Purpose: Sagittal vertical axis (SVA) is the most commonly used parameter for evaluating global sagittal alignment (GSA) in a static condition. However, its dynamic statuses remain unclear. The aim of this study was to evaluate dynamic GSA of degenerative lumbar kyphoscoliosis (DLKS) using three-dimensional motion analysis system (3D-MAS).
Methods: Twenty-six patients with DLKS underwent gait analysis using 3D-MAS. Static (S-) and dynamic (D-) trunk angle (TA) (the angle between the vertical axis and the line connecting C7 and S1 spinous processes) and S-sagittal trunk shift (STS) and D-STS (the distance between the two vertical lines running through C7 and S1 spinous process) were recorded during treadmill walking. Pelvic angle (PA) (the angle between the horizontal axis and the line connecting the posterior and anterior superior iliac spine) were also recorded. S-PA and D-PA represent retroversion or anteversion of the pelvis, which can be substituted for pelvic tilt. As to dynamic parameters, those at the initial five steps (Di) and the final five steps (Df) of treadmill walking were also recorded.
Results: The median S-TA, S-STS, and S-PA were 16.0°, 11.9 cm, and -5.5° (retroversion). The median D parameters were Di-TA/Df-TA 21.8°/26.9°; Di-STS/Df-STS 14.1/21.1 cm; and Di-PA/Df-PA 15.7°/22.8° (anteversion). All D parameters were significantly greater than S parameters (P < 0.01) and all Df parameters were also significantly worse than Di parameters (P < 0.001). Thus, compensated GSA by pelvic retroversion in static condition was lost due to anteversion change of the pelvis immediately after start of walking and worsened over time.
Conclusion: Dynamic GSA assessment using 3D-MAS can avoid underestimation of GSA loss that is detected by static standing full-length radiography.
Keywords: Adult spinal deformity; Degenerative lumbar kyphoscoliosis; Dynamic balance; Gait analysis; Global sagittal alignment.