title: Fixation strength of biocomposite wedge interference screw in ACL reconstruction: effect of screw length and tunnel/screw ratio. A controlled laboratory study.
abstract: BACKGROUND
  Primary stability of the graft is essential in anterior cruciate ligament surgery. An optimal method of fixation should be easy to insert and provide great resistance against pull-out forces.A controlled laboratory study was designed to test the primary stability of ACL tendinous grafts in the tibial tunnel. The correlation between resistance to traction forces and the cross-section and length of the screw was studied.
  
  
  METHODS
  The tibial phase of ACL reconstruction was performed in forty porcine tibias using digital flexor tendons of the same animal. An 8 mm tunnel was drilled in each specimen and two looped tendons placed as graft. Specimens were divided in five groups according to the diameter and length of the screw used for fixation. Wedge interference screws were used. Longitudinal traction was applied to the graft with a Servohydraulic Fatigue System. Load and displacement were controlled and analyzed.
  
  
  RESULTS
  The mean loads to failure for each group were 295,44 N (Group 1; 9 x 23 screw), 564,05 N (Group 2; 9 x 28), 614,95 N (Group 3; 9 x 35), 651,14 N (Group 4; 10 x 28) and 664,99 (Group 5; 10 x 35). No slippage of the graft was observed in groups 3, 4 and 5. There were significant differences in the load to failure among groups (ANOVA/P < 0.001).
  
  
  CONCLUSIONS
  Longer and wider interference screws provide better fixation in tibial ACL graft fixation. Short screws (23 mm) do not achieve optimal fixation and should be implanted only with special requirements.
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Miguel Servet University Hospital, Zaragoza, Aragón Health Science Institute, Spain. aherrera@salud.aragon.es
authors.forename: Antonio
authors.initials: A
authors.lastname: Herrera
authors.forename: Fernando
authors.initials: F
authors.lastname: Martínez
authors.forename: Daniel
authors.initials: D
authors.lastname: Iglesias
authors.forename: José
authors.initials: J
authors.lastname: Cegoñino
authors.forename: Elena
authors.initials: E
authors.lastname: Ibarz
authors.forename: Luis
authors.initials: L
authors.lastname: Gracia
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D001863:Bone Screws / Q000592:standards*; D019544:Equipment Failure Analysis; D005260:Female; D016268:Internal Fixators / Q000592:standards; D007718:Knee Injuries / Q000601:surgery*; D007719:Knee Joint / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery; D008297:Male; D023421:Models, Animal; D019637:Orthopedic Procedures / Q000295:instrumentation* / Q000379:methods; D019651:Plastic Surgery Procedures / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical; D034421:Sus scrofa; D013710:Tendons / Q000502:physiology / Q000637:transplantation; D013977:Tibia / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery; D016474:Weight-Bearing / Q000502:physiology