title: Biomechanical analysis of a volar variable-angle locking plate: the effect of capturing a distal radial styloid fragment.
abstract: OBJECTIVE
  Variable-angle volar locked constructs for distal radius fractures are a recent treatment addition. This study sought to biomechanically evaluate a variable-angle volar locking plate as compared with a fixed-angle construct.
  
  
  METHODS
  We created 2 different AO-C3 osteotomies in fourth-generation synthetic composite distal radiuses and labeled them proximal and distal. The distal osteotomy consisted of a smaller radial styloid fragment. We then fixed both sets of specimens with either a fixed-angle or variable-angle volar locking construct. We tested samples in axial compression with regard to cyclical loading and load to failure. Articular stepoff, stiffness, and load to failure data were then analyzed.
  
  
  RESULTS
  Neither the proximal nor the distal osteotomy groups showed articular failure after cyclic loading, significant loss of stiffness over cycling, or superior stiffness compared with the other. After load to failure in the proximal osteotomy, 1 of 8 fixed-angle and none of 8 variable-angle constructs had articular failure, whereas in the distal osteotomy, all 8 fixed-angle and none of 8 variable-angle constructs had articular failure.
  
  
  CONCLUSIONS
  Variable-angle and fixed-angle volar locked fixation of unstable intra-articular distal radius fractures in fourth-generation composite radii provide mechanically sound constructs with high load to failure values and no loss of stiffness over testing. The variable-angle construct exhibited excellent resistance to articular stepoff at load to failure and no loss of stiffness throughout cyclic loading, and did not exhibit significantly less overall stiffness compared with fixed-angle constructs. The variable-angle fixation exhibited a distinct mechanical advantage over fixed-angle fixation in the setting of a smaller radial styloid fragment.
  
  
  CONCLUSIONS
  Variable-angle constructs could be expected to hold up to standard loads in the postoperative period as well as traditional fixed-angle devices. The additional cost associated with variable-angle constructs may be warranted when treating distal radius fractures with radial styloid fragments, owing to the fragment-specific fixation allowed by customized screw placement.
authors.affiliation: Department of Orthopaedic Surgery and Sports Medicine, University of Rochester, Rochester, NY 14608, USA. spencer_stanbury@urmc.rochester.edu
authors.forename: Spencer J
authors.initials: SJ
authors.lastname: Stanbury
authors.forename: Art
authors.initials: A
authors.lastname: Salo
authors.forename: John C
authors.initials: JC
authors.lastname: Elfar
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D004867:Equipment Design; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D057072:Intra-Articular Fractures / Q000601:surgery*; D008422:Materials Testing; D010027:Osteotomy / Q000379:methods; D011474:Prosthesis Design; D011885:Radius Fractures / Q000601:surgery*