Three-dimensional vertebral wedging and pelvic asymmetries in the early stages of adolescent idiopathic scoliosis

Background context: Scoliosis is a three-dimensional (3D) deformation of the spine and the pelvis. Although the relation between the pelvic asymmetries and scoliosis progression was proposed by several authors, it has not been documented over time in adolescent idiopathic scoliosis (AIS).

Purpose: The objective was to determine whether vertebral wedging and pelvic asymmetries progress in the early stages of AIS before any orthopedic treatment.

Study design: The study design included an observational cohort study.

Patient sample: Nineteen AIS girls participated in this study.

Outcome measures: The outcome measures were pelvic and spine geometries from simultaneous biplanar radiographs.

Methods: At the diagnosis, the girls (12.6±1.3 years) had a Cobb angle of 13.9°±6.0°. At the end of their observation period (11 months on average), the scoliosis progressed to 20.5°±5.5°. Bone 3D geometry was reconstructed from biplanar radiographs. Sagittal and frontal wedgings were calculated for five vertebral levels, namely, at the apex and at the two vertebral bodies above and below it. The pelvic geometry was described using five 3D homologous right-left lengths to estimate pelvic asymmetries. Paired t tests were performed on vertebral wedging and pelvic asymmetries to assess their progression between the two evaluations. Principal component (PC) analyses were applied to determine whether vertebral wedging or pelvic asymmetries were predominant at each evaluation.

Results: Vertebral wedging was present at the diagnosis (1.76°-5.92°) and generally did not progress until brace prescription. The mean difference between the right and left pelvic normalized lengths was 1.4% and 2.4% for the initial and final evaluations, respectively. Results revealed the width of the right pelvis to be superior by 3%, and this asymmetry progressed to 4.0%. Principal component analysis revealed that initial vertebral wedging was present in seven out of eight parameters of the first three PCs, whereas at the final examination, vertebral wedging and pelvic asymmetries were evenly present.

Conclusions: Our study confirms the presence of vertebral wedging at the early stages of scoliosis. This is the first to document the association between spinal and pelvic deformities over time. Pelvic asymmetries could be responsible for trunk muscle imbalances and lead to reduced neuromuscular control reported in AIS patients. These results could influence body brace fitting.