EMG Study of Adolescent Idiopathic Scoliosis Patients Treated with the Boston Brace

Institut de génie biomédical, Université de Montréal/École Polytechnique; Research Center,
Ste-Justine Hospital., Montréal, Canada

PURPOSE: Despite knowledge on the clinical outcomes of the Boston brace (BB) treatment, there is a lack of understanding of its action mechanisms. To reduce the pressures exerted by the brace pads, the patient could actively induce specific trunk muscle recruitment patterns capable of correcting the scoliosis [1]. Although simulation models identified trunk muscles on the convex side of the lumbar curve as being potentially able to reduce the magnitude of the scoliosis, there is no clinical evidence to support this [3,4]. This study was conducted to investigate the immediate muscular reaction in response to bracing in scoliosis patients.

METHODS: We collected data from 11 female adolescent idiopathic scoliosis patients (King I or II type) treated with the BB. Surface electromyographic (EMG) signals from 22 trunk muscles were obtained with and without the brace under 4 controlled isometric tasks: 1) maintaining an upright stable posture; 2) resisting a trunk flexion moment; 3) resisting a right lateral trunk bending moment; 4) resisting a left lateral trunk bending moment. A motion analysis system was also used to evaluate the magnitude of the load-induced trunk movements during the execution of the last 3 tasks. ANOVA tests were conducted with p ‹ 0.05.

RESULTS: When the brace was worn, an increase in back muscles EMG activity was observed in 93% of individual observations (43% statistically significant) but no significant effect on the EMG of abdominal muscles was observed. Individual significant braced/unbraced EMG ratios for back muscles ranged from 1.28 to 2.34 while significant group ratios varied from 1.49 to 1.61 for tasks 1), 3) and 4). When specific muscular regions were analyzed, larger increases were found for muscles spanning the convex side of the lumbar curve.

CONCLUSIONS: Our results indicate that BB has a stimulating effect on back muscle activities particularly on muscles on the convex side of the lumbar curve. As previously suggested, the recruitment of this muscle group could have a beneficial effect on the scoliosis [3]. It thus seems that by seeking to reduce the pressures exerted by the brace pads, the patient could actively recruit back muscles that can have a corrective effect on the spinal deformity.

References:
[1] Emans, J.B., Brace manual. Scoliosis Research Society, 1988.
[2] Katz D. et al., Spine, 22(12), 1302-1312, 1997.
[3] Schultz A., Haderspeck K., Takashima S., Spine, 6(5), 468-476, 1981.
[4] Wynarsky, G.T., Ph.D. thesis, University of Michigan, 1988.