title: In vitro biomechanical testing of different configurations of acrylic external skeletal fixator constructs.
abstract: OBJECTIVE
  To evaluate the in vitro biomechanical properties of four different configurations of acrylic external skeletal fixator constructs.
  
  
  METHODS
  Simulated bone constructs were prepared using two segments of 20 mm ultra-high-density polyethylene rods with a gap of 5 mm. The full pins (1.5 mm) were passed through the proximal and distal segments of ultra-high-density polyethylene rods, in the same plane, parallel to each other in configuration U, and were crossed in the M1, M2 and C configurations at a 90° angle to each other. Configuration U was a single bilateral uniplanar construct, M1 was a double orthogonal bilateral construct, M2 was a double orthogonal bilateral construct with proximal and distal connecting articulations, and C was a double orthogonal bilateral construct with proximal and distal circumferential articulations. Temporary scaffolds of different external skeletal fixator configurations were constructed using commercially available polyvinyl chloride pipes (20 mm) connected and secured to the fixation pins at a fixed distance from the rods. Acrylic powder (polymer) mixed with liquid (monomer) was poured into the pipes and allowed to solidify to form the side bars and rings. The external skeletal fixator constructs were then subjected to axial compression, cranio-caudal three-point bending and torsion (n = 4 each) using a universal testing machine. Mechanical parameters, namely stress, strain, modulus of elasticity, stiffness and bending moment of fixator constructs, were determined from load-displacement curves.
  
  
  RESULTS
  Configuration U was the weakest and configuration C was the strongest under all the testing modes. Under compression, the M1, M2 and C configurations were similar. Under bending, a significant difference was observed among the uniplanar, multiplanar and circular configurations with no difference between M1 and M2. However, under torsion, all the external skeletal fixator configurations differed significantly.
  
  
  CONCLUSIONS
  The freeform external skeletal fixator using acrylic as a replacement for a metallic bar may be useful to treat bone fractures and luxations in small animals, as it is mechanically strong, lightweight, economical, and pins can be passed from any direction depending upon the clinical situation.
authors.forename: S K
authors.initials: SK
authors.lastname: Tyagi
authors.affiliation: Dr. Hari Prasad Aithal, MVSc, PhD, Division of Surgery, Indian Veterinary Research Institute, Izatnagar-243 122, Uttar Pradesh, India, Phone: +91 0581 2315262, Fax: +91 0581 2303284, E-mail: aithal@ivri.res.in or hpaithal@rediffmail.com.
authors.forename: H P
authors.initials: HP
authors.lastname: Aithal
authors.forename: P
authors.initials: P
authors.lastname: Kinjavdekar
authors.lastname: Amarpal
authors.forename: A M
authors.initials: AM
authors.lastname: Pawde
authors.forename: T
authors.initials: T
authors.lastname: Srivastava
authors.forename: J
authors.initials: J
authors.lastname: Singh
authors.forename: D N
authors.initials: DN
authors.lastname: Madhu
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails; D019245:Compressive Strength; D004548:Elasticity; D016267:External Fixators / Q000592:standards; D005592:Fracture Fixation / Q000379:methods*; D050723:Fractures, Bone / Q000628:therapy; D066298:In Vitro Techniques; D019904:Polymethyl Methacrylate / Q000627:therapeutic use*; D054159:Torsion, Mechanical
chemical_list: D019904:Polymethyl Methacrylate
keywords: Biomechanical study; acrylic fixator; external skeletal fixation