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Research Papers

Experimental Analysis of Model-Based Roentgen Stereophotogrammetric Analysis (MBRSA) on Four Typical Prosthesis Components

[+] Author and Article Information
Frank Seehaus1

Department of Orthopaedics, Laboratory for Biomechanics and Biomaterials, Hannover Medical School, Anna-von-Borries-Strasse 1-7, 30625 Hannover, Germanyfrank.seehaus@annastift.de

Judith Emmerich

Department of Orthopaedics, Laboratory for Biomechanics and Biomaterials, Hannover Medical School, Anna-von-Borries-Strasse 1-7, 30625 Hannover, Germanyjudith.emmerich@annastift.de

Bart L. Kaptein

Department of Orthopaedics and Division of Image Processing, and Department of Radiology, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, Netherlandsb.l.kaptein@lumc.nl

Henning Windhagen

Department of Orthopaedics, Laboratory for Biomechanics and Biomaterials, Hannover Medical School, Anna-von-Borries-Strasse 1-7, 30625 Hannover, Germanywindhagen@annastift.de

Christof Hurschler

Department of Orthopaedics, Laboratory for Biomechanics and Biomaterials, Hannover Medical School, Anna-von-Borries-Strasse 1-7, 30625 Hannover, Germanychristof.hurschler@annastift.de

1

Corresponding author.

J Biomech Eng 131(4), 041004 (Feb 02, 2009) (10 pages) doi:10.1115/1.3072892 History: Received April 22, 2008; Revised October 27, 2008; Published February 02, 2009

Classical marker-based roentgen stereophotogrammetric analysis (RSA) is an accurate method of measuring in vivo implant migration. A disadvantage of the method is the necessity of placing tantalum markers on the implant, which constitutes additional manufacturing and certification effort. Model-based RSA (MBRSA) is a method by which pose-estimation of geometric surface-models of the implant is used to detect implant migration. The placement of prosthesis markers is thus no longer necessary. The accuracy of the pose-estimation algorithms used depends on the geometry of the prosthesis as well as the accuracy of the surface models used. The goal of this study was thus to evaluate the experimental accuracy and precision of the MBRSA method for four different, but typical prosthesis geometries, that are commonly implanted. Is there a relationship existing between the accuracy of MBRSA and prosthesis geometries? Four different prosthesis geometries were investigated: one femoral and one tibial total knee arthroplasty (TKA) component and two different femoral stem total hip arthroplasty (THA) components. An experimental phantom model was used to simulate two different implant migration protocols, whereby the implant was moved relative to the surrounding bone (relative prosthesis-bone motion (RM)), or, similar to the double-repeated measures performed to assess accuracy clinically, both the prosthesis and the surrounding bone model (zero relative prosthesis-bone motion (ZRM)) were moved. Motions were performed about three translational and three rotational axes, respectively. The maximum 95% confidence interval (CI) for MBRSA of all four prosthesis investigated was better than −0.034 to 0.107 mm for in-plane and −0.217 to 0.069 mm for out-of-plane translation, and from −0.038 deg to 0.162 deg for in-plane and from −1.316 deg to 0.071 deg for out-of-plane rotation, with no clear differences between the ZRM and RM protocols observed. Accuracy in translation was similar between TKA and THA components, whereas rotational accuracy about the long axis of the hip stem THA components was worse than the TKA components. The data suggest that accuracy and precision of MBRSA seem to be equivalent to the classical marker-based RSA method, at least for the nonsymmetric implant geometries investigated in this study. The model-based method thus allows the accurate measurement of implant migration without requiring prosthesis markers, and thus presents new opportunities for measuring implant migration where financial or geometric considerations of marker placement have thus far been prohibitive factors.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Phantom-model setup. Bone and bone markers were simulated by an inner soft tissue by an outer Plexiglas cylinder. The implant was attached to a Plexiglas beam, and micromanipulators allowed motion to be applied to the implant alone in the relative motion arrangement, or to both the implant and the bone model together in the zero relative motion arrangement. A fixture (visible in the photo) allows rigid fixation of the Plexiglas tube representing bone to the micromanipulators for ZRM, a separate fixture (not shown) allows attachment of the bone tube to the base for RM. The phantom model itself is rigidly attached to the carbon fiber calibration box.

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Figure 2

Schematic diagram showing the implants investigated and their differing geometry, as well as the applied measurement protocols and analysis steps for each of the RSA radiographs

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Figure 3

Box plots of the calculated migration for the ZRM protocol, using the CMS-Marker (white boxes) and MBRSA (gray boxes) methods (n=10 repetitions per axis and implant). Calculated migration for translation (left) and rotation (right) are shown for each anatomic axis: the medial-lateral, superior-inferior, and anterior-posterior directions, respectively. The boxes shown bound the 25th–75th percentile, with the median indicated by the horizontal line. The whisker bars indicate the smallest and largest observed value with exception of outliers (circles) and extreme values (stars). Outliers are data points that lie greater than 1.5 times the interquartile range (difference between the 25th and 75th percentiles) above the 75th percentile and below the first quartile. Extreme values are data points that lie greater than three times the interquartile range above and below the third and first quartiles, respectively. The dashed lines indicate the bounding range of RSA accuracy reported in literature (i.e., between 0.05 mm and 0.5 mm, and between 0.15 deg and 1.15 deg).

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Figure 4

Box plots of the calculated migration results by CMS-Marker and MBRSA in a RM protocol (n=10 repetitions per axis and implant). Calculated migration for translation (left) and rotation (right) about each axis, for analysis by marker-based (white boxes) and MBRSA (gray boxes) methods, are shown, as well as for medial-lateral, superior-inferior, and anterior-posterior directions, respectively (see Fig. 3 heading for a description of the box plots).

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Figure 5

Scatter plots derived from the suggestions of Bland and Altman (36) presenting the computed differences between CMS-Marker and MBRSA migration results (n=10 per axis and prosthesis component). Within these scatter plots the results for tibial (circle) and femoral (triangle) component of TKA, as well as for the first (Hip 1, star) and the second stem (Hip 2, square) of a THA, were shown. Each point represents the computed difference between the marker- and the model-based method (ordinate) plotted versus the mean difference (abscissa), respectively, from the same pairs of RSA radiographs. The horizontal and vertical dashed line represents the mean of the differences between the methods (bias), which should ideally be zero.

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