title: An In Vitro Robotic Assessment of the Anterolateral Ligament, Part 1: Secondary Role of the Anterolateral Ligament in the Setting of an Anterior Cruciate Ligament Injury.
abstract: BACKGROUND
  Recent investigations have described the structural and functional behavior of the anterolateral ligament (ALL) of the knee through pull-apart and isolated sectioning studies. However, the secondary stabilizing role of the ALL in the setting of a complete anterior cruciate ligament (ACL) tear has not been fully defined for common simulated clinical examinations, such as the pivot-shift, anterior drawer, and internal rotation tests.
  
  
  OBJECTIVE
  Combined sectioning of the ALL and ACL would lead to increased internal rotation and increased axial plane translation during a pivot-shift test when compared with isolated sectioning of the ACL.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Ten fresh-frozen human cadaveric knees were subjected to a simulated pivot-shift test with coupled 10-N·m valgus and 5-N·m internal rotation torques from 0° to 60° of knee flexion and a 5-N·m internal rotation torque and an 88-N anterior tibial load, both from 0° to 120° of knee flexion via a 6 degrees of freedom robotic system. Kinematic changes were measured and compared with the intact state for isolated sectioning of the ACL and combined sectioning of the ACL and ALL.
  
  
  RESULTS
  Combined sectioning of the ACL and ALL resulted in a significant increase in axial plane tibial translation during a simulated pivot shift at 0°, 15°, 30°, and 60° of knee flexion and a significant increase in internal rotation at 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, and 120° when compared with the intact and ACL-deficient states. Based on the model results, ALL sectioning resulted in an additional 2.1 mm (95% CI, 1.4-2.9 mm; P < .001) of axial plane translation during the pivot shift when compared with ACL-only sectioning, when pooling evidence over all flexion angles. Likewise, when subjected to IR torque, the ACL+ALL-deficient state resulted in an additional 3.2° of internal rotation (95% CI, 2.4°-4.1°; P < .001) versus the intact state, and the additional sectioning of the ALL increased internal rotation by 2.7° (95% CI, 1.8°-3.6°; P < .001) versus the ACL-deficient state.
  
  
  CONCLUSIONS
  The results of this study confirm the ALL as an important lateral knee structure that provides rotatory stability to the knee. Specifically, the ALL was a significant secondary stabilizer throughout flexion during an applied internal rotation torque and simulated pivot-shift test in the context of an ACL-deficient knee.
  
  
  CONCLUSIONS
  Residual internal rotation and a positive pivot shift after ACL reconstruction may be attributed to ALL injury. For these patients, surgical treatment of an ALL tear may be considered.
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Rasmussen
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Marco
authors.initials: M
authors.lastname: Nitri
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Brady T
authors.initials: BT
authors.lastname: Williams
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Samuel G
authors.initials: SG
authors.lastname: Moulton
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Raphael Serra
authors.initials: RS
authors.lastname: Cruz
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Grant J
authors.initials: GJ
authors.lastname: Dornan
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Mary T
authors.initials: MT
authors.lastname: Goldsmith
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA The Steadman Clinic, Vail, Colorado, USA drlaprade@sprivail.org.
authors.forename: Robert F
authors.initials: RF
authors.lastname: LaPrade
mesh_terms: D000328:Adult; D016118:Anterior Cruciate Ligament / Q000502:physiology / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology; D007718:Knee Injuries / Q000503:physiopathology; D007719:Knee Joint / Q000503:physiopathology; D008023:Ligaments, Articular / Q000502:physiology*; D008875:Middle Aged; D010808:Physical Examination / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology; D065287:Robotic Surgical Procedures; D012399:Rotation; D013977:Tibia / Q000503:physiopathology; D019415:Torque
keywords: Segond fracture; anterior cruciate ligament; anterolateral ligament; pivot shift; rotational knee instability