Introduction: The low bone mass concomitantly occurred in patients with adolescent idiopathic scoliosis (AIS) and could still persist after skeletal maturity. The purpose of this study was to assess the asymmetrical loss of vertebral bone mineral density (vBMD) and its correlation with curve severity in patients with AIS using Hounsfield unit (HU) values measured from computed tomography (CT) scans.

Methods: Nighty-three AIS patients were retrospectively recruited. The HU values of vertebral body (VB-HU) and pedicle screw trajectory (PST-HU) were measured from 4 vertebras above (Apex-4) to 4 below (Apex+4) the apical vertebra (Apex) of the major curve. The VB-HU and PST-HU at UEV, Apex, LEV within concave and convex sides of major and minor curves, and stable vertebras were also obtained.

Results: Significant correlation was detected between Cobb angle and VB-HU at periapical levels of major curve. VB-HU and PST-HU at periapical levels were significantly greater within concavity than convexity of both major and minor curves. The asymmetric ratio of VB-HU and PST-HU were significantly correlated to the major curve Cobb angle, and peaked at Apex and gradually diminished from Apex to end vertebras. The asymmetrical loss of vBMD aggravated with the progression of curve severity, presenting as VB-HU significantly decreased within convexity and insignificantly decreased within concavity of the major curve.

Discussion: The asymmetrical loss of vBMD was associated with the progression of curve severity in AIS. For patients with severe AIS, distraction of the pedicle screws at concave side should be a priority to correct the major curve, and supplemental anchors as well as larger sized screws should be placed within convex side around Apex of major curve, in order to reduce the risk of screw loosening after surgery.