Vertebral Body Tethering in Skeletally Immature Patients: Results of a Prospective U.S. FDA Investigational Device Exemption Study.

Abstract

Background: The purpose of this study was to report on 2-year results of vertebral body tethering (VBT), performed under a Food and Drug Administration protocol, to obtain insight into outcomes and complications.

Methods: Forty prospectively enrolled patients with adolescent idiopathic scoliosis (AIS) who had a Sanders score of ≤4 or a Risser score of ≤2 underwent VBT for curves between 40° and 70°. Surgical, radiographic, and patient-reported outcomes were reviewed at a minimum 2-year follow-up.

Results: Mean age at surgery was 13 (range, 10 to 16) years. The 40 patients were 90% female; 95% White, 2.5% other, and 2.5% unreported; and 92.5% non-Hispanic, 5% Hispanic, and 2.5% unreported. A mean of 8 (range, 5 to 12) levels were instrumented. Most patients were at Sanders 4 (65%) and Risser 0 (63%). Mean length of stay was 3 ± 1 days, estimated blood loss was 236 ± 158 (range, 25 to 740) mL, and operative time was 4.4 ± 1.4 hours. Mean correction of the major curve was 44% (range, 22% to 95%) on the 3-month standing radiograph, 49% at 1 year, and 46% (range, -10% to 93%) at 2 years. The mean major Cobb angle improved from 51° ± 8° (range, 40° to 70°) preoperatively to 27° ± 11° (range, 3° to 56°) at 2 years. Success at 2 years, defined by a Cobb angle of <35° and no reoperation, was seen in 30 patients (75%) and was associated with a mean Cobb angle of <35° on the first postoperative standing radiograph (p < 0.001). Twelve patients (30%) demonstrated improvement in the curve with growth. By 2 years, 2 (5%) of the patients underwent repeat surgery (1 release for overcorrection, 1 lumbar VBT for lumbar curve progression after thoracic VBT). The Scoliosis Research Society (SRS) satisfaction score improved 2 years following surgery (p < 0.001), but other SRS domains only remained stable over time. Beyond 2 years, 1 additional lumbar tether was required after thoracic VBT, 1 implant was removed, and 3 fusions were performed, for a 10% fusion rate and overall 20% reoperation rate at a mean of 3.8 ± 1.1 years of follow-up. The rate of cord breakage in the study population was 20%.

Conclusions: In skeletally immature patients treated in the U.S. under a prospective Investigational Device Exemption, there was a 75% rate of successful outcomes at 2 years. Most correction was obtained at the time of surgery, and inadequate intraoperative curve correction was associated with a higher Cobb angle on the first postoperative standing radiograph and failure by 2 years.

Level of evidence: Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.