title: Comparison of outside-in and inside-out technique for tibial fixation of a soft-tissue graft in ACL reconstruction using the Shim technique.
abstract: BACKGROUND
  The aim of this study was to compare the biomechanical properties of tibial fixation of a free tendon graft in ACL reconstruction using the Shim, a new wedge-shaped implant, in an outside-in technique to fixation by the Shim used in an inside-out technique and fixation by interference screw in a porcine model.
  
  
  METHODS
  Porcine tibia and flexor tendons were used. In Group 1, the Shim was applied outside-in. In Group 2, the Shim was inserted inside-out. In the Group 3, an 8-mm interference screw was used. Ten specimens were tested in each group. Load-to-failure, elongation, stiffness and failure mode were recorded. Cyclic loading was performed between 5 and 250 N for 1,000 cycles, followed by a load to failure testing.
  
  
  RESULTS
  Mean maximum load-to-failure was 629.53 N in Group 1,648.54 N in Group 2 and 749.53 N in Group 3. There was no significant difference between the groups. Stiffness varied between 127.34 N/mm in Group 1, 151.27 N/mm in Group 2 and 182.25 N/mm in Group 3. No significant differences were found between outside-in Shim and interference screw fixation. No significant difference was found for elongation among the three groups. The main failure mode was a rupture of the tendon in the IFS group and a slippage of either the implant or the tendon in both groups using the Shim.
  
  
  CONCLUSIONS
  As no statistically significant difference could be seen concerning load to failure, stiffness and elongation between the inside-out and the outside-in techniques, the Shim can be used for tibial fixation in an outside-in or inside-out technique depending on the preference of the surgeon. To prevent slippage of the graft a hybrid fixation should be considered.
authors.affiliation: Department of Trauma, Hand and, Reconstructive Surgery, Wilhelms University Muenster, Waldeyerstraße 1, 48149, Münster, Germany, simon.lenschow@ukmuenster.de.
authors.forename: S
authors.initials: S
authors.lastname: Lenschow
authors.forename: B
authors.initials: B
authors.lastname: Schliemann
authors.forename: M
authors.initials: M
authors.lastname: Schulze
authors.forename: M
authors.initials: M
authors.lastname: Raschke
authors.forename: C
authors.initials: C
authors.lastname: Kösters
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction / Q000295:instrumentation / Q000379:methods*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D009984:Orthopedic Fixation Devices; D013552:Swine; D013710:Tendons / Q000637:transplantation*; D013977:Tibia / Q000601:surgery*; D016474:Weight-Bearing