Alpine skiing : injury profile, ACL risk factors and prevention

Sammanfattning: Alpine skiing is a popular winter sport among children and adolescents. The combination of great physical demands and ever-changing external conditions makes competitive alpine skiing to one of our most complex sports. To reach the highest level of skiing skill, the skier needs to take part in a long and carefully planned physical training in order to improve skiing performance. This often starts when the skier enters a Swedish ski high school. Like other sports, alpine skiing may unfortunately lead to injuries. The main aim of the present thesis was to try to reduce ACL injuries in competitive alpine skiers by the use of van Mechelen´s four steps model “Sequence of Prevention”. The first step was to identify the magnitude of the injury problem in terms of injury incidence and injury severity. The second step was to identify risk factors for ACL injuries. The third step was to introduce ACL injury prevention strategies, and finally the fourth step was to evaluate the prevention by repeating the first step. The cohort of this thesis consisted of alpine ski students, attending ski high schools in Sweden during at least one season between the seasons 2006/2007 and 2012/2013. In a prospective five year study, injuries in 431 skiers (215 males, 216 females) were recorded. Totally 312 injuries occurred in 193 skiers. The overall injury incidence was 1.7 injuries/1000 skiing hours or 3.11 injuries/100 months as a student at a ski high school. In both male and female skiers most injuries occurred to the knee joint. ACL injuries represented one third of these knee injuries. ACL injury risk factors were studied. A family history, where either the skier´s father and/or mother had had an ACL injury, increased the risk for this particular skier to sustain an ACL injury. A number of other possible intrinsic and extrinsic risk factors for ACL injuries have also been prospectively studied in 339 skiers (176 males, 163 females). During the study period 25 skiers (11 males, 14 females) sustained a first time ACL injury. There was a higher risk to sustain an ACL injury of the left knee than of the right knee, irrespective of gender. The ACL injured skiers showed a greater side-to-side difference between legs according to functional performance tests. The effect of an ACL injury prevention program was evaluated. The prevention was conducted during a period of 21 months and included those skiers (n=308) that were studying at a ski high school during the seasons 2011/2012 and 2012/2013. Skiers, who attended a ski high school between the seasons 2006/2007 and 2010/2011 were regarded as controls (n=456). The prevention program consisted of a video, and the goal was to teach the skiers how to avoid getting into ACL injury risk situations while skiing. Since there are the same demands on both legs in competitive alpine skiers a number of different neuromuscular exercises as well indoors as outdoors on snow were implemented with the purpose that the skier should carry out equally good performance on both legs. Twelve ACL injuries occurred in the prevention group and 35 ACL injuries occurred in the control group. The incident rate decreased with 0.22 (CI -0.44- 0.00) ACL injuries/ 100 month attending a ski high school in favor of the intervention group. The conclusion is that the prevention strategies reduced the ACL injuries with 45 %. Although, not quite statistically significant, this result could be considered to be of clinical importance on an individual level.