Purpose: The purpose of this study is to detect the changes occurring occur in patients with adolescent idiopathic scoliosis in terms height and Cobb’s angle during a specific period of time by means of a mathematic model.

Materials and methods: This was a retrospective study of a cohort of 132 girls. The inclusion criteria were the following: adolescent idiopathic scoliosis, Cobb’s angle greater than 10°, follow-up of at least 2 years with half-yearly controls. The variables were: year of onset of menstruation (menarche), height, Cobb’s angle and treatment. The changes in height and Cobb’s angle which occurred with time were adjusted through curved regression models. The gradient was calculated between each of the consecutive time points (first-degree derivative). Growth was considered stable when the gradient changed direction or was illegible.

Results: The cubic measure was found to be best fitted to the height (R2=0.329) and signal-change parameters of the gradient a year after the onset of menstruation (menarche). The force function was the best for Cobb’s angle, albeit with a slight adaptation (R2=0.038). A correlation was found between the mean height and the angles. This value was found to be higher for girls treated with a brace. Comparing the mean heights recorded in one semester with those of the previous semester, one can observe statistically significant differences up to 2.5– 3 years post-menarche.

Conclusions: Cobb’s angle and height in conservatively-treated adolescent idiopathic scoliosis often stabilize 2,5 years and after the onset of menstruation. Patients treated with a brace stabilize when they reach menarche.