow vs. fresh snow, respectively). It is the same with slush snow versus powder snow which is not a snow condition but a skiing condition in Figure 3 and powder snow vs. slush snow in Table 1, respectively. In addition, old snow seems to be in contrast to fresh snow. Does fresh snow mean powder snow? However, can old snow not be also old artificial snow? Therefore, it is not clear which snow condition actually increases or decreases injury risk.

Thirdly, seasonal checking of skiing equipment showed a trend to decrease injury risk (OR: 0.46, p = 0.056). In our opinion, seasonal checking of skiing equipment includes primarily an adjustment of the bindings. In accordance, Burtscher et al. (2) showed that female carving skiers with a binding adjustment older than 1 year had a twofold knee injury rate compared to those with newly adjusted bindings. The release of a binding is primarily important in preventing injuries to the lower extremity. Therefore, it would be better to define risk factors with regard to the injured body location.

Fourthly, injured skiers showed a higher readiness for risk taking in this study. In contrast, other studies  reported that injured skiers did not take more risk but were less skilled compared to uninjured skiers (6-8). Therefore, it would make sense to include skill level.

Fifthly, Hasler et al. showed a higher injury risk when skiing under bad weather conditions which is well in accordance with the study by Aschauer et al. (9). However, poor snow and weather conditions may be misjudged by injured skiers because they may look for an explanation as to why the injury occurred. In general, self-report to questions might lead to underreport or overreport of health-risk behaviours affected by cognitive and situational factors (10).

Sixthly, gender has not been found to be a significant risk factor in this study. That might be due to the fact that Hasler et al. did not differentiate between injured parts of the body, e.g. females have a higher knee injury risk (2) and males have a higher head injury risk (11) compared to the other gender.

Seventhly, Hasler et al. calculated that injury risk is higher when warming up. This result contrasts general preventive recommendations (12) and also the findings by Ruedl et al. (13) who demonstrated a twofold injury reduction in a cohort of 36.000 participants of 12 ski schools when warming up.

Eighthly, there seems a mistake concerning the presented data about drug consumption. Figure 3 shows an OR > 1 for abstinence from drugs while inTable 1 drug consumption was presented vice versa. In  addition, in Table 1 an OR of 5.92 was presented while in the discussion the OR was 1.78 for drug consumption.

Since a case control design was used, the amount of exposure to the suggested risk factors was unknown which should be taken into account when interpreting the results (14). In the study by Hasler et al. the controls were interviewed when coming off slopes after skiing. This implies that controls skied probably more than 3 hours although other studies showed that most injuries to the lower extremity occurred within the first 2 or 3 hours of skiing (15, 16). A total of 782 patients were recruited over a period of 5 and a half month and 496 controls were interviewed in six different ski resorts. This means an average of about 83 controls per ski resort and an average of 15 uninjured skiers per month, respectively. However, Hasler et al. (2009) did not specify when controls have been recruited, e.g. every second day. A continuous recruitment of controls seems of utmost importance to compare prospectively potential external risk factors like snow, weather and slope conditions. In general, a prospective study design concerning internal and external risk factors in relation to gender and type of injury should be used. However, at least a case-control-design should be applied matching controls according to gender, age and skill level.

Gerhard Ruedl & Martin Burtscher
Department of Sport Science
University of Innsbruck, Austria


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