title: Anterior cruciate ligament fixation: is radial force a predictor of the pullout strength of soft-tissue interference devices?
abstract: BACKGROUND
  In anterior cruciate ligament (ACL) reconstruction, an interference device achieves soft-tissue graft fixation by radially compressing the graft against the bone.
  
  
  OBJECTIVE
  The objective of this study was to measure the radial force generated by different interference devices and evaluate the effect of this radial force on the pullout strength of graft-device constructs.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  A resultant force (F(R)) was used as a representative measure of the total radial force generated. Bovine tendons were fixated in either synthetic bone or porcine tibia using one of following devices: (1) RCI titanium screw, (2) PEEK screw, (3) IntraFix sheath-and-screw device, and (4) ExoShape sheath-and-insert device. F(R) was measured while each device was inserted into synthetic bone mounted on a test machine (n=5 for each device). In a subsequent test series, graft-device constructs were loaded to failure at 50mm/min. The pullout strength was measured as the ultimate load before failure (n=10 for each device).
  
  
  RESULTS
  The F(R) values generated during insertion into synthetic bone were 777 ± 86N, 865 ± 140N, 1313 ± 198N, and 1780 ± 255N for the RCI screw, PEEK screw, IntraFix, and ExoShape, respectively. The pullout strengths in synthetic bone for the RCI screw, PEEK screw, IntraFix and ExoShape were 883 ± 125N, 716 ± 249N, 1147 ± 142N, and 1233 ± 190N, respectively.
  
  
  CONCLUSIONS
  These results suggest that the F(R) generated during interference fixation affects the pullout strength with sheath-based devices providing superior F(R) compared with interference screws. The use of synthetic bone was validated by comparing the pullout strengths to those when tested in porcine tibia.
  
  
  CONCLUSIONS
  These results could be valuable to a surgeon when determining the best fixation device to use in the clinical setting.
authors.affiliation: MedShape, Inc., Research and Development, Atlanta, GA 30318, USA. Kathryn.smith@medshape.com
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Smith
authors.forename: Mateo
authors.initials: M
authors.lastname: Garcia
authors.forename: Kadija
authors.initials: K
authors.lastname: McAnuff
authors.forename: Robert
authors.initials: R
authors.lastname: Lamell
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Yakacki
authors.forename: Jack
authors.initials: J
authors.lastname: Griffis
authors.forename: Geoffrey B
authors.initials: GB
authors.lastname: Higgs
authors.forename: Ken
authors.initials: K
authors.lastname: Gall
mesh_terms: D000818:Animals; D059549:Anterior Cruciate Ligament Reconstruction / Q000295:instrumentation*; D001863:Bone Screws; D018786:Bone Substitutes; D002417:Cattle; D004867:Equipment Design; D008422:Materials Testing; D053441:Suture Anchors; D013552:Swine; D013718:Tensile Strength
chemical_list: D018786:Bone Substitutes