Anterior vertebral body tether (AVBT)

Anterior vertebral body tethering (AVBT) is a fusionless technique for treating and managing idiopathic scoliosis in skeletally immature patients to reduce the typical side effects of rigid posterior fusion (such as loss of spinal motion and risks adjacent segment degeneration later in life) ^1,3.

Indications

There is currently no consensus on the indications for this technique due to its recent implementation among surgical techniques currently available to correct idiopathic scoliosis in immature subjects.

The current indications for this technique remain limited, and patients are carefully selected. Current indications include ²:

• skeletally immature Lenke type 1 patients with Cobb angles between 40-70°
• premenarchal female patients
• Risser 0 patients with open triradiate cartilage and a Sanders score <4

Contraindications

• Cobb angle >50° and no residual growth
• kyphosis >40° (relative)

This is because the treatment aims to correct the vertebral curvature. If the patient has no margin of vertebral growth, the intervention will be ineffective.

Procedure

The procedure involves a thoracic and abdominal approach ².

The instrumentation is placed thoracoscopically using 4-5 access portals, ensuring single lung ventilation for the thoracic approach. 

An open retroperitoneal approach is used in the placement of the lumbar fixation devices.

Hydroxyapatite screws stretched with a single polyethylene terephthalate cable are then fixed. There is no set degree of tension, but this is done subjectively by the surgeon using tactile feedback of the tensioner under fluoroscopic guidance.

Outcomes

The primary outcome was a surgical success, defined by a total Cobb angle < 35° and no revision surgery. Secondary outcomes included: final curve magnitudes, radiographically visible tether breakage, complications, and revision surgeries.

History and etymology

The first case of AVBT was reported by Crawford and Lenke in 2010 ⁴, and it was not until 2019 that the United States of America's Food and Drug Administration (FDA) approved an instrumentation system for AVBT.

As the AVBT technique has only been relatively recently proposed, the literature on it remains limited, especially regarding indications, benefits, risks, complications, and long-term benefits.