Subjective Visual Vertical and Adolescent Idiopathic Scoliosis (AIS)

Objective The AIS is pathology with multifactorial origin. It affects between 1 – 3% of the population aged 10 – 16 years. Many authors suggest orthostatic postural control disorders in AIS. The orthostatic postural control is the ability to organize the standing posture on the earth-vertical. The longitudinal body axis, the trunk and the spinal axis are oriented in an internal representation of the gravitational vertical. Our hypothesis is that AIS is the consequence of a re-organization of orthostatic postural control, on an erroneous internal representation of earth-vertical. Our objective is to show a disturbance of the sense of verticality in the AIS, by measuring the Subjective Visual Vertical (SVV) in AIS, particularly in dynamic visual condition. Methods Prospective study: a group of adolescents with AIS versus a control group of non-scoliotic adolescents. The test is a measure of the SVV (Synapsis), standing posture, in static and dynamic visual conditions (visual disturbance by optokinetic stimulation 40°/sec). Six measures are evaluated. Norms for static condition–2.5° to +2.5°, and for dynamic condition–4 to +4°. Results Preliminary results on 35 scoliotic adolescents (Group S: 31 girls, 14.2 ± 1.74 years, angle: 38.4 ± 15.7°), versus 5 non-scoliotic adolescents (Group C: 5 girls, 14.9 ± 1.14 years). Group S: static VVS = 1.59 ± 1.45°; dynamic VVS = 4.7 ± 8.27°. 57.1% with a least 1 pathological value, 28.5% with a least 2 pathological values, particularly in dynamic visual condition (clockwise rotation with right tilt of the VVS, average 12.39°). Group C: static VVS = 0.72 ± 0.5°; dynamic VVS = 2.17 ± 1.5°. No subject control with pathological value. Discussion This preliminary study shows a disturbance in the vertical evaluation in the AIS. One possible explanation is a disturbance of the sense of verticality by impaired multisensory central integration. The authors are grateful to the Harps Association's members, for their helpful comments.