title: Biomechanical evaluation of knee endpoint during anterior tibial loading: Implication for physical exams.
abstract: BACKGROUND
  Physical exams that apply anterior tibial loads are typically used to evaluate knees with anterior cruciate ligament (ACL) injuries. The amount of anterior tibial translation that occurs during these exams can be difficult to assess due to a "soft" endpoint. Therefore, the objective of this study is to determine the biomechanical characteristics of the endpoint for the intact and ACL deficient knee using quantitative criteria.
  
  
  METHODS
  Eight porcine knees were tested using a robotic testing system. An 89N anterior tibial load was applied to the intact and ACL deficient knee at 30°, 45°, 60° and 75° of flexion. The stiffness of the toe and linear regions was determined from the load-translation curve. The width of the transition region was defined by the distance between the points where the best-fit lines used to define the stiffness of the toe and linear regions diverged from the load-translation curve.
  
  
  RESULTS
  Stiffness of the toe and linear regions significantly decreased after transecting the ACL at all flexion angles (71-85% and 38-62%, respectively). Width of the transition region was significantly increased in the ACL deficient knee at all flexion angles (approximately four to five times and four to nine times, respectively).
  
  
  CONCLUSIONS
  The novel quantitative criteria developed in this study have the potential to be deployed in clinical practice by coupling them with data from knee arthrometers that are commonly used in clinical practice. Thus, additional information from the load-translation curve can be provided to improve the diagnosis of ACL injury.
authors.affiliation: Orthopaedic Robotics Laboratory, Department of Orthopaedic Surgery, Department of Bioengineering, University of Pittsburgh, 408 Center for Bioengineering, 300 Technology Drive, Pittsburgh, PA 15219, USA; Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Building Suite 1011, 3471 Fifth Avenue, Pittsburgh, PA 15213, USA.
authors.forename: Ata A
authors.initials: AA
authors.lastname: Rahnemai-Azar
authors.affiliation: Orthopaedic Robotics Laboratory, Department of Orthopaedic Surgery, Department of Bioengineering, University of Pittsburgh, 408 Center for Bioengineering, 300 Technology Drive, Pittsburgh, PA 15219, USA; Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Building Suite 1011, 3471 Fifth Avenue, Pittsburgh, PA 15213, USA.
authors.forename: Fabio V
authors.initials: FV
authors.lastname: Arilla
authors.affiliation: Orthopaedic Robotics Laboratory, Department of Orthopaedic Surgery, Department of Bioengineering, University of Pittsburgh, 408 Center for Bioengineering, 300 Technology Drive, Pittsburgh, PA 15219, USA; Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Building Suite 1011, 3471 Fifth Avenue, Pittsburgh, PA 15213, USA.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Bell
authors.affiliation: Orthopaedic Robotics Laboratory, Department of Orthopaedic Surgery, Department of Bioengineering, University of Pittsburgh, 408 Center for Bioengineering, 300 Technology Drive, Pittsburgh, PA 15219, USA; Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Building Suite 1011, 3471 Fifth Avenue, Pittsburgh, PA 15213, USA.
authors.forename: Freddie H
authors.initials: FH
authors.lastname: Fu
authors.affiliation: Orthopaedic Robotics Laboratory, Department of Orthopaedic Surgery, Department of Bioengineering, University of Pittsburgh, 408 Center for Bioengineering, 300 Technology Drive, Pittsburgh, PA 15219, USA; Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Building Suite 1011, 3471 Fifth Avenue, Pittsburgh, PA 15213, USA; Department of Bioengineering, University of Pittsburgh, 302 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA 15260, USA.
authors.forename: Volker
authors.initials: V
authors.lastname: Musahl
authors.affiliation: Orthopaedic Robotics Laboratory, Department of Orthopaedic Surgery, Department of Bioengineering, University of Pittsburgh, 408 Center for Bioengineering, 300 Technology Drive, Pittsburgh, PA 15219, USA; Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Building Suite 1011, 3471 Fifth Avenue, Pittsburgh, PA 15213, USA; Department of Bioengineering, University of Pittsburgh, 302 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA 15260, USA. Electronic address: genesis1@pitt.edu.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Debski
mesh_terms: D000818:Animals; D000070598:Anterior Cruciate Ligament Injuries / Q000175:diagnosis* / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D005269:Femur / Q000503:physiopathology; D007719:Knee Joint / Q000503:physiopathology*; D023421:Models, Animal; D010808:Physical Examination; D012371:Robotics; D013552:Swine; D013977:Tibia / Q000503:physiopathology
keywords: Anterior cruciate ligament; Anterior tibial load; Anterior translation; End-point; Knee; Stiffness