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  1. Rick Howell
  1. Howell SkiBindings, Stowe, USA


    Background ACL-ruptures are the most prevalent injury in alpine skiing competition. Shaped skis produce 2 abduction forces with a centroid that can generate large abduction/valgus-moments and small tibia-torques that cause ACL-rupture before tibia-fracture. Ordinary alpine ski bindings address tibia-fracture.

    Objective Prove, biomechanically, that ordinary bindings cannot release in response to applied-abduction forces before ACL-rupture, whereas bindings with additional lateral heel release can.

    Design A ski is affixed to an anthropometrically-correct metallic foot-tibia-femur test-frame that simulates skiing-ACL slip-catch injury-kinematics similar to ISO 9462 Annex-B — also measuring applied abduction force and resultant abduction/valgus-moment. Initially, no ski-bindings are utilized: the ski is bolted beneath the metallic foot. The proximal end of the metallic femur is rigidly attached to the test frame as during maximal internal rotation. Abduction force is applied to a range of positions along the medial edge of the ski while measuring combined peak abduction/valgus-moments and peak tibia-torques—at ACL-rupture—according to a validated ACL-rupture algorithm of an average US male. 2-mode and 3-mode bindings are interposed to quantify their interaction.

    Setting Biomechanical.

    Patients (or Participants) None, biomechanical.

    Interventions (or Assessment of Risk Factors) None, biomechanical.

    Main Outcome Measurements 3-mode-release bindings can release below the rupture-limit of the ACL; 2-mode bindings cannot.

    Results An abduction centroid can produce ACL rupture before tibia-fracture when applied to a ski -70 cm to -20 cm aft of the tibia at 155 N to 200 N (21% to 27% of average US male body weight) whereas tibia-fracture is produced when an abduction centroid is applied aft of −70 cm.

    Conclusions Abduction centroids applied to the medial edge of a ski can produce tibia-fracture or ACL-rupture depending upon the magnitude and the central position of the applied abduction forces. 3-mode bindings with additional lateral heel release can release below the ACL-rupture limit. A prospective intervention study is needed for full-proof.

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