Vertebral Body Tether

Vertebral Body Tethering Part 2

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
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.

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