Vertebral Body Tethering in Progressive Adolescent Idiopathic Scoliosis
Fusionless emerging technology case
A 12 5/12 -year old healthy girl presented with progressive scoliosis. She does not have significant back pain or limitations in her activities. The patient is an avid lacrosse and basketball player and enjoys horseback riding.
The family had a great deal of concern about spinal fusion, although they had sought consultation to discuss surgical correction due to the progressive nature of their child's scoliosis as well as a stated desire to have the deformity corrected.
Her past medical history was unremarkable except for the scoliosis as was the review of systems.
Examination revealed a healthy appearing girl. Height was 59.75 inches; weight was 112 lbs. Gait was normal, leg lengths equal, thoracolumbar range of motion was physiologic and painless. Rotational prominences in the thoracic and thoracolumbar regions were 9 and 13 degrees, respectively. There were no skin lesions of significance. She had normal ligamentous laxity.
Motor, sensory, and reflex examination of the extremities was normal. Abdominal reflexes were symmetric; ankle clonus was negative, and Babinski reflexes were normal.
Pulmonary function testing performed as part of a registry protocol revealed FVC (forced vital capacity) and FEV1 (forced expiratory volume) of 73% and 84% predicted, respectively.
Posteroanterior (PA), lateral, and fulcrum bending x-rays are shown in the figures below.
Progressive adolescent idiopathic scoliosis (AIS)
Treatment Options and Discussion with Family
Corrective surgery was offered to the family for their child in the form of posterior spinal arthrodesis from T4 to L3. Classification of this curvature indicated it to be a Lenke type 6 (thoracolumbar major with structural thoracic curvature). Although one can consider a selective thoracic fusion (STF) in patients with highly flexible thoracolumbar curvature when thoracolumbar apical translation and rotation are less than for the thoracic curvature and with acceptable clinical deformity as a so-called rule-breaker to the classification, STF was not appropriate in this case since those conditions were not met.
The family had great concern about the impact of fusion on their child's flexibility and function. They were assured, based on published data on range of motion, showing preservation of lumbar mobility following arthrodesis for AIS (Marks, et al)1 as well as retrospective data we have presented on return to sport following posterior arthrodesis (Lonner, et al)2 that there would be little impact on early and intermediate term function.
A discussion was then conducted on the alternative of vertebral body tethering (VBT) involving both curvatures. The procedure, considered experimental, and the implants, not FDA-approved for this indication, as explained to the family, is performed via a right anterior approach through video-assisted thoracoscopy for the thoracic curvature and a left thoracoabdominal approach for the thoracolumbar curvature.
Vertebral body screws, which are hydroxyapatite-coated titanium screws (6.4mm), are placed from proximal to distal Cobb end vertebrae with 2 screws, one from the right, one from the left, placed into the inflexion vertebra (T10 in this case) through vertebral body staples to minimize toggling of the screws. A combination of endoscopic, direct visualization, and fluoroscopic evaluation are utilized for placement of the instrumentation. Linkage of screws with a (polyethylene) cord followed by tensioning of the cord at each segment in order to achieve correction and tightening of set screws level by level is performed.
The family was eager to pursue this fusion-less approach despite a lack of long-term data as opposed to arthrodesis for which long-term experience and some data is available.
- Potential advantages of tethering as explained to the family include maintenance of flexibility within operated spinal segments, preservation of at least partial growth within those segments, growth modulation leading to correction of vertebral body wedging, and the potential to decrease adjacent segment degenerative disease over time.
- Unknowns and concerns with the procedure include the potential for fixation failure or cord breakage, overcorrection through growth modulation in a skeletally immature patient, and disc degeneration within the instrumented spine.
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The family elected to proceed with the VBT procedure.
The operation was performed without complication.
- Total operative time was just under 300 minutes
- Estimated blood loss was 250 cc
- Postoperatively, thoracic epidural analgesia was utilized for pain control
- Hospital stay was 5 day.
The video below of the patient was recorded at 3 weeks postoperatively; it reveals comfortable and physiologic thoracolumbar range of motion.
Activity restriction consisting of limited bending, lifting, and twisting was maintained for 6 weeks. Physical therapy, consisting of core strengthening and flexibility exercises was conducted for 6 weeks thereafter. Return to full activity was allowed over this period of time.
The patient returned to her lacrosse team, participating without restriction and playing at full strength by 4 months postoperatively.
Clinical photographs of the patient (below) show a desirable result.
Postoperative x-rays at 6 months reveal balanced correction. Rotational prominences decreased from 9 degrees in the thoracic region to 2 degrees and from 13 degrees in the thoracolumbar region to 1 degree.
1. Marks M, Newton PO, Petcharaporn M, Bastrom TP, Shah S, Betz R, Lonner B, Miyanji F. Postoperative segmental motion of the unfused spine distal to the fusion in 100 patients with adolescent idiopathic scoliosis. Spine (Phila Pa 1976). 2012 May 1;37(10):826-32. doi: 10.1097/BRS.0b013e31823b4eab.
2. Lonner B, Ren Y, Rieger M, Petrizzo A, Rogers P, Toombs C. Level of Play: Return to Sports Following Surgery For Adolescent Idiopathic Scoliosis. Paper 96. 29th Annual North American Spine Society (NASS) Meeting and Course, November 12-15, 2014. San Francisco, CA.
This is an interesting case. I agree with the way it is characterized. The Cobb measurements of the thoracic and lumbar curves are almost identical, but it looks like the thoracolumbar curve is the bigger of the two. The stable vertebra is T10 or T11. The thoracolumbar curve is more flexible than the thoracic curve, but it has more rotation and deviation from the midline than the thoracic curve. The thoracolumbar curve is actually more structural than the thoracic even though it's more flexible on the side bending films. I don't think a selective thoracic fusion would work. Usually, if the stable vertebra is T11 or higher, a selective thoracic fusion won't do well. The other preoperative film we at Washington University Medical Center(WUMC) find very helpful is a prone or supine 36" coronal film. It shows what the patient's spine will look like on the operating table and will influence which curve to fix and fuse and how much correction to shoot for if we are going to fix one of the two curves. That actually helps us more than the side bending films. I agree if the patient is VERY athletic and hopes to be highly competitive in high school and college, fixing and fusing both curves T3, T4 or T5 to L3 or L4 is not the best choice.
If a selective thoracic fusion can be done, in my opinion, there is little reason to consider a vertebral body tethering procedure. Patients with a T3, T4 or T5 to T12, L1 or L2 instrumented fusion seem to lose very little functional motion and many of these patients we at WUMC have done have gone on to be division I college athletes with great success. If an instrumented fusion is done from T3, T4 or T5 to L3 or L4, the likelihood that patient can become a division I college athlete seems to be much less likely, but selective thoracic fusion is not a terribly good option for this patient as the thoracolumbar curve is bigger.
One could consider a definitive fusion of the thoracic curve and then vertebral body tethering of just the thoracolumbar curve. The other option would be to do just a selective thoracolumbar fusion. We at WUMC have had more success doing this posteriorly than anteriorly. If we selectively fix the thoracolumbar curve anteriorly, we usually correct the curve too much. We have had success doing a selective thoracolumbar fusion in similar cases, meaning along the lines of a T10 or T11 to L3 POSTERIOR instrumented fusion, trying to keep L3 neutral, stable and horizontal, but accepting somewhat less curve correction. We at WUMC have found that patients with a posterior instrumented fusion T10 or T11 to L3 often can go on to be division I college athletes. So, there are several surgical options here.
The surgical results shown here look quite good. There is very nice correction, and it's very balanced. However, there are some concerns with this procedure. The thoracoscopic approach is not too bad, but that plus a thoracoabdominal approach represent a lot of surgery and two sets of scars. If the patient is a very avid athlete, she will stress her spine substantially more than the average teenager. Dr. Lonner did not fuse these segments, so I would think there is a reasonable chance the instruments will fail somewhere and lose correction.
The other problem with doing vertebral body tethering of the lumbar spine is that we know if motion is limited in lumbar segments, these discs will degenerate. We know this from the rod long/fuse short literature and experience with fractures. Almost always the segments that are instrumented and not fused degenerate if the instruments aren't removed within six months or so of the surgery. I would have concern that these instrumented lumbar segments will degenerate with time.
On the postoperative films, the last instrumented vertebra is L3, but there are only four functional lumbar vertebrae. So there are only two functioning discs below the construct. I believe the L5 segment is sacralized. It looks like the transverse processes are very large, and the disc is very narrow in the sagittal plane at L5-S1. And the L3-L4 disc is now jacked the other way, meaning the disc is jacked so it is convex on the left and concave on the right, the opposite of preop. If a selective thoracolumbar posterior instrumented fusion was performed, the desired end result would be two curves (thoracic and thoracolumbar) measuring 30-35° with L3 being neutral, horizontal and stable with no jack to the L3-L4 disc.
There might be concern with this approach (selective posterior thoracolumbar fusion) that the thoracic curve would progress with growth, but our experience at WUMC is if they have some ossification of the iliac cartilage, this is not likely. From what I see on the hand film, the patient has growth left, but not so much that the thoracic curve would progress with a selective thoracic thoracolumbar fusion from T10 to L3. This is not a major deformity. The reason for operating is to be sure the curves don't progress as the patient grows. Getting these curves down to 10-15° is not mandatory. It's better to preserve function than to have postop films with low Cobb measurements.
As stated, the surgical result looks very nice, but this patient will need to be followed for 10 years to know if this is really a good result. Because there is no fusion, will the instrumentation and correction hold? Will the lumbar discs degenerate with time, and then an instrumented fusion be needed? I hope she does well. The immediate surgical result looks very good. I fully agree if this patient has substantial sports aspirations, the surgeon should look for options other than fusing BOTH curves. If there is a way to selectively fuse the thoracic curve, that is best, but I don't think that would apply for this patient. Selectively fusing the thoracolumbar curve is something we have had substantial success with at WUMC, but I bet many Scoliosis Research Society surgeons would say that is not as predictable a treatment as a selective thoracic fusion is for a King 2.
In conclusion, the immediate surgical result is excellent. Dr. Lonner is to be commended for thinking outside the box and trying to control this patient's progressive scoliosis but still let her be highly competitive with sports. Patients that are highly motivated to play sports and otherwise would require a long instrumented fusion do require individualization of surgical treatment and additional planning and discussion.
I appreciate the thoroughness of Dr. Bridwell’s response and his wisdom and experience in the arena of adolescent and adult idiopathic spinal deformities. My approach to the patient with adolescent idiopathic scoliosis has evolved slowly after very careful consideration. Despite a large experience with thoracoscopically-performed anterior spinal fusion for thoracic curvature as well as open thoracoabdominal approaches for anterior fusion of thoracolumbar curvature, I have been slow to move to the anterior fusionless tethering procedure due to the concerns raised by Dr. Bridwell. I have observed the experience of others and have noted very satisfactory outcomes out to five years in a majority of patients. Clearly, long-term study is required and this is diligently explained to all applicable surgical candidates in my practice. All potential candidates are offered standard posterior procedures in addition to the alternative, non-FDA approved tethering procedure. I am looking forward to studying this approach further over the next 2-3 decades.