title: Primary stability of bone-patellar tendon-bone graft fixation with biodegradable pins.
abstract: OBJECTIVE
  We evaluated the initial bone-patellar tendon-bone (BPTB) graft fixation strength of biodegradable pins compared with interference screws in anterior cruciate ligament reconstruction using bovine knees.
  
  
  METHODS
  Biomechanical in vitro study.
  
  
  METHODS
  Ten BPTB grafts from human donors fixed with 2 biodegradable 2.7-mm pins (Rigid Fix; Ethicon, Mitek Division, Norderstedt, Germany) crossing the bone block perpendicular and 10 BPTB grafts fixed with conventional biodegradable interference screws (Absolute Absorbable Interference Screw; Innovasive Devices, Marlborough, MA) underwent ultimate single-cycle failure loading at a rate of 200 mm/min. The grafts were fixed to bovine tibia to simulate young human femoral bone density. Failure mode, displacement before failure, and ultimate failure load were tested with a testing machine. The pullout force was in line with the bone tunnel to simulate a worst case scenario.
  
  
  RESULTS
  The failure mode for cross pins was either fracture of the bone block (5 specimens) or fracture of the articular pin (5 specimens). The failure mode for interference screws was slippage past the screw in all specimens. In the single cycle loading test, the mean yield load for the biodegradable pins was 400.2 (+/- 122.4) N, maximum load, 524.6 (+/- 136.6) N, with a mean stiffness of 155.2 (+/- 32.4) N/mm. The yield load at failure for the interference screw was 402.7 (+/- 143.9) N, maximum load 515.7 (+/- 168.5) N with a mean stiffness of 168 (+/- 42) N/mm.
  
  
  CONCLUSIONS
  Fixation of a BPTB graft with 2 biodegradable 2.7-mm pins (Rigid Fix) leads to primary stability that is comparable to fixation with biodegradable interference screws.
authors.affiliation: Department of Orthopaedic Surgery, Christian-Albrechts-University Kiel, Kiel, Germany.
authors.forename: Andre
authors.initials: A
authors.lastname: Weimann
authors.forename: Thore
authors.initials: T
authors.lastname: Zantop
authors.forename: Markus
authors.initials: M
authors.lastname: Rümmler
authors.forename: Joachim
authors.initials: J
authors.lastname: Hassenpflug
authors.forename: Wolf
authors.initials: W
authors.lastname: Petersen
mesh_terms: D020341:Absorbable Implants; D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D001696:Biomechanical Phenomena; D001858:Bone Nails; D001863:Bone Screws; D002417:Cattle; D006801:Humans; D007719:Knee Joint / Q000502:physiology / Q000601:surgery; D023421:Models, Animal; D010329:Patella / Q000601:surgery*; D013710:Tendons / Q000502:physiology / Q000637:transplantation*