Roentgen stereophotogrammetry (RSA) is a highly accurate technique for the assessment of three-dimensional migration and micromotion of a
joint replacement
Joint replacement is a procedure of orthopedic surgery known also as arthroplasty, in which an arthritic or dysfunctional joint surface is replaced with an orthopedic prosthesis. Joint replacement is considered as a treatment when severe joint pai ...
prosthesis relative to the bone it is attached to. It was introduced in 1974 by Göran Selvik.
Several studies have found implant migration to be predictive of long-term implant survival and, for most devices, measurement over 2 years might therefore provide a surrogate outcome measure with relatively low numbers of subjects, e.g. from 15 to 25 patients in each group in randomized studies. A smaller number of subjects can be used in these studies as a consequence of the high accuracy of the measurement technique. Because of this, RSA is an important technique in early
clinical trials
Clinical trials are prospective biomedical or behavioral research studies on human subject research, human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel v ...
for screening new joint replacement prostheses.
Methodology
To achieve the high accuracy, the following steps are carried out: Small
radio opaque markers are introduced in the bone and attached to the prosthesis to serve as well-defined artificial landmarks. Two synchronised
x-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
foci are used to obtain a stereo image of the bone and the prosthesis. The positions of the foci are assessed using a calibration object that holds
tantalum
Tantalum is a chemical element; it has Symbol (chemistry), symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology. Tantalum is a very hard, ductility, ductile, lustre (mineralogy), lustrous, blue-gray transition ...
markers at accurately known positions. The coordinates of the bone and prosthesis markers are accurately measured and the
three-dimensional position of the markers is reconstructed using software. The change in the position (
translation
Translation is the communication of the semantics, meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The English la ...
and
rotation
Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...
) of the prosthesis markers relative to the bone markers is then determined. The reported accuracy of RSA ranges between 0.05 and 0.5 mm for translations and between 0.15˚ and 1.15˚ for rotations (95%
confidence interval). New RSA techniques that avoid the need for attaching markers to the prosthesis have been introduced.
See also
*
Roentgen radiation
*
Stereophotogrammetry
*
Dynamic Roentgen stereophotogrammetry
References
External links
Digital Roentgen Stereophotogrammetry: Development, Validation, and Clinical Application
{{DEFAULTSORT:Medical Imaging
Prosthetics
Medical imaging