Medical Care ,  Orthopaedics

Innovative scoliosis surgery presents a conundrum for patients

November 12, 2021

Vertebral body tethering could become the new gold standard treatment for curved spine if we figure out the right candidates

Innovative scoliosis surgery presents a conundrum for patients

A novel surgical technique for the abnormal curvature of the spine, or idiopathic scoliosis, is offering some patients a refined treatment that spares them from the limited mobility that can result from standard surgery, but it’s also exposing others to multiple interventions that increase the risks of post-operative complications. And we still don’t know how to predict who’s going to benefit and who’s not.


A common type of spine deformity that often presents in adolescents, idiopathic (from an unknown cause) scoliosis can lead to uneven hips and shoulders as well as back pain. In severe cases, it could be disabling, affecting lung function and making breathing difficult.


In most instances, the condition either requires no treatment or can be managed by having children wear braces to prevent the curvature from getting worse, but a minority of patients have to undergo major surgery to correct the deformity.


In such severe cases, the standard procedure is spinal fusion, where surgeons straighten and then screw metal rods to the spine to hold it in place. The approach is often a powerful way to fix scoliosis once and for all, but it can also affect mobility, raising fears in some patients and their families.


“If you remove the motion from a portion of the spine, you’ve changed what the body can do and what the body was designed to do by eliminating some of the flexibility that we were built with and designed to have,” said Dr Peter Newton, chief of the Division of Orthopedics & Scoliosis at Rady Children’s Hospital in San Diego, in an interview with Global Health Asia-Pacific.


But in practical terms, this loss of mobility often has little impact on daily life, he added, with limitations ranging from the inability to fully bend into a ball or perform a somersault to difficulty extending the back in extreme ways.


“The more elite athlete or the more flexibility required for a specific activity, the more effect patients appreciate. But we clearly have people who participate in nearly every sport you can imagine at quite a high level who had spinal fusion done,” he said.


Even if the impact on routine activities turns out to be minimal, it’s understandable that young patients, who have their entire life ahead of them, would want a curative treatment that preserves complete mobility.

“In a perfect world, we would be able to fix scoliosis without having to fuse the spine,” emphasised Dr Newton, who has toyed with the idea of replacing spinal fusion with a better approach his entire career and has pioneered a new procedure that promises to fit the bill.


Meet vertebral body tethering


A surgical technique that has been developed over the last decade or so, vertebral body tethering (VBT) aims to correct the deformity caused by scoliosis in a way that preserves the full flexibility of the spine.


It involves screwing a tight cord to the curved area of the spine in order to apply pressure on the curvature and gradually make it straight. This US FDA-approved system, called tether, is left in after surgery to limit growth on the side of the curved spine while allowing the other side to catch up. Typically, this process takes a few years and harnesses the growing process that makes the spine longer, allowing children to become taller. With the tether preventing any further curvature, the spine can grow only in a straight line over time, thus reshaping itself into an orderly form that doesn’t cause problems.


“This approach has the potential to be game-changing if we can use it in patients young enough to use their growth to truly drive permanent shape change in the vertebral bodies which have become deformed as a result of scoliosis,” said Dr Newton.


Unlike spinal fusion, VBT affects mobility to a limited extent during the growing process but after that allows patients to regain it completely as soon as the cord breaks down or is removed.


“When growth is finished, we don’t need the tether to be performing any function because it did its job, it changed the shape of the spine,” he explained.


Despite its clear potential to become the new treatment of choice for severe scoliosis, a key challenge around VBT is identifying the patients who can benefit from it.


“The ideal candidate remains unknown and controversial,” said Dr Newton, who describes them as those who have “enough growth remaining to fully correct the deformity present at the time of surgery, which is unfortunately very difficult to predict.”


On the one hand, if you do the surgery too late, there’s not enough time for the spine to correct itself and is still dangerously curved when patients stop growing. On the other, if you put the tether in too early there will be an overcorrection, meaning that “the spine will straighten, because the growth causes the curve to straighten, and then it will actually start to curve in the other direction.”


This explains why VBT has led to both “amazing successes and very disappointing failures,” acknowledged Dr Newton, noting that surgeons who select patients for VBT need to pinpoint the “sweet spot based on growth remaining and amount of deformity” to make the procedure a success.


In his view, the right patients have a considerable deformity (curves between 40 and 60 degrees) and are usually 11 or 12 because you need two to three years of growth to make VBT work, and most girls, who have a higher prevalence than boys, will grow until 14. The assessment varies by sex and curve magnitude, with some boys being good candidates even if they’re 13.


“So, for a given patient, it’s really difficult for us to predict with certainty whether the outcome of VBT will be really ideal or not at this point in time,” he stressed.


The terms of the dilemma


Opting for either spinal fusion or VBT is therefore a dicey affair that patients and their families have to disentangle based on their preferences, though doctors will have to play a crucial role in advising them honestly.


“Advising patients and their parents requires the surgeon to have a realistic discussion of what we know and we don’t know,” said Dr Newton.


Since it’s been around longer than VBT, spinal fusion is backed up by much more evidence that helps prognosticate both its good and negative outcomes. “If you have a spinal fusion, I can give you a very precise number of what your curve correction and rate of revision surgery will be, and what outcome you can expect at 10 and 20 years because we have data on it,” he explained.


Though spinal fusion can often cure scoliosis for good, in rare instances it fails and needs to be repeated due to a variety of reasons, including infection and implant misplacement. This happens in about two percent of cases two years after the operation, while the failure rate increases to six percent at 10 years.


The same level of certainty is not yet there for VBT because it’s still a fairly new and experimental procedure, with doctors struggling to quantify with accuracy how likely patients are to require a second operation. Two years after VBT, only about five percent of patients require either a revision operation to remove the tether and avoid overcorrection or a spinal fusion to fix the problem, according to Dr Newton, who has performed more than 100 VBT surgeries so far. But this jumps to about 50 percent at five years, and we don’t have any numbers to predict outcomes after 10 or more years.


“Some people hear those data and say, ‘I don’t want an unknown outcome with unknown risk of revision surgery, that just sounds crazy to me.’ Other people say, ‘I don’t want to have my spine stiffened if I don’t need it stiffened, even if it’s going to have only a modest effect on my functions and maybe no effect on my daily life. I just don’t think that’s normal, and I’m willing to try this new technology,’” he said.


It’s worth noting that undergoing a second surgery exposes patients to increased risks. All scoliosis surgeries are invasive operations and VBT involves opening up the chest and possibly damaging vital organs like the lungs and the heart. “That shouldn’t be taken lightly by any patient on the first go and particularly on the second go because there’s now scar inside that chest,” said Dr Newton, highlighting that the life-threatening risks associated with revision VBT surgeries are small but several folds higher than those of the first procedure, though it’s hard to translate that into clear-cut numbers.


One challenge patients and families might encounter while picking one procedure over another is the hype surrounding VBT as well as the negative side effects of spinal fusion.


“All the nonsense and rhetoric around the benefits of VBT that exist on the internet, both in social media and promotional information from surgeons, are disgraceful because they suggest to families and parents that we have clear answers about the outcomes of the procedure and we don’t. They just sell it as a panacea that it isn’t,” cautioned Dr Newton.


By contrast, spinal fusion is sometimes mistakenly portrayed as a procedure that will cause a lifetime of pain due to disc disease, together with major mobility impairment. “Some patients believe that after a spinal fusion they will never be able to bend over, touch their toes, or even walk-in adult life,” but nothing could be further from the truth, he said.


What’s next for VBT?


The hope is that better tools to predict the period of growth remaining in children with scoliosis will improve VBT outcomes.


Currently, standard methods to quantify how much kids will grow to look at both the pelvic and hand bones, but they’re rudimentary and sometimes contradictory. However, researchers are working towards improving predictions.


“We really need to be able to transfer duration of growth into prediction of final height based on parents and other variables, and we don’t have precision in this right now,” explained Dr Newton, noting that better predictors of growth based on hand bones analysis are being developed and look promising.


Researchers at Montréal University have already managed to predict the final scoliosis curvature in half of the patients enrolled in a trial based on parameters including curve size, age, menstruation status, and a combination of information from the standard methods called Sanders and Risser scores, said Dr Stefan Parent, the lead researcher, to STAT.


Others are looking into both blood and genetic tests to gather more clues into growth and curve progression over time. For instance, the levels of the protein collagen X, which is involved in bone formation, could help understand how long children will keep growing.


If we are able to translate all this information into an accurate predictor of final height or length in the spine, Dr Newton said, then VBT success rates will rise significantly by improved patient selection. Though he believes the novel procedure will eventually become the gold standard in scoliosis surgery for some patients, it’s not going to happen any time soon.


“We’ve been at it for a decade, and it will probably take another decade.”

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