title: Rotationally stable screw-anchor versus sliding hip screw plate systems in stable trochanteric femur fractures: a biomechanical evaluation.
abstract: OBJECTIVE
  The rotationally stable screw-anchor plate system (RoSA) is unique in using a novel screw-blade combination. This investigation tested the hypothesis whether RoSA is advantageous over the sliding hip screw plate system (SHS) with regard to stiffness, failure load, displacement, and migration in stable trochanteric femur fractures (OTA 31A1.1).
  
  
  METHODS
  Thirteen femur pairs (mean age = 79 years; range, 64-92 years) received implants of either the RoSA or SHS (Koenigsee Implants, Allendorf, Germany). Beginning with 300 N and under consecutive 300 N load-increase steps (2000 cycles, 0.5 Hz) the femurs were cycled until failure. Specimens were evaluated for fragment displacement in both frontal and rotational planes and for migration. A survival analysis was carried out.
  
  
  RESULTS
  With regard to stiffness (526 ± 195 N/mm vs 358 ± 143 N/mm; P = 0.006) and the failure load (2838 ± 781 N vs 2262 ± 863 N; P = 0.012), the RoSA proved superior to the SHS. Furthermore, RoSA demonstrated higher rotational stability in comparison to the SHS (1800 N: 0 ± 0 degrees vs 1.1 ± 1.3 degrees; P = 0.015; failure point: 0 ± 0 degrees vs 2.3 ± 2.6 degrees; P = 0.008), measuring rotation about femoral neck axis over time. Whereas cutout occurred only in the RoSA system (n = 3; P = 0.110), the SHS underwent plastic deformation in 7 cases (n = 7; P = 0.003). In one case (7%), the insertion of the RoSA blade resulted in iatrogenic cut-through caused by a jamming of the screw and the blade.
  
  
  CONCLUSIONS
  The fixation of stable trochanteric femur fractures with RoSA in cadavers led to greater primary stability under cyclic load, with significant advantages with regard to stiffness, failure load, and rotational stability, compared with the SHS. A detrimental effect was its migration tendency, which began at 1800 N and occurred in the cranial direction. A meticulous insertion technique was a prerequisite to avoid iatrogenic perforation of the femoral head. Our results will have to be substantiated by further biomechanical and clinical trials using an optimized RoSA system.
authors.affiliation: Department of Orthopaedic Trauma, University of Aachen Medical Center, Aachen, Germany. mknobe@ukaachen.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Knobe
authors.forename: Gertraud
authors.initials: G
authors.lastname: Gradl
authors.forename: Klaus-Jürgen
authors.initials: KJ
authors.lastname: Maier
authors.forename: Wolf
authors.initials: W
authors.lastname: Drescher
authors.forename: Arne
authors.initials: A
authors.lastname: Jansen-Troy
authors.forename: Andreas
authors.initials: A
authors.lastname: Prescher
authors.forename: Toralf
authors.initials: T
authors.lastname: Knechtel
authors.forename: Pia
authors.initials: P
authors.lastname: Antony
authors.forename: Hans-Christoph
authors.initials: HC
authors.lastname: Pape
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D019544:Equipment Failure Analysis; D005264:Femoral Fractures / Q000503:physiopathology* / Q000601:surgery*; D005269:Femur / Q000503:physiopathology* / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D011474:Prosthesis Design; D013718:Tensile Strength; D016896:Treatment Outcome