Relations between standing stability and body posture parameters in adolescent idiopathic scoliosis.

Abstract:  STUDY DESIGN: A retrospective study of standing imbalance and body posture in 71 able-bodied girls and subjects with adolescent idiopathic scoliosis was conducted. OBJECTIVE: To test the hypothesis that postural parameters are related to standing stability parameters. SUMMARY OF BACKGROUND DATA: Spinal deformity not only modifies the shape of the trunk, but also changes the relations between body segments affecting posture in scoliotic children. These postural adaptations to the scoliotic curve progression could be linked in part to increased body sway in upright standing. This has not yet been related to specific postural parameters involving the head, trunk, and pelvis in nontreated idiopathic scoliosis. METHODS: The head, trunk, and pelvis orientations of each subject were measured by a Flock of Bird system. An AMTI force platform was used to assess quiet standing stability and to monitor the position and displacement of the center of pressure (COP). The center of mass (COM) excursion was estimated from a biomechanical model using force plate information only. Analyses of variance (ANOVAS) were performed to determine the statistical differences between the scoliotic and nonscoliotic subjects, and backward stepwise multiple regression analyses were performed to identify any correlation between measures of quiet standing stability and body postural parameters RESULTS: The scoliotic group was characterized by a decrease in standing stability. There was an increase in the sway areas measured by the variations of the COP and COM. From the backward stepwise multiple regression analysis, it appears that for the able-bodied girls, the body posture parameters were correlated only with the mean anteroposterior center of pressure (COP(AP)) position. For the scoliotic group, the sway areas and the mean position of the centers of pressure and the COP(AP)-COM(AP) were correlated significantly with body posture parameters. The higher COP-COM differences for the scoliotic group were attributed to a greater neuromuscular demand to maintain standing balance. The coefficients of correlation of the multiple regression analyses ranged from 0.64 to 0.85 for the nonscoliotic group and from 0.55 to 0.72 for the scoliotic group. CONCLUSIONS: The use of backward stepwise multiple correlations highlighted the interaction between several body parameters and their relation to standing stability in both able-bodied girls and scoliotic subjects. The scoliotic group displayed a much larger number of correlations between standing stability and body posture parameters than the nonscoliotic group. Standing imbalance was related to altered body posture parameters measured in the frontal and horizontal planes only. Although the correlation coefficients were relatively high, factors other than body posture parameters appeared related to standing imbalance in adolescent idiopathic scoliosis. These findings support the concept of either a primary or a secondary dysfunction in the postural regulation system of scoliotic subjects.