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Biomechanical Comparison of Orthofix Pins and Cortical Bone Screws in a Canine Humeral Condylar Fracture Model

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To compare shear stability of simulated humeral lateral condylar fractures reduced with either a self-compressing pin or cortical bone screw. Study Design

In vitro biomechanical tests. Sample Population

Bilateral cadaveric canine humeri (n=18) without evidence of elbow disease. Methods

Lateral condylar fracture was simulated by standardized osteotomy. Bone fragments were stabilized with a self-compressing pin or a cortical bone screw (2.7 or 3.5 mm) inserted in lag fashion. Specimens were mounted in a materials testing system and the condylar fragment displaced in a proximal direction until failure. Mechanical testing variables derived from load–deformation curves were compared between stabilization methods using a Student's paired t-test. Results

There were no statistically significant differences for mechanical testing variables between pin and screw stabilized specimens at expected walk and trot loads. Three yield points subjectively coincided with yield of the interfragmentary interface (Y1), bone at the implant interface (Y2), and implant deformation (Y3). Displacements at Y1 were 48–156% greater for pin than screw stabilized specimens. Y2 and Y3 loads were higher for screw than pin stabilized specimens, but likely supraphysiologic for dogs convalescing after surgical repair. Conclusions

A self-compressing pin or a cortical bone screw inserted in lag fashion both provided adequate strength in applied shear to sustain expected physiologic loads through the repaired canine elbow during postoperative convalescence. Clinical Relevance

Because self-compressing pins were easy to implant and mechanical properties were not significantly different than cortical screws at expected physiologic loads, pins should be considered for the repair of traumatic humeral condylar fractures.
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Keywords: bone screw; dog; humeral lateral condylar fracture; lag fashion; orthofix pin; self-compressing pin

Document Type: Research Article

Affiliations: From the Veterinary Medical Teaching Hospital, J.D. Wheat Veterinary Orthopedic Research Laboratory and the Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA

Publication date: September 1, 2005

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