VBT

Progression overtime with VBT as the patient has grown

VBT or vertebral body tethering has become a surgical approach that is more available for the treatment of scoliosis. It is a modulation technique that involves a tether attached to one side of the spine (the convex) and relies on the patients growth to reach the full correction. VBT is used to treat younger children because of the fact it relies on growth. The growing from the patient helps pull the tether straighter whilst guiding the spine to go against the curve and results in a straighter spine.

During the procedure for VBT, the surgeon will access the spine through the side going in between the patients ribs and chest cavity. This allows for the operation to be done anteriorly (on the front of the spine). When done this way more segments of bone can be avoided and a smaller incision can be made.

The actual procedure of VBT most of the time involves deflating the lung to allow for access to the spine. A telescopic instrument is used to enter the chest cavity and perform the operation. Using this technique it is less invasive for the patient. There is one screw per vertebrae that is inserted onto the spine where the tether will be located on the convex of the curve (The part of the spine that protrudes out). Connected to the screws is the polyethylene strap/tether which works to correct the curve. When the tether is pulled tight during initial application the spine will not go completely straight as that will happen over time. The use of the tether growing over time and having such a small incision helps with the patient's recovery time and their movement later on in life.

VBT placed on one side of the patient on the convex of the curve. (The part of the curve that protrude out)

Animated image of the procedure of a tether being attached to the screws

VBT is currently standing at very low reoperation and failure rate at 10-15%. Failures can be considered failures when the curve has overcorrected, under corrected the tether broke before the curve was stable or the curve was never controlled and was able to increase. Under correction can happen when not enough growth is done and the curve is still at a high degree. In the event that a broken tether occurs, it would depend on how long after surgery this happens to determine the procedure failure. Tethers that have broken can be very hard to see on an x-ray since they have no metal and only really show up if it is effecting the curve. Tethers do their main correction of the curve in the first few months post op and they get to a point where the curve is stable enough that if the tether broke it would not effect the curve and would allow the patient more mobility. Which is evident to how a broken tether does not immediately mean failure.

An x ray displaying a broken tether

The broken tether can be seen in this patients x ray as it has slanted down and is not holding the spine in the right position but due to the patient having had the operation for a while the tethers brake will not have any affect.

VBT preserves a lot of movement compared to more conventional surgical interventions for scoliosis. Knowing this combined with the added benefits of further corrections with growth it seems to be the most conventional method for younger children. VBT also requires patients to have a fully flexible curve which can be seen through x rays where the patient is bending to the side. Due to the nature of the tether and the growth needed it can be implemented earlier in adolescent idiopathic scoliosis diagnosis but when curves get bigger especially in the lower spine or the lumbar segments VBT will not suit as it can not go lower than L5 so is not suited for curves that may effect the pelvis. (It is rare for curves in younger patients to effect the pelvis)

Overcorrection from VBT which has pushed the curve a little the other way which is an overcorrection from wanting to be straight to leaning the opposite way

Since VBT is a newer technique there is not a whole lot of research out there for long term effects or knowing if its a definite fix for your curve although it does offer mobility and shorter time in hospital. Current research has shown that although VBT preserves movement better when compared to patients who had fusions in their thoracic area compared to those who had VBT movement was similar. The movement only differed when looking at fusions and VBT in the lumbar vertebrae. This research prompted many surgeons to reconsidered the modern approaches and have come out with an approach called a hybrid fusion and tethering that minimises the fusion length and tethers the bottom to allow for movement in the lumbar to keep the patient active long term.

Of course with all surgeries no technique is perfect. The main risks of VBT are not getting the right curve correction and issues with the deflation of the lung (which is avoided where possible when doing VBT or hybrid surgeries) and having to reoperate. In many cases reoperation after failed VBT ends with doing a spinal fusion (which is what is being avoided by doing VBT earlier) with this reoperation with the fusion comes having to perform longer fusions with more vertebrae that could have been avoided if done before going down the path VBT. However, the new found approach of Hybrid spinal fusion with the use of tethering down in the lower spine can be down after a broken tether by fusing the thoracic, redoing the tether and/or adding another tether elsewhere on the spine.