Is It Enough to Stop Distal Fusion at L3 in Adolescent Idiopathic Scoliosis with Major Thoracolumbar/lumbar Curves?

Purpose: The choice of distal fusion level in adolescent idiopathic scoliosis (AIS) patients with major thoracolumbar or lumbar (TL/L) curves (Lenke type 3C, 5C, or 6C) remains debatable. One of the most controversial issues involves stopping the distal fusion at L3, which might result in an increased risk of decompensation but save more mobile spinal segments. The purpose of this study was to evaluate and compare the clinical and radiological outcomes of corrective surgery for AIS with major TL/L curves according to the distal fusion level.

Methods: 229 AIS patients with Lenke type 3C, 5C, or 6C curves that underwent corrective surgery were included. Patients were grouped according to distal fusion level, either L3 (group A) or L4 (group B), and followed up for over 2 years. Group A was further divided into lower end vertebra (LEV) and last touching vertebra (LTV). The SRS-22 score was used to assess clinical outcomes. All radiological parameters were assessed pre- and postoperatively by standing anteroposterior whole-spine radiographs. Clinical and radiological parameters were compared between the groups.

Results: Postoperative decompensation was found in 4.6 % (9/197) of group A patients and 9.3 % (3/32) of group B patients. This difference was not statistically significant (P = 0.258). No difference was found in the clinical and radiological parameters between the two groups either pre- or postoperatively. Subgroup analysis showed that the scoliosis correction rate and postoperative apical vertebral translation were lower in cases with an LEV ≤ L4 or LTV = L5 when the fusion stopped at L3 distally. The adjacent disc wedge angle was aggravated postoperatively in these cases, although this did not reach statistical significance.

Conclusions: There is no difference in the radiological and clinical outcomes in AIS according to the distal fusion level. Major TL/L curve correction in AIS may be sufficient distally at L3 in cases with an LEV ≥ L3 and LTV ≥ L4. However, stopping fusion at L3 requires caution in LEV ≤ L4 or LTV = L5 patients, as this correction rate might be suboptimal and causes a possible progression of the adjacent disc wedge angle.