• Søren Ohrt-Nissen, LukKeith D KKDKDepartment of Orthopedics and Traumatology, The University of Hong Kong, Queen Mary Hospital, 5/F Professorial Block, Pokfulam, Hong Kong, SAR, China., Dino Samartzis, and CheungJason Pui YinJPYDepartment of Orthopedics and Traumatology, The University of Hong Kong, Queen Mary Hospital, 5/F Professorial Block, Pokfulam, Hong Kong, SAR, China. cheungjp@hku.hk..
• Spine Unit, Department of Orthopedic Surgery, Copenhagen University Hospital, Rigshospitalet University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. ohrtnissen@gmail.com.
• Eur Spine J. 2020 Aug 1; 29 (8): 2018-2024.

HypothesisFusing shorter than the last touched vertebra (LTV) is a safe approach in flexible main thoracic (MT) adolescent idiopathic scoliosis (AIS) curves.MethodsThis was a prospective study on consecutive AIS patients surgically treated with selective fusion of the MT curve. Fusion-level selection was based on the fulcrum-bending radiograph method. Patients were grouped based on the position of the lowest instrumented vertebra as proximal to the LTV (proxLTV, n = 43), at the LTV (atLTV, n = 45), and distal to the LTV (distLTV, n = 21).ResultsA total of 109 patients were included in the study. Preoperatively, the distLTV group had greater lumbar Cobb angle, lumbar apical translation, and less flexibility in the MT curve. At 2-year follow-up, the groups did not differ in MT curve correction, but the distLTV had larger lumbar Cobb angle, more apical translation, and worse coronal balance. Distal adding-on was observed in 11 patients (26%) in the proxLTV group, four patients (9%) in the atLTV group, and one patient (5%) in the distLTV group (p = 0.031). Adding-on was associated with younger patients and lower Risser grade at the time of surgery but not with any other radiographic parameter. No differences in SRS-22r scores were observed between the groups.ConclusionsProximal fusion carries the risk of adding-on, but leaving unfused segments in the lower spine increases the potential for compensatory mechanisms to improve spinal and truncal balance. In mature patients with a flexible MT curve, surgeons may consider fusion at or cranial to the LTV.

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