Sagittal malalignment in patients with adult spinal deformity seems to increase frontal instability during gait

To evaluate instability during gait and their determinants in ASD patients.

123 ASD patients and 42 controls underwent biplanar radiographs with calculation of spinopelvic and global alignment parameters, and performed 3D gait analysis to calculate full-body kinematics. They all filled the SF-36 with its physical component (PCS). The frontal and sagittal Center of Mass-Center of Pressure (CoM-CoP) angles were calculated during the gait cycle. Patients were classified as ASD-unstable or ASD-stable based on the corridor of normality of the CoM-CoP angle. Kinematics, radiographic parameters and PCS were compared between groups.

All ASD patients had a normal CoM-CoP angle in the sagittal plane. 38 ASD were classified as unstable in the frontal plane and 85 as stable (14 ± 3° vs 8 ± 2° resp., p < 0.001). While the 2 groups had a similar pelvic incidence (PI = 53°), ASD-unstable patients had an increased SVA (69 vs 20 mm), and global tilt (GT: 33 vs 24°, all p < 0.05), compared to ASD-stable. The frontal Cobb was similar between the 2 groups (Cobb = 17°). ASD-unstable also had an increased sagittal kinematic ODHA (10 vs 6°), and a decreased normalized step length (0.30 vs 0.34, both p < 0.05). They also had a decreased PCS (33 vs 37).

ASD patients with increased global sagittal malalignment (SVA & GT) appear to have increased frontal instability during gait. Frontal instability during gait was associated with kinematic limitations in the sagittal plane and deterioration in quality of life. Future work will focus on changes in gait stability in ASD patients after corrective spinal malalignment surgery.