title: Non-invasive, non-radiological quantificationof anteroposterior knee joint ligamentous laxity: A study in cadavers.
abstract: OBJECTIVE
  We performed in vitro validation of a non-invasive skin-mounted system that could allow quantification of anteroposterior (AP) laxity in the outpatient setting.
  
  
  METHODS
  A total of 12 cadaveric lower limbs were tested with a commercial image-free navigation system using trackers secured by bone screws. We then tested a non-invasive fabric-strap system. The lower limb was secured at 10° intervals from 0° to 60° of knee flexion and 100 N of force was applied perpendicular to the tibia. Acceptable coefficient of repeatability (CR) and limits of agreement (LOA) of 3 mm were set based on diagnostic criteria for anterior cruciate ligament (ACL) insufficiency.
  
  
  RESULTS
  Reliability and precision within the individual invasive and non-invasive systems was acceptable throughout the range of flexion tested (intra-class correlation coefficient 0.88, CR 1.6 mm). Agreement between the two systems was acceptable measuring AP laxity between full extension and 40° knee flexion (LOA 2.9 mm). Beyond 40° of flexion, agreement between the systems was unacceptable (LOA > 3 mm).
  
  
  CONCLUSIONS
  These results indicate that from full knee extension to 40° flexion, non-invasive navigation-based quantification of AP tibial translation is as accurate as the standard validated commercial system, particularly in the clinically and functionally important range of 20° to 30° knee flexion. This could be useful in diagnosis and post-operative evaluation of ACL pathology. Cite this article: Bone Joint Res 2013;2:233-7.
authors.affiliation: Golden Jubilee National Hospital, OrthopaedicDepartment, Agamemnon Street, Clydebank, WestDunbartonshire G81 4DY, and Faculty of Biomedicaland Life Sciences, Thomson Building, University Avenue, GlasgowG12 8QQ, UK.
authors.forename: D F
authors.initials: DF
authors.lastname: Russell
authors.forename: A H
authors.initials: AH
authors.lastname: Deakin
authors.forename: Q A
authors.initials: QA
authors.lastname: Fogg
authors.forename: F
authors.initials: F
authors.lastname: Picard
keywords: ACL; Accuracy; Anterior cruciate ligament; Cadaveric; In vitro; Laxity; Non-invasive; Precision