Curve progression after vertebral body tether rupture may be mild with low revision rate
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Key takeaways:
- Curve progression greater than 5° occurred in 43% and 50% of patients at 1 year and 2 years, respectively, after vertebral body tether rupture.
- Patients had an overall revision rate of 14% after tether rupture.
Results showed patients who had a vertebral body tether rupture experienced mild general curve progression with a low rate of revision. However, younger patients with larger curves may have an increased chance of undergoing revision.
“We are still trying to refine the indications for vertebral body tethering. Ultimately, having a non-fusion option for the treatment of scoliosis in kids is going to be important,” Tyler A. Tetreault, MD, pediatric orthopedic surgeon in the Jackie and Gene Autry Orthopedic Center at Children’s Hospital Los Angeles, told Healio. “[Vertebral body tethering] is an option that is available, though it might not be the ideal solution that we were optimistic it would be earlier. But this gives us information to continue to refine our techniques and change our practice going forward.”
Curve progression
Using the Pediatric Spine Study Group Registry, Tetreault and colleagues from the Pediatric Spine Study Group identified 84 patients with adolescent or juvenile idiopathic scoliosis who underwent vertebral body tethering with 2-years of follow-up and sustained a tether rupture.
“We measured their curve magnitude at 1 year, at 2 years and then after final follow-up after their rupture was identified,” Tetreault said about results presented at the International Meeting on Advanced Spine Techniques. “We also evaluated how many patients underwent revision surgery after their tether broke.”
Tetreault said 43% and 50% of patients had a curve progression greater than 5° at 1 year and 2 years, respectively. At final follow-up, more than two-thirds of patients had a curve greater than 35° and 23% of patients had a curve greater than 45°.
“We found that the main impact of how large the curve got after tether breakage was how quickly after they had the tethering procedure did the tether break,” Tetreault said. “The average time from tethering until the cord broke was 30 months, but there is a small portion of our group that had a breakage within 12 months. They had significantly greater curve progression than those who had a breakage at a later time.”
Revision rate
He added they found a 14% overall revision rate after tether rupture, with six patients undergoing tether revision and six patients undergoing fusion. Patients who were skeletally immature or who had a curve greater than 35° had a greater risk for revision, according to Tetreault.
“We had no patients with a curve less than 35° at the time of rupture that ended up having revision surgery,” Tetreault said. “We found that the time from the [vertebral body tethering] VBT procedure to tether rupture was also associated with undergoing revision surgery, about a three times as great rate for those patients.”
Perspective
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Surgeons who treat scoliosis in children continue the quest for the holy grail: spinal deformity correction with motion preservation. Vertebral body tethering aims to correct scoliosis over time in adolescents with remaining growth while allowing motion of the spine and potentially avoiding fusion. As innovation in this area surges, we must protect patients and exercise responsibility when introducing new, unproven techniques to the bedside. As with any motion-preserving device, vertebral body tethering is subject to wear and breakage. We have come to the realization that, for most patients, this will be the eventual outcome. What is the fate of a curve after tether breakage? If the curve is corrected and the patient is mature, all should be well. However, if a significant curve remains and/or growth continues, the curve could progress.
Tyler A. Tetreault, MD, and colleagues should be commended for reporting on patients who underwent vertebral body tethering, had broken tethers and were available in the Pediatric Spine Study Group for minimum 2-year review. The study reveals three main conclusions: nearly half of the patients with broken tethers had curve progression; residual curve (greater than 35°) at the time of breakage was an important predictor of progression after breakage; and the earlier the tether breaks, the higher the rate of progression.
Naturally, these results are sobering for a technology with lots of promise. At follow-up, more than two-thirds of the study patients had a curve greater than 35°. These would all be considered failures by current consensus of clinical vertebral body tethering success. What should concern us even more is that with longer follow-up, we are likely to see more revisions. While a 2-year follow-up period may be a minimum for clinical studies, it may not be enough for a dynamic process involving a motion-preservation device in a growing child.
The current database contains many cases enrolled at the beginning of the vertebral body tethering experience, reflecting the learning curve of a new technique with a first-generation device and patient selection that lacked the current refinement based on curve magnitude, flexibility and remaining spinal growth.
Fortunately, first-generation devices have been upgraded with better screw design, cord durability and tensioning instruments. Operative techniques have been debated and improved regarding level selection, implant position, cord tensioning, on table correction and, most importantly, trying to define who the best candidates are for the procedure.
Regulatory status of the devices has plagued the research and registry efforts, ie many patients are not being followed appropriately and the true results of vertebral body tethering may not be represented by presentations and publications from the study groups. With partnership from regulatory bodies, societies, study groups and industry partners, we will be able to advance this technology further with greater success.
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Tetreault TA, et al. Paper 41. Presented at: International Meeting on Advanced Spine Techniques; April 10-13, 2024; San Diego.
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