title: Femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction: a comparative biomechanical study.
abstract: BACKGROUND
  Optimization of anterior cruciate ligament (ACL) fixation is desired to improve graft healing. New soft tissue cortical suspension devices for femoral tunnel fixation should be biomechanically evaluated.
  
  
  OBJECTIVE
  All femoral fixation devices would prevent a clinically significant amount of displacement and support loads significantly larger than in situ forces experienced by the ACL during early rehabilitation.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Four cortical soft tissue ACL graft suspension devices were tested under cyclic and pull-to-failure loading conditions in both an isolated device-only setup and as a complete bone-device-tendon construct in porcine femurs using a tensile testing machine.
  
  
  RESULTS
  There were significant differences in the ultimate failure loads among the devices. The highest ultimate failure loads when tested as a construct were observed for the XO Button (1748 N), followed by the Endobutton CL (1456 N), ToggleLoc with ZipLoop (1334 N), and TightRope RT (859 N). Cyclic displacement after 1000 cycles during isolated device testing was less than 1 mm for all devices. Cyclic displacements after 1000 cycles in the porcine construct were 1.88 mm, 2.74 mm, 3.34 mm, and 1.82 mm for the Endobutton, TightRope, ToggleLoc, and XO Button, respectively; all were significantly different from each other except when the Endobutton was compared with the XO Button. The ToggleLoc exceeded the 3.0-mm displacement threshold defined as a clinical failure. The most displacement occurred during the first cycle, especially for the adjustable-length loop devices. Stiffness reapproximated the native ACL stiffness for all constructs.
  
  
  CONCLUSIONS
  The Endobutton, TightRope, and XO Button have the necessary biomechanical properties with regard to ultimate failure strength, displacement, and stiffness for initial fixation of soft tissue grafts in the femoral tunnel for ACL reconstruction. The ToggleLoc had sufficient ultimate failure strength but crossed our 3.0-mm clinical failure threshold for cyclic displacement. Although this study was not designed to compare fixed and adjustable-length loop devices, it was noted that both fixed-loop devices allowed less cyclic displacement and initial displacement.
  
  
  CONCLUSIONS
  Adjustable-length loop devices may need to be retensioned after cycling the knee and fixing the tibial side to account for the increased initial displacement seen with these devices.
authors.affiliation: Department of BioMedical Engineering, Steadman Philippon Research Institute, CO, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Petre
authors.forename: Sean D
authors.initials: SD
authors.lastname: Smith
authors.forename: Kyle S
authors.initials: KS
authors.lastname: Jansson
authors.forename: Peter-Paul
authors.initials: PP
authors.lastname: de Meijer
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Hackett
authors.forename: Robert F
authors.initials: RF
authors.lastname: LaPrade
authors.forename: Coen A
authors.initials: CA
authors.lastname: Wijdicks
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000503:physiopathology / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D004195:Disease Models, Animal; D005269:Femur / Q000601:surgery*; D016268:Internal Fixators; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D013552:Swine