Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech Postural control of individuals with spinal fusion for adolescent idiopathic scoliosis Yumeng Li a, ⁎ , Rumit Singh Kakar b , Yang-Chieh Fu c , Marika Walker d , Cathleen N. Brown e , Timothy S. Oswald f , Kathy J. Simpson d a Department of Health and Human Performance, Texas State University, 601 University Dr., San Marcos, TX, USA b Department of Physical Therapy, Ithaca College, Ithaca, NY, USA c Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan d Department of Kinesiology, University of Georgia, Athens, GA, USA e Department of Athletic Training and Kinesiology, Oregon State University, Corvallis, OR, USA f Department of Pediatric Orthopedics, Pediatric Orthopaedic Associates, Atlanta, GA, USA ARTICLE INFO Keywords: Balance Postural stability Spinal surgery Nonlinear analysis Limit of stability Sensory organization ABSTRACT Background: The purpose of the study was to assess the postural stability and complexity of postural control for moderately physically active individuals with spinal fusion for adolescent idiopathic scoliosis at two years post- operation. Methods: Limit of stability test and sensory organization test were conducted for 10 moderately physically-active participants with spinal fusion and 10 controls pair-matched for mass, height and physical activity level. During the limit of stability test, participants were instructed to lean the center of gravity as far as possible toward 8 predetermined directions and the maximum excursion and direction control were analyzed. During the sensory organization test, participants were instructed to maintain as still as possible in six test conditions and equili- brium scores and sway area of center of pressure were analyzed. Multi-scale entropy of center of pressure was calculated to quantify sway complexity. Findings: Most postural stability outcomes of spinal fusion participants were comparable to controls except for significantly reduced equilibrium scores (p = 0.039, partial η 2 = 0.217). Moreover, spinal fusion participants exhibited tendencies of reduced direction control (p = 0.053) during the limit of stability test and greater sway area (p = 0.052) during the sensory organization test. Interpretation: Although the center of gravity control might be affected, spinal fusion individuals who were moderately physically active likely progressively learned to adapt postoperatively to their fused spine to meet the postural demands required when performing physical movements. We suggest that spinal fusion is a sa- tisfactory treatment in regard to the recovery of postural stability. 1. Introduction Adolescent idiopathic scoliosis (AIS) is the most common spinal deformity during adolescence, which primarily affects the frontal plane (e.g., lateral deviation) but also influences other planes (e.g., axial ro- tation and lordosis) (Kojima and Kurokawa, 1992; Ueno et al., 2011). The prevalence rate in children aged 11–14 years old has been reported at 0.87% (Ueno et al., 2011). Treatment of AIS is usually based on the magnitude of spinal curvature measured by Cobb angles (curvature angle of the spine measured in the frontal plane using a radiograph). For patients with a Cobb angle < 40°, careful monitoring and brace treatment is frequently utilized (Kakar et al., 2017b). For patients with curvature > 40°, spinal fusion surgery may be recommended based on the severity of the curvature, likelihood of continued progression and potential for pain reduction (Kakar et al., 2017b; Lonstein, 2006). Spinal fusion could largely correct the lateral curvature and patients with spinal fusion for AIS (SF-AIS) have demonstrated satisfactory outcomes during high-effort physical activities (Kakar et al., 2017a; Li et al., 2017). Appropriate motor responses and the ability to maintain an upright posture is crucial for basic physical activities (e.g., standing, walking, running) in daily life (Lim et al., 2017). Postural stability has been defined as the ability to control the center of gravity (COG) within the base of support (Huang and Brown, 2013). However, impaired postural https://doi.org/10.1016/j.clinbiomech.2018.11.001 Received 31 March 2018; Accepted 6 November 2018 ⁎ Corresponding author. E-mail address: yumeng.li@txstate.edu (Y. Li). Clinical Biomechanics 61 (2019) 46–51 0268-0033/ © 2018 Published by Elsevier Ltd. T