This is a cross-sectional study on screened school children recommended for radiographic assessment in the scoliosis screening program of SHS in Hong Kong. Both x-ray, ultrasound and ATR measurement of the spine will be performed on the same day at Prince of Wales Hospital.

Scolioscan, the ultrasound system reported to be reliable and valid for spinal deformity assessment, will be used. The system composes of an ultrasound scanner with a linear probe of 100 mm in width and frequency range of 4-10MHz, a frame structure and a spatial sensor which is attached to the ultrasound probe for spatial data capture. Daily calibration will be performed using a phantom to assure accuracy of spine image formation and subsequent angle measurement.

Subjects will stand on the Scolioscan platform with a standardized posture kept stable with pegs throughout the scanning process.. After adjusting the ultrasound scanner setting, the probe will be steered from L5 to T1 spinous process for scanning.

SPA will be used to determine the ultrasound-based Referral Status through predicting whether the Cobb angle is beyond the referral threshold of ≥20° or not. There are two values for the Referral Status: either "for specialist referral" or "not for specialist referral".

"for specialist referral" or "not for specialist referral", through predicting whether the Cobb angle is beyond the referral threshold of ≥20° or not in scoliosis screening

evaluate if this parameter can increase the accuracy of ultrasound assessment