Postoperative Distal Coronal Decompensation After Fusion to L3 for Adolescent Idiopathic Scoliosis Is Affected by Sagittal Pelvic Parameters.

STUDY DESIGN

Retrospective study.

OBJECTIVE

To identify on early postoperative radiographs the risk factors for late distal decompensation in adolescent idiopathic scoliosis (AIS) patients undergoing posterior fusion surgery to L3.

SUMMARY OF BACKGROUND DATA

Sparing distal fusion levels in AIS surgery is considered beneficial for postoperative mobility and outcomes; nonetheless, late distal decompensation is of concern. L3 is often advocated as lower instrumented vertebra in posterior fusion, but progressive angulation of the L3/4 disc is commonly observed.

METHODS

A retrospective analysis was conducted on 78 AIS patients who underwent posterior fusion to L3 from 2007 to 2014. Patients' demographic data, early and 2-year postoperative standing radiographs by biplanar imaging system were investigated. Late decompensation was defined as progressive increase of L3-4 disc wedging angle at 2-year follow-up. Coronal, sagittal, and rotational radiographic parameters were compared between those with and without decompensation. SRS-30 scores were reviewed.

RESULTS

Mean age was 14.5-year, and fusion levels averaged 12.0 (range: 6-15); 43 out of 78 patients (55%) experienced progressive L3-4 disc wedging, with 6 showing wedging >5°. L3 translation from the central sacral vertical line (13.9 vs. 11.1 mm, P = 0.13) and increased pelvic tilt (13.3° vs. 8.6°, P = 0.06) on the early postoperative radiograph were associated with increased L3-4 disc wedging. Multivariate analysis revealed that larger pelvic tilt was a significant risk factor for decompensation (odds ratio = 1.1 per 1°, 95% confidence interval: 1.0-1.1, P = 0.04). SRS-30 scores did not differ significantly between the two groups (4.0 vs. 4.1, P = 0.44).

CONCLUSIONS

Pelvic retroversion and increased translation of L3 from the central sacral line on the early postoperative radiograph were associated with late L3-4 disc wedging in AIS fusions to L3. Careful surgical planning and correction of sagittal alignment are imperative to ensure the long-term outcomes.

LEVEL OF EVIDENCE