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TECHNICAL BRIEFS

A Device for the Measurement of Pedicle Screw Moments by Means of Internal Strain Gauges

[+] Author and Article Information
Tait S. Smith, Scott A. Yerby, Robert F. McLain, Todd O. McKinley

Orthopaedic Research Laboratories, University of California, Davis, School of Medicine, Sacramento, CA 95817

J Biomech Eng 118(3), 423-425 (Aug 01, 1996) (3 pages) doi:10.1115/1.2796027 History: Online October 30, 2007

Abstract

Pedicle screws are commonly used in spinal reconstruction, and failure of pedicle screws due to bending is a significant clinical problem. To measure the moments typically placed on pedicle screws in situ we instrumented 7 mm Cotrel-Dubousset (CD) pedicle screws with internally mounted strain gauges. The screws were designed to measure flexion-extension moments at a single cross-section as dictated by strain gauge placement. It is possible to measure moments of up to 12 Nm at any location along the length of the screw by constructing transducers with varying strain gauge placements. These transducers are capable of measuring moments at points located within the vertebra including the pedicle, which is where failure usually occurs clinically. Transducer output was both linear and reproducible. These transducers are being used to investigate the load transfer characteristics between the pedicle screw and the vertebra. This technique could be applied to investigations of load sharing in reconstruction plates, lag-screws, and cross-locked intra-medullary nails.

Copyright © 1996 by The American Society of Mechanical Engineers
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