Machine Learning-Guided LIV Selection for Adolescent Idiopathic Scoliosis

This study will evaluate whether a machine learning-based decision support model, called the Drum Tower Rule, can help surgeons select the lowest instrumented vertebra during corrective surgery for adolescent idiopathic scoliosis. Patients with Lenke type 1 or Lenke type 5 adolescent idiopathic scoliosis who are scheduled for posterior spinal fusion will be randomly assigned to one of two groups. In the model-guided group, surgeons will receive the model-predicted risk of postoperative distal adding-on and a recommendation for lowest instrumented vertebra selection. In the conventional-experience group, surgeons will select the lowest instrumented vertebra according to routine clinical experience and existing surgical principles, without access to the model output. All patients will receive standard posterior spinal fusion. The main outcome is the incidence of distal adding-on at 24 months after surgery, assessed by blinded radiographic reviewers.

Inclusion Criteria: * Diagnosis of adolescent idiopathic scoliosis classified as Lenke type 1A or Lenke type 5C. * Age 10 to 18 years, inclusive. * Scheduled to undergo posterior spinal fusion using an all-pedicle screw instrumentation system. * Planned selective thoracic fusion or selective lumbar fusion, with a clinical need for lowest instrumented vertebra decision-making. * Availability of required preoperative standing full-spine radiographs and bending radiographs. * Ability and willingness to complete the planned 24-month postoperative follow-up. * Written informed consent provided by the participant and legal guardian. Exclusion Criteria: * \- Congenital scoliosis, neuromuscular scoliosis, syndromic scoliosis, or other non-idiopathic scoliosis. * History of spinal trauma, spinal tumor, spinal tuberculosis, or spinal infection. * Previous spinal surgery. * Severe sagittal spinal deformity, such as Scheuermann disease, for which the study model is not applicable. * Neurological symptoms or signs. * Leg length discrepancy greater than 10 mm. * The surgeon determines that there is no clinical equipoise for lowest instrumented vertebra selection because one option is clearly contraindicated for safety or anatomical reasons. * Inability to complete follow-up or required study assessments.