title: The mechanical consequences of dynamic frontal plane limb alignment for non-contact ACL injury.
abstract: This study investigated the mechanical consequences of differences in dynamic frontal plane alignment of the support limb and the influence of anticipatory muscle activation at the hip and ankle on reducing the potential for non-contact ACL injury during single-limb landing. A frontal plane, three-link passive dynamic model was used to estimate an ACL non-contact injury threshold. This threshold was defined as the maximum axial force that the knee could sustain before the joint opened 8 degrees either medially or laterally, which was deemed sufficient to cause injury. The limb alignment and hip and ankle muscle contractions were varied to determine their effects on the ACL injury threshold. Valgus or varus alignment reduced the injury threshold compared to neutral alignment, but increasing the anticipatory contraction of hip abduction and adduction muscle groups increased the injury threshold. Increasing anticipatory ankle inversion/eversion muscle contraction had no effect. This study provides a mechanical rationale for the conclusion that a neutral limb alignment (compared to valgus or varus) during landing and increasing hip muscle contraction (abductors/adductors) prior to landing can reduce the possibility of ACL rupture through a valgus or varus opening mechanism.
authors.affiliation: Department of Mechanical Engineering, Stanford University, Division of Biomechanical Engineering, Durand Bldg, Room 201, Stanford, CA 94305-4038, USA. ajit.chaudhari@stanford.edu
authors.forename: Ajit M
authors.initials: AM
authors.lastname: Chaudhari
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Andriacchi
mesh_terms: D000843:Ankle Joint / Q000503:physiopathology; D016118:Anterior Cruciate Ligament / Q000503:physiopathology*; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena / Q000379:methods; D003198:Computer Simulation; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D007866:Leg / Q000503:physiopathology*; D008954:Models, Biological; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D004856:Postural Balance; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D013314:Stress, Mechanical; D016474:Weight-Bearing