title: Comparison of the ACL and ACL graft forces before and after ACL reconstruction: an in-vitro robotic investigation.
abstract: BACKGROUND
  Long-term follow-up studies have indicated that there is an increased incidence of arthrosis following anterior cruciate ligament (ACL) reconstruction, suggesting that the reconstruction may not reproduce intact ACL biomechanics. We studied not only the magnitude but also the orientation of the ACL and ACL graft forces.
  
  
  METHODS
  10 knee specimens were tested on a robotic testing system with the ACL intact, deficient, and reconstructed (using a bone-patella tendon-bone graft). The magnitude and orientation of the ACL and ACL graft forces were determined under an anterior tibial load of 130 N at full extension, and 15, 30, 60, and 90 degrees of flexion. Orientation was described using elevation angle (the angle formed with the tibial plateau in the sagittal plane) and deviation angle (the angle formed with respect to the anteroposterior direction in the transverse plane).
  
  
  RESULTS
  ACL reconstruction restored anterior tibial translation to within 2.6 mm of that of the intact knee under the 130-N anterior load. Average internal tibial rotation was reduced after ACL reconstruction at all flexion angles. The force vector of the ACL graft was significantly different from the ACL force vector. The average values of the elevation and deviation angles of the ACL graft forces were higher than that of the intact ACL at all flexion angles.
  
  
  CONCLUSIONS
  Contemporary single bundle ACL reconstruction restores anterior tibial translation under anterior tibial load with different forces (both magnitude and orientation) in the graft compared to the intact ACL. Such graft function might alter knee kinematics in other degrees of freedom and could overly constrain the tibial rotation. An anatomic ACL reconstruction should reproduce the magnitude and orientation of the intact ACL force vector, so that the 6-degrees-of-freedom knee kinematics and joint reaction forces can be restored.
authors.affiliation: Bioengineering Laboratory, Department of Orthopedic Surgery, Massachusetts General Hospital/Harvard Medical School, Boston, MA, USA. gli1@partners.org
authors.forename: Guoan
authors.initials: G
authors.lastname: Li
authors.forename: Ramprasad
authors.initials: R
authors.lastname: Papannagari
authors.forename: Louis E
authors.initials: LE
authors.lastname: DeFrate
authors.forename: Jae Doo
authors.initials: JD
authors.lastname: Yoo
authors.forename: Sang Eun
authors.initials: SE
authors.lastname: Park
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gill
mesh_terms: D000368:Aged; D016118:Anterior Cruciate Ligament / Q000502:physiology* / Q000601:surgery; D001696:Biomechanical Phenomena; D016025:Bone Transplantation; D002102:Cadaver; D006801:Humans; D066298:In Vitro Techniques; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000209:etiology / Q000473:pathology; D016059:Range of Motion, Articular / Q000502:physiology; D019651:Plastic Surgery Procedures / Q000009:adverse effects; D012371:Robotics / Q000379:methods