Joo YS, et al. - Researchers identified the risk factors for postoperative distal adding-on in Lenke 1A adolescent idiopathic scoliosis. In the L4-left (L4-L) type, the sacral slanting typically occurs to the left and in the L4-right (L4-R) type, it occurs to the right. In patients with Lenke type 1A scoliosis, an independent risk factor that caused adding-on was the size of the preoperative lumbar curve. In the L4-R type, the last touching vertebra (LTV) was lowered with right-sided sacral slanting. Hence, to save the motion segments the fusion level might be shorter resulting in distal adding-on.