One Year Results of the Randomized BiPOWR Trial Comparing the Spring Distraction System (SDS) and the One Way Self-Expanding Rod (OWSER) for the Correction of Neuromuscular and Syndromic Early Onset Scoliosis.

Abstract

Background: Current "growth-friendly" implants for treatment of Early Onset Scoliosis (EOS) have limitations that reduce their efficacy and cost-effectiveness. Recently, two systems have been developed that mitigate many of these limitations, the Spring Distraction System (SDS) and the One Way Self-Expanding Rod (OWSER). The purpose of the multicenter BiPOWR trial was to compare 1-year efficacy and -safety of both strategies in the treatment of neuromuscular or syndromic EOS.

Methods: Non-ambulant, neuromuscular/syndromic EOS patients were included in three academic hospitals. They were randomized to treatment with SDS or OWSER and were blinded until after surgery. Outcomes were coronal curve, spinal growth and the occurrence of (serious) adverse events ((S)AEs). In addition, spinal growth and implant lengthening were calculated. Data were collected pre-operatively, immediately post-operatively, and at 1-, 3-, 6-, and 12-month follow-up.

Results: Thirty patients were included. Two patients passed away during follow-up, and these patients were replaced. All collected data were used for analysis. Mean age at surgery was 9.0 years, and 20/30 patients were male. Mean coronal curve decreased from 74.9° pre-operatively, to 37.6° post-operatively, remaining stable at 37.7° at the 1-year follow-up, with no group differences. T1-T12 length increased by 18 mm/year for SDS and 9 mm/year for OWSER. For T1-S1 length, this was 26 mm/year (SDS) and 18 mm/year (OWSER). Five (S)AEs occurred in the SDS group and 11 (S)AEs in the OWSER group. Two SDS patients passed away, unrelated to the surgery or implant. One (S)AE in the SDS group and 6 (S)AEs in the OWSER group were implant-related.

Conclusions: The SDS and the OWSER achieved coronal curve correction of 50%, which was maintained at 1-year follow-up. Spinal length increase was excellent for both systems. The (S)AE rate was 30%/patient/year for SDS and 78%/patient/year for OWSER.

Key concepts: (1) The current study is the first RCT that compares two "growth-friendly" implants in a neuromuscular early onset scoliosis (EOS) population.(2) The Spring Distraction System (SDS) and the One Way Self-Expanding Rod (OWSER) both achieve around 50% curve correction which is maintained at 1 year follow-up.(3) Both systems achieve excellent T1-T12- and T1-S1 height increase, without the need for repetitive lengthenings.(4) The (S)AE rate of SDS was 30%/patient/year. For OWSER, the (S)AE rate was 78%/patient/year.

Study design: RCT.

Level of evidence: Level 1.