title: Biomechanical Evaluation of the Femoral Neck System in Unstable Pauwels III Femoral Neck Fractures: A Comparison with the Dynamic Hip Screw and Cannulated Screws.
abstract: OBJECTIVE
  To evaluate the biomechanical performance of femoral neck system (FNS) in comparison with established methods for fixation of femoral neck fractures in a cadaveric model.
  
  
  METHODS
  Twenty pairs of fresh-frozen human cadaveric femora were instrumented either with dynamic hip screw and antirotation screw (DHS-screw), DHS-blade, 3 cannulated screws (3CS) or with FNS in a partially paired design. The specimens were randomized to 2 paired treatment groups based on the bone mineral density (BMD), namely DHS-screw/DHS-blade and FNS/3CS. A reduced unstable femoral neck fracture with postero-caudal comminution, OTA/AO 31-B2.3, 70 degrees Pauwels III, was simulated by cutting 30 degrees distal and 15 degrees posterior wedges. Cyclic axial loading was applied in 16 degrees adduction, starting at 500 N and with progressive peak force increase of 0.1 N/cycle until construct failure. Axial stiffness was measured in the third loading cycle. Femoral neck and leg shortening, and varus tilting and implant migration were calculated by means of optical motion tracking.
  
  
  RESULTS
  Mean axial stiffness was 688.8 ± 132.6 N/mm for DHS-screw, 629.1 ± 94.1 N/mm for DHS-blade, 748.9 ± 211.4 N/mm for FNS, and 584.1 ± 156.6 N/mm for 3CS, with no statistical significances. Cycles until 15-mm leg shortening were comparable for DHS-Screw (20,542 ± 7465), DHS-blade (19,161 ± 3793) and FNS (17,372 ± 2996), however significantly higher than for 3CS (7293 ± 2819), P < 0.001. Similarly, cycles until 15 mm femoral neck shortening were comparable between DHS-screw (20,846 ± 7339), DHS-blade (18,974 ± 4032) and FNS (18,171 ± 2585), and significantly higher than 3CS (8039 ± 2778), P < 0.001.
  
  
  CONCLUSIONS
  From a biomechanical point of view, the femoral neck system is a valid alternative to treat unstable femoral neck fractures, representing the advantages of a minimally invasive implant with comparable stability to the 2 DHS systems and superior to cannulated screws.
authors.affiliation: *Cantonal Hospital Baselland, Orthopedic and Musculoskeletal Traumatology Clinic, Bruderholz, Switzerland; †University of Basel, Basel, Switzerland; ‡AO Research Institute Davos, Biomedical Development Program, Davos, Switzerland; §Department of Trauma-, Hand-, and Reconstructive Surgery, University Hospital Jena, Friedrich Schiller University Jena, Jena, Germany; ‖Department of Surgery, Cantonal Hospital Graubuenden, Chur, Switzerland; ¶DePuy Synthes, Zuchwil, Switzerland; and **DePuy Synthes, Suzhou, China.
authors.forename: Karl
authors.initials: K
authors.lastname: Stoffel
authors.forename: Ivan
authors.initials: I
authors.lastname: Zderic
authors.forename: Florian
authors.initials: F
authors.lastname: Gras
authors.forename: Christoph
authors.initials: C
authors.lastname: Sommer
authors.forename: Ursula
authors.initials: U
authors.lastname: Eberli
authors.forename: David
authors.initials: D
authors.lastname: Mueller
authors.forename: Martin
authors.initials: M
authors.lastname: Oswald
authors.forename: Boyko
authors.initials: B
authors.lastname: Gueorguiev
mesh_terms: D000368:Aged; D001863:Bone Screws / Q000145:classification / Q000706:statistics & numerical data*; D002102:Cadaver; D055119:Elastic Modulus; D019544:Equipment Failure Analysis; D005260:Female; D005265:Femoral Neck Fractures / Q000503:physiopathology* / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D017759:Fractures, Malunited / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D013223:Statistics as Topic; D013718:Tensile Strength