Does screw alignment affect tether breakage in vertebral body tethering?

Vertebral body tethering (VBT) is a non-fusion surgery for treating idiopathic scoliosis, with tether breakage as a common complication that occurs in 19–52% of patients. It has been reported in mechanical studies that screw malalignment > 1 mm may cause tether breakage. This is a clinical study aiming to assess the effect of screw alignment on tether breakage. This was a retrospective multicenter cohort study of 115 patients with idiopathic scoliosis who underwent VBT. Clinical data and radiographic parameters such as Cobb angle, screw malalignment, and inter-screw angle were evaluated postoperatively and at 2-year and 3-year follow-ups. Tether breakage was defined as increase in inter-screw angle ≥ 5°, while screw malalignment was defined as > 25% displacement relative to adjacent screws. Mean screw malalignment was compared between broken and intact tether segments. Mean screw malalignment across all levels was 20.6 ± 17%. Overall, screw malalignment was not found to be significantly associated with tether breakage. For the 36 screws (6%) and 5 screws (0.7%) with moderate and severe malalignment, none were associated with tether breakage. In this cohort with satisfactory overall screw alignment, screw malalignment was not found to be associated with tether breakage. Other risk factors that could contribute to tether breakage should be investigated. While excellent screw alignment is unlikely to prevent tether breakage, relative alignment should still be achieved to maintain curve correction and avoid damage to nearby organs.