High-density and moderate-density implant constructs for adolescent idiopathic scoliosis have equivalent clinical and radiographic outcomes at 2 years

Purpose Implant density for posterior spinal fusion in AIS remains controversial. As limited data exist to guide surgeons, we aimed to evaluate the effect of implant density on radiographic and patient reported outcomes (PROMs). Methods This is a retrospective review of prospectively collected multicenter data. Radiographic, perioperative, and PROMs were compared for patients treated with high-density (> 1.8) and moderate-density (<= 1.8-1.4) screw constructs. Patients were stratified according to the Lenke classification. Results 1865 patients met inclusion criteria: 1225 high-density and 640 moderate-density screw construct patients. The groups had similar mean age (14.7 vs 14.6, p > 0.05) and sex (81.5% vs 79.5% female, p > 0.05). There were similar radiographic outcomes between groups [final curve magnitude (19 degrees vs 19 degrees, p = 0.540)] with only small differences in the percent correction for Lenke 2 curves (66% vs 61%, p = 0.001) producing a 1 degrees difference in curve correction (19 degrees vs 20 degrees, p = 0.001) in the high-density group at 2 years. Excluding thoracoplasty patients, 2-year rib rotation was similar between the two groups (4.5 degrees vs 6.3 degrees, p < 0.05). The mean time to follow-up was shorter in the high-density group (4.5 vs 5 years, p < 0.001), but no statistically significant differences in the two-year SRS-22 scores. Conclusion Patients treated with both high and moderate-density constructs had similar SRS scores and radiographic results at 2-year follow-up. High-density constructs produced marginally better axial, sagittal, and coronal correction. However, these differences are small and not clinically meaningful with no difference in PROMs in curves <= 70 degrees. The use of a moderate-density construct should be considered for routine AIS surgery.