THORACOSCOPIC ANTERIOR VERTEBRAL BODY TETHERING IN LENKE TYPE-1 RIGHT ADOLESCENT IDIOPATHIC SCOLIOSIS

Background: Vertebral body tethering (VBT) is indicated for skeletally immature patients with progressive adolescent idiopathic scoliosis (AIS) who have failed or are intolerant of bracing and who have a major coronal curve of 40 degrees to 65 degrees. The vertebral body must be structurally and dimensionally adequate to accommodate screw fixation, as determined radiographically. The best indication for VBT is a flexible single major thoracic curve with nonstructural compensating lumbar and proximal thoracic curves (Lenke 1A or 1B). VBT allows for progressive correction of the deformity without spinal fusion by utilizing a minimally invasive fluoroscopic technique. Description: The procedure for a right thoracic curve is performed with use of a right thoracoscopic approach with the patient in the left lateral decubitus position. The thoracoscope is introduced through a portal at the apex of the curvature in the posterior axillary line. Instrument portals are created lateral to each vertebral body in the mid-axillary line. Screws are inserted into each vertebral body under biplanar fluoroscopic control and with intraoperative neuromonitoring. An electroconductivity probing device, while not mandatory, is routinely utilized at our practice. The tether is attached to the most proximal screw of the construct, and then reduction is obtained sequentially by tensioning the tether from one vertebral screw to the next. Alternatives: Bracing is the gold-standard treatment for progressive AIS involving the immature spine. The most commonly utilized surgical treatment is posterior spinal fusion (PSF), which should be considered when the major coronal curve exceeds 45 degrees. Rationale: PSF has proven to be a dependable technique to correct scoliotic deformities. It has a low complication rate and good long-term outcomes. However, concerns exist regarding the stiffness conferred by PSF and the long term effects of adjacent segment disease. Thus, interest had developed in nonfusion solutions for AIS correction. VBT utilizes the Hueter-Volkmann principle to guide growth and correct deformity. Compressive forces applied to the convexity of the deformity by a polyethylene tether allow the patient's growth to realign the spine. Intraoperative correction triggers growth modulation, and most of the modulation seems to occur during the first 12 months post operatively. The best results have been seen with a short Lenke type-1A curve in a patient with closed triradiate cartilage, a Risser 3 or lower (ideally Risser 0) iliac apophysis, and a flexible curve characterized by a 50% reduction of the major coronal curve angle on side-bending radiographs. Expected Outcomes: In 57 immature patients with a Lenke type-1A or 1B curve (i.e., a 30 degrees to 65 degrees preoperative Cobb angle), Samdani et al.(3) found a main thoracic Cobb angle reduction from 40 degrees 67 degrees preoperatively to 19 degrees +/- 13 degrees at 2 years after VBT. In the sagittal plane, the T5-T12 kyphosis measured 15 degrees +/- 10 degrees preoperatively, 17 degrees +/- 10 degrees postoperatively, and 20 degrees +/- 13 degrees at 2 years. No major neurologic or pulmonary complications occurred. A total of 7 (12.3%) of the 57 patients underwent surgical revision, including 5 for overcorrection and 2 to span additional vertebrae. In a study of 21 skeletally mature patients, Pehlivanoglu et al.4 found that theCobb angle was reduced from 48 degrees preoperatively to 16 degrees on the first-erect postoperative radiograph and finally to 10 degrees at the latest follow-up (mean, 27.4 months). The 2 main complications of VBT reported in the literature are overcorrection and tether breakage. Both may require revision, which explains the higher rate of revision observed for VBT compared with PSF.