title: A novel non-bridging external fixator construct versus volar angular stable plating for the fixation of intra-articular fractures of the distal radius--a biomechanical study.
abstract: Non-bridging external fixation has recently been introduced as an alternative to volar angular stable plating for the fixation of unstable intra-articular distal radial fractures. The purpose of this study was to biomechanically compare a new non-bridging external fixator construct to volar angular stable plate fixation in a dorsally comminuted intra-articular fracture model of the distal radius.
  
  
  METHODS
  Five pairs of fresh frozen human cadaveric radii were randomly supplied with either a non-bridging external fixator or a stainless steel volar locking plate. A three-fragmental AO 23-C2.1 fracture was created by removing a 15 degrees dorsal wedge with remaining volar cortical contact and by an intra-articular osteotomy lateral to the lister-tubercle. Physiological load transfer via the wrist was simulated by means of a custom-made seesaw. For biomechanical testing, the bones were loaded in cyclic axial compression. Starting at 100N, the load was monotonically increased at 0.025 degrees N per cycle until failure of the construct. Motion of the lunate and scaphoid fragments with respect to the radial diaphysis was acquired by optical three-dimensional (3D) motion tracking. Plastic wedge deformation was determined after 2000, 4000 and 6000 cycles.
  
  
  RESULTS
  The amplitude of wedge motion at the beginning of the test as a measure for construct stiffness was significantly lower for the fixator group (P=0.003, power=0.99). Plastic wedge deformation after 2000, 4000 and 6000 cycles was found significantly lower for the external fixator (repeated measures analysis of variance (ANOVA), P=0.009, power=0.86). Displacement of the intra-articular gap was found below 0.6mm (mean) for both groups (P>0.05).
  
  
  CONCLUSIONS
  The study revealed superior biomechanical properties of the proposed non-bridging external fixation compared to volar locked plating in an unstable intra-articular fracture model with volar cortical support. However, both fixation techniques seem to apply sufficient stabilisation to restore and retain anatomy after fracture of the most distal part of the radius and should be individually chosen according to distinct criteria.
authors.affiliation: AO Research Institute, AO Foundation, Clavadelerstrasse 8, 7270 Davos, Switzerland. markus.windolf@aofoundation.org
authors.forename: Markus
authors.initials: M
authors.lastname: Windolf
authors.forename: Karsten
authors.initials: K
authors.lastname: Schwieger
authors.forename: Ben
authors.initials: B
authors.lastname: Ockert
authors.forename: Jesse B
authors.initials: JB
authors.lastname: Jupiter
authors.forename: Georg
authors.initials: G
authors.lastname: Gradl
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D002102:Cadaver; D004867:Equipment Design; D016267:External Fixators; D005260:Female; D005592:Fracture Fixation / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D057072:Intra-Articular Fractures / Q000601:surgery*; D008297:Male; D008422:Materials Testing / Q000379:methods*; D008954:Models, Biological; D011885:Radius Fractures / Q000601:surgery*; D013314:Stress, Mechanical; D016474:Weight-Bearing; D014955:Wrist Joint