title: Locked plating of comminuted distal femur fractures: does unlocked screw placement affect stability and failure?
abstract: OBJECTIVE
  Locked plates provide greater stiffness, possibly at the expense of fracture healing. The purpose of this study is to evaluate construct stiffness of distal femur plates as a function of unlocked screw position in cadaveric distal femur fractures.
  
  
  METHODS
  Osteoporotic cadaveric femurs were used. Four diaphyseal bridge plate constructs were created using 13-hole distal femur locking plates, all with identical condylar fixation. Constructs included all locked (AL), all unlocked (AUL), proximal unlocked (PUL), and distally unlocked (DUL) groups. Constructs underwent cyclic axial loading with increasing force per interval. Data were gathered on axial stiffness, torsional stiffness, maximum torque required for 5-degree external rotation, and axial force to failure.
  
  
  RESULTS
  Twenty-one specimens were divided into AL, AUL, PUL, and DUL groups. Axial stiffness was not significantly different between the constructs. AL and PUL demonstrated greater torsional stiffness, maximum torque, and force to failure than AUL and AL showed greater final torsional stiffness and failure force than DUL (P < 0.05). AL and PUL had similar axial, torsion, and failure measures, as did AUL and DUL constructs. All but 2 specimens fractured before medial gap closure during failure tests. Drop-offs on load-displacement curves confirmed all failures.
  
  
  CONCLUSIONS
  Only the screw nearest the gap had significant effect on torsional and failure stiffness but not axial stiffness. Construct mechanics depended on the type of screw placed in this position. This screw nearest the fracture dictates working length stiffness when the working length itself is constant and in turn determines overall construct stiffness in osteoporotic bone.
authors.affiliation: Department of Orthopaedic Surgery, St Louis University, St Louis, MO.
authors.forename: Shari
authors.initials: S
authors.lastname: Cui
authors.forename: J G
authors.initials: JG
authors.lastname: Bledsoe
authors.forename: Heidi
authors.initials: H
authors.lastname: Israel
authors.forename: J T
authors.initials: JT
authors.lastname: Watson
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Cannada
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005264:Femoral Fractures / Q000150:complications / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D018460:Fractures, Comminuted / Q000150:complications / Q000601:surgery*; D006801:Humans; D010024:Osteoporosis / Q000150:complications*; D019415:Torque