title: The best location for proximal locking screw for femur interlocking nailing: A biomechanical study.
abstract: BACKGROUND
  Proximal locking screw deformation and screw fracture is a frequently seen problem for femur interlocking nailing that affects fracture healing. We realized that there is lack of literature for the right level for the proximal locking screw. We investigated the difference of locking screw bending resistance between the application of screws on different proximal femoral levels.
  
  
  METHODS
  We used a total of 80 proximal locking screws for eight groups, 10 screws for each group. Three-point bending tests were performed on four types of screws in two different trochanteric levels (the lesser trochanter and 20 mm proximal). We determined the yield points at three-point bending tests that a permanent deformation started in the locking screws using an axial compression testing machine.
  
  
  RESULTS
  The mean yield point value of 5 mm threaded locking screws applied 20 mm proximal of lesser trochanter was 1022 ± 49 (range 986-1057) (mean ± standard deviation, 95% confidence interval). On the other hand, the mean yield point value of the same type of locking screws applied on the lesser trochanteric level was 2089 ± 249 (range 1911-2268). Which means 103% increase of screw resistance between two levels (P = 0.000). In all screw groups, on the lesser trochanter line we determined 98-174% higher than the yield point values of the same type of locking screws in comparison with 20 mm proximal to the lesser trochanter (P = 0.000).
  
  
  CONCLUSIONS
  According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels. To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.
authors.affiliation: Department of Orthopedics and Traumatology, Faculty of Medicine, Şifa University, İzmir, Turkey.
authors.forename: Ahmet A
authors.initials: AA
authors.lastname: Karaarslan
authors.affiliation: Department of Orthopedics and Traumatology, Faculty of Medicine, Dokuz Eylul University, Izmir, Turkey.
authors.forename: Ahmet
authors.initials: A
authors.lastname: Karakaşli
authors.affiliation: Department of Orthopedics and Traumatology, Faculty of Medicine, Şifa University, İzmir, Turkey.
authors.forename: Hakan
authors.initials: H
authors.lastname: Aycan
authors.affiliation: Department of Biomechanics, Institute of Health Sciences, Dokuz Eylul University, Izmir, Turkey.
authors.forename: Berivan
authors.initials: B
authors.lastname: Çeçen
authors.affiliation: Department of Biomechanics, Institute of Health Sciences, Dokuz Eylul University, Izmir, Turkey.
authors.forename: Didem Venüs
authors.initials: DV
authors.lastname: Yildiz
authors.affiliation: Department of Orthopedics and Traumatology, Faculty of Medicine, Şifa University, İzmir, Turkey.
authors.forename: Erhan
authors.initials: E
authors.lastname: Sesli
keywords: Femoral; Femur nail; femur shaft fractures; fixation; fracture; intramedullary; locking screw; nailing; three-point bending test