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Notes on the use and interpretation of radiostereometric analysis.

Derbyshire B, Prescott RJ, Porter ML - Acta Orthop (2009)

Bottom Line: With increasing numbers of research groups carrying out radiostereometric analysis (RSA), it is important to reach a consensus on how the main aspects of the technique should be carried out and how the results should be presented in an appropriate and consistent way.In this collection of guidelines, we identify a number of methodological and reporting issues including: measurement error and precision, migration and migration direction data, and the use of RSA as a screening technique.Alternatives are proposed, and a statistical analysis is presented, from which a sample size of 50 is recommended for screening of newly introduced prostheses.

View Article: PubMed Central - PubMed

Affiliation: Centre for Hip Surgery, Wrightington Hospital, Appley Bridge, UK. Brian.Derbyshire@wwl.nhs.uk

ABSTRACT
With increasing numbers of research groups carrying out radiostereometric analysis (RSA), it is important to reach a consensus on how the main aspects of the technique should be carried out and how the results should be presented in an appropriate and consistent way. In this collection of guidelines, we identify a number of methodological and reporting issues including: measurement error and precision, migration and migration direction data, and the use of RSA as a screening technique. Alternatives are proposed, and a statistical analysis is presented, from which a sample size of 50 is recommended for screening of newly introduced prostheses.

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Vector plane chart (created using RSA DataViewer: www.orthomech.co.uk) showing all the vectors in the transverse plane at the 6-month stage of a cemented hip stem study. The ellipse shows the variation of the resultant of the repeatability (precision) error in the transverse (x–z) plane. The intersection of the ellipse with the x-axis (mediolateral) and z-axis (anteroposterior) is the precision (determined from double examinations) in the x- and z-directions, respectively. A summary of the vector directions is given by the percentage of vectors (beyond the repeatability error, i.e. outside the ellipse) in each direction quadrant. In this case, 36% of the vectors were within the ellipse and they were not therefore considered in the calculations of the proportions in each quadrant. The mean scalar value of all the vectors in that plane is shown at the bottom of the chart.
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Figure 0005: Vector plane chart (created using RSA DataViewer: www.orthomech.co.uk) showing all the vectors in the transverse plane at the 6-month stage of a cemented hip stem study. The ellipse shows the variation of the resultant of the repeatability (precision) error in the transverse (x–z) plane. The intersection of the ellipse with the x-axis (mediolateral) and z-axis (anteroposterior) is the precision (determined from double examinations) in the x- and z-directions, respectively. A summary of the vector directions is given by the percentage of vectors (beyond the repeatability error, i.e. outside the ellipse) in each direction quadrant. In this case, 36% of the vectors were within the ellipse and they were not therefore considered in the calculations of the proportions in each quadrant. The mean scalar value of all the vectors in that plane is shown at the bottom of the chart.

Mentions: A simple descriptive approach is to plot the individual translations in a specified plane. Figure 5 shows stem centroid translation vectors at 6 months in the transverse (x–z) plane for 25 cemented femoral stems. Each translation vector is represented by a single point, the line to each point emphasizing the magnitude and direction of the vector with respect to the immediate postoperative position. The point is determined from the 2 orthogonal translation components in the plane of interest (the x–z plane in Figure 5), with signs according to the medial/lateral, anterior/posterior, proximal/distal directions (medial, anterior, and proximal positive). The magnitude of each vector is the length of the line (i.e. the square root of X2 + Z2 in this case). Its direction can be reported in terms of the anticlockwise angle to the horizontal, right axis. The directions of the vectors have been summarized as a proportion of vectors in each quadrant, expressed as a percentage. The mean scalar magnitude of all the vectors (line lengths) in that plane is presented at the base of the graph. In the text, a confidence interval for this mean could be included. Where necessary, this sort of chart could be presented for the 2 other planes. A plane chart at a particular examination could be presented as a supplement to standard migration-time charts.


Notes on the use and interpretation of radiostereometric analysis.

Derbyshire B, Prescott RJ, Porter ML - Acta Orthop (2009)

Vector plane chart (created using RSA DataViewer: www.orthomech.co.uk) showing all the vectors in the transverse plane at the 6-month stage of a cemented hip stem study. The ellipse shows the variation of the resultant of the repeatability (precision) error in the transverse (x–z) plane. The intersection of the ellipse with the x-axis (mediolateral) and z-axis (anteroposterior) is the precision (determined from double examinations) in the x- and z-directions, respectively. A summary of the vector directions is given by the percentage of vectors (beyond the repeatability error, i.e. outside the ellipse) in each direction quadrant. In this case, 36% of the vectors were within the ellipse and they were not therefore considered in the calculations of the proportions in each quadrant. The mean scalar value of all the vectors in that plane is shown at the bottom of the chart.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2823227&req=5

Figure 0005: Vector plane chart (created using RSA DataViewer: www.orthomech.co.uk) showing all the vectors in the transverse plane at the 6-month stage of a cemented hip stem study. The ellipse shows the variation of the resultant of the repeatability (precision) error in the transverse (x–z) plane. The intersection of the ellipse with the x-axis (mediolateral) and z-axis (anteroposterior) is the precision (determined from double examinations) in the x- and z-directions, respectively. A summary of the vector directions is given by the percentage of vectors (beyond the repeatability error, i.e. outside the ellipse) in each direction quadrant. In this case, 36% of the vectors were within the ellipse and they were not therefore considered in the calculations of the proportions in each quadrant. The mean scalar value of all the vectors in that plane is shown at the bottom of the chart.
Mentions: A simple descriptive approach is to plot the individual translations in a specified plane. Figure 5 shows stem centroid translation vectors at 6 months in the transverse (x–z) plane for 25 cemented femoral stems. Each translation vector is represented by a single point, the line to each point emphasizing the magnitude and direction of the vector with respect to the immediate postoperative position. The point is determined from the 2 orthogonal translation components in the plane of interest (the x–z plane in Figure 5), with signs according to the medial/lateral, anterior/posterior, proximal/distal directions (medial, anterior, and proximal positive). The magnitude of each vector is the length of the line (i.e. the square root of X2 + Z2 in this case). Its direction can be reported in terms of the anticlockwise angle to the horizontal, right axis. The directions of the vectors have been summarized as a proportion of vectors in each quadrant, expressed as a percentage. The mean scalar magnitude of all the vectors (line lengths) in that plane is presented at the base of the graph. In the text, a confidence interval for this mean could be included. Where necessary, this sort of chart could be presented for the 2 other planes. A plane chart at a particular examination could be presented as a supplement to standard migration-time charts.

Bottom Line: With increasing numbers of research groups carrying out radiostereometric analysis (RSA), it is important to reach a consensus on how the main aspects of the technique should be carried out and how the results should be presented in an appropriate and consistent way.In this collection of guidelines, we identify a number of methodological and reporting issues including: measurement error and precision, migration and migration direction data, and the use of RSA as a screening technique.Alternatives are proposed, and a statistical analysis is presented, from which a sample size of 50 is recommended for screening of newly introduced prostheses.

View Article: PubMed Central - PubMed

Affiliation: Centre for Hip Surgery, Wrightington Hospital, Appley Bridge, UK. Brian.Derbyshire@wwl.nhs.uk

ABSTRACT
With increasing numbers of research groups carrying out radiostereometric analysis (RSA), it is important to reach a consensus on how the main aspects of the technique should be carried out and how the results should be presented in an appropriate and consistent way. In this collection of guidelines, we identify a number of methodological and reporting issues including: measurement error and precision, migration and migration direction data, and the use of RSA as a screening technique. Alternatives are proposed, and a statistical analysis is presented, from which a sample size of 50 is recommended for screening of newly introduced prostheses.

Show MeSH