title: Biomechanical evaluation of interlocking lag screw design in intramedullary nailing of unstable pertrochanteric fractures.
abstract: OBJECTIVE
  Intramedullary nails with special lag screw designs may provide improved mechanical performance and alleviate clinical problems. We hypothesize that the proximal design of trochanteric nails affects mechanical performance.
  
  
  METHODS
  Ten pairs of human cadaveric femora were implanted with 2 different short intramedullary nails without (Gamma3) and with an interlocking lag screw (Intertan). An unstable, multifragmentary, pertrochanteric fracture was created. Bones were tested in a cyclic testing protocol with increasing loads until failure simulating 1 leg stance. Stiffness, failure load, cycles to failure, and fracture gap movements were measured.
  
  
  RESULTS
  Initially stiffness of the interlocking lag screw nail was almost 40% larger (P = 0.005) compared with the noninterlocking nail. During the test, the difference in stiffness gradually decreased. Failure load (13%, P = 0.02) and cycles to failure (18%, P = 0.02) were larger for the interlocking nail construct. Rotation and varus collapse of the head were initially up to 84% lower (P = 0.013) for the interlocking technique. During the test, the rate of rotational instability gradually increased for both techniques.
  
  
  CONCLUSIONS
  The interlocking lag screw design reduced movement of the femoral head and relative movement between fracture fragments. Beyond that the trapezoidal nail design of the Intertan reduced toggling within the trochanteric area and prolonged survival. Although this study showed a decrease in the retention of stability over time, failure did not occur until the equivalent of 2-3 months of reduced physical activity in which healing may have occurred under normal clinical conditions.
authors.affiliation: Institute of Biomechanics, Trauma Center Murnau, Murnau, Germany. stefanie.hofffmann@bgu-murnau.de
authors.forename: Stefanie
authors.initials: S
authors.lastname: Hoffmann
authors.forename: Robert
authors.initials: R
authors.lastname: Paetzold
authors.forename: Daniel
authors.initials: D
authors.lastname: Stephan
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Volker
authors.initials: V
authors.lastname: Buehren
authors.forename: Peter
authors.initials: P
authors.lastname: Augat
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001858:Bone Nails; D001863:Bone Screws; D002102:Cadaver; D004867:Equipment Design; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods; D006620:Hip Fractures / Q000601:surgery*; D006801:Humans; D008297:Male; D008422:Materials Testing / Q000379:methods; D008875:Middle Aged; D016474:Weight-Bearing