The Fate of The Broken Tether: How Do Curves Treated With Vertebral Body Tethering Behave After Tether Breakage?

STUDY DESIGN

Retrospective, multicenter.

OBJECTIVE

The aim of this study was to assess curve progression and occurrence of revision surgery following tether breakage after vertebral body tethering (VBT).

SUMMARY OF BACKGROUND DATA

Tether breakage after VBT is common with rates up to 50% reported. In these cases, it remains unknown whether the curve will progress or remain stable.

MATERIALS AND METHODS

Adolescent and juvenile idiopathic scoliosis patients in a multicenter registry with ≥2-year-follow-up after VBT were reviewed. Broken tethers were listed as postoperative complications and identified by increased screw divergence of >5 degrees on serial radiographs. Revision procedures and curve magnitude at subsequent visits were recorded.

RESULTS

Of 186 patients who qualified for inclusion, 84 (45.2%) patients with tether breakage were identified with a mean age at VBT of 12.4±1.4 years and mean curve magnitude at index procedure of 51.8±8.1 degrees. Tether breakage occurred at a mean of 30.3±11.8 months and mean curve of 33.9±13.2 degrees. Twelve patients (12/84, 14.5%) underwent 13 revision procedures after tether breakage, including six tether revisions and seven conversions to fusion. All tether revisions occurred within 5 months of breakage identification. No patients with curves <35 degrees after breakage underwent revision. Revision rate was greatest in skeletally immature (Risser 0-3) patients with curves ≥35 degrees at time of breakage (Risser 0-3: 9/17, 53% vs. Risser 4-5: 3/23, 13%, P =0.01). Curves increased by 3.1 and 3.7 degrees in the first and second year, respectively. By 2 years, 15/30 (50%) progressed >5 degrees and 8/30 (26.7%) progressed >10 degrees. Overall, 66.7% (40/60) reached a curve magnitude >35 degrees at their latest follow-up, and 14/60 (23.3%) reached a curve magnitude >45 degrees. Skeletal maturity did not affect curve progression after tether breakage ( P >0.26), but time to rupture did ( P =0.048).

CONCLUSIONS

While skeletal immaturity and curve magnitude were not independently associated with curve progression, skeletally immature patients with curves ≥35 degrees at time of rupture are most likely to undergo additional surgery. Most patients can expect progression at least 5 degrees in the first 2 years after tether breakage, though longer term behavior remains unknown.

LEVEL OF EVIDENCE

Level III.