Monday, November 13, 2017

Vertebral Body Tethering Part 2

Vertebral Body Tethering for Scoliosis

As mentioned in the last blog there is a paucity of information/evidence on the use of VBT in skeletally-immature patients with scoliosis.  Animal studies have demonstrated VBTs can modulate spinal growth with few changes to the intervertebral disc or growth plates.  Early, short-term, single institution series have been encouraging with few reported serious complications.  More research is necessary on VBT safety, timing of VBT placement, VBT tensioning, intervertebral disc health, long-term patient reported and radiographic outcomes of VBT.

Current indications for VBT
1     1. Skeletally immature patient (Risser 0-3, Sander digital hand score <5).  Optimal timing of VBT surgery is necessary to produce a satisfactory spinal alignment at the completion of spinal growth.  At present there is insufficient information available to accurately predict when to place a VBT.
2     2.  Deformity location: main thoracic
3     3. Idiopathic diagnosis
4     4. Coronal deformity: main thoracic (30-70 degrees), thoracolumbar/lumbar (30-60 degrees)
5     5. Flexibility on side-bending radiographs to less than 30 degrees.
6     6. Less than 20 degrees of axial rotation. 
7     7. Less than 40 degrees of kyphosis

Surgical Technique: VBT for Scoliosis
VBT is a thoracoscopic, minimally-invasive technique in which screws are placed into the vertebral bodies on the convex side of the coronal deformity.  The screws are placed into the middle of the vertebral body with bicortical purchase under fluoroscopic guidance.  A high-strength, braided polypropylene tether is then placed into the screw heads and then sequentially secured to each screw after segmental compression.  The technique achieves modest correction of the spinal deformity immediately postoperative.  

Technical challenges for this technique do exist.  Placement of anterior body screws above T5 and below L4 is not typically possible patient anatomy.  There are questions about the number of vertebra which should be included into the VBT construct, how much to tension to place across each vertebral motion segment within the VBT construct, optimal screw trajectory and screw size, placement of VBT across the diaphragm for thoracolumbar curves, and implant prominence.