Trunk rotation and hip joint range of rotation in adolescent girls with idiopathic scoliosis: does the "dinner plate" turn asymmetrically ?

BACKGROUND In patients with structural idiopathic scoliosis the body asymmetries involve the pelvis and the lower limbs; they are included in many theories debating the pathogenesis of idiopathic scoliosis. METHODS Hip joint range of motion was studied in 158 adolescent girls, aged 10-18 years (mean 14.2 +/- 2.0) with structural idiopathic scoliosis of 20-83 degrees of Cobb angle (mean 43.0 degrees +/- 14.5 degrees ) and compared to 57 controls, sex and age matched. Hip range of rotation was examined in prone position, the pelvis level controlled with an inclinometer; hip adduction was tested in five different positions. RESULTS In girls with structural scoliosis the symmetry of hip rotation was less frequent (p = 0.0047), the difference between left and right hip range of internal rotation was significantly higher (p = 0.0013), and the static rotational offset of the pelvis, calculated from the mid-points of rotation, revealed significantly greater (p = 0.0092) than in healthy controls. The detected asymmetries comprised no limitation of hip range of motion, but a transposition of the sector of motion, mainly towards internal rotation in one hip and external rotation in the opposite hip. The data failed to demonstrate the curve type, the Cobb angle, the angle of trunk rotation or the curve progression factor to be related to the hip joint asymmetrical range of motion. CONCLUSION Numerous asymmetries around the hip were detected, most of them were expressed equally in scoliotics and in controls. Pathogenic implications concern producing a "torsional offset" of muscles patterns of activation around the spine in adolescent girls with structural idiopathic scoliosis during gait.