title: In situ forces in the anteromedial and posterolateral bundles of the anterior cruciate ligament under simulated functional loading conditions.
abstract: BACKGROUND
  The in situ forces of the anteromedial (AM) and posterolateral bundles (PL) of the anterior cruciate ligament (ACL) under simulated functional loads such as simulated muscle loads have not been reported. These data are instrumental for improvement of the anatomical double-bundle ACL reconstruction.
  
  
  OBJECTIVE
  The load-sharing patterns of the 2 bundles are complementary under simulated muscle loads.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Eight cadaveric knees in this study were sequentially studied using a robotic testing system. Each knee was tested under 3 external loading conditions including (1) a 134-N anterior tibial load; (2) combined rotational loads of 10 N x m of valgus and 5 N x m internal tibial torques; and (3) a 400-N quadriceps muscle load with the knee at 0 degrees , 15 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. The in situ forces of the 2 bundles of ACL were determined using the principle of superposition.
  
  
  RESULTS
  Under the anterior tibial load, the PL bundle carried peak loads at full extension and concurrently had significantly lower force than the AM bundle throughout the range of flexion (P <.05). Under the combined rotational loads, the PL bundle contributed to carrying the load between 0 degrees and 30 degrees , although less than the AM bundle. Under simulated muscle loads, both bundles carried loads between 0 degrees and 30 degrees . There was no significant difference between the 2 bundle forces at all flexion angles (P > .05).
  
  
  CONCLUSIONS
  Under externally applied loads, in general, the AM bundle carried a greater portion of the load at all flexion angles, whereas the PL bundle only shared the load at low flexion angles. The bundles functioned in a complementary rather than a reciprocal manner to each other.
  
  
  CONCLUSIONS
  The data appear to support the concept that both bundles function in a complementary manner. Thus, how to re-create the 2 bundle functions in an ACL reconstruction should be further investigated.
authors.affiliation: Bioengineering Laboratory, Department of Orthopaedic Surgery, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Jia-Lin
authors.initials: JL
authors.lastname: Wu
authors.forename: Jong Keun
authors.initials: JK
authors.lastname: Seon
authors.forename: Hemanth R
authors.initials: HR
authors.lastname: Gadikota
authors.forename: Ali
authors.initials: A
authors.lastname: Hosseini
authors.forename: Karen M
authors.initials: KM
authors.lastname: Sutton
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gill
authors.forename: Guoan
authors.initials: G
authors.lastname: Li
mesh_terms: D016118:Anterior Cruciate Ligament / Q000502:physiology*; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D019415:Torque; D016474:Weight-Bearing / Q000502:physiology*