Spatial Micromovements of Uncemented Femoral Components After Torsional Loads

[+] Author and Article Information
W. Görtz

Biomechanical Research Laboratory, Orthopaedic Surgery Hospital, University of Heidelberg, Schlierbacher Landstr. 200a, 69118 Heidelberg, Germany

U. V. Nägerl

Max-Planck Institute of Neurobiology, Am Klopferspitz 18A, 82152 München-Martinsried, Germany

H. Nägerl

IV. Physical Institute, University of Göttingen, Bunsenstr. 13-15, 37073 Göttingen, Germany

M. Thomsen

Biomechanical Research Laboratory, Orthopaedic Surgery Hospital, University of Heidelberg, Schlierbacher Landstr. 200a, 69118 Heidelberg, Germanye-mail: Marc.Thomsen@ok.uni-heidelberg.de

J Biomech Eng 124(6), 706-713 (Dec 27, 2002) (8 pages) doi:10.1115/1.1517565 History: Received September 01, 2001; Revised July 01, 2002; Online December 27, 2002
Copyright © 2002 by ASME
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The axial torque was produced by weights w1 (30 N) and w2 (30 N) whose horizontal distance was adjusted by two computer-controlled steppermotors. The weights w3 and w4 produced the axial preload of 80 N.
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A-D. Survey of the 4 prostheses: (A) ABG, (B) CLS, (C) S-ROM, (D) Alloclassic
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Survey of the levels of the measured sites with respect to the lesser trochanter
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Insert from Fig. 1 showing the six dimensional measuring system. Six linear variable differential transducers in a three (S1, S2, S3)-two (S4, S5)-one (S6) setting to measure the spatial position of the movable cube shown here rigidly tied to the site #3 (8 cm below the lesser trochanter).
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Rotational angle α as a function of torque Tz: typical characteristics. The dashed line represents the linear fit.
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A-D. Examples of the 4 typical patterns of torque transfer. The micromotions between stem twist and bone twist are graphically indicated. The ordinate shows rotational displacement in millidegrees/Nm. The abscissa reveals these measurements dependent on site of measurement. Graph A (ABG) is typical for a proximal fixation. Graph B (CLS) represents proximal torque transfer with more distal fixation then A (distally shifted). The S-ROM (C) has proximal and distal torque transfer (overall fixation). Note that there is movement between sleeve and stem. The Alloclassic (D) is a representative for distal fixation with significant rotational displacement in the proximal part.
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Distal limit of the area of maximum torque transfer to the composite femur for the 4 prostheses




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