Posterior Spinal Fusion With Pedicle Screws vs. Anterior Vertebral Body Tethering in Adolescent Idiopathic Scoliosis (AIS): an International Multicenter Randomized Clinical Trial

Background- Adolescent idiopathic scoliosis is the most common indication for major surgery in adolescents (between 10 and 18 years of age). The current standard of care for adolescent idiopathic scoliosis (AIS) with a curve magnitude of over 40-50˚ in skeletally immature patients, is posterior spinal fusion with pedicle screws. The aim of spinal fusion is to prevent further curve progression but also to correct the spinal deformity and achieve a cosmetically pleasing result by reducing the rib hump and balancing the trunk and shoulders. While this procedure has been very successful, it has inherent downsides such as the decreased range of motion and loss of spinal mobility in addition to the inhibition of growth along the instrumentation. To prevent distal adding on (continued curve below instrumentation) due to continued anterior spinal growth, it is often necessary to fuse the spine into stable vertebra resulting into even longer spinal fusion levels in the lumbar spine (Sponseller et al. JPO 2016; Oksanen et al. SJS 2018). Spinal fusion increases loading of the remaining mobile segments (Parsch et al. JBJS Br 2001).

In a five-year follow-up study spinal fusion resulted into better health-related quality of life (HRQoL) as compared with untreated AIS (Helenius et al. JBJS 2019). However, the function domain of HRQoL was significantly less after spinal fusion as compared with healthy controls. In contrast, vertebral body tethering using screws connected by a tether in the anterior vertebral body, has the potential to initially correct the still flexible deformity, but most importantly modulate growth and ultimately result in scoliosis correction with a mobile spine.

There is currently a paucity of literature on the effectiveness of vertebral body tethering (VBT) with only retrospective case series published and reported in conference proceedings, and a comparative study is completely lacking. Initial complication rates with the implants for tethering have also sparked caution amongst surgeons and payers whether or not to adopt this technique despite its theoretical advantages. Thus, a high-quality comparative prospective study is missing to demonstrate the effectiveness and safety of vertebral body tethering compared to posterior spinal fusion. If this can be shown in a well-designed study, it is likely to result in a paradigm shift in the treatment of AIS similar to the impact earlier technical novelties and achievements had.

Randomised controlled trials are rare in paediatric orthopaedic research. It would be unprecedented that evidence from an RCT is driving a change in practice in scoliosis surgery.

Aims and hypothesis- To compare posterior fusion to VBT for the treatment of AIS. Aim is to demonstrate non-inferiority of VBT compared to posterior fusion in terms of main curve correction of AIS at the 2 year follow up, to demonstrate comparable outcomes for SRS-22/24 at the 2 year follow up. Aim is also to compare complication and revision rates and to compare spinal mobility including flexion and side bending between the study groups.