Non-fusion surgical treatment or scoliosis tethering (otherwise known as vertebral body tethering or VBT) is a less invasive surgical procedure that has been used for the past 15 years by a select number of Orthopedic surgeons. While still a highly invasive surgical procedure, as all spinal surgeries are, it does offer some significant advantages over the more widely used spinal fusion for scoliosis procedures. For patients who have undergone brace treatment for progressive idiopathic scoliosis and whose bone density is adequate to hold surgical hardware, the vertebral body tethering system is indicated. Patients should be unacceptably brace-wear Intolerant and have failed bracing. VBT surgery is believed to be beneficial in the treatment of spinal deformities and the avoidance of spinal fusion, according to clinical data. Please note, as with all surgical procedures, there are risks and complications associated with a certain percentage of cases and scoliosis tethering procedures should only be considered as an alternative to fusion surgery for scoliosis.
What is vertebral body tethering?
A: To allow the convex side of the spine to expand more and create a straighter spine, this treatment exerts a compressive force over the convex side (slowing down development). Modulating growth of the concave and convex sides of the spine was previously achieved with staples, until the vertebral body tether, which employs screws inserted into the vertebral body, was introduced. Instead of being positioned in the middle of the vertebral body, these essentials were positioned across the disc spaces between each vertebral body.
How effective is VBT for scoliosis?
A: Animal studies have shown that anchoring of the immature spine can effect its development, thus providing evidence for VBT. In 2010, a case report was published describing the use of VBT in humans. Early, short-term, single institution studies have shown to have few serious complications, thus far. Furthermore, an additional set of 57 patients showed correction of scoliosis and the avoidance of spinal fusion in all but one, according to the FDA (as of fall 2019). Nonetheless, the reoperation rate was higher than that of gold standard 4th generation fusions due to adjustments for overcorrection and tether breakage.
What are the advantages of vertebral body tethering over spinal fusion?
A: Significant advances in scoliosis surgery have been made during the last 100 years. More efficient fusion rates, lower complication incidence, better three-dimensional correction of the deformity, and quicker postoperative recovery have all resulted from these developments. Fewer motion segments (less spine mobility) may result in reduced function in high-level physical activity (e.g., in fusions below the 2nd Lumbar vertebra). As a consequence, maintaining spinal mobility, particularly in the low back, is critical.
Spinal Motion Sparing
Unlike multiple level spinal fusion, tethering for scoliosis does not create intersegmental fusion and has very little negative impact on spinal biomechanics. The spine is composed of 24 individual segments that work together in a lever arm fashion to produce the torque force that drives the pelvis and shoulder girdles to provide human locomotion (walking/running). Fusion surgeries in scoliosis patients often involved 6-8 segments and essentially meld them all together into one long bar of bone. This has a profound impact on the spinal biomechanics and often leads to many pain syndromes as a result of dis-coordinated spinal muscle firing patterns leading to inflammation and muscle spasms.
Vertebral Body Tethering (VBT) is a relatively spinal motion sparing procedure that still allows for almost all normal spinal biomechanics and an almost full range of spinal motion as well. Although long term data isn’t yet available, it is likely the long term pain syndromes associated with tethering for scoliosis should be much lower than those found in long term post fusion treated scoliosis patients.
Less Blood Loss and Faster Recovery Time with Scoliosis Tethering
Many of the scoliosis tethering procedures are done endoscopically, meaning the actual surgery is performed via an endoscope, and do not require an open back incision. This means a 4-6 inch scar under one of the arm pits (usually the right side), rather than a full spine incision down the middle of the back. Cosmetically, this is obviously desirable, but clinically it means a lot less blood loss (and little or no blood transfusions), less risk for infection, and a much faster recovery time since less muscle, bone, tendon, tissues are damaged during the procedure. Clearly these advantages are significant to clinical outcomes, but can and do have a positive effect on the financial burden of surgical intervention for scoliosis.
Scoliosis Tethering can be used at Younger Ages to “Guide Spinal Growth”
Scoliosis curve progression is typically seen during periods of rapid growth, particularly in female patients, and unbalanced pressure on the vertebrae may cause uneven growth of the spinal bones. For centuries, yes centuries, doctors have attempted vertebra growth modulation in scoliosis patients with rigid braces. While it sounds good in theory, practical application of applying pressure to the spine through the muscles, organs, and lungs with a brace have proven rather ineffective and psychologically traumatizing for patients. The end results indicate widespread use of braces for scoliosis do not reduce the number of patients for whom surgical fusion is recommended.
The pressure placed on the convexity (outside part) of the spinal curvature by the scoliosis tethering procedure works to re-balance the pressure being placed on the vertebrae during growth and can effectively guide spinal growth during growth spurts until skeletal maturity. Some concerns and complications have arisen leading to unintended spinal compensation patterns, but innovative newer physical therapy programs are being developed to address these issues.
Less Hardware = Less Complications
Spinal fusion procedures being utilized in the treatment of scoliosis require a lot of surgical hardware. Very long screws, hooks, long rods, and dissection of the entire posterior spinal joint system in order to install the hardware. As everyone knows, the more hardware, pieces, and parts, the more likely the chance for complications and breakage in the future, which is also supported by the published long term data on traditional scoliosis fusion procedures.
Scoliosis tethering requires much less hardware and no destruction of any spinal joint systems since it is implanted in the side of the spine. In fact, the only “moving parts” is a flexible cord that is secured at each and every spinal level making systemic failure of the tether virtually impossible. As stated else where in this article, follow-up long term data on vertebral body tethering (VBT) isn’t yet available, but the minimal used of hardware, lack of invasive spinal joint dissection, and stress being place on a nylon cord, rather than metal rods, is widely expected to outperform the long term complication rates and surgical site infections seen in post fusion treated patients due to the small incision.
The treatment of adolescent idiopathic scoliosis who have not reached skeletal maturity has and continues to be a challenge for all healthcare providers who seek to help patients overcome it. Treatment options implemented via braces and fusion surgeries have not proved an effective treatment model given the unpredictability of results and reality of long term complication rates. Less invasive, spinal motion sparing approaches like tethering surgery for scoliosis are a welcome and necessary step forward in an effort to convert the current scoliosis treatment model into an active approach which may prove more effective with less risk of unintended long term complications. It is the hope and expectation that more Orthopedic surgeons will begin to offer and recommend vertebral body tethering as the primary recommendation as an alternative to spinal fusion surgery as long term data becomes available.
What are any long-term issues with VBT?
A: We don't know is the easy answer. The actual tether, on the other hand, is something we know about. We can roughly sketch out some possible scenarios for the system currently used for VBT if we look at other implant systems used in the spine and other bones of the body over the last 50-plus years. Screws, as a group, have a long history of safety and efficacy. The fixation in the vertebra is screws. The screws appear to be effective and safe, with few concerns of prominence, migration, or pullout based on the collective experience.
The tether, which is made of braided polypropylene, is another aspect of VBT. This is the system's workhorse, compressing across convex discs and growth plates to regulate spinal development. The tether will be constantly moving since there is no fusion across the vertebral bodies. The tether is susceptible to fatigue, which may cause failure or breakage, as are any non-regenerating material that is continually moving. Given that it is placed in teens and will undoubtedly be strained for the next 60 years or more, it makes sense that the tether would eventually break.
The tether has been observed to fail in segments (between two screws), thus it is predicted that it will eventually break in numerous places over time. It's possible that this won't cause a failure. We only need it to last until the completion of spinal growth with hopefully permanent correction of the scoliosis for the sake of VBT's goal to modulate growth in the immature spine.