Research Vertebral Body Tether

Recent Publication on Anterior Vertebral Body Tethering (AVBT) Compared with Posterior Spinal Fusion for Major Thoracic Curves: A Retrospective Comparison by the Harms Study Group

Study Cohort:
Thoracic Idiopathic Scoliosis patients who underwent Anterior Vertebral Body Tethering (AVBT) with minimum 2-year follow-up after surgery and propensity matched to Posterior Spinal Fusion (PSF) patients from Harms Study Group multicenter database.

237 AVBT patients (thoracic curve tethered only) vs. 237 PSF patients

Propensity matched using: age, preoperative thoracic curve magnitude, sex, and grouped Risser sign

All but one AVBT were Lenke 1 or 2

Compared preoperatively and at >/= 2-year follow-up.

  • Radiographic data
  • Clinical data 
  • Scoliosis Research Society 22-Item Questionnaire (SRS-22)


Preoperatively AVBT patients:

  • 1.3 years younger (p<0.001) than PSF group
  • Triradiate cartilage were open in 59% (vs. 19% in PSF)
  • Smaller preoperative curves (5 degrees; p<0.001) than PSF group
  • More Lenke 1 curves (81%) vs. PSF (64%)

Postoperatively AVBT patients:

  • 21 degrees correction from preop (44% correction) vs. PSF 33 degrees (62% correction)
  • 1 degree improvement from initial postop to final vs. 4 degrees worsening for PSF.
  • Residual thoracic curve

<35 degrees in 76% (vs. 97% for PSF)

  • Improvement of Angle of Trunk Rotation: 6 degrees (preop to postop) vs. 9 degrees (PSF)
  • LIV: T10-L3 vs. PSF T10-L4; on average PSF was 1 level longer than AVBT


  • AVBT broken tethers documented in 20%
  • Secondary surgeries:
    • AVBT: 46 procedures in 38 patients (16%)
    • PSF: 4 procedures in 3 patients (1.3%)
  • SRS-22: AVBT group with less improvement in pain and self-image

Secondary, more stringent propensity matching:

  • AVBT improved 22 degrees (preop to postop) and PSF 33 degrees
  • Revision rate: AVBT 10% vs. PSF 2%

Study Problems and Issues:

No reporting of Lumbar Modifiers. This can impact the outcomes of AVBT and PSF.

No power analysis was reported.

Despite primary propensity matching, the two groups were statistically different for age and curve magnitude.

There were separate cohorts analyzed in the study which is confusing. It can be assumed by the reader the more stringent propensity-matching was done primarily, and was likely underpowered, so there were few significant findings. Hence a less stringent propensity-matching analysis was performed and is the bulk of the statistical findings.

“Angle of trunk rotation” was not defined but could be assumed to be from a scoliometer measurement.

No report on how missing data was handled statistically

No Sanders grading (only Risser grades)

Minimum follow-up 2 years and mean follow-up 2.2 years +/-0.5 (which means some patients did not reach two-year follow-up). This is a very short follow-up for AVBT and longer follow-up will likely demonstrate high tether breakage, loss of correction and higher reoperation rate.

Take-away message:

  • In this short follow-up study, Posterior Spinal Fusions (PSFs) when compared to Anterior Vertebral Body Tethering (AVBT) of the thoracic spine:
  • Better corrected the deformity (+11 degrees coronal, +3 degrees rotational)
  • Were instrumented with 1 more vertebral level distally 5-12 times lower reoperation rate
  • Had 21% more patients with a thoracic curve less than 35 degrees
  • Reported better improvement in pain and self-image

This information needs to be discussed before surgery to achieve shared decision-making.  Both procedures correct the deformity but due to the short length of follow-up the
use of AVBT in this patient population should be approached with caution.

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