Study Design. A prospective case series. Objective. The aim of this study was to compare the standing balance and posture between patients with adult spinal deformity (ASD) and healthy volunteers (HVs). Summary of Background Data. The effect of ASD on standing posture and balance has not been fully documented. Methods. Forty consecutive female patients with ASD (65.4 ± 6.7 yrs, Cobb angle 48.6 ± 20.2°, C7PL 9.1 ± 6.4 cm, and PI-LL 41.1 ± 25.2°) and 33 matched HV (72.4 ± 4.6 yrs) were included. We reviewed charts and x-rays from ASDs and categorized the patients as having a PI-LL mismatch that was severe (>20°) or moderate (10°<PI-LL<20°). We compared the standing balance with that of 33 matched HVs. All subjects underwent motion analysis while standing naturally on a custom-built force platform using optical markers on the ear canal and on all joints and spinal processes. The distances from the center of gravity (CoG) to the head, heel, and sacrum were also measured, and the spinal tilt, pelvic obliquity, and pelvic tilt were calculated. Results. There were significant differences between the ASDs and HVs in the recorded CoG area (RecCoG), and the left-to-right differences in ground reaction force (dGRF), hip angle (dHip), and the knee angle (dKnee) while standing. The sagittal CoG distance, head-CoG distance, and sacrum-CoG distance were significantly worse in ASDs. Multiple regression analysis showed a significant correlation between two-dimensional head deviation and hip angle, thoracolumbar kyphosis, spinal tilt, and head-sacrum distance in the severe PI-LL mismatch group and in knee angle, pelvic obliquity, and pelvic retroversion in the moderate PI-LL mismatch group. Conclusion. ASDs had significantly worse standing balance, and were found to compensate for spinal malalignment mostly through the knee and pelvis in both the coronal and sagittal planes to maintain the CoG. As a surrogate of this compensation, we observed significant head deviation, pelvic shift, and truncal sway in ASDs.
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