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Videos help specialists identify ACL injury mechanisms, risk factors
More than 25% of freestyle mogul skiers have previously experienced an ACL injury.
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INNSBRUCK, Austria — For decades, referees, coaches and analysts have used instant replay and game footage to scrutinize plays and scout opposing teams. Now, European, North American and Japanese sports medicine specialists use skiing videos to determine how athletes, including freestyle mogul skiers, get anterior cruciate ligament injuries.
An incredible 25% of active freestyle downhill mogul skiers have suffered ACL injuries during their career, Stig Heir, MD, of Oslo, told colleagues at the European Society of Sports, Traumatology and Knee Arthroscopy (ESSKA) 12th Congress, here.
“When you have an unacceptably high rate of injuries and you want to prevent the injuries, you need to know something about the risk factors and the injury mechanisms,” Heir said.
Heir showed a video of a male freestyle mogul skier making a hard landing and rupturing his left ACL. He asked, “When is the ACL actually tearing: When the ski touches the ground, or later?” He also questioned whether the skier had made an earlier move that may have been a risk factor for injury.
About half of the experts believed the skier’s ACL injury occurred when the rear end of the ski “clapped” along the snow and drove to the right, exerting load on the leg and rupturing the ligament, Heir said. The other half of the panel thought the injury stemmed from the skier struggling, off-balance to the rear and left.
Injury mechanisms
Heir and his colleagues watched 11 skiing videos and consulted with a panel comprising three groups of experts: general knee specialists, skiing injury specialists and skiing authorities. The videos were formatted to 25 frames per second and time-coded to facilitate frame-by-frame study. Injury time points varied from 2 to 5, with most of the experts seeing injury early, Heir said.
Most of the experts suggested that the injury mechanisms were related to “boot-induced anterior drawer” (BIAD) and “phantom foot,” Heir said. In the BIAD mechanism, force is transmitted from the rear of the ski to the boot, which draws the lower leg anteriorly and causes the ACL to tear. Loading must be just right to cause the ligament, not the bone, to fail.
In eight of the 11 videos, ACL ruptures occurred at landings from jumps in the mogul hill. In six of those eight, landing injuries may have stemmed from the skiers being off-balance to the side or rear, and landing on the injured leg, Heir said.
Poor landing is to blame
Ultimately, an athlete’s altered balance and placing weight on an injured leg are the key factors leading to ACL ruptures, Heir said.
Likewise, injured skiers usually believe their injuries occurred during a landing, Heir added. However, as the landing area is long; studying videos should help skiers and doctors ascertain where the injuries occurred.
Heir expressed uncertainty whether rear-release ski boots help prevent ACL injuries.
For more information:
- Heir S. Prevalence of previous ACL injuries in freestyle mogul skiers. Free Paper #2. Presented at the European Society of Sports, Traumatology and Knee Arthroscopy 12th Congress and 5th World Congress on Sports Trauma. May 23-27, 2006. Innsbruck, Austria.