Background Context The effect of corrective spine surgery on standing stability in adult spinal deformity (ASD) has not been fully documented. Purpose To compare pre- and postoperative standing balance and posture in patients with ASD. Study Design/Setting This study is a prospective case series. Patient Sample Standing balance before and after corrective spine surgery was compared in 35 consecutive female patients with ASD (65.6±6.9 years, body mass index 22.3±2.7 kg/m2, Cobb angle 50.2±19.2° C7 plumb line 9.3±5.6 cm, and pelvic incidence-lumbar lordosis mismatch 40.8±23.3°). Outcome Measures The Scoliosis Research Society Patient Questionnaire, the Oswestry Disability Index, and force-plate analysis were used to evaluate the patient outcomes. Materials and Methods We reviewed patient charts and X-rays and compared standing balance before and after corrective spine surgery. All subjects were assessed by force-plate analysis using optical markers while standing naturally on a custom-built force platform. The spinal tilt, pelvic obliquity, pelvic tilt, and joint angle were calculated. The lower leg lean volume was obtained by whole-body dual X-ray absorptiometry to assess muscle strength. Results ASD patients showed significant differences between the left and right sides in ground reaction force (dGRFs), hip (dHip), and knee angle (dKnee) while standing (dGRF 15.1±8.7%, dHip 7.1±6.6° dKnee 5.9±5.5°). The recorded center-of-gravity (CoG) area was not improved after surgery, whereas the dGRF, dHip, and dKnee all decreased. The spinal tilt, pelvic obliquity, and pelvic tilt were all significantly improved after surgery. We found significant correlations between the radiographic trunk shift and the postoperative coronal CoG distance and recorded CoG area, and between the sagittal CoG distance and the age and the lean volume of the lower extremities (trunk shift R=0.33, 0.45; age R=0.32; lean volume R=0.31). Conclusions Corrective spinal surgery improved the spinal alignment and joint angles in patients with ASD but did not improve the standing stability. A correlation found between the sagittal CoG distance and the lean volume of the lower extremities indicated the importance of the leg muscles for stability when standing, whereas a correlation found between the coronal CoG distance and trunk shift reflected the attenuated postural response in the ASD patients.
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