# Segmental range of motion of vertebral body tethering: an in-vitro analysis of single-tether, double-tether, and hybrid constructs

## TL;DR

This study examines how different vertebral body tethering techniques affect spinal motion in cadavers, showing that these methods preserve most motion while providing stability.

## Contribution

The study experimentally evaluates the biomechanical effects of single-tether, double-tether, and hybrid VBT constructs on spinal motion.

## Key findings

- Instrumented cases preserved at least 80% of native segmental ROM during flexion and extension.
- Hybrid constructs preserved 65% ROM in axial rotation and 29% in lateral bending.
- Hybrid constructs increased ROM at adjacent levels near the titanium rod compared to single or double tethers.

## Abstract

Vertebral Body Tethering (VBT) is emerging as a promising approach for treating Adolescents with Idiopathic Scoliosis. This study aims to address the limited experimental research on vertebral body tethering by examining its biomechanical effects on the segmental spinal range of motion (ROM).

Six human spine samples (T10-L3) were subjected to pure moment testing under four different conditions: native, and instrumentation with single-tether (T10-L3), double-tether (T11-L3), and hybrid (T12-L2) techniques in flexion (FL) and extension (EX), lateral bending (LB), and axial rotation (AR). The intersegmental ROM was measured from sensors inserted in each vertebra using an electromagnetic tracking system.

All instrumented cases preserved at least 80% of the native segmental ROM during FL-EX for all tested segments. In AR, all segments preserved at least 88% ROM mobility for single-tether and double-tether, or 65% for the hybrid technique. In LB, the ROM was reduced to 55% for a single-tether, 47% for a double-tether, and 29% for a hybrid system. The hybrid construct tended to relatively increase the ROM of adjacent levels near the titanium rod when compared with the single-tether or double-tether.

This study provided experimental data on individual segment motion under VBT. The findings indicate that VBT techniques preserve a significant portion of FL-EX and AR ROM for all segments. However, the tested VBT constructs provide stability for the spine in LB.