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ASC or VBT?

Updated: Aug 15, 2020

What cases can benefit most from vertebral body tethering (VBT) and who needs anterior scoliosis correction (ASC)? In this post we will discuss the main differences and what type of patient is better candidate for either procedure.


Vertebral body tethering is a concept that leverages on the remaining spinal growth. Basically, it consists in placing an inextensible cord on the longest side of the scoliotic spine (the convexity of the curve) in a patient whose spine is still growing. It is important to remember that the growth of the spine stops before the growth of the limbs, that's why we insist in "spinal remaining growth". The cord will constrain the growth of the convexity of the scoliotic curve (which has actually overgrown compared to the concavity) while allowing for unconstrained growth of the concavity. Typically, VBT procedures are performed in patients with relatively small curves (below 55 to 60°, usually not more than 50°). The curve needs to be flexible (correcting to under 30° in side bending radiographs) and the patient has to have an incomplete spinal growth (Sanders stage ≤ 3). VBT corrects the curve to 25°-30° and in the following one to two years, the asymmetrical growth of the spine is expected to increase the correction.


VBT comes with limitations: Large curves and rigid curves are not good candidates, and patients who have low spine growth left do not have enough potential for growth-modeling. In patients who are too immature at the time of VBT surgery excessive growth modeling can result in an inversion of the curve. For these reasons, less than 15% of all the patients with idiopathic scoliosis are good candidates for VBT.


Anterior scoliosis correction (ASC) brings some improvements over VBT. It applies stronger corrective forces to the spine, releases the ligaments that limit the correction of the curve and uses in most cases a double cord to maintain a stronger corrective effect. With these improvements, ASC can provide correction to patients with large curves, stiff spine and mature patients (grown adolescents and even adults). At Istituto Ortopedico Galeazzi we have treated successfully with ASC patients with curves as large as 85° and 95°, obtaining corrections similar to what we used to achieve with metal rods ...but maintaining the mobility of the spine. Of course, ASC can be applied successfully to smaller, more flexible curves and to more immature patients.


ASC was developed by Drs Darryl Antonacci and Randal Betz in the USA. Dr Berjano is one of the few surgeons trained by Drs Antonacci and Betz in the ASC procedure.


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