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Postural Control Strategies Related to Anticipatory Perturbation and Quick Perturbation in Adolescent Idiopathic Scoliosis

Kuo, Fang-Chuan PhD*; Hong, Chang-Zern MD*; Lai, Chung-Liang MD†,‡; Tan, Shih-Hsin PT§

doi: 10.1097/BRS.0b013e3181d0f80c

Study Design. Cross-sectional study.

Objective. To investigate the automatic balance correction related to anticipatory perturbation (AP) and quick backward perturbation in adolescent idiopathic scoliosis (AIS).

Summary of Background Data. Most previous studies on AIS patients focused on posture sway and lacked analysis of muscle activated patterns in dynamic standing control.

Methods. Thirty-two AIS patients and 23 age- matched normal subjects received perturbation balance tests on an unstable platform. The tilting angle of the platform and the muscle activity of the bilateral lumbar multifidi, gluteus medii, and gastrocnemii muscles were recorded. Electromyographic (EMG) amplitude, onset latencies, and duration were calculated with software accompanied with machine.

Results. The AIS group had less posture tilting but higher muscle activities than normal subjects under both perturbation conditions (P < 0.05). Under the AP test, AIS showed earlier onset and prolonged activation of left multifidus and right gastrocnemius compared with normal subjects (P < 0.05). The latency of the multifidus on the lumbar convex side occurred earlier than on the concave side. However, the asymmetric onset timing of the gastrocnemius was the opposite of the multifidi in the AIS group (P < 0.05). In contrast to the AP condition, bilateral leg and trunk muscles activated at similar latencies and durations in the AIS group (P < 0.05). Under the quick backward perturbation test, the control group had longer active duration of right multifidus and bilateral gastrocnemii than AIS to cope with larger platform tilting. In addition, asymmetric onset of gluteus medii and duration of multifidi was observed in the control group (P < 0.05).

Conclusion. There were significant differences in posture control patterns between AIS and normal subjects. AIS subjects have asymmetric habitual muscle activities for AP, whereas when coping with sudden balance threats, they react with synchronized recruitment of bilateral postural muscles.

Study on responses to anticipatory and quick balance perturbation in scoliosis adolescents revealed that there were significant differences in posture control patterns between AIS and normal subjects. AIS subjects had asymmetric habitual muscle activities to cope with sudden balance threats; they reacted with the synchronized recruitment of bilateral postural muscles.

*Department of Physical Therapy, Medicine, and Nursing College, Hungkuang University, Taichung, Taiwan

[Department of Physical Medicine and Rehabilitation, Taichung Hospital, Taichung, Taiwan

Department of Health, Taichung Hospital, Executive Yuan, Taichung, Taiwan

§Department of Rehabilitation Medicines, Taichung Veterans General Hospital, Taichung, Taiwan

Address correspondence and reprint requests to Fang-Chuan Kuo, PhD, Department of Physical Therapy, Medicine, and Nursing College, Hungkuang University, 34 Chung-Chie Rd, Shalu, Tai-Chung County, Taiwan; E-mail:

Acknowledgment date: July 30, 2009. Revision date: December 3, 2009. Acceptance date: December 15, 2009.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

Institutional funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

© 2011 Lippincott Williams & Wilkins, Inc.