This study was conducted as a retrospective case‐control study of ACL‐injured and uninjured female and male recreational alpine skiers during the two winter seasons 2016/17 and 2017/18 in a large Austrian ski area. The study has been approved by the Institutional Review board of the Department of Sport Science Innsbruck and the ethical advisory board of the University of Innsbruck. Cases and controls were informed about the aims of the study and gave their written informed consent for participating.
Cases were yearly interviewed between the months December and April (23 days on average per season) using a questionnaire. The ACL injury was diagnosed via magnetic resonance imaging (MRI) in a ski clinic, which is directly located in the ski area. Inclusion criteria were a skiing‐related noncontact ACL injury after a self‐inflicted fall, an age >17 years, and the use of any type of carving ski (in contrast to long and unshaped traditional skis as well as to so called short ski boards).
Uninjured control participants were selected at different spots in the same ski area mostly at the same days to minimize the potential impact of environmental factors (eg, weather and slope conditions) on ACL injury risk. Controls were recruited throughout the whole skiing day. In controls, a similar questionnaire was used as in cases. Similar to cases, inclusion criteria were an age >17 years and the use of any type of carving ski.
According to the questionnaire used in a recent study by Ruedl et al,17 Burtscher et al8 and Burtscher et al5 on ACL injuries among male and female recreational skiers, cases and controls in this study were asked on age, sex, height, weight, and self‐reported skill level (expert, advanced, intermediate, and beginner) according to Sulheim et al18 In addition, ACL‐injured skiers were asked about a failure of binding release of the injured knee at the moment of accident. Furthermore, we divided participants into more skilled (expert and advanced) and into less skilled (intermediate and beginner) skiers as a tendency was shown to underestimate individual skiing skills, especially among female skiers.18 Absolute ski length and sidecut radius were directly notated from the ski. Additionally, ski length was relativized by body height and weight according to a previous study14 to enable further analysis. In both, cases and controls, sole height of the front and rear part of the ski boot was measured by the use of a digital sliding calliper (Figure 1 ), and then, the difference between the norm height of ski boot soles and the measured height was calculated as a measure of sole abrasion.
In total, six intrinsic risk and six extrinsic risk variables were considered for the use in the risk factor analysis. Intrinsic risk factors comprised age (years), height (m), weight (kg), body mass index (BMI) (kg/m2), sex (male vs female), and skiing skill level (more vs less skilled). Extrinsic equipment‐related risk factors consisted of ski length (cm), ski length to height ratio (%), ski length to weight ratio (cm/kg), sidecut radius (m), and sole abrasion at the front and rear part of the ski boot (mm).
Cases were yearly interviewed between the months December and April (23 days on average per season) using a questionnaire. The ACL injury was diagnosed via magnetic resonance imaging (MRI) in a ski clinic, which is directly located in the ski area. Inclusion criteria were a skiing‐related noncontact ACL injury after a self‐inflicted fall, an age >17 years, and the use of any type of carving ski (in contrast to long and unshaped traditional skis as well as to so called short ski boards).
Uninjured control participants were selected at different spots in the same ski area mostly at the same days to minimize the potential impact of environmental factors (eg, weather and slope conditions) on ACL injury risk. Controls were recruited throughout the whole skiing day. In controls, a similar questionnaire was used as in cases. Similar to cases, inclusion criteria were an age >17 years and the use of any type of carving ski.
According to the questionnaire used in a recent study by Ruedl et al,
In total, six intrinsic risk and six extrinsic risk variables were considered for the use in the risk factor analysis. Intrinsic risk factors comprised age (years), height (m), weight (kg), body mass index (BMI) (kg/m2), sex (male vs female), and skiing skill level (more vs less skilled). Extrinsic equipment‐related risk factors consisted of ski length (cm), ski length to height ratio (%), ski length to weight ratio (cm/kg), sidecut radius (m), and sole abrasion at the front and rear part of the ski boot (mm).
