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

PURPOSE: 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).

METHODS

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.

RESULTS

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.

CONCLUSION

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.