title: Biomechanical evaluation of fracture fixation constructs using a variable-angle locked periprosthetic femur plate system.
abstract: BACKGROUND
  In the United States there are more than 230,000 total hip replacements annually, and periprosthetic femoral fractures occur in 0.1-4.5% of those patients. The majority of these fractures occur at the tip of the stem (Vancouver type B1). The purpose of this study was to compare the biomechanically stability and strength of three fixation constructs and identify the most desirable construct.
  
  
  METHODS
  Fifteen medium adult synthetic femurs were implanted with a hip prosthesis and were osteotomized in an oblique plane at the level of the implant tip to simulate a Vancouver type B1 periprosthetic fracture. Fractures were fixed with a non-contact bridging periprosthetic proximal femur plate (Zimmer Inc., Warsaw, IN). Three proximal fixation methods were used: Group 1, bicortical screws; Group 2, unicortical screws and one cerclage cable; and Group 3, three cerclage cables. Distally, all groups had bicortical screws. Biomechanical testing was performed using an axial-torsional testing machine in three different loading modalities (axial compression, lateral bending, and torsional/sagittal bending), next in axial cyclic loading to 10,000 cycles, again in the three loading modalities, and finally to failure in torsional/sagittal bending.
  
  
  RESULTS
  Group 1 had significantly greater load to failure and was significantly stiffer in torsional/sagittal bending than Groups 2 and 3. After cyclic loading, Group 2 had significantly greater axial stiffness than Groups 1 and 3. There was no difference between the three groups in lateral bending stiffness. The average energy absorbed during cyclic loading was significantly lower in Group 2 than in Groups 1 and 3.
  
  
  CONCLUSIONS
  Bicortical screw placement achieved the highest load to failure and the highest torsional/sagittal bending stiffness. Additional unicortical screws improved axial stiffness when using cable fixation. Lateral bending was not influenced by differences in proximal fixation.
  
  
  CONCLUSIONS
  To treat periprosthetic fractures, bicortical screw placement should be attempted to maximize load to failure and torsional/sagittal bending stiffness.
authors.affiliation: Van Andel Research Institute, Grand Rapids, MI, USA; Grand Rapids Medical Education Partners, Grand Rapids, MI, USA; Orthopaedic Associates of Michigan, Grand Rapids, MI, USA; Department of Surgery, BG-University Hospital Bergmannsheil, Ruhr-University Bochum, Germany. Electronic address: martinfhoffmann@gmx.net.
authors.forename: Martin F
authors.initials: MF
authors.lastname: Hoffmann
authors.affiliation: Van Andel Research Institute, Grand Rapids, MI, USA.
authors.forename: Travis A
authors.initials: TA
authors.lastname: Burgers
authors.affiliation: Van Andel Research Institute, Grand Rapids, MI, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Mason
authors.affiliation: Van Andel Research Institute, Grand Rapids, MI, USA.
authors.forename: Bart O
authors.initials: BO
authors.lastname: Williams
authors.affiliation: Van Andel Research Institute, Grand Rapids, MI, USA; Orthopaedic Associates of Michigan, Grand Rapids, MI, USA.
authors.forename: Debra L
authors.initials: DL
authors.lastname: Sietsema
authors.affiliation: Van Andel Research Institute, Grand Rapids, MI, USA; Orthopaedic Associates of Michigan, Grand Rapids, MI, USA.
authors.forename: Clifford B
authors.initials: CB
authors.lastname: Jones
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D005260:Female; D005264:Femoral Fractures / Q000209:etiology / Q000503:physiopathology*; D005593:Fracture Fixation, Internal / Q000009:adverse effects / Q000379:methods; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008422:Materials Testing; D057068:Periprosthetic Fractures / Q000209:etiology / Q000503:physiopathology*; D011183:Postoperative Complications / Q000473:pathology* / Q000601:surgery; D011474:Prosthesis Design; D012307:Risk Factors; D014481:United States
keywords: Biomechanics; Fracture; Locked angle; Periprosthetic; Plate; Total hip replacement