Altered sensory-weighting mechanisms is observed in adolescents with idiopathic scoliosis

Abstract

Background: Scoliosis is the most common type of spinal deformity. In North American children, adolescent idiopathic scoliosis (AIS) makes up about 90% of all cases of scoliosis. While its prevalence is about 2% to 3% in children aged between 10 to 16 years, girls are more at risk than boys for severe progression with a ratio of 3.6 to 1. The aim of the present study was to test the hypothesis that idiopathic scoliosis interferes with the mechanisms responsible for sensory-reweighting during balance control.

Methods: Eight scoliosis patients (seven female and one male; mean age: 16.4 years) and nine healthy adolescents (average age 16.5 years) participated in the experiment. Visual and ankle proprioceptive information was perturbed (eyes closed and/or tendon vibration) suddenly and then returned to normal (eyes open and/or no tendon vibration). An AMTI force platform was used to compute centre of pressure root mean squared velocity and sway density curve.

Results: For the control condition (eyes open and no tendon vibration), adolescent idiopathic scoliosis patients had a greater centre of pressure root mean squared velocity (variability) than control participants. Reintegration of ankle proprioception, when vision was either available or removed, led to an increased centre of pressure velocity variability for the adolescent idiopathic scoliosis patients whereas the control participants reduced their centre of pressure velocity variability. Moreover, in the absence of vision, adolescent idiopathic scoliosis exhibited an increased centre of pressure velocity variability when ankle proprioception was returned to normal (i.e. tendon vibration stopped). The analysis of the sway density plot suggests that adolescent idiopathic scoliosis patients, during sensory reintegration, do not scale appropriately their balance control commands.

Conclusion: Altogether, the present results demonstrate that idiopathic scoliosis adolescents have difficulty in reweighting sensory inputs following a brief period of sensory deprivation.

Figures

Figure 1

Temporal sequencing across sensory deprivation and sensory reintegration interval. A trial is made of a series of two 15 s intervals. The first interval, sensory deprivation, is performed under sensory deprivation (i.e. perturbed ankle proprioception and/or no vision). For the second interval (sensory reintegration interval), ankle proprioception and/or vision returned to normal. For the sensory deprivation interval, only the last 5 s epoch is used for data analysis. From the 15 s of the sensory reintegration interval, two epochs are selected. The first epoch represents the first 5 s whereas the second epoch concerns the last 5 s.

Figure 2

Balance control performance in absence of sensory inputs manipulation. Upper panel – Group means for the CP RMS velocity along the medio-lateral (ML) and antero-posterior (AP) axes for the control condition. Lower panel – Groups means of the distance between consecutive zones of stability (mean distance – left vertical axis) and the time spent within the zones of stability (mean peak – right vertical axis) for the control condition. On both panels, the error bars indicate 95% confidence intervals.

Figure 3

Balance control performance during reintegration of vision. Upper panel – Group means for the CP RMS velocity along the medio-lateral (ML) and antero-posterior (AP) axes for the proprioception/no-vision to proprioception/reintegration vision condition. Lower panel illustrates the interaction Group by Epoch for the time spent within the zones of stability (mean peak) for the last 5 s epoch of the proprioception/no vision interval (NV10–15) and first 5 s epoch (RV0–5) and last 5 s epoch (RV10–15) of the proprioception/vision reintegration intervals. On both panels, the error bars indicate 95% confidence intervals.

Figure 4

Balance control performance during reintegration of ankle proprioception when vision is available. Upper panel illustrates the interaction Group by Epoch for the CP RMS velocity for the last 5 s epoch of sensory deprivation internal (PP-V10–15 perturbed proprioception/vision) and for the first and last 5 s epoch of the sensory reintegration interval (RP-V0–5 and RP-V10–15 reintegration proprioception/vision). Lower panel shows the interaction Group by Epoch for the time spent within the zone of stability for the same 5 s epochs as the upper panels. On all panels, the error bars correspond to 95% confidence intervals.

Figure 5

Balance control performance during reintegration of ankle proprioception in absence of vision. Upper panel presents the interaction Group by Epoch for the CP RMS velocity for the last 5 s epoch of sensory deprivation interval (PP-NV10–15 perturbed proprioception/no-vision) and for the first and last 5 s epoch of the sensory reintegration interval (RP-NV0–5 and RP-NV10–15 reintegration proprioception/no-vision condition). Lower panel illustrates the interaction Group by Epoch for the time spent within the zone of stability for the same 5 s epochs as the upper panels. On all panels, the error bars indicate 95% confidence interval.