In Vivo Calibration of a Femoral Fixation Device Transducer for Measuring Anterior Cruciate Ligament Graft Tension: A Study in an Ovine Model

[+] Author and Article Information
Isaac Zacharias, Stephen M. Howell

Department of Mechanical Engineering, University of California, Davis, CA 95616

M. L. Hull

Department of Mechanical Engineering and Biomedical Engineering Program, University of California, Davis, CA 95616

Keith W. Lawhorn

Department of Orthopedics, David Grant Medical Center, Travis Air Force Base, CA 90909

J Biomech Eng 123(4), 355-361 (Feb 27, 2001) (7 pages) doi:10.1115/1.1385842 History: Received March 07, 2000; Revised February 27, 2001
Copyright © 2001 by ASME
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Diagram showing the threaded body and hexagonal head welded to the instrumented beam of the FDT. The strain gages were applied to the larger rectangular section and oriented at ±45 deg relative to the long axis of the beam. The threaded body and hexagonal head were hollow to accommodate the three-pronged socket for data transmission.
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Diagram showing the detachment of the common digital extensor tendon from its origin on the lateral femoral condyle
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Diagram showing alignment of the L-shaped wrench to the hollow cylindrical alignment tool. The alignment tool was inserted into the graft tunnel with the cable passing through the center. The L-shaped wrench fit over the hexagonal head of the FDT such that the rod pointed in the direction of the long-axis of the cross section of the FDT beam. When the rod of the L-shaped wrench was parallel to the hollow alignment tool, the FDT was oriented correctly.
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Diagram of the completed FDT surgery. The common digital extensor graft was looped around the post of the FDT and passed back out of the graft tunnel where it was sewn to itself.
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Diagram of the testing setup showing the alignment of the bone tunnel with the axis of the materials testing machine
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Calibration regressions and graft loads for animal S202. The after-graft insertion calibration was nearly identical to the before-graft insertion calibration. The post-mortem calibration matched the before-graft insertion calibration well with a relative percent error of only 4.3 percent using before-graft insertion calibration as the standard. The voltages caused by loading of the graft were very low compared to those in the post-mortem calibration indicating that only a small fraction of the load applied to the graft was actually transmitted to the FDT. The majority of the load was supported by the biological bond between the graft and bone tunnel.




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