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Comparison of torsional properties between a Fixateur Externe du Service de Santé des Armées and an acrylic tie-in external skeletal fixator in a red-tailed hawk (Buteo jamaicensis) synthetic tibiotarsal bone model

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  • 1 1Veterinary Medical Teaching Hospital, University of California-Davis, Davis, CA 95616.
  • | 2 2Department of Surgical and Radiological Sciences, University of California-Davis, Davis, CA 95616.
  • | 3 3Department of Medicine and Epidemiology, University of California-Davis, Davis, CA 95616.

Abstract

OBJECTIVE

To compare the torsional mechanical properties of 2 external skeletal fixators (ESFs) placed with 2 intramedullary pin (IP) and transfixation pin (TP) size combinations in a model of raptor tibiotarsal bone fracture.

SAMPLE

24 ESF-synthetic tibiotarsal bone model (polyoxymethylene) constructs.

PROCEDURES

Synthetic bone models were fabricated with an 8-mm (simulated fracture) gap. Four types of ESF-synthetic bone model constructs (6/group) were tested: a FESSA with a 1.6-mm IP and 1.6-mm TPs, a FESSA with a 2.0-mm IP and 1.1-mm TPs, an acrylic connecting bar with a 1.6-mm IP and 1.6-mm TPs, and an acrylic connecting bar with a 2.0-mm IP and 1.1-mm TPs. Models were rotated in torsion (5°/s) to failure or the machine angle limit (80°). Mechanical variables at yield and at failure were determined from load deformation curves. Effects of overall construct type, connecting bar type, and IP and TP size combination on mechanical properties were assessed with mixed-model ANOVAs.

RESULTS

Both FESSA constructs had significantly greater median stiffness and median torque at yield than both acrylic bar constructs; FESSA constructs with a 1.6-mm IP and 1.6-mm TPs had greatest stiffness of all tested constructs and lowest gap strain at yield. No FESSA constructs failed during testing; 7 of 12 acrylic bar constructs failed by fracture of the connecting bar at the interface with a TP.

CONCLUSIONS AND CLINICAL RELEVANCE

Although acrylic bar ESFs have been successfully used in avian patients, the FESSA constructs in this study were mechanically superior to acrylic bar constructs, with greatest benefit resulting from use with the larger TP configuration.

Contributor Notes

Address correspondence to Dr. Kapatkin (askapatkin@ucdavis.edu).

Dr. Kerrigan's present address is Vista Veterinary Specialists, Sacramento, CA 95831.

Dr. Robinson's present address is BluePearl Specialty and Emergency Pet Hospital, Seattle, WA 98133.