A three-dimensional (3D) ultrasound imaging system (10) for assessing scoliosis, the system (10) comprising: an ultrasound scanner (11) to capture ultrasound images; a spatial sensor (13) to record the position and orientation of the captured ultrasound images; and a software module (21) to mark features of vertebra in the captured ultrasound images, and the marked features (41) are connected with lines (42) in order to calculate angles and distances between the marked features (41) for the calculation of the Cobb angle and spinal rotation angle based on the calculated angles and distances; wherein the marked features (41) are a reflection of the surfaces of the vertebra.