Biomechanical analyses of the load at the apical vertebra, postural balance, and gait for subjects with adolescent idiopathic scoliosis

Abstract

Idiopathic scoliosis (IS) is the most common type of scoliosis. If it is not properly treated, it may lead to cosmetic problems and functional disabilities. Despite a lot of research have been done, there is no generally accepted scientific theory of etiology of IS. Failures of postural balance of the body and in particular the spine as well as neurological imbalance have been suspected to be the cause IS. However, the dysfunction of IS in postural stability control, gait pattern and mechanical loads are still not clear. The results of the current study may lead to further understanding of the etiology of IS in the postural equilibrium influencing aspects. Eighteen girls with Adolescent Idiopathic Scoliosis (AIS) were recruited. Eight of them (mean age 14.6; mean Cobb angle = 24.9?) showed abnormality in their posterior tibial nerve somatosensory cortical evoked potentials (PTN-SCEPs) while the others (mean age = 14.0; mean Cobb angle = 24.2?) showed normal PTN-SCEPs. All the subjects with AIS had right thoracic curve with apical vertebra at the region of T7 and T8. In addition, eight normal age-matched volunteers (mean age =14.8) were recruited as controls. The static balance, gait pattern and mechanical loads acting at the apical vertebra of the subjects were determined and compared using two force plates (Advanced Mechanical Technology Inc., USA) and a 3-D motion analysis system (Vicon 370, oxford Metrics Ltd., UK). For the static balance measurement, four conditions including standing on a solid/foam base with eye open/close were investigated. There was no significant difference in the body sway between the subjects with AIS and the normal controls while standing on a solid-base support. However, when perturbation of proprioception is induced using a foam-base support, all of the subjects with AIS either with or without abnormal PTN-SCEPS show significantly poorer stability control. Gait analysis showed all subjects with AIS either with or without abnormal PTN-SCEPs have normal symmetric temporal-distance parameters. However, subjects with AIS and abnormal PTN-SCEPs show asymmetry in ground reaction forces and sagittal ankle joint moment, knee joint moment and hip joint moment. For the load acting at the apical vertebra, the subjects with AIS and abnormal PTN-SCEPS showed significantly greater axial force and side-bending moment than the subjects with AIS and normal PTN-SCEPS and the controls. The clinical implications of this observed result should be further investigated.