The Effect of Implant Density on Adolescent Idiopathic Scoliosis Fusion

Background:Severe adolescent idiopathic scoliosis (AIS) can be treated with instrumented fusion, but the number of anchors needed for optimal correction is controversial.Methods:We conducted a multicenter, randomized study that included patients undergoing spinal fusion for single thoracic curves between 45 degrees and 65 degrees, the most common form of operatively treated AIS. Of the 211 patients randomized, 108 were assigned to a high-density screw pattern and 103, to a low-density screw pattern. Surgeons were instructed to use >= 1.8 implants per spinal level fused for patients in the high-implant-density group or <= 1.4 implants per spinal level fused for patients in the low-implant-density group. The primary outcome measure was the percent correction of the coronal curve at the 2-year follow-up. The power analysis for this trial required 174 patients to show equivalence, defined as a 95% confidence interval (CI) within a +/- 10% correction margin with a probability of 90%.Results:In the intention-to-treat analysis, the mean percent correction of the coronal curve was equivalent between the high-density and low-density groups at the 2-year follow-up (67.6% versus 65.7%; difference, -1.9% [95% CI: -6.1%, 2.2%]). In the per-protocol cohorts, the mean percent correction of the coronal curve was also equivalent between the 2 groups at the 2-year follow-up (65.0% versus 66.1%; difference, 1.1% [95% CI: -3.0%, 5.2%]). A total of 6 patients in the low-density group and 5 patients in the high-density group required reoperation (p = 1.0).Conclusions:In the setting of spinal fusion for primary thoracic AIS curves between 45 degrees and 65 degrees, the percent coronal curve correction obtained with use of a low-implant-density construct and that obtained with use of a high-implant-density construct were equivalent.Level of Evidence:Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.