title: Femoral fixation of hamstring grafts in posterior cruciate ligament reconstruction: biomechanical evaluation of different fixation techniques: is there an acute angle effect?
abstract: BACKGROUND
  The literature provides little biomechanical data about femoral fixation of hamstring grafts in posterior cruciate ligament reconstruction.
  
  
  OBJECTIVE
  A hybrid fixation technique with use of an undersized screw has sufficient strength to provide secure fixation of posterior cruciate ligament grafts. Additional aperture fixation with a biodegradable interference screw can prevent graft damage that might be caused by an acute angle on the edge of the femoral tunnel.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  In part 1, extracortical fixation of posterior cruciate ligament reconstructions with quadrupled porcine flexor digitorum grafts to simulate human hamstring grafts was compared with hybrid fixation methods using 6-, 7-, and 8-mm screws. Groups were tested in cycling loading with the load applied in line with the bone tunnel. In part 2, extracortical fixation was compared with hybrid fixation using a 1-mm undersized screw anterior and posterior to the graft. Structural properties and graft abrasion were evaluated after cyclic loading with the load applied at 90 degrees to the tunnel. In each group, 8 porcine knees were tested.
  
  
  RESULTS
  In part 1, stiffness, maximum load, and yield load were significantly higher for hybrid fixation than for extracortical fixation. Hybrid fixation with an 8-mm screw resulted in higher yield load than with a 7-mm screw. In part 2, graft laceration was more pronounced in specimens with extracortical fixation than with hybrid fixation. Posterior screw placement was superior to the anterior position.
  
  
  CONCLUSIONS
  For all parameters, hybrid fixation with an interference screw provided superior structural results. No relevant disadvantages of undersized screws could be found. Graft damage due to abrasion at the edge of the femoral bone tunnel was reduced by use of an interference screw. The posterior screw placement seems favorable.
  
  
  CONCLUSIONS
  Hybrid fixation of hamstring grafts in posterior cruciate ligament reconstruction is superior to extracortical fixation alone with no relevant disadvantages of undersized screws. The results raise the suspicion of an acute angle effect of the femoral bone tunnel.
authors.affiliation: Department of Trauma, Hand, and Reconstructive Surgery, Wilhelms University Muenster, Muenster, Germany.
authors.forename: Patricia
authors.initials: P
authors.lastname: Niedzwietzki
authors.forename: Thore
authors.initials: T
authors.lastname: Zantop
authors.forename: Andre
authors.initials: A
authors.lastname: Weimann
authors.forename: Mirco
authors.initials: M
authors.lastname: Herbort
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Raschke
authors.forename: Wolf
authors.initials: W
authors.lastname: Petersen
mesh_terms: D000818:Animals; D001182:Arthroscopy; D001696:Biomechanical Phenomena; D006085:Graft Survival; D016268:Internal Fixators; D018482:Muscle, Skeletal / Q000637:transplantation*; D016119:Posterior Cruciate Ligament / Q000601:surgery*; D019651:Plastic Surgery Procedures; D013314:Stress, Mechanical; D013552:Swine; D013710:Tendons / Q000637:transplantation*; D020858:Tissue and Organ Harvesting; D014182:Transplantation, Autologous