title: Torsional stability of interference screws derived from bovine bone--a biomechanical study.
abstract: BACKGROUND
  In the present biomechanical study, the torsional stability of different interference screws, made of bovine bone, was tested. Interference screws derived from bovine bone are a possible biological alternative to conventional metallic or bioabsorbable polymer interference screws.
  
  
  METHODS
  In the first part of the study we compared the torsional stability of self-made 8 mm Interference screws (BC) and a commercial 8 mm interference screw (Tutofix). Furthermore, we compared the torsional strength of BC screws with different diameters. For screwing in, a hexagon head and an octagon head were tested. Maximum breaking torques in polymethyl methacrylate resin were recorded by means of an electronic torque screw driver. In the second part of the study the tibial part of a bone-patellar tendon-bone graft was fixed in porcine test specimens using an 8 mm BC screw and the maximum insertion torques were recorded. Each interference screw type was tested 5 times.
  
  
  RESULTS
  There was no statistically significant difference between the different 8 mm interference screws (p = 0.121). Pairwise comparisons did not reveal statistically significant differences, either. It was demonstrated for the BC screws, that a larger screw diameter significantly leads to higher torsional stability (p = 9.779 x 10(-5)). Pairwise comparisons showed a significantly lower torsional stability for the 7 mm BC screw than for the 8 mm BC screw (p = 0.0079) and the 9 mm BC screw (p = 0.0079). Statistically significant differences between the 8 mm and the 9 mm BC screw could not be found (p = 0.15). During screwing into the tibial graft channel of the porcine specimens, insertion torques between 0.5 Nm and 3.2 Nm were recorded. In one case the hexagon head of a BC screw broke off during the last turn.
  
  
  CONCLUSIONS
  The BC screws show comparable torsional stability to Tutofix interference screws. As expected the torsional strength of the screws increases significantly with the diameter. The safety and in vivo performance of products derived from xenogeneic bone should be the focus of further investigations.
authors.affiliation: Department of Orthopaedics and Rheumatology, University Hospital Marburg, Baldingerstrasse, 35043 Marburg, Germany.
authors.forename: Joscha
authors.initials: J
authors.lastname: Bauer
authors.forename: Turgay
authors.initials: T
authors.lastname: Efe
authors.forename: Silke
authors.initials: S
authors.lastname: Herdrich
authors.forename: Leo
authors.initials: L
authors.lastname: Gotzen
authors.forename: Bilal Farouk
authors.initials: BF
authors.lastname: El-Zayat
authors.forename: Jan
authors.initials: J
authors.lastname: Schmitt
authors.forename: Nina
authors.initials: N
authors.lastname: Timmesfeld
authors.forename: Markus Dietmar
authors.initials: MD
authors.lastname: Schofer
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000592:standards*; D018786:Bone Substitutes / Q000592:standards* / Q000627:therapeutic use; D016025:Bone Transplantation / Q000295:instrumentation* / Q000379:methods; D002417:Cattle; D019544:Equipment Failure Analysis / Q000379:methods; D008422:Materials Testing / Q000379:methods*; D017847:Patellar Ligament / Q000502:physiology / Q000637:transplantation; D019904:Polymethyl Methacrylate / Q000592:standards; D013242:Sterilization / Q000379:methods; D013314:Stress, Mechanical; D034421:Sus scrofa; D019415:Torque; D014183:Transplantation, Heterologous / Q000295:instrumentation / Q000379:methods; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D018786:Bone Substitutes; D019904:Polymethyl Methacrylate