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 degrees and +/- 0.153 degrees; respectively), and accuracy was also slightly better for the 0.6 mm focal spot value compared to 1.2 mm (- 0.137 degrees and - 0.170 degrees; 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 degrees and +/- 0.015 degrees, respectively; accuracy: - 0.041 degrees and - 0.035 degrees). 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 degrees for both focal spot values, the choice between these is of minor clinical relevance.
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