title: Comparison of fixation properties between coil-type and screw-type anchors for rotator cuff repair: A virtual pullout testing using 3-dimensional finite element method.
abstract: BACKGROUND
  Pullout of inserted anchor constitutes one of the pathomechanisms of re-tearing after rotator cuff repair. The purpose of the present study was to investigate the fixation properties of suture anchors using 3-dimensional finite element method.
  
  
  METHODS
  The computer models of three types of anchors (TwinFix Ti, HEALICOIL PK and HEALICOIL RG) were inserted into the isotropic cube model that simulated cancellous bone. In the virtual pullout testing, a tensile load (500 N) along the long axis of the inserted anchor was applied to the site of suture thread attachment to simulate a traction force. The distribution of von Mises equivalent stress, the failure patterns of elements inside the cube and the anchor displacement were compared among the three anchors.
  
  
  RESULTS
  In TwinFix Ti, the highest stress concentration was seen around the anchor threads close to the surface of the cube, which caused element failure at this site. On the other hand, both HEALICOIL PK and HEALICOIL RG demonstrated a high stress concentration as well as element failure around the anchor tip. Comparing the anchor displacement, HEALICOIL RG showed the smallest displacement among the three anchors. The tensile loads that required a 0.1-mm displacement for TwinFix Ti, HEALICOIL PK and HEALICOIL RG were 400 N, 370 N, and greater than 500 N, respectively.
  
  
  CONCLUSIONS
  The bony structures close to the footprint surface may be damaged during surgery due to preparation for the bony bed as well as the insertion of anchors. Thus, we assumed that HEALICOIL RG represented the best initial fixation properties among the three anchors tested. Virtual pullout testing using 3-dimensional finite element method could reveal the detailed biomechanical characteristics of each suture anchor, which would be important for shoulder surgeons to improve the clinical outcomes of rotator cuff repair.
authors.affiliation: Division of Orthopedics, Sendai City Hospital, Sendai, Japan(1). Electronic address: sanohirotaka@gmail.com.
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Sano
authors.affiliation: Division of Orthopedics, Sendai City Hospital, Sendai, Japan(1).
authors.forename: Masako
authors.initials: M
authors.lastname: Tokunaga
authors.affiliation: Division of Orthopedics, Sendai City Hospital, Sendai, Japan(1).
authors.forename: Moriyuki
authors.initials: M
authors.lastname: Noguchi
authors.affiliation: Division of Orthopedics, Sendai City Hospital, Sendai, Japan(1).
authors.forename: Takashi
authors.initials: T
authors.lastname: Inawashiro
authors.affiliation: Division of Orthopedics, Sendai City Hospital, Sendai, Japan(1).
authors.forename: Taichi
authors.initials: T
authors.lastname: Irie
authors.affiliation: Division of Orthopedics, Sendai City Hospital, Sendai, Japan(1).
authors.forename: Hiroo
authors.initials: H
authors.lastname: Abe
authors.affiliation: Orthopaedic Surgery and Traumatology HUG, Genève, Switzerland.
authors.forename: Sophie
authors.initials: S
authors.lastname: Abrassart
authors.affiliation: Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Itoi
mesh_terms: D001863:Bone Screws; D004867:Equipment Design; D020342:Finite Element Analysis; D006801:Humans; D008422:Materials Testing; D008954:Models, Biological; D000070636:Rotator Cuff Injuries / Q000601:surgery*; D053441:Suture Anchors; D013718:Tensile Strength