title: Reverse Anterior Cruciate Ligament Reconstruction Fixation: A Biomechanical Comparison Study of Tibial Cross-Pin and Femoral Interference Screw Fixation.
abstract: OBJECTIVE
  To evaluate the biomechanical performance of tibial cross-pin (TCP) fixation relative to femoral cross-pin (FCP), femoral interference screw (FIS), and tibial interference screw (TIS) fixation.
  
  
  METHODS
  We randomized 40 porcine specimens (20 tibias and 20 femurs) to TIS fixation (group 1, n = 10), FIS fixation (group 2, n = 10), TCP fixation (group 3, n = 10), or FCP fixation (group 4, n = 10) and performed biomechanical testing to compare ultimate load, stiffness, yield load, cyclic displacement, and load at 5-mm displacement. We performed cross-pin fixation of the looped end and interference screw fixation of the free ends of 9-mm-diameter bovine extensor digitorum communis tendon grafts. Graft fixation constructs were cyclically loaded and then loaded to failure in line with the tunnels.
  
  
  RESULTS
  Regarding yield load, FIS was superior to TIS (704 ± 125 N vs 504 ± 118 N, P = .002), TCP was superior to TIS (1,449 ± 265 N vs 504 ± 118 N, P < .001), and TCP was superior to FCP (1,449 ± 265 N vs 792 ± 397 N, P < .001). Cyclic displacement for FCP was superior to TCP. Cyclic displacement for TIS versus FIS showed no statistically significant difference (2.5 ± 1.0 mm vs 2.2 ± 0.6 mm, P = .298). Interference screw fixation consistently failed by graft slippage, whereas TCP fixation failed by tibial bone failure. FCP fixation failed by either femoral bone failure or failure elsewhere in the testing apparatus.
  
  
  CONCLUSIONS
  Regarding yield load, TCP fixation performed biomechanically superior to the clinically proven FCP at time zero. Because TIS fixation shows the lowest yield strength, it represents the weak link, and combined TCP-FIS fixation theoretically would be biomechanically superior relative to combined FCP-TIS fixation with regard to yield load. Cyclic displacement showed a small difference in favor of FCP over TCP fixation and no difference between TIS and FIS.
  
  
  CONCLUSIONS
  Time-zero biomechanics of TCP fixation paired with FIS fixation show that this method of fixation can be considered a potential alternative to current practice and may pose clinical benefits in different clinical scenarios of anterior cruciate ligament reconstruction.
authors.affiliation: Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois, U.S.A.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lawley
authors.affiliation: Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, U.S.A.. Electronic address: Samuel.klein@my.rfums.org.
authors.forename: Samuel E
authors.initials: SE
authors.lastname: Klein
authors.affiliation: Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois, U.S.A.; Hinsdale Orthopedics, Hinsdale, Illinois, U.S.A.; Orthopaedic Surgery and Sports Medicine Teaching and Research Foundation, Westmont, Illinois, U.S.A.
authors.forename: Steven C
authors.initials: SC
authors.lastname: Chudik
mesh_terms: D000818:Animals; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D001696:Biomechanical Phenomena; D001858:Bone Nails; D001863:Bone Screws; D002417:Cattle; D005269:Femur / Q000601:surgery*; D008422:Materials Testing; D013552:Swine; D013710:Tendons / Q000637:transplantation; D013977:Tibia / Q000601:surgery*