Where does the tether break in vertebral body tethering cases? Clinical insights from revision cases after tether breakage.

Purpose: To evaluate the sites where the tether breaks in vertebral body tethering (VBT) cases.

Methods: Intraoperative evaluation of broken tethers in patients who had anterior revision.

Inclusion criteria: anterior revision of VBT cases with explantation of the full implant and photo documentation. Eight patients met the inclusion criteria. The primary variable of interest was the location of tether breakage in relation to the vertebral curve and the tether-screw interface. Another variable of interest was to evaluate the difference in breakage rates between anterior and posterior tethers in double tether cases.

Results: Sixty tethers bridging the intervertebral disc within this cohort of eight patients were found. Seven implants were removed from thoracolumbar curves and one implant from a thoracic curve. We identified 32 tether breakages. Double tethers were used in six patients. In these six cases, 15 breakages were found in the posterior tether and 13 in the anterior tether. Four cases (50%) exhibited breakages at the apex, eight cases (100%) at the lowest instrumented vertebra (LIV), and five cases (63%) at the uppermost-instrumented vertebra (UIV). Five tether breakages (in three cases with double tether) were observed at the screw sites, while the remaining 27 exhibited cord breakages near the intervertebral discs. In double tether systems, statistical analysis did not reveal any significant difference in breakage rates between anterior and posterior tethers.

Conclusions: In VBT cases, the tether breaks mostly at the level of the intervertebral disc, adjacent to the lowest instrumented vertebra.

Level of evidence: Level IV (Case series with no comparison group).