title: The effect of interlocking parallel screws in subcapital femoral-neck fracture fixation: a cadaver study.
abstract: BACKGROUND
  A new locking-plate for femoral-neck fractures that provides angular stability to three screws in an inverted triangle configuration was evaluated. The plate is not fixed to the lateral cortex and therefore represents a new treatment principle.
  
  
  METHODS
  Twelve pairs of cadaver femurs (mean T-score -1,95 (range -4,5-0)) with subcapital femoral-neck fractures angulating 60° were randomly allocated to fracture-fixation using either three individual screws or three interlocked screws. Subject-specific axial force and torque were applied by a hip simulator and three-dimensional migrations were recorded. The femurs underwent 10,000 cycles of simulated partial weight-bearing, followed by 10,000 cycles of simulated full weight-bearing and stair climbing.
  
  
  RESULTS
  On average interlocking reduced femoral-head centre migrations 1.6mm (95% CI 0.1-3.1, P = 0.04). The intra-pair correlation of migration was 0.953 (Pearson's r). Interlocking did not change rotational stability (P = 0.87). Adding a locking plate did not affect the risk of failure, however all failed femurs were fixed using the smallest-sized aiming guide.
  
  
  CONCLUSIONS
  Adding a lateral interlocking plate to three screws might improve the fracture stability. However, none of the implants were able to resist the unwanted deformation of the proximal femur. Regardless of the fixation, female sex, reduced bone quality and small sized femurs appear to increase risk of failure.
authors: Orthopaedic Research Centre, Trondheim University Hospital, Norway. Electronic address: trude.basso@ntnu.no.
authors: Trude
authors: T
authors: Basso
authors: Orthopaedic Research Centre, Trondheim University Hospital, Norway.
authors: Jomar
authors: J
authors: Klaksvik
authors: Orthopaedic Research Centre, Trondheim University Hospital, Norway; The Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway.
authors: Olav Andreas
authors: OA
authors: Foss
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D005265:Femoral Neck Fractures / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D016268:Internal Fixators; D008297:Male; D008875:Middle Aged; D011897:Random Allocation; D016474:Weight-Bearing
keywords: Biomechanics; Femoral-neck fracture; Femoral-neck shortening; Internal fixation; Locking plate