Assessing radiographic spinopelvic alignment parameters using motion capture

While radiographic imaging is the gold standard for assessing spinopelvic alignment, it may not fully reflect symptom severity in patients with lumbar spinal stenosis (LSS) as patients employ dynamic compensatory strategies. This study aimed to develop a method to align static spinopelvic alignment parameters derived from motion capture with radiographic definitions. 27 patients underwent EOS radiography and motion capture analysis in a standardized posture. Radiopaque and retroreflective markers were placed on the same anatomical landmarks before EOS radiography and motion capture analysis, respectively. Offset angles were calculated to align motion capture-derived with radiographic parameters. Postural agreement between the two modalities was assessed using Bland-Altman analysis of the vertical distances between the posterior and anterior superior iliac spine markers (ASIS-PSIS) and the horizontal distances between the C7 and sacrum markers (SACR-C7). The influence of postural variation between modalities on alignment parameters was estimated using trigonometric analysis. Radiographic parameters differed notably from motion-capture derived parameters, particularly sacral slope, with an average offset of 31.1° (range: -0.4°-46.4°). The mean vertical ASIS-PSIS distance was -3.3 mm (LoA (limits of agreement): [-21.4; 14.8] mm) and the mean horizontal SACR-C7 distance was +4.9 mm (LoA: [-16.3; 26.1] mm), corresponding to maximum angular deviations of 5.9° for sacral slope and 3.7° for spine inclination. In conclusion, the large offset ranges underscore the need for radiography and individual offset corrections to approximate spinopelvic alignment parameters using motion capture. However, the close replication of the EOS posture highlights this method's potential for assessing spinopelvic alignment in dynamic conditions.