Vertebral body tethering may not improve Cobb angle in adolescent idiopathic scoliosis
Click Here to Manage Email Alerts
Vertebral body tethering may not improve major Cobb angle in patients with adolescent idiopathic scoliosis, according to results presented at the International Congress on Early Onset Scoliosis and the Growing Spine.
“We’re still in the learning curve of [vertebral body tethering] and whether it’s technique, technology or patient selection, we haven’t figured out the optimal timing to consistently harness growth,” Lindsay M. Andras, MD, associate division chief and director of the spine program at the Jackie and Gene Autry Orthopedic Center at Children’s Hospital Los Angeles, told Healio.
Change in Cobb angle
Using the Pediatric Spine Study Group database, Andras and colleagues calculated change in Cobb angle from first erect postoperative radiograph to final follow-up in 113 patients with adolescent idiopathic scoliosis who underwent vertebral body tethering between December 2013 and January 2020. Researchers considered a change in Cobb angle less than 5° to be within normal measurement variability.
Results showed patients had a preoperative mean major Cobb angle of 51.1°, which corrected to a mean major Cobb angle of 27.4° on first erect radiographs and a mean major Cobb angle of 31.1° at final follow-up.
Researchers found stable curves in 50.4% of patients and greater than a 5° increase in Cobb angle following the initial erect radiograph in 41.6% of patients. During the follow-up period, 8% of patients had more than 5° decrease in Cobb angle and 4.4% of patients had greater than 10° of correction, according to researchers.
“It was surprising how few patients were seeing growth modulation. We had a suspicion of that because the overall averages weren’t changing after the first [radiograph], but ... we don’t know what that means long-term,” Andras said. “Is it good enough that the curve hasn’t progressed and worsened after the tether is put in? That accounts for about 50% of patients and that might be fine long-term, but that isn’t what we had anticipated when this was initially proposed as a technique.”
Search for optimal outcomes
In a subanalysis, patients who had a curve greater than 35° on their first standing radiograph after vertebral body tethering did not show improvement in major Cobb angle over time, according to Andras. She added patients who had a Risser sign of greater than 2 did not show improvement in Cobb angle after initial correction.
“This suggests that if we’re going to try to get optimal outcomes, [vertebral body tethering] probably needs to be done in a slightly younger population and that we need to be going for a little more correction on the table and during the procedure than what was previously thought,” Andras said.
Perspective
Back to Top
Tiffany N. Phan, BA, and colleagues have reported on changes in the scoliotic curve from the first erect X-ray to final follow-up following the performance of non-fusion vertebral body tethering. The procedure is based on the premise of curve correction at the time of surgery with further correction over time during adolescent growth in a process termed, “growth modulation.” The authors report little change of the curve in approximately 50% of patients in their study of 113 patients. Furthermore, approximately 12% had greater than 5° of correction, with two patients having substantial overcorrection to 30° and 50° in the opposite direction, respectively. This abstract points to the importance of refining indications for vertebral body tethering including size of the curve, skeletal maturity of the patient, amount of correction achieved at the first surgery, as well as timing of intervention to remove or cut the tether in cases of overcorrection. The series reported presumably represents the earliest vertebral body tethering procedures performed, likely representing cases with a significant learning curve. I would encourage the authors to explore the optimal indications for vertebral body tethering in order to refine the technique and improve outcomes for a procedure that preserves spinal flexibility and at least some growth and is associated with less blood loss, faster recovery and less pain than the gold-standard spinal fusion. Correction that is less than the predicate spinal fusion is not necessarily a less desirable outcome if patient goals are met and if outcomes are durable and as good as, or better than spinal fusion over the long-term.
Perspective
Back to Top
Lindsay M. Andras, MD, and colleagues’ recent presentation points out clearly that we are still learning a lot about vertebral body tethering and should be cautious in recommending it for all patients with adolescent idiopathic scoliosis. But the findings in this study were expected and should not dampen enthusiasm for further research in this space and the promise of vertebral body tethering at least for a group of patients with adolescent idiopathic scoliosis with the proper indications.
This study contained a wide spectrum of patients, techniques, devices and indications. The indications for vertebral body tethering were not standardized in this cohort, and variability in patient selection was one of the many reasons for inconsistent outcomes. The chronologic age and skeletal age of the patients constitute a majority of patients that we could not consider to have enough growth left to modulate their scoliosis after vertebral body tethering today. At almost 13 years old and Risser stage 2, the average patient was well past peak height velocity, when we can expect rapid curve progression if left untreated or growth modulation if tethered. Sanders skeletal maturation staging should have been used for the most accurate growth assessment, because Sanders 3 and 4 patients have the best outcomes.
By most longer-term outcome studies, a patient who has a residual curve of less than 35° after vertebral body tethering is still considered a success, even if the tether is broken. The range of outcome in the Andras study is massive: –50° to 69°. Perhaps a better way to evaluate the results would be to look at the median curve magnitude at follow-up or those patients with curves greater 35° or, most importantly, those patients who had to be revised to posterior fusion after vertebral body tethering due to curve progression or tether failure.
Some of these patients had surgery as long as 10 years ago and, since then, we have more experience and better tools and techniques to accomplish surgery. The previous generation device was not even designed for this procedure, but rather modified for vertebral body tethering. Current generation devices are more appropriate and allow significantly more tensioning during implantation and, thus, better intraoperative curve correction. We know this is a critical factor in success: On-table correction does predict growth modulation, continued curve correction and better success.
Andras and her colleagues are to be congratulated for bringing this issue to light and stimulate further work in this area.
Collapse
Andras LM, et al. Major Cobb angle did not decrease in 92% of patients after vertebral body tethering (VBT) surgery following first erect radiograph. Presented at: International Congress on Early Onset Scoliosis and the Growing Spine; Nov. 16-18, 2022; Rome.
Click Here to Manage Email Alerts