Scoliosis is a complex three-dimensional deformity of the spine. Even though it has been known for centuries, treatment of the deformity has focused on correcting only in the frontal plane. In the last decades, the need for three-dimensional assessment regarding scoliosis has been highlighted to better understand the cause and the principles of treating scoliosis. The overall aim of this dissertation is to provide knowledge to assess scoliosis as a three-dimensional problem.

The severity of scoliosis is measured with the Cobb angle from standing radiographs. Computed tomography (CT) examinations are used throughout this thesis. The first paper investigates the difference in Cobb angle measured from standing radiographs and supine CT examinations. The standing radiographs had larger Cobb angles with a mean difference of 11° and a linear correlation between the two examinations from 128 consecutive patients with adolescent idiopathic scoliosis (AIS) planned for surgery.

The second paper compares the axial shape of vertebrae in 20 patients with AIS with a reference group. Clear asymmetry was observed in all vertebrae – superior and inferior end vertebrae as well as the apical vertebra – compared with corresponding vertebrae among the reference group. The asymmetry was most pronounced in the apical vertebra. A novel parameter, frontal vertebral body rotation (FVBR), was introduced to describe the internal rotation of the vertebrae in the axial plane.

Pelvic incidence (PI) is a measurement of the position of the sacrum in relation to the femoral heads. This is relevant in scoliosis because PI determines the pelvic configuration acting as a foundation to the spine. PI has traditionally been measured from standing radiographs. The third study investigates PI three-dimensionally, based on low-dose CT examinations, in 37 patients with Lenke type 1 or 5 curves compared with a reference group. A significantly higher PI was observed in patients with Lenke type 5 curves compared with the reference group and patients with Lenke type 1 curves.

Severe AIS is treated with corrective surgery. Two approaches are available: the predominant posterior approach and the anterior approach. In the fourth paper, these two approaches are evaluated with regard to three-dimensional correction, how well the correction is maintained over a 2-year follow-up and patient-reported outcome measures. Twenty-seven patients treated with the posterior approach and 26 patients treated with the anterior approach, all with Lenke type 1 curves, were included. Fewer vertebrae were fused in the anterior group, but the posterior group had a better correction of the deformity in the frontal plane. No difference was observed regarding three-dimensional correction and patient-reported outcome measures.

AIS is truly a complex three-dimensional deformity. More research is needed to fully comprehend the complexity of the scoliotic spine.