Strict fasting (NPO) for at least 8 hours prior to surgery. Baseline spinal radiographs and MRI to confirm flexibility and exclude intraspinal anomalies. Pre-operative pulmonary function testing, blood work including coagulation profile, and antibiotic prophylaxis within 60 minutes of incision. Informed consent for hardware implantation and potential revision surgery.
Immediate post-operative care in the surgical ward with monitoring of neurological status and respiratory function. Early mobilization and physical therapy commencement on post-operative day 1. Pain management via multimodal analgesia. Routine wound care and physical activity restrictions (no contact sports) for 3-6 months. Follow-up radiographs at 6 weeks, 6 months, and annually.
Vertebral Body Tethering (VBT): A Comprehensive Clinical Guide
Vertebral Body Tethering (VBT), often referred to as Anterior Scoliosis Correction (ASC), represents a paradigm shift in the management of pediatric idiopathic scoliosis. Historically, the gold standard for treating progressive, severe scoliosis has been posterior spinal fusion (PSF), a procedure that permanently immobilizes segments of the spine using metallic instrumentation and bone grafts. While effective, PSF sacrifices spinal flexibility and carries long-term implications for adjacent segment degeneration.
VBT is a motion-sparing, growth-modulating technique designed to correct spinal curvature while preserving spinal mobility. By utilizing the patient’s remaining skeletal growth to gradually straighten the spine, VBT offers a less invasive, non-fusion alternative for patients who meet specific clinical criteria.
Technical Specifications and Mechanisms of Action
VBT operates on the principle of "guided growth," similar to how orthopedic surgeons have historically corrected limb length discrepancies or genu valgum (knock-knees) in children.
The Mechanism
The procedure involves the placement of bone screws into the convex (outer) side of the scoliotic vertebral bodies. A flexible, high-strength polyethylene cord (the tether) is then secured to these screws.
- Growth Modulation: By applying tension to the convex side of the curve, the tether restricts growth on that side while allowing the concave (inner) side of the curve to continue growing.
- Spinal Remodeling: Over time, the differential growth rate corrects the deformity as the spine straightens naturally during the patient’s growth spurts.
- Motion Preservation: Because there is no fusion of the vertebral segments, the patient retains a significant degree of spinal rotation, flexion, and extension, which is the primary advantage over traditional fusion.
Instrumentation
- Bone Screws: Titanium or cobalt-chrome screws with specialized heads to accommodate the tether.
- Tether: A braided, flexible, ultra-high-molecular-weight polyethylene (UHMWPE) cable.
- Access System: Typically performed via video-assisted thoracoscopic surgery (VATS) to minimize incision size and trauma to the chest wall.
Clinical Indications and Patient Selection
Patient selection is the single most critical factor in the success of VBT. Unlike fusion, which can be performed on skeletally mature patients, VBT is strictly a growth-dependent procedure.
Ideal Candidates
- Skeletal Maturity: Patients must have significant growth remaining (Risser sign 0–2). If the patient has finished growing, the tether will not be able to modulate the spine.
- Curve Magnitude: Typically indicated for curves between 30 and 60 degrees.
- Flexibility: The curve must be flexible on bending radiographs, indicating that the deformity is not yet rigid or fixed.
- Failure of Bracing: Patients who have experienced curve progression despite compliant use of a thoracolumbar sacral orthosis (TLSO).
Contraindications
- Skeletal Maturity: Patients who have reached skeletal maturity (Risser 4-5) are poor candidates, as the tether will provide no corrective force.
- Severe Deformity: Rigid curves or curves exceeding 65–70 degrees often require the structural stability of fusion.
- Kyphosis: Patients with significant thoracic hypokyphosis or hyperkyphosis may require different surgical approaches.
| Category | Criteria |
|---|---|
| Age | Typically 8–14 years (pre-pubescent to early puberty) |
| Risser Grade | 0 to 2 (High growth potential) |
| Curve Type | Thoracic or Thoracolumbar idiopathic scoliosis |
| Flexibility | Must be flexible on side-bending films |
The Procedure: Surgical Protocol
Pre-Operative Preparation
- Imaging: Full-spine standing AP/Lateral radiographs, side-bending films, and MRI of the entire spine to rule out intraspinal anomalies (e.g., syrinx, Chiari malformation).
- Pulmonary Function Testing (PFTs): Assessment of lung capacity, as the surgery involves deflation of a lung for thoracoscopic access.
- Nutritional Optimization: Ensuring adequate Vitamin D and calcium levels to support bone healing around the screws.
Intra-Operative Steps
- Anesthesia & Positioning: General anesthesia with double-lumen endotracheal tube placement for single-lung ventilation. The patient is placed in a lateral decubitus position.
- Thoracoscopic Access: 3–4 small incisions are made in the chest wall. The lung is deflated, and the diaphragm is identified.
- Discectomy (Optional): In some cases, a partial discectomy is performed at each level to increase curve flexibility.
- Hardware Placement: Screws are placed into the vertebral bodies under fluoroscopic guidance.
- Tether Tensioning: The tether is passed through the screw heads and tensioned to a specific force, providing immediate partial correction.
- Closure: Chest tube placement for post-operative drainage and lung re-expansion.
Post-Operative Recovery and Outcomes
Hospital Stay
- Duration: Typically 3 to 5 days.
- Management: Focus on pain control (multimodal analgesia), physical therapy, and respiratory exercises (incentive spirometry) to prevent atelectasis.
Recovery Timeline
- Weeks 1–6: Activity restriction. No heavy lifting, contact sports, or extreme spinal twisting.
- Months 3–6: Gradual return to non-contact sports.
- Long-term: Radiographic monitoring every 6 months to assess curve correction and tether integrity.
Typical Outcomes
- Correction: Most patients achieve a 50% or greater reduction in curve magnitude within the first year.
- Growth: Continued growth usually leads to further "self-correction."
- Mobility: Patients report significantly better spinal range of motion compared to fusion patients.
Risks, Side Effects, and Potential Complications
While VBT is less invasive than fusion, it is not without risks.
- Tether Breakage: The most common complication. If the tether snaps before the spine is fully remodeled, the curve may progress.
- Over-correction: The spine may grow too straight or develop a curve in the opposite direction (lordoscoliosis).
- Pulmonary Issues: Potential for pleural effusion or persistent pneumothorax.
- Instrumentation Failure: Screw pull-out or loosening.
- Revision Surgery: Approximately 10–15% of patients may require a secondary procedure (either a revision of the tether or a conversion to a posterior spinal fusion if the curve continues to progress).
Frequently Asked Questions (FAQ)
1. How is VBT different from spinal fusion?
Fusion uses rods and bone graft to turn the spine into a single solid bone. VBT uses a flexible cord to guide growth, keeping the spine flexible.
2. Is VBT a permanent procedure?
The hardware stays in, but the correction is achieved through the patient's own growth. Once the patient is fully grown, the tether becomes essentially passive.
3. What happens if the tether breaks?
Tether breakage is often asymptomatic. If the spine remains stable, no surgery is needed. If the curve progresses, revision surgery may be necessary.
4. Can adults get VBT?
No. VBT requires the patient to be growing. Adults have finished growing and would not benefit from growth modulation.
5. How long is the recovery compared to fusion?
Recovery is generally faster for VBT, with patients often returning to school within 2–3 weeks and sports within 3–6 months.
6. Will I set off metal detectors at the airport?
It is possible, though the amount of metal is significantly less than in a full spinal fusion. Carrying a surgeon-provided medical card is recommended.
7. Does VBT affect lung function?
Because the surgery involves the chest cavity, there is a temporary reduction in lung function, but this typically resolves within a few months post-op.
8. What is the "ideal" age for this surgery?
Usually, the onset of the adolescent growth spurt (age 10–13 for girls, 12–14 for boys) provides the best window for correction.
9. Is this covered by insurance?
Most major insurers cover VBT for idiopathic scoliosis, but it is often classified as a "specialized" procedure requiring prior authorization.
10. Can VBT be used for neuromuscular scoliosis?
No. VBT is strictly indicated for idiopathic scoliosis. Neuromuscular scoliosis is typically more rigid and requires the structural support of fusion.
Alternative Treatments
- Observation: For curves <25 degrees.
- Bracing (TLSO): The standard for curves 25–45 degrees in growing children.
- Posterior Spinal Fusion (PSF): The standard for curves >50 degrees or for patients who are skeletally mature.
- Physical Therapy (Schroth Method): Used as an adjunct to bracing to maintain muscle symmetry and postural awareness.
Summary Comparison Table
| Feature | Vertebral Body Tethering (VBT) | Posterior Spinal Fusion (PSF) |
|---|---|---|
| Flexibility | Preserved | Eliminated (in fused levels) |
| Invasiveness | Minimally Invasive (VATS) | Invasive (Open Surgery) |
| Growth Potential | Utilized for correction | Arrested |
| Primary Use | Adolescent Idiopathic Scoliosis | Severe/Rigid Scoliosis |
| Hospital Stay | 3–5 days | 5–7 days |
Final Clinical Outlook
Vertebral Body Tethering represents the future of pediatric spine care. By shifting the focus from "fixing" a spine through immobilization to "guiding" a spine through natural growth, we minimize the long-term morbidity associated with fusion. However, it requires a disciplined approach to patient selection and a commitment to long-term follow-up. Surgeons must be transparent with families regarding the risk of tether breakage and the potential for future revision, ensuring that the patient's skeletal maturity and curve flexibility are perfectly aligned with the procedure's capabilities.
As technology advances and tether materials improve, VBT is likely to become the standard of care for a broader range of patients, further reducing the reliance on permanent spinal fusion in the pediatric population.
