Purpose: Adolescent idiopathic scoliosis occurs far more often in girls than in boys, and its initiation and progression normally takes place around the adolescent growth spurt. Despite extensive research into the topic, no solid explanation for both well-known phenomena has been offered. The sagittal profile of the growing spine has been demonstrated previously to play an important role in the spine's rotational stiffness. Changes in this sagittal alignment around the growth spurt can be inferred to play an important role in the spine's propensity to develop a rotatory deformity, i.e. scoliosis. The aim of this study was to quantify sagittal spino-pelvic alignment and orientation in space of each individual vertebra in normal boys and girls in the beginning, at the peak and at the end of pubertal growth.
Methods: Standardized lateral radiographs of the spine of boys (n = 57) and girls (n = 99) between the age of seven and eighteen who underwent screening for scoliosis, but had a normal spine were enrolled in this study. Children with spino-pelvic pathology at initial screening or during follow-up were excluded. According to Dimeglio's data, subjects were classified into three groups: before, at and after the peak growth spurt. Seven regional sagittal spino-pelvic parameters, as well as the inclination angles of each individual vertebra between C7 and L5 compared to the gravity line, were measured semi-automatically using in-house developed software.
Results: In all subjects, the posteriorly tilted segment was longer, vertebrae T1-T8 were more posteriorly inclined and thoracic kyphosis, pelvic incidence and pelvic tilt were lower before as well as during the peak of the growth spurt, when compared to after the growth spurt (P ≤ 0.023). Furthermore, in girls, thoracic kyphosis was smaller (P = 0.023), the posteriorly inclined segment was longer (P < 0.001) and T1 as well as levels T3-T11 were more posteriorly inclined (P < 0.05) compared to boys at all stages of development. At the peak of the growth spurt, girls had more posterior inclination of upper thoracic vertebrae and lower values for thoracic kyphosis than boys (P = 0.005).
Conclusions: These results imply that the spines of girls during the growth spurt are more posteriorly inclined, and thus rotationally less stable, compared to boys at the same stage of development, as well as compared to girls after the growth spurt. This may explain why initiation and progression of adolescent idiopathic scoliosis are more prevalent in girls around puberty.