Trunk rotational strength asymmetry in adolescents with idiopathic scoliosis: an observational study

BACKGROUND: Recent reports have suggested a rotational strength weakness in rotations to the concave side in patients with idiopathic scoliosis. There have been no studies presenting normative values of female adolescent trunk rotational strength to which a comparison of female adolescents with idiopathic scoliosis could be made. The purpose of this study was to determine trunk rotational strength asymmetry in a group of female adolescents with AIS and a comparison group of healthy female adolescents without scoliosis. METHODS: Twenty-six healthy adolescent females served as the healthy group (HG) (average age 14 years) and fourteen otherwise healthy adolescent females with idiopathic scoliosis served as the idiopathic scoliosis group (ISG) (average age 13.5 years, average Cobb 28°). Participant's isometric trunk rotational strength was measured in five randomly ordered trunk positions: neutral, 18° and 36° of right and left pre-rotation. Rotational strength asymmetry was compared within each group and between the two groups using several different measures. RESULTS: The HG showed strength asymmetry in the 36° pre-rotated trunk positions when rotating towards the midline (p < 0.05). The ISG showed strength asymmetry when rotating towards the concavity of their primary curve from the neutral position (p < 0.05) and when rotating towards the concavity from the 18° (p < 0.05) and 36° (p < 0.05) concave pre-rotated positions. The ISG is significantly weaker than the HG when rotating away from the midline toward the concave (ISG)-left (HG) side from the concave/left pre-rotated 18° (p < 0.05) and 36° (p < 0.05) positions. CONCLUSION: The AIS females were found to be significantly weaker when contracting toward their main curve concavity in the neutral and concave pre-rotated positions compared to contractions toward the convexity. These weaknesses were also demonstrated when compared to the group of healthy female adolescent controls. Possible mechanisms for the strength asymmetry in ISG are discussed.