title: Reliability of threaded locking screws.
abstract: OBJECTIVE
  A frequent problem for interlocking nailing that affects the treatment of the fracture is locking screw deformation. The aim of this study is to determine whether bending resistance is different between high, low, and unthreaded locking screws of interlocking femoral nails.
  
  
  METHODS
  Ninety screws were used in this experimental study, with 10 screws used in each of 9 groups. Three-point bending tests were performed on 6 groups of 5 mm screws (titanium, stainless steel, crossed with unthreaded, low threaded, and high threaded) and the same 3 thread types of 5.5 mm stainless steel screws in a 30-mm inner diameter steel tube, imitating the level of the lesser trochanter. An axial compressor was used to determine the yield points for permanent deformation in the locking screws by way of 3-point bending tests.
  
  
  RESULTS
  The mean yield point value of the 3-point bending tests of 5-mm low threaded stainless steel locking screws was 2071 N, 53% less than that of unthreaded screws (3169 N). The mean yield point value of 5-mm high threaded stainless steel locking screws was 556 N, 272% less than that of low threaded screws (2071 N).
  
  
  CONCLUSIONS
  To avoid locking screw deformation, high threaded screws must not be used as locking screws. In cases of unreliable patients, 5-mm low threaded screws should not be used in the nailing of comminuted or oblique femur shaft fractures. All 5-mm unthreaded screws and 5.5-mm low threaded stainless steel screws can be used safely in full weight-bearing conditions of unreliable patients.
authors.affiliation: Şifa University Faculty of Medicine, Department of Orthopedics and Traumatology, İzmir, Turkey.
authors.forename: Ahmet Adnan
authors.initials: AA
authors.lastname: Karaarslan
authors.affiliation: Dokuz Eylül University Faculty of Medicine, Department of Orthopedics and Traumatology, İzmir, Turkey.
authors.forename: Ahmet
authors.initials: A
authors.lastname: Karakaşlı
authors.affiliation: Şifa University Faculty of Medicine, Department of Orthopedics and Traumatology, İzmir, Turkey.
authors.forename: Tolga
authors.initials: T
authors.lastname: Karcı
authors.affiliation: Şifa University Faculty of Medicine, Department of Orthopedics and Traumatology, İzmir, Turkey.
authors.forename: Hakan
authors.initials: H
authors.lastname: Aycan
authors.affiliation: Şifa University Faculty of Medicine, Department of Orthopedics and Traumatology, İzmir, Turkey.
authors.forename: Erhan
authors.initials: E
authors.lastname: Sesli
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D008422:Materials Testing / Q000379:methods*; D015203:Reproducibility of Results; D013718:Tensile Strength; D016474:Weight-Bearing