title: Altered landing mechanics in ACL-reconstructed patients.
abstract: OBJECTIVE
  This longitudinal study aimed to examine whether patients with anterior cruciate ligament (ACL) reconstruction show a similar landing strategy during the single-leg hop test (SLHT) postsurgery analog to that previously identified when ACL deficient. It is hypothesized that ACL-reconstructed patients demonstrate greater trunk flexion to reduce knee joint moments at the cost of postural dynamic stability at their involved leg compared to their uninvolved leg.
  
  
  METHODS
  Ten ACL-reconstructed patients performed a bilateral SLHT 6 and 12 months after surgery. Landing mechanics were determined by means of a soft tissue artifact optimized, rigid, full-body model, and the margin of stability was quantified using an inverted pendulum approach. Knee extensor muscular strength (KS) was assessed during isometric maximal voluntary knee extension contractions.
  
  
  RESULTS
  ACL-reconstructed patients showed similar landing strategies as previously reported in their ACL-deficient state. By flexing their trunk, patients repositioned the ground reaction force vector more anteriorly in relation to the joints of the lower extremity (P < 0.05) and, in doing so, were able to transfer joint moments from the knee to the adjacent joints (P < 0.05). This upper body strategy reduced the margin of stability in the ACL-reconstructed leg during landing (P < 0.05). Twelve months after surgery, the ACL-reconstructed leg showed lower KS compared to the uninvolved leg (P < 0.05), and knee joint moment output during landing was significantly correlated to KS.
  
  
  CONCLUSIONS
  The results highlight the important role of KS on the interaction between trunk angle, joint kinetics, and postural dynamic stability during landing and show that ACL-reconstructed patients use an analogous feedforward strategy (e.g., more flexed trunk) to that used in their ACL-deficient state, aiming to compensate for KS deficits and thereby sacrificing postural dynamic stability and increasing the risk of loss of balance during landing maneuvers.
authors.affiliation: Institute of Biomechanics and Orthopaedics, German Sport University Cologne, Germany. mail: k.oberlaender@dshs-koeln.de
authors.forename: Kai Daniel
authors.initials: KD
authors.lastname: Oberländer
authors.forename: Gert-Peter
authors.initials: GP
authors.lastname: Brüggemann
authors.forename: Jürgen
authors.initials: J
authors.lastname: Höher
authors.forename: Kiros
authors.initials: K
authors.lastname: Karamanidis
mesh_terms: D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction; D001696:Biomechanical Phenomena; D006801:Humans; D007717:Knee / Q000503:physiopathology*; D007718:Knee Injuries / Q000503:physiopathology* / Q000601:surgery; D008137:Longitudinal Studies; D009068:Movement; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000502:physiology; D060726:Torso / Q000502:physiology; D016474:Weight-Bearing; D055815:Young Adult