title: Femoral suspension devices for anterior cruciate ligament reconstruction: do adjustable loops lengthen?
abstract: BACKGROUND
  Cortical suspension devices are commonly used for femoral graft fixation during anterior cruciate ligament (ACL) reconstructive surgery. Adjustable-length fixation devices provide technical advantages over fixed-length loops but may be more susceptible to lengthening during cyclic loading.
  
  
  OBJECTIVE
  Both fixed-length and adjustable-length femoral cortical suspension devices would withstand ultimate loads greater than those normally experienced by the native ACL and would prevent clinically significant lengthening during prolonged cyclic loading.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Mechanical testing was performed on 3 ACL graft cortical suspensory devices by use of an extended cyclic loading (4500 cycles at 10-250 N) and pull-to-failure protocol. Two adjustable-length devices were additionally tested with the free suture ends tied.
  
  
  RESULTS
  Total displacement after 4500 cycles of tensioning at variable loads (expressed as mean ± SD) was 42.45 mm (±7.01 mm) for the Arthrex TightRope RT, 5.76 mm (±0.35 mm) for the Biomet ToggleLoc, and 1.34 mm (±0.03 mm) for the Smith & Nephew EndoButton CL Ultra (P < .001). The Arthrex TightRope reached clinical failure of 3 mm lengthening after fewer cycles (1349 ± 316) than the Biomet ToggleLoc (2576 ± 73) (P < .001). The Smith & Nephew EndoButton did not reach clinical failure during cyclic testing. With the free suture ends tied, after 4500 cycles, the Arthrex TightRope had a significant decrease in lengthening to 13.36 ± 1.86 mm (P < .037) There was also a significant difference in ultimate load between the TightRope (809.11 ± 52.94 N) and the other 2 constructs (P < .001).
  
  
  CONCLUSIONS
  The ultimate load of all graft-fixation devices exceeded the forces likely to be experienced in a patient's knee during the early postoperative rehabilitation period. However, the adjustable-length fixation devices experienced a clinically significant increase in loop lengthening during cyclic testing. This lengthening is partially caused by suture slippage into the adjustable-length loop.
  
  
  CONCLUSIONS
  Adjustable-length ACL graft cortical suspension devices lengthen under cyclic loads because free suture ends are pulled into the adjustable loop. This may allow for graft-fixation device lengthening during the acute postoperative period.
authors.affiliation: Travis C. Burns, Deparment of Orthopedics and Rehabilitation, San Antonio Military Medical Center, 3551 Roger Brooke Drive, Fort Sam Houston, TX 78234. travis.c.burns.mil@mail.mil.
authors.forename: Aaron E
authors.initials: AE
authors.lastname: Barrow
authors.forename: Marcello
authors.initials: M
authors.lastname: Pilia
authors.forename: Teja
authors.initials: T
authors.lastname: Guda
authors.forename: Warren R
authors.initials: WR
authors.lastname: Kadrmas
authors.forename: Travis C
authors.initials: TC
authors.lastname: Burns
mesh_terms: D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D005269:Femur / Q000601:surgery*; D016268:Internal Fixators; D008422:Materials Testing; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013536:Suture Techniques
keywords: ACL reconstruction; EndoButton; TightRope; ToggleLoc; cortical button; cortical suspension; cyclic loading; soft tissue graft