Purpose:

There is no identified consensus for the curve magnitude at which an adolescent idiopathic scoliosis (AIS) patient is indicated for posterior spinal fusion (PSF). We aimed to identify a benchmark for curve magnitude at which fusion is indicated; we also aimed to evaluate which patients were being fused under 50°.

Methods:

A prospective multicenter AIS database was queried to identify patients who underwent PSF for AIS. Clinical outcome and demographic information was collected along with anatomic area of the primary curve. Benchmarking was assessed by median and IQR. Patients were stratified by fusion prior to 50° or at 50° or more, and statistical analysis was performed to assess risk factors for fusion < 50°.

Results:

4229 patients were included in the analysis. The median indication for PSF in the thoracic curve cohort was 55°, and in the lumbar curve cohort was 51°. Site-specific evaluation showed that two sites were more likely to fuse < 50° compared to all other sites (p < 0.05). Over time, the percentage of patients being fused < 50° has declined (p < 0.05). On univariate and multivariate analysis, lumbar curve location, increasing Risser score and female sex were all risk factors for fusion < 50° (p < 0.05). Low SRS-24 scores did not correlate to fusion below 50°.

Conclusion:

There exist location-specific indications for posterior spinal fusion that vary throughout the country. Additionally, increasing maturity, female sex, and lumbar curve location are independent risk factors for fusion under 50°.