Developing a Spinal Model for Gait Analysis: A Technical Feasibility Study of a Dynamic Sagittal Alignment Model

Introduction: Modern geometric measurements of the spine like gait analysis have been increasingly used in spine deformity. Due to its novelty, few models have observed sagittal spinopelvic parameters, particularly for evaluating spatial changes after deformity correction. Additionally, spatial differences from static versus motion have not been clearly defined.

Methods: A Gait Analysis model was developed and performed for four spinal deformity patients preoperatively. This model was created to evaluate spinal geometry as inspired by spinopelvic and hip-axis parameters, such as the C2-pelvic angle (C2PA), L1-pelvic angle (L1PA), sagittal vertical axis (SVA), pelvic tilt (PT), thoracic kyphosis (TK), and lumbar lordosis (LL). These gait representations assessed spinal balance and changes with the same principles demonstrated by traditional spinopelvic parameters but should not be considered equivalent due to fundamentally different markers.

Results: Markers were placed where the sacrum, bilateral ASIS, bilateral TMJ, and spinous processes for C7, T6, T9, T12, and L3 were palpated. Calculated hip markers were created from the ASIS markers and measured pelvic depth. A calculated head marker was formed from TMJ markers. Global balance analogous to C2PA was measured via an angle composed of vertices at head, center of ASIS, and the sacral markers. Balance analogous to SVA assessed horizontal distance between the sacral and C7 markers. Hip axis analogous to the L1PA was assessed via the angle between T12, center of hip joint, and sacral markers. Pelvic retroversion, analogous to PT, was assessed with the hip joint center, sacral marker, and vertical axis. TK and LL was also represented via angles between the lines formed by C7-T6 and T9-T12 (TK); and T12-L3 and L3-Sacrum (LL).
The average difference between static and dynamic gait measurements were minimal except SVA (14.6mm, Motion>Static).

Conclusion : A dynamic model for measuring spine geometry was developed and implemented for spine deformity. The measured difference between dynamic and static were relatively small except for “SVA,” (larger in motion). Evaluation of the model in capturing post-operative measurements will be performed in the following months.