Experimental evaluation of precision and accuracy of RSA in the lumbar spine
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ORIGINAL ARTICLE
Experimental evaluation of precision and accuracy of RSA in the lumbar spine Marie Christina Keller1 · Christof Hurschler1 · Michael Schwarze1 Received: 22 June 2020 / Revised: 4 November 2020 / Accepted: 17 November 2020 © The Author(s) 2020
Abstract Purpose Roentgen stereophotogrammetric analysis is a technique to make accurate assessments of the relative position and orientation of bone structures and implants in vivo. While the precision and accuracy of stereophotogrammetry for hip and knee arthroplasty is well documented, there is insufficient knowledge of the technique’s precision and, especially accuracy when applied to rotational movements in the spinal region. Methods The motion of one cadaver lumbar spine segment (L3/L4) was analyzed in flexion–extension, lateral bending and internal rotation. The specific aim of this study was to examine the precision and accuracy of stereophotogrammetry in a controlled in vitro setting, taking the surrounding soft tissue into account. The second objective of this study was to investigate the effect of different focal spot values of X-ray tubes. Results Overall, the precision of flexion–extension measurements was found to be better when using a 0.6 mm focal spot value rather than 1.2 mm (± 0.056° and ± 0.153°; respectively), and accuracy was also slightly better for the 0.6 mm focal spot value compared to 1.2 mm (− 0.137° and − 0.170°; respectively). The best values for precision and accuracy were obtained in lateral bending for both 0.6 mm and 1.2 mm focal spot values (precision: ± 0.019° and ± 0.015°, respectively; accuracy: − 0.041° and − 0.035°). Conclusion In summary, the results suggest stereophotogrammetry to be a highly precise method to analyze motion of the lumbar spine. Since precision and accuracy are better than 0.2° for both focal spot values, the choice between these is of minor clinical relevance. Keywords RSA · In-vitro · Validation · Lumbar spine
Introduction Roentgen stereophotogrammetric analysis (RSA) is used to make accurate assessments of the relative position and orientation of bone structures and implants in vivo. Application of the technique allows the detection of clinically relevant motion, or the lack thereof. In this technique, two X-ray images are taken simultaneously from different directions in order to perform a three-dimensional rigid body movement analysis [1]. Clinical applications of RSA in the spinal context have included verification of the rigidity of spinal fusions and evaluation of dynamic stabilization of the * Michael Schwarze Schwarze.michael@mh‑hannover.de 1
Laboratory for Biomechanics and Biomaterials, Hannover Medical School, Anna‑von‑Borries‑Str. 1‑7, 30625 Hannover, Germany
cervical, thoracic and lumbar spine [2–12]. In hip and knee arthroplasty, RSA has been widely used to analyze migration of implants (relative motion of bone and implant), due to its high precision and accuracy. The accuracy of marker-based RSA for rotational measurements is 0.18° (with a precision of 0.5°) for hip stems
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