Vertebral Body Tethering for Scoliosis

Since the first description of spinal fusions for the treatment of scoliosis over 100 years ago, there have been significant advancements in the surgical technique, which have led to improved fusion rates, lower complication frequency, greater three-dimensional correction of the deformity and more rapid postoperative recovery.  However, spine fusions mean fewer motion segments (less spine motion) which may lead to lower function in high-level physical activity (e.g. competitive athletics) and greater chance for spine arthritis. Hence preservation of spinal motion, particularly in the low back, is a highly attractive goal.  The desire to maintain spine motion has fueled the development of various growth modulation procedures, whose goals are correct the spinal deformity and maintain motion (without fusion).  One of these promising techniques which has gained traction in the last 10 years is vertebral body tethering (VBT).

The concept of VBT in scoliosis is to alter the relative vertebral growth (right vs. left) of the front of the spine.  This is accomplished by relative slowing the vertical growth on the convex side (by tensioning of the tether) with unloading of the concave side of the vertebra, to permit greater growth.  In order for growth modulation to occur the spine need to have enough spinal growth remaining.    

 This is a patient 4 days after VBT

At present in 2017 there is no FDA-approved devices for use in the U.S. in a nonfusion, growth-modulation technique in a skeletally immature patients.  This means the use of this tether system to the children and adolescents is in an “off-label” manner. 

Studies on VBT in animal models have demonstrated proof of concept that tethering of the immature spine can alter its growth.  The first description of VBT use in humans was a case report in 2010.  Reports of VBT use in children/adolescents have been encouraging with a low frequency of complications.  At present there is limited data available on the use of VBT in skeletally-immature patients with scoliosis. 

MAGEC (Part 3)

Follow-up on the reported complications of the MAGEC device.

In the last blog post three modes of failure of this device were described: rod breakage, actuator pin breakage (inside the device) and rod breakage.  It should be noted that with traditional growing rods, breakage of the rods is a common occurrence, so this problem is due to rigid rods taking the stress from a flexible child’s spine. Remember, all metals gradually fatigued over time as they are stressed by bending and twisting.  The smaller the diameter the rod the greater the chance of it breaking.

As mentioned in the previous blog the actuator pin, which is inside the device, has been re-engineered to be stronger.  Children who had their MAGEC devices implanted after the FDA clearance of this device have the improved, stronger MAGEC device design.

What are the outcomes of this new device?  Better, worse or the same?

Research in Early-Onset Scoliosis (EOS), like many areas of medicine, is very hard to complete.  For one thing it is a relatively uncommon problem in our population.  EOS also encompasses a wide variety of diagnoses, deformities types and severity.  The combination of being uncommon and highly variable patient to patient makes research challenging.  As such, it can be difficult for one surgeon or even one hospital to have enough patients to study a particular problem or treatment.  This is why many published research studies on EOS are from surgeon study groups, which are research collaborations between institutions around the world.  This permits surgeons to pool their data, unidentified to protect the patient, with other surgeons from around the world in order to get enough patients to study a research hypothesis. 

Since the MAGEC device has only been approved in the U.S. since 2014, the longest study follow-up in the U.S. is only a couple of years, too short to really help us at all.  The longer follow-up studies, which are really only intermediate length, are from Europe and Asia.  There are no comparative, long-term studies (>7 years) on the MAGEC device.  So we have to rely on short-term and intermediate-term studies on this device.

Most of the studies published and presented on MAGEC growing rods have reported similar radiographic outcomes when compared to traditional growing rods (TGR).  Correction of the spinal deformity and providing vertical growth of the chest appear to be overall similar.  However, there are many questions about the device longer-term such as:

1.       Will actuator failure frequency increase the longer the device is implanted?

2.       Will the spine become more rigid over time like is seen in traditional growing rods? 

3.       Is the MAGEC device cost-effective in it real world applications?  Each actuator costs as much as a new compact automobile, and typically two of these are implanted in each child.

4.       How much should the MAGEC device be lengthened at each office visit and how often should the device be lengthened? 

5.       Are the indications for the use of MAGEC devices the same as for TGRs?

We have many unanswered questions about the device, however the device appears to have more positive aspects than negative.

 

Is the surgery to place a MAGEC growing rod different than traditional growing rods (TGR)?

The surgical approach is the same for both procedures, but the big difference is the MAGEC rods are one long rod whereas each TGR is actually two short rods connected together.  So the MAGEC rods are much more difficult to place in a child, especially when the child is short, is thin and has a large spinal deformity.  The MAGEC devices need between 9 and 11 centimeters of relatively straight spine to place the MAGEC rod without it being too prominent under the skin.  Optimal placement of this device requires a high level of surgical skill with strong spine (pedicle screws) or pelvic fixation points.

How do I find a surgeon who uses MAGEC devices?

It is important to pick a surgeon who frequently cares for EOS as they can decide, based on their experience with all types of treatment options, if MAGEC or another type of surgery is optimal.

A good way to find one of these surgeons is to go the Growing Spine Foundation Website to find a center near you: https://www.growingspine.org/research/gssg

Our EOS spine centers at St. Louis Children’s Hospital (314-454-2045) and Shriner’s Hospital for Children, St. Louis unit (314-432-3600) are always willing to help.

MAGEC (Part 2)

In the last posting the MAGEC system for Early Onset Scoliosis was introduced.  This system is a significant improvement when compared to Traditional Growing Rods, mainly due to the ability to lengthen the instrumentation without the need for anesthesia or a trip to the operating room.  The benefits of this device are easy to see, but was with any new technology there are some drawbacks or limitations.  The MAGEC device is a cutting-edge, high-tech magnetic lengthener and complicated devices may not function as intended.  The MAGEC device requires a magnetic field from the ERC (shown below) to spin the magnets in the implanted actuator.

It is possible the distance between skin and the actuator is too great, making the magnetic field too weak to lengthen the actuator

 

 This can happen, in children with more subcutaneous fat, an older patient and if the actuator was deeply buried in soft tissues around the spine.  Personally I have had only one patient in whom the MAGEC device was unable to be magnetically lengthened.  The remaining 30+ patients in my practice with this device have been easy to lengthen.

The other problem with the MAGEC device was in breakage of the actuator pin.  If this happens the actuator will not lengthen with the ERC.  Several reports of actuator pin breakage have surfaced, with most of them being from Asia and Europe.  This is because the MAGEC system was first released overseas so there is a slightly longer experience with this device outside of the U.S.  This was also the first-generation of the MAGEC device.  When the MAGEC device was released in the U.S. the actuator pin design had been improved, creating a second-generation.  This is what we currently use in the U.S.  I have not seen any actuator pin breakage yet in my patient population. 

Another mode of failure of the MAGEC device is rod breakage, either above or below the actuator.  This type of failure is the same as what is seen in Traditional Growing Rods.  The metal rods are constantly stressed, or cycled, by the child on a daily basis.  These stresses are cumulative on the rods and will gradually weaken until there is a fracture or breakage of the rod. 

 

This problem can be partially avoided by using the larger sizes of the MAGEC rods, specifically the 5.5 mm rods instead of 4.5 mm rods.  However, due to patient size we cannot use 5.5 mm rods as the patient is just too small to hide the rods in their back without breaking through the skin or being painful.