A novel classification method for mild adolescent idiopathic scoliosis using 3D ultrasound imaging

Abstract

Mild adolescent idiopathic scoliosis (AIS), with Cobb<20°, was hypothesized as the right stage to intervene to prevent progression. AIS curve can be categorized into either structural or non-structural depending on the spine morphology (flexibility). Using X-ray to characterize AIS curves remains the clinical gold standard while compromising the risks of radiation exposure. In previous works, 3D ultrasound imaging had proved the reliability of the coronal spinal curvature measurement. This research aimed at developing a mild AIS classification scheme through examining spine flexibility using 3D ultrasound imaging. For the preliminary study, 90 mild AIS subjects (21 ​M and 69 ​F; Age:14.5 ​± ​1.7 years old; Cobb: 18.2 ​± ​6.4°) underwent both 3D ultrasound and X-ray scanning on the same day. For each case, a clinician measured Cobbs and denoted major curve as ground truth. Bending Asymmetry Index (BAI) was developed to indicate the presence of a possible structural curve. The curve classification was coded to a modified Lenke classification for mild cases (m-Lenke). The results of 3D ultrasound classification were evaluated with the X-ray. It was shown that 70.1% of the subjects had identical curve classification results and 72.0% had the correct major curve detection. Lumbar-dominated curves had distinctive performance (p ​= ​0.91, r ​= ​0.91) against others. The study demonstrated the possibility of a 3D ultrasound-based method for mild AIS curve classification. The discrepancies could be partially explained by the limitations of the ultrasound scanning in proximal thoracic region. Subsequent studies will validate the proposed method with a larger cohort.