Can we stop fusion distally at L3 instead of L4 vertebra in the surgical treatment of adolescent idiopathic scoliosis with Lenke type 3C, 5C and 6C curves

Important decision after determination of a patient requiring surgery for idiopathic scoliosis is the selection of the segments of the spine for fusion. Ideally, the distal extent of the fusion should be as proximal as possible to preserve lumbar motion segments, yet long enough to avoid creating trunk imbalance in the modern thinking about scoliosis surgery. When instrumentation of both the thoracic and the lumbar curves especially in double major or major thoracolumbar/lumbar (TL/L) curves (Lenke Type 3C, 5C and 6C or King Type I and IV) is required, the distal extention of fusion is usually L4 or rarely L3 level. Choosing between L3 and L4 can be difficult. The most predictable spinal balance occurs when the fusion/instrumentation extends distally to the stable vertebra. The purpose of this study is to determine preoperative radiological criteria to stop the fusion distally at L3 level instead of L4 in Lenke 3C, 5C and 6C curves even when CSVL does not touch L3.This study reviewed 140 patients with adolescent idiopathic scoliosis surgically treated between 2002 and 2007 in a single institution and 118 of them were available for minimum 2-year follow-up evaluation. Included in the study were patients who underwent an instrumented posterior spinal fusion for adolescent idiopathic scoliosis with Lenke type 3C, 5C and 6C curves. For the 118 patients, the average follow-up period was 42 months, ranging from 24 to 60 years. The average age at surgery was 15.4 years, ranging from 13 to 18 years. Distal fusion was stopped at L3 in all patients.In the current study; in nearly one third of our cases, CSVL does not touch L3 but L3 becomes level to pelvis at bending radiographs and traction radiographs, especially when taken under general anesthesia. It is possible to stop fusion at L3 in those cases. In two thirds of cases, CSVL does not touch L3 and it does not become level at bending radiographs. Traction radiographs taken under general anesthesia are especially helpful in these cases because L3 becomes level, CSVL touches or bisects L3 and L3 is completely in Harrington?s stable zone. Thus, according to bending radiographs you can not stop at L3 but you can do so according to traction radiographs taken under general anesthesia.These findings encouraged us to stop the fusion distally at L3 level instead of L4. Thus, it is possible to save more motion segments distally without unbalancing the vertebral column.