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Abstract
Objectives The study aimed to (1) determine the incidence and gender-specific risk ratio of acute on-snow severe injury events (SIE) in elite alpine ski racing, (2) examine the development of SIE over 22 seasons, and (3) analyse SIE with respect to the severely injured body parts and structures.
Methods Data recorded in the Austrian Ski Federation’s Injury Surveillance System over 22 seasons were analysed. The Austrian Ski Team consists of four groups: Team National (n=477), Team A (n=444), Team B (n=696) and Team C (n=608). Team National and Team A comprised World Cup, Team B European Cup and Team C junior alpine ski racers. Simple and multiple Poisson regressions were calculated.
Results The SIE incidence was 15.7 (95% CI 14.2 to 17.5) per 100 skier seasons. ACL injury events accounted for 70.8% of severe knee injury events and 48.6% of SIE. The incidence of severe ACL injury events was 7.6 (95% CI 6.6 to 8.9). Female World Cup alpine ski racers had a 1.65 times (95% CI 1.02 to 2.69) higher risk of severe ACL injury events than their male counterparts.
Conclusion The incidence of acute on-snow SIE in World Cup alpine ski racing was higher than previously reported. Despite various prevention efforts, the average seasonal incidence of SIE in World and European Cup alpine ski racers has grown from approximately 11 in 1997 to 23 in 2019; thus with roughly one more injured athlete every second season.
- alpine skiing
- injuries
- knee injuries
- knee ACL
- anterior cruciate ligament
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information. All data generated or analysed during this study are included in this published article.
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Introduction
First scientific discourses on injuries in alpine ski racing date back to the 1970s and 1980s.1–3 However, data on the injury incidence in elite alpine ski racers have remained scarce.4 Aiming at ‘reducing the number of injuries suffered by elite athletes’,5 the International Ski Federation (FIS) introduced the Injury Surveillance System (ISS) in 2006 and has launched several further projects in the years to follow.6 The better availability of data and increased attention to the issue have led to some recent original research articles as well as reviews.4 7 We analysed the original epidemiological studies on injuries in World Cup and European Cup alpine ski racing by applying the recently published consensus statement for the ‘recording and reporting of epidemiological data on injury and illness in sport 2020’8 as an analysis grid (table 1). This enabled us to consider the comparability of the results in more detail and consequently detect existing research gaps.
Analysis of epidemiological studies on injuries in World Cup and European Cup alpine ski racing
The most striking insights of our analysis were that (1) the longest period analysed by a study comprised nine seasons, (2) the three studies based on the FIS ISS included in-competition season injuries only, (3) most studies included off-snow training injuries, and (4) only one study contained injuries with a gradual onset.
From the analysis’ results it can be derived that so far only in a single study9 injuries recorded over the entire season were analysed. The available information on the incidence of (severe) injuries during the competitive season and respective gender differences in terms of risk ratios (RR) are displayed in table 2.
Incidence of (severe) in-competition season injuries and gender-specific RR
To the best of our knowledge, the incidence of severe on-snow injuries throughout the entire season has only been calculated once in European Cup alpine ski racers (33.89) and not at all in World Cup alpine ski racers.
Already in 2017, Spörri et al 4 demanded that the ISS should include out-of-competition season training as well as a wider spectrum of levels of racers (ie, European Cup, FIS and youth alpine ski racers). Furthermore, information on the temporal course and variance of the injury incidence are highly important, especially if attempts to evaluate modifications of equipment regulations are made. Such evaluations were done by Haaland et al 10 as well as recently by Platzer et al.11 All considered publications, however, were based on data records covering less than two decades. Moreover, alpine skiing is one of those sports in which the injury epidemiology in male and female athletes has not been frequently investigated in the past.12
The objective of this study was therefore threefold: first, describing the incidence and gender-specific RR of acute on-snow severe injury events (SIE) in elite alpine ski racing; second, examining the development of the SIE incidence over 22 seasons; and third, analysing the SIE with respect to the severely injured body parts and body structures.
Methods
Data collection
The Austrian Ski Federation established its own ISS in 1993. Due to methodological issues, data from the seasons 1993 to 1996 and 1999 had to be discarded. A season lasted from 1 May of 1 year to 30 April of the next. We differentiated between in-competition season and out-of-competition season with the help of the official FIS Alpine Ski World Cup calendar (considering the first and last Alpine Ski World Cup race in each season13). To reduce recall bias, all team members were advised to record injuries immediately after occurrence. Until 2009, data collection was done by using a paper-and-pencil questionnaire; afterwards, an adapted online version of this instrument was applied. At the end of each season checks on the correctness of the records (eg, validation of entries by comparing them with the respective doctor’s reports, checks for completeness with coaches, correctness of a priori (from injury and medical reports derived) entered time loss) were conducted.
Definition of injury
In line with the classification system of the International Olympic Committee consensus statement8 injuries included in this study met three criteria: (1) the injury was directly related to alpine skiing; (2) the injury occurred during competition or on-snow training; and (3) there was a sudden presentation of the injury with an acute mechanism. Although the distinction between acute and repetitive cannot be determined directly from the records, the characteristics of the sport, injury circumstances and types of injuries seem to justify this classification. Internal studies (retrospective interviews with coaches, medical staff and athletes) revealed that a complete coverage of minor to moderate time-loss injuries cannot be guaranteed; therefore, only events that resulted in a severe injury were analysed. For this study, we distinguished between SIE and severe injury because within one SIE several body parts and body structures can be affected severely. An injury (event) was classified as severe if the duration of an athlete’s absence from training or competition was longer than 5 weeks.
Population
Over the 22 analysed seasons, the number of elite alpine ski racers in the Austrian Ski Team fluctuated between 91 and 109 athletes. This resulted in 2225 skier seasons (1231 male and 994 female). The Austrian Ski Team consisted of four different squads, namely Team National (n=477), Team A (n=444), Team B (n=696) and Team C (n=608). Based on the team qualification criteria, we classified the alpine ski racers of Team National and Team A as Team World Cup (Team WC). Team B consisted largely of European Cup alpine ski racers; accordingly, this team is hereinafter referred to as Team European Cup (Team EC). Team C was composed of junior alpine ski racers. The approach for European Cup alpine ski racers is comparable to Alhammoud et al. 9
Data analysis
The interest in modelling count data has increased in the last decade, and Poisson distribution has been used widely. It seems reasonable to assume that the annual count of injuries depends on the number of athletes exposed to the risk of injury. Therefore, 
was used as ‘offset’ in our models. Besides simple Poisson regressions, we also calculated three multiple Poisson regressions:
Model Team WC:
(1)
Model Team EC and Model Team C:
(2)
Verification of equidispersion14 was done by applying the dispersion_test (AER v1.2-9).15 16 No model violated this assumption. However, in Model Team WC we observed one more zero than expected. All goodness-of-fit tests (residual deviances)17 were non-significant. Due to the results, we refrained from applying zero-inflated Poisson distributions18 to our models or using hurdle regressions.
To account for possible non-linear effects over time we applied generalised additive models (gam, mgcv v1.8-3119) to our regression problems. For comparisons, Vuong statistics (eg, ref 20; vuong, pscl v1.5.521) were calculated. Linear models (glm, stats v3.6.222) were superior in all cases. Therefore, only results from our linear models were reported.
For an easier interpretation, estimated coefficients and their respective 95% (Wald) CIs (coefci, lmtest v0.9-3723) were exponentiated. The value of the exponentiated coefficients corresponded to the RR.
To describe the development of the SIE incidence throughout 22 seasons as well as to assess the models’ adequacy24 we made graphical representations of the predictions (by holding all other predictors constant at their mean values), their 95% CI (predict, stats v3.6.222) and the observations of the SIE incidence in each season.
Incidence is expressed as injury events per 100 ski racers per season. All gender-specific RRs are reported as female/male RR. Incidence and RR are presented with their 95% CI.
The level of significance was set to 5%. Implementation of all analysis was done with R (V.3.6.1).
Patient and public involvement
The Department of Sport Science of the University of Innsbruck and the Austrian Ski Federation look back on a long-term and very successful cooperation, which already guaranteed a very fruitful collaboration in the context of injury prevention in alpine ski racing in the past. The specific cooperation in the context of the present contribution was as follows (initials of the authors): conceptualisation of the project and methodology: WN, AG, PS, HPP, MB; data collection and organisation: WN, AG, PS, HPP; data analysis: MB; writing original draft: MB, WN, HPP; manuscript review and editing: MB, WN.
Results
SIE incidence and corresponding gender-specific RR
In 2225 skier seasons 350 SIEs were reported. Around a quarter (26.9%) of the SIEs occurred out of competition season. Nearly half of the SIEs happened during training, 51.3% in racing. The incidence and RR for the teams are presented in table 3.
Number of athletes, number of SIE, SIE incidence and RR with 95% CI in Austrian alpine skiing teams
In total, the SIE incidence was 15.7 (95% CI 14.2 to 17.5). The SIE incidence was higher in female ski racers than in their male counterparts in Teams A, EC, C and WC, but not in Team National.
Development of seasonal SIE incidence
The presented varying results of Team National and Team A question the (usual) unification in Team WC. However, a separated description of the development of the seasonal SIE incidence was not possible in Team National due to the low number of injuries. Therefore, model calculations and descriptions were done for Teams WC, EC and C. To verify whether male and female ski racers show different developments of seasonal SIE incidence, respective illustrations were prepared (figure 1).
Male and female ski racers’ seasonal severe injury event (SIE) incidence in Team World Cup (Team WC), Team European Cup (Team EC) and Team C.
Although outliers were present in the development of the seasonal SIE incidence for Teams WC and EC, the patterns for male and female ski racers were roughly comparable within each team. The found difference between the SIE incidence of male and female ski racers in Team C (see tables 2 and 3) is also reflected in figure 1. The female athletes of Team C showed conspicuous peaks and a relatively higher variance within their seasonal SIE incidence than their male counterparts. This high variance, but especially the low number of severely injured male athletes, impeded meaningful gender-separated analyses for Team C.
Team WC showed an impressive decrease in seasonal SIE incidence between 2011 and 2013. However, this was followed by an even stronger increase in seasonal SIE incidence until 2016. Team EC showed two outstanding peaks in the development of the seasonal SIE incidence, and a reduction of the seasonal SIE incidence from 36.4 to 0 within only two seasons (2012–2014) (figure 2).
Ski racers’ seasonal severe injury event (SIE) incidence and predictions with 95% CI for Team World Cup (Team WC), Team European Cup (Team EC) and Team C.
Team C’s seasonal SIE incidence did not increase within the analysed time period. On the contrary, a significant increase in seasonal SIE incidence was identified for Team WC and Team EC (table 4).
Regression results of equation (1) and equation (2): ski racers’ RR with 95% CI for Teams WC, EC and C
For Team WC both variables, gender (p=0.07) as well as team membership (p=0.05), narrowly exceeded the significance level. In Team EC and Team C, the above-found gender difference was still present (compare table 3). Calculations of the average seasonal growth rate of the SIE incidence (predictions for 1997–2019) resulted in 0.49 for Team WC and 0.57 for Team EC.
Severe knee injury events
A severe knee injury event occurred 240 times (accounting for 68.6% of all SIEs). Accordingly, the incidence of a severe knee injury event was 10.8 (95% CI 9.5 to 12.2). An overall gender-specific difference was to be found (RR=1.79 (95% CI 1.39 to 2.32)); it was true for each of the teams analysed. The respective incidence and female-male RR were: Team WC (11.2 (95% CI 9.2 to 13.6), RR=1.62 (95% CI 1.10 to 2.39)); Team EC (10.8 (95% CI 8.6 to 13.5), RR=1.71 (95% CI 1.08 to 2.72)); and Team C (10.2 (95% CI 8.0 to 13.1), RR=2.33 (95% CI 1.37 to 3.97)).
On average, 1.85 knee structures were severely injured in each severe knee injury (241 in total; in one SIE the left and the right knee were severely injured). Severe knee injuries can therefore be seen as multiple severe injuries. Within the 445 severely injured knee structures the ACL was the most severely injured structure (38.2%), followed by meniscus lateralis (16.6%), meniscus medialis (13.0%) and medial collateral ligament (13.0%). One hundred and seventy severe ACL injury events were recorded. Thus, ACL injury events accounted for 70.8% of the severe knee injury events and nearly half of the SIEs (48.6%). In 63.5% of the severe ACL injuries at least one more structure of the knee was severely injured.
The incidence of a severe ACL injury event was 7.6 (95% CI 6.6 to 8.9). An overall gender-specific difference was to be found (RR=1.86 (95% CI 1.37 to 2.52)). Such a difference was also apparent within Team WC and Team C. The respective incidence and female-male RR for the teams were: Team WC (7.1 (95% CI 5.5 to 9.0), RR=1.65 (95% CI 1.02 to 2.69)); Team EC (8.5 (95% CI 6.6 to 10.9), RR=1.55 (95% CI 0.93 to 2.60)); and Team C (7.6 (95% CI 5.7 to 10.1), RR=2.82 (95% CI 1.48 to 5.36)).
Discussion
This is the first study describing the development of seasonal SIE incidence in elite alpine ski racing over a period of more than two decades. Moreover, it includes SIE that took place out of competition season and specifically analyses SIE in terms of severely injured body parts and body structures.
With 16.5 SIE per 100 skier seasons, the SIE incidence in World Cup alpine ski racers exceeds the incidence of severe injuries reported by Flørenes et al 25 (11.3), Bere et al 26 (12.9) as well as Haaland et al 10 (12.9). Considering that those studies were based on FIS ISS data, which included only in-competition season injuries (compare table 1), this seems not surprising. In our study, the on-snow SIE incidence in European Cup alpine ski racers (16.3) was below the incidence found by Alhammoud et al 9 (33.8). There might be two obvious explanations for their higher number: first, the more comprehensive definition of injury, including overuse injuries; and second, the data recording between 2014 and 2018. However, it seems unlikely that those two factors account for a doubling of SIE incidence.
Compared with their male counterparts, female elite alpine ski racers showed significantly higher SIE incidence in all teams with the exception of the highest level team (Team National, top 15 World Cup alpine ski racers) and Team WC when analysed in the multiple model. Thus, results comparable to Bere et al 26 (RR=0.88) and Flørenes et al 25 (RR=0.94) were found only in case of Team National (RR=1.14).
The calculated average seasonal growth rates of the SIE incidence were 0.49 in World Cup alpine ski racers and 0.57 in European Cup alpine ski racers. During the sample period several attempts have been made to reduce injuries. Most remarkable are the five competition equipment regulations introduced by the FIS in average intervals of 4 years beginning with the year 2000.11 Furthermore, the Austrian Ski Federation has initiated educational programmes regarding skiing technique and tactic, course and jump design, and snow preparation as well as special athletic fitness programmes to reduce presumed neuromuscular risk factors. The applied prevention efforts were not effective or contradicted by other factors, such as the intensified water preparation of slopes, which demands a more aggressive tuning of the ski-plate-boot system. Additionally, more focus should be put on the exposure to injury situations since the number of races skied by the individual may have increased during the sample period.
Within the 22 investigated seasons severe knee injury events occurred 240 times. Thus, severe knee injury events accounted for 68.6% of all SIEs, a percentage which is in line with Flørenes et al 25 (62.7%). Severe knee injuries were multiple injuries with an average of 1.85 knee structures severely injured. Most strikingly, ACL injury events accounted for 70.8% of severe knee injury events and nearly half of all SIEs (48.6%). The incidence of a severe ACL injury event of 7.6 (95% CI 6.6 to 8.9) was in line with Pujol et al 27 (8.5). In 63.5% of severe ACL injuries at least one more knee structure was severely injured.
Contrary to Bere et al 26 (RR=1.03), Flørenes et al 25 (RR=1.08) and Pujol et al 27 (RR=1.28), we found female World Cup alpine ski racers to be at a higher risk of suffering an ACL injury than their male counterparts (RR=1.65). Our results support the findings of the recently published meta-analysis on ACL injuries by Montalvo et al,12 who reported that—across several sports—female athletes have on average a 1.5 times increased risk of suffering an ACL injury compared with male athletes. Higher incidence of ACL injuries in female compared with male alpine ski racers was also found by Raschner et al,28 Stenroos and Handolin29 as well as Stevenson et al.30 However, these results were not based on investigations of elite alpine ski racers.
This study is not without limitations. First, our investigation was based on data from one national ski federation, resulting in low numbers of injury cases in the subgroups, which precluded specific analyses of these groups. Second, the definition of ‘severe injury’ with an absence period of 5 weeks (instead of 4 weeks) has been used by the Austrian Ski Federation since the introduction of its ISS in 1993 and was thus applied in this study. However, the higher strictness of our definition of severe injuries limits the comparability of results only slightly. There were only very few cases of injuries in alpine ski racers that caused an absence of 4 but not of 5 weeks. Hence, the overall in-competition season SIE incidence was 11.5 in our study, which is comparable with the incidence reported by Bere et al 26 (12.9), Flørenes et al 25 (11.3) and Haaland et al 10 (12.9). Third, the results may be affected by the different exposure to injury risk in male and female athletes as well as in the various teams. The fact that alpine ski racers’ exposure to injury risk for the whole period analysed is quantifiable for racing but not for on-snow training inhibited the respective analysis for all injuries.
In conclusion, the incidence of acute on-snow SIE in World Cup alpine ski racing was found to be higher than previously reported. Severe ACL injury events accounted for nearly half of the SIE. We saw that female World Cup as well as elite junior alpine ski racers are at a higher risk of suffering from a severe ACL injury than their male counterparts. In spite of various prevention efforts, the SIE incidence in World and European Cup alpine ski racers has grown from approximately 11 in 1997 to 23 in 2019; thus, with roughly one more injured athlete every second season within the last two decades.
Key messages
What are the findings?
In the last two decades, the incidence of severe injury events in World Cup and European Cup alpine ski racers has increased from approximately 11 in 1997 to 23 in 2019; thus, with roughly one more injured athlete within 100 athletes every second season.
Female World Cup alpine ski racers had a 1.65 times (95% CI 1.02 to 2.69) higher risk of severe ACL injuries than male elite alpine ski racers.
Severe knee injuries can be seen as multiple severe injuries with an average of 1.85 knee structures severely injured.
How might it impact on clinical practice in the future?
Our finding that 63.5% of severe ACL injuries were accompanied by at least one more severely injured knee structure calls for more detailed investigations and attempts to identify different ACL injury categories in alpine ski racing. This information is valuable for short-term rehabilitation and the return to sport programmes as well as in the context of long-term effects for injured athletes.
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information. All data generated or analysed during this study are included in this published article.
Ethics statements
Ethics approval
This survey was conducted according to the ‘ethical guidelines for surveys’ approved by the Institutional Review Board of the Department of Sport Science as well as the Board for Ethical Issues of the University of Innsbruck. Approval number (‘Ethical Guidelines for Surveys conducted at the Department of Sport Science’): Certificate of Good Standing, 25/2016. All athletes gave written informed consent that anonymised data could be used for scientific purpose.
Acknowledgments
The authors would like to thank the Austrian Ski Federation, especially its athletes, coaches and medical team personnel.
References
Footnotes
Contributors Conceptualisation of the project and methodology: MB, HPP, WN, PS, AG. Data collection and organisation: MB, HPP, WN, PS, AG. Data analysis: MB, HPP, WN. Writing original draft: MB, HPP, WN. Manuscript review and editing: MB, HPP, WN.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were involved in the design, or conduct, or reporting, or dissemination plans of this research. Refer to the Methods section for further details.
Provenance and peer review Not commissioned; externally peer reviewed.