title: The biomechanical function of the anterolateral ligament of the knee.
abstract: BACKGROUND
  Recent anatomic investigations of the lateral structures of the knee have identified a new ligament, called the anterolateral ligament (ALL). To date, the anterolateral ligament has not been biomechanically tested to determine its function.
  
  
  OBJECTIVE
  The ALL of the knee will resist internal rotation at high angles of flexion but will not resist anterior drawer forces.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Eleven cadaveric knees were subjected to 134 N of anterior drawer at flexion angles between 0° and 90° and separately to 5 N·m of internal rotation at the same flexion angles. The in situ forces of the ALL, anterior cruciate ligament (ACL), and lateral collateral ligament (LCL) were determined by the principle of superposition.
  
  
  RESULTS
  The contribution of the ALL during internal rotation increased significantly with increasing flexion, whereas that of the ACL decreased significantly. At knee flexion angles greater than 30°, the contribution of the ALL exceeded that of the ACL. During anterior drawer, the forces in the ALL were significantly less than the forces in the ACL at all flexion angles (P < .001). The forces in the LCL were significantly less than those in either the ACL or the ALL at all flexion angles for both anterior drawer and internal rotation (P < .001).
  
  
  CONCLUSIONS
  The ALL is an important stabilizer of internal rotation at flexion angles greater than 35°; however, it is minimally loaded during anterior drawer at all flexion angles. The ACL is the primary resister during anterior drawer at all flexion angles and during internal rotation at flexion angles less than 35°.
  
  
  CONCLUSIONS
  Damage to the ALL of the knee could result in knee instability at high angles of flexion. It is possible that a positive pivot-shift sign may be observed in some patients with an intact ACL but with damage to the ALL. This work may have implications for extra-articular reconstruction in patients with chronic anterolateral instability.
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, USA.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Parsons
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, USA.
authors.forename: Albert O
authors.initials: AO
authors.lastname: Gee
authors.affiliation: Department of Oral Health Sciences, University of Washington, Seattle, Washington, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Spiekerman
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, USA cavanagh@uw.edu.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Cavanagh
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016118:Anterior Cruciate Ligament / Q000502:physiology; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D017844:Lateral Ligament, Ankle / Q000502:physiology; D008023:Ligaments, Articular / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012399:Rotation
keywords: anterior cruciate ligament; anterolateral ligament; biomechanics; knee; robotics