For decades, our traditional methods to treat idiopathic scoliosis have included only observation, bracing, or spinal fusion. More recently, another option, growth modulation, has gained popularity and interest.
The use of growth modulation for limb deformities is not new. Techniques for physeal arrest date back at least 80 years and have evolved into the more common plate and screw techniques popular today. More recently, growth modulation techniques have been applied to the spine as well, creating a new category of scoliosis treatment. Efforts to modify spine growth include growing rod techniques, vertebral body stapling and, more recently, vertebral
body tethering. The indications and results for vertebral body stapling have been published previously (Ref. 1-3). Vertebral body tethering, the newest technique, will be discussed here.
Vertebral Body Tethering is a technique in which pedicle screws are placed into the anterior vertebral bodies (usually thoracoscopically) and are attached to a flexible, polyethylene-terephthalate (PET) cable on the convexity of the curve. The cable is tightened, providing some immediate improvement in the curvature. The cable tethers the convexity and allows the concavity to continue growing, further decreasing the size of the curve over time (Figures 1a-d).
In general, the procedure is most likely to benefit patients whose skeletal immaturity and curve size suggest that
they will progress beyond the traditional threshold for posterior spinal fusion despite bracing.
Dr. Randal Betz, formerly of Shriners Hospitals for Children-Philadelphia, and now with the Institute for Spine & Scoliosis in Lawrenceville, New Jersey, was one of the first surgeons to employ the vertebral body tethering technique for his patients with spine deformity.
I recently spoke with Dr. Betz about his experience:
Q: Dr. Betz, how did you first get interested in vertebral body tethering?
A: I was seeing a lot of patients who were struggling with brace wear, so I was searching for other alternatives for nine or ten year olds who were looking at wearing a brace for four or five years. I became interested in vertebral body stapling around 2001. After I started doing this procedure, I learned that the staples worked well for thoracic curves under 35°. However, they were not powerful enough to control curves over 35°, so I began looking for another option. I thought the Zimmer Dynesys system, which had FDA approval
for low back surgery, would be a perfect device
for tethering. In 2011, I talked to Dr. John Braun in Vermont, and he had just started doing the same exact thing. So, we started doing them at Shriners Hospital- Philadelphia in February, 2011.
Q: How many cases have you done?
A: There is a collective experience of approximately 115 surgeries with Drs. Amer Samdani, Joshua Pahys, Patrick Cahill and myself at Shriners Hospital- Philadelphia, and with Dr. Darryl Antonacci in my current practice at The Institute for Spine & Scoliosis, in Lawrenceville, New Jersey.
Q: How common is the vertebral body tethering surgery?
A: Probably 20 surgeons have come and observed the procedure, and there may be eight who are currently doing at least one every quarter or so.
Q: What are the indications for tethering?
A: Our primary indication is a thoracic curve between 35° and 65° that bends below 30° on the bend film. Immaturity seems to be an important feature, because we’re hypothesizing that if you tether the spine while the child is still growing, the vertebral bodies and the disk anatomy will become more normal. Also, if ten years down the line the tether breaks,
it won’t make much of a difference because the spinal anatomy has been relatively restored to normal.
Q: Can the procedure be done in skeletally mature people?
A: If you talk to orthodontists who are moving teeth, even in adults, they are seeing significant bone remodeling. It has encouraged us to consider that there may be some late remodeling opportunities, not just for growth modulation, but for bone remodeling. So even though in the past we were doing patients who were Risser 0, Sanders 4 or less, we now are considering patients who are a little bit older, Sanders 7 and up to Risser 4, because we just don’t know how much remodeling there is in late adolescence.
Q: Would you describe the procedure as a “fusionless cure” for scoliosis?
A: I never use the word “cure.” What I do tell patients is that it leaves them open to all options in the future. We haven’t really had any failures yet, but should they arise, we have not “burned any bridges,” and other treatments can still be considered. We tell patients that a spinal fusion is once and then hopefully done, but it’s forever, and there may be issues with mobility down the road. At least with the tether, if something does start to fail, you can replace the tether and have not fused the spine.
Q: In ten years, do you think this will be the standard treatment for idiopathic scoliosis patients with the curve size and maturity parameters you’ve described?
A: I do, and I think the number of patients and indications will expand immensely. We’ve been doing primary lumbar and thoracolumbar curves. We’ve also been doing double-major curves, where we tether the thoracic curve on the right and the lumbar curve on the left. More recently, I’ve started doing what I call
a “combo” for patients who have really stiff thoracic curves that are not amenable to the tether because
they don’t bend down below 30° and where they don’t look like they’re good candidates for selective fusion. (Remember that 42% of Lenke C curves that have had a selective thoracic fusion will decompensate the lumbar spine.) So the “combo” involves fusing the thoracic spine posteriorly and then tethering the lumbar
spine. It’s pretty new and pretty preliminary, but very exciting.
Q: Are there any issues with the Zimmer Dynesys system being used in an off-label manner?
A: The off-label status of Zimmer Dynesys shouldn’t scare anyone away. The only thing the ff-label designation does is prevent the company from formalizing the training. It requires that the surgeon take the initiative to attend a course and observe the procedure, and all of us doing it are very happy to take someone through the steps of learning how to do it appropriately. Of course, the insurance companies like to misuse the words “investigational” and “experimental.” Peer to peer calls with the carrier MDs
and quoting current published literature is the best route to counterbalance insurance denials.
Q: What is the current status of development of an FDA- approved device for tethering?
A: I am familiar with the regulatory efforts of DePuy Synthes Spine and Zimmer Spine. DePuy has started down the pathway to approval by doing the procedure on patients outside the US. I think they will eventually propose to the FDA a trial with fewer patients to prove efficacy, instead of a randomized controlled trial, which is cost-prohibitive. Zimmer Spine is preparing some protocols for studies to show safety and efficacy to submit to the FDA for a clearance pathway. I think it’s still going to be at least two or three years before any vertebral body tethering system gets approved.
Q: Is there anything else that you would like orthopaedic residents to know about spine tethering?
A: This area of growth modulation is totally unexplored. We have absolutely no data on trying to use available markers to predict how much the spine is going to
grow. For example, one significant problem is that sometimes we get overcorrection with tethering. We don’t know exactly how much residual curve to leave in the OR. If you leave more than 30°, it may not end up being an outstanding result; it’s probably not going to correct any further. However, if you make the spine too straight (for example, if you leave a ten year old with a 15° curve), it’s probably going to overcorrect
to beyond -10° and require lengthening. It would be nice to have some data on growth and would make for some excellent resident and fellow research projects. Especially with 3D X-rays, I think one could obtain really good data on growth.
Q: What about the future improvements in tethering?
A: My vision is that in ten years we will have tethers that have more elasticity in them to accommodate different patients’ bone growth and modulus of elasticity. Hopefully, in ten years we’ll have better tethers and technology that we can’t even envision right now.
- Betz RR, Kim J, D’Andrea LP, Mulcahey MJ, Balsara RK, Clements DH. An innovative technique of vertebral body stapling for
the treatment of patients with adolescent idiopathic scoliosis: a feasibility, safety, and utility study. Spine (Phila Pa 1976) 28(20):S255- 65, 2003.
- Betz RR, Ranade A, Samdani AF, Chafetz R, D’Andrea LP, Gaughan JP, Asghar J, Grewal
H, Mulcahey MJ. Vertebral body stapling: a fusionless treatment option for a growing child with moderate idiopathic scoliosis. Spine (Phila PA 1976) 35(2):169-76, 2010.
- Theologis AA, Cahill P, Auriemma M, Betz R, Diab M. Vertebral body stapling in children with idiopathic scoliosis < 10 years of age with curve magnitude 30-39 degrees. Spine (Phila Pa 1976) 38(25):E1583-8, 2013.
- Sanders JO, Khoury JG, Kishan S, Browne RH, Mooney JF 3rd, Arnold KD, McConnell SJ, Bauman JA, Finegold DN. Predicting scoliosis progression from skeletal maturity: a simplified classification during adolescence. J Bone Joint Surg Am. 90(3):540-53, 2008.
- Samdani AF, Singla A, Ames R, Pahys JM, Betz RR.Early recognition of overcorrection after anterior vertebral body tethering. 48th annual Scoliosis Research Society meeting (case discussion), Lyon, France, September 18-21, 2013.
- Samdani AF, Ames RJ, Kimball JS, Pahys JM, Grewal H, Pelletier GJ, Betz RR. Anterior vertebral body tethering for idiopathic scoliosis: two-year results. Spine (Phila Pa 1976) 39(20:1688-93, 2014.
- Samdani AF, Ames RK, Kimball JS, Pahys JM, Grewal H, Pelletier GJ, Betz RR. Anterior vertebral body tethering for immature idiopathic scoliosis: one-year results on the first 32 patients. Eur Spine J 2014 Dec 16, Epub ahead of print.