title: Restrained tibial rotation may prevent ACL injury during landing at different flexion angles.
abstract: BACKGROUND
  Internal tibial rotation is a risk factor for anterior cruciate ligament (ACL) injury. The effect of restraining tibial rotation (RTR) to prevent ACL injury during single-leg landing is not well understood. We aimed to investigate the effect of impact load and RTR on ACL injury with respect to flexion angle. We hypothesized that RTR could protect the knee from ACL injury compared to free tibial rotation (FTR) regardless of flexion angle and create a safety zone to protect the ACL.
  
  
  METHODS
  Thirty porcine specimens were potted in a rig manufactured to replicate single-leg landing maneuvers. A mechanical testing machine was used to apply external forces in the direction of the tibial long axis. A 3D displacement sensor measured anterior tibial translation (ATT). The specimens were divided into 3 groups of 10 specimens and tested at flexion angles of 22 ± 1°, 37 ± 1° and 52 ± 1° (five RTR and five FTR) through a consecutive range of actuator displacements until ACL failure. After dissection, damage to the joint was visually recorded. Two-way ANOVA were utilized in order to compare compressive forces, torques and A/P displacements with respect to flexion angle.
  
  
  RESULTS
  The largest difference between peak axial compressive forces (~3.4 kN) causing ACL injury between RTR and FTR was reported at a flexion angle of 22°. Tibial torques with RTR was in the same range and < 20 Nm at the instance and just before ACL failure, compared to a significant reduction when cartilage/bone damage (no ACL failure) was reported. Isolated ACL injuries were observed in ten of the 15 FTR specimens. Injuries to bone and cartilage were more common with RTR.
  
  
  CONCLUSIONS
  RTR increases the threshold for ACL injury by elevating the compressive impact load required at lower flexion angles. These findings may contribute to neuromuscular training programs or brace designs used to avoid excessive internal/external tibial rotation. Caution must be exercised as bone/cartilage damage may result.
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Victoria 3010 Australia.
authors.forename: Hossein
authors.initials: H
authors.lastname: Mokhtarzadeh
authors.affiliation: Department of Orthopaedic Surgery The Royal Melbourne Hospital Victoria, 3050, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Ng
authors.affiliation: Department of Biomedical Engineering National University of Singapore 9 Engineering Drive 1, 117575 Singapore.
authors.forename: Chen Hua
authors.initials: CH
authors.lastname: Yeow
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Victoria 3010 Australia.
authors.forename: Denny
authors.initials: D
authors.lastname: Oetomo
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Victoria 3010 Australia.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Malekipour
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Victoria 3010 Australia. Electronic address: pvlee@unimelb.edu.au.
authors.forename: Peter Vee Sin
authors.initials: PV
authors.lastname: Lee
mesh_terms: D000818:Animals; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D006801:Humans; D007718:Knee Injuries / Q000517:prevention & control*; D007719:Knee Joint / Q000502:physiology*; D012307:Risk Factors; D012399:Rotation; D013552:Swine; D013977:Tibia / Q000502:physiology*
keywords: Anterior cruciate ligament; In-vitro cadaveric study; Sport injury; Tibial rotation