The spinal curve in standing and sitting postures in children with idiopathic scoliosis

Study Design. A sample of convenience of children with moderate idiopathic scoliosis without bracing or surgery was studied. The sample consisted of 1 9 children, aged 9 to 16 years, with mean Cobb angle of 24 degrees(.) The s pinal configurations and paraspinal muscle activity in several commonly ass umed postures were examined. Objectives. To determine how the apex angles, verticality of spine, and mus cle activity vary with the assumed posture and whether the location and the number of spinal curves affect these variables. Summary of Background Data. It has been suggested that the configuration of the spine is commonly assumed postures can affect the spinal curve in scol iosis because of gravitational bending moments. there is, however, a paucit y of data obtained in subjects in sitting postures that school-age children assume daily for prolonged periods. Absence of bilateral symmetry in press ure during sitting has been described, but its effect on the spinal apex an gle has not be investigated. Methods. Infrared-emitting markers, whose three-dimensional positions could be tracked by a pair of cameras, were affixed to the spine. The natural po stures studied were relaxed standing, relaxed sitting, erect sitting, and w riting while seated. Electromyographic activity in muscles close to the spi nal apexes was recorded bilaterally for each test posture. Results. Subjects leaned laterally and, in general, anteriorly, in all test postures, rather than placing the C7 vertebra vertically above S1. The dir ection of lean and the change in the spinal apex angle from standing to sit ting varied depending on whether the spinal curve was single or double, tho racic or lumber. Subjects with single curves, whether thoracic or lumbar, t ended to lean laterally toward the convexity of their curve apex - that is, the lean was in a direction that reduced the apex angle. Subjects with dou ble curves (thoracic and lumbar), in all postures except relaxed sitting, t ended to lean toward the convexity of the lumbar curve, thereby reducing th e lumbar apex angle and exacerbating the thoracic angle. Most subjects; ape x angles were smaller in relaxed or erect sitting than in relaxed standing. Electromyographic activity was in general greater on the convex side of th e curve, with greatest activity in erect sitting. Conclusions. The findings indicate that in self-selected postures the gravi tational effect of leaning and the muscle activity in paraspinal muscles ma y serve to reduce the apex angle. Thus, a fully upright, centered posture m ay not be best for correction of every patient's spinal curve.