title: Three-dimensional kinematic and kinetic analysis of knee rotational stability in ACL-deficient patients during walking, running and pivoting.
abstract: BACKGROUND
  Anterior cruciate ligament (ACL) deficiency leads to altered stability of the knee. The purpose of this study was to compare the dynamic, rotational stability of the knee, expressed as rotational stiffness, between anterior cruciate ligament-deficient (ACLD) knees, their contralateral intact knees (ACLI) and a knee healthy control group during walking, running and 90° pivoting. We hypothesized a larger tibial internal rotation, a smaller knee joint external moment and a lower rotational stiffness in the ACLD group compared to the ACLI and the control group.
  
  
  METHODS
  Kinematic and kinetic data were collected from both legs of 44 ACLD patients and 16 healthy controls during walking, running and a pivoting maneuver (descending a staircase and immediately pivoting 90° on the landing leg). Motion data were captured using 8 high-speed cameras and a force-plate. Reflective markers were attached to bony landmarks of the lower limb and rigid clusters on the shank and thigh (CASH model). Maximum internal tibial rotation and the corresponding rotational moment were identified for all tasks and groups and used to calculate rotational stiffness (= Δmoment /Δrotation) of the knee.
  
  
  RESULTS
  The tibial internal rotation of the ACLD knee was not significantly different from the ACLI knee during all three tasks. During walking and running, the tibial rotation of the control group was significantly different from both legs of the ACL-injured patient. For pivoting, no difference in tibial rotation between knees of the ACLD, ACLI and the control group was found. Knee joint external moments were not significantly different between the three groups during walking and pivoting. During running, the moments of the ACLI group were significantly higher than both the knees of the ACLD and the control group. Rotational stiffness did not differ significantly between groups in any of the three tasks.
  
  
  CONCLUSIONS
  A high-intensity activity combining stair descent and pivoting produces similar angular rotations, knee joint external moments and rotational stiffness in ACLD knees compared to ACLI knees and the control group. During running, the ACLI knee displayed a higher external moment than the ACLD and the healthy control group. This could indicate some type of protective strategy or muscular adaptation in the ACL-injured patients.
authors.affiliation: Division of Sportstrauma, Department of Orthopedics, Aarhus University Hospital, Tage Hansens Gade 2, 8000, Aarhus C, Denmark. marie.bagger.bohn@clin.au.dk.
authors.forename: Marie Bagger
authors.initials: MB
authors.lastname: Bohn
authors.affiliation: Department of Physiotherapy and Occupational Therapy, Aarhus University Hospital, Palle Juul-Jensens Boulevard 99, 8200, Aarhus N, Denmark.
authors.forename: Annemette Krintel
authors.initials: AK
authors.lastname: Petersen
authors.affiliation: Department of Public Health - Sport, Aarhus University, Dalgas Avenue 4, 8000, Aarhus C, Denmark.
authors.forename: Dennis Brandborg
authors.initials: DB
authors.lastname: Nielsen
authors.affiliation: Department of Public Health - Sport, Aarhus University, Dalgas Avenue 4, 8000, Aarhus C, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Sørensen
authors.affiliation: Division of Sportstrauma, Department of Orthopedics, Aarhus University Hospital, Tage Hansens Gade 2, 8000, Aarhus C, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Lind
keywords: ACL; ACL-deficient; Laxity; Motion analysis; Pivoting; Stiffness