Anterior vertebral body tethering: a promising non-fusion scoliosis treatment

Anterior vertebral body tethering: a promising non-fusion scoliosis treatment

Ahmet Alanay, Caglar Yilgor, Gokhan Ergene, Nuray Sogunmez and Barbaros Omer Cebeci discuss an alternative to bracing and fusion for the treatment of progressive scoliosis.

The current standard of care for skeletally immature adolescent idiopathic scoliosis patients is observation for mild (<20°), bracing for moderate (20–40°) and posterior fusion for more severe curves [1]. Although spinal fusion stands effective, it limits motion and it is not without complications [2,3]. Likewise, bracing is reported to be effective with the recent BrAIST study, but not for every single patient and all curve types [4]. In addition, the cumbersome bracing treatment can also be associated with psychosocial and practical problems [5,6]. Consequently, there remains a practical need for viable growth- and motion-sparing treatment options. Several growth preservation, growth stimulation, growth guidance, growth modulation and hybrid constructs have been used as non-fusion surgical techniques for early-onset and immature adolescent scoliosis. Among others, growth modulation with anterior vertebral body tethering is a promising alternative to bracing and fusion surgery for paediatric scoliosis.

Background

The natural history of skeletally immature idiopathic scoliosis with moderate curves is progression. In a study based on observation alone, Charles et al. reported that 75 per cent of pubertal onset curves between 21° and 30°, and 100 per cent of patients with curves greater than 30° required spinal fusion [7]. Bracing has therefore remained the standard of care for skeletally immature idiopathic scoliosis with moderate curves although clinical results have varied widely. The most recent BrAIST study showed that when appropriately prepared and worn, bracing may lower the need for surgical treatment by 50 per cent [4]. Yet bracing is an uncomfortable treatment requiring serious commitment of the patient: the brace needs to be worn for 16 to 23 hours a day, typically for three to five years and even longer in some cases. Furthermore, several studies have reported psychosocial stresses related to bracing regarding body image concerns [5,6].

Patients who fail bracing and whose curves reach 50° are often offered surgical treatment. Although spinal fusion remains the most viable surgical option in scoliosis treatment, it comes with decreased mobility, inhibition of growth over the length of the construct and possible development of adjacent segment degeneration [2,3,8].

Growth- and motion-sparing anterior vertebral body tethering (VBT) modulates the growth of the spine and stabilises the curve. VBT is an alternative to both bracing and fusion surgery for the treatment of progressive scoliosis.

 

Vertebral body tethering

The purpose of VBT is to harness the patient’s inherent spinal growth and redirect it to achieve correction, rather than progression, of the curve [9]. This is accomplished by applying compressive forces on convexity via a minimal invasive thoracoscopic anterior approach.

The logic behind VBT stems from the Hueter-Volkmann law, which states that when an epiphyseal growth plate is under pressure, its growth is reduced [10]. The technique involves the placement of vertebral body screws on the convexity and then attaching a polyethylene tether, which is shortened and tightened. VBT is performed via a minimally invasive thoracoscopic approach. When the tether applies compression on the convexity, the remaining growth potential of the child will urge more growth on the concavity, thereby lessening or reversing the deformity.

 

Surgical technique

The patient is placed in lateral decubitus position with the convex side of the curve facing up. An axillary roll is used for slight curve correction, positioned underneath the concave side. Video-assisted thoracoscopy is used with carbon dioxide insufflation and single lung ventilation. Vertebral bodies are identified using bi-planar fluoroscopy. The pleura is dissected from the lateral aspect of the vertebral bodies along the length of the curve [11]. Segmental vessels are identified, coagulated and divided. Screws are inserted anterior to the rib head and directed toward the concavity across the anterolateral aspect of the vertebral body [11], the screws can either be directly placed to the vertebral body or a three- or four-prong staple may be used to facilitate insertion and stabilisation. Instrumentation can be done down to L1 or L2 via this approach, whereas a retroperitoneal mini open approach is needed for the instrumentation of L3 (and occasionally L2) [11]. After securely placing the screws, a polyethylene tether is placed across the tulip of each screw. The tether is than sequentially tensioned and fixed, resulting in an initial correction of the curve [11]. A chest tube drain is placed at the end of the surgery.

 

Indications

Current indications for VBT are:

  • Skeletally immature patients with idiopathic scoliosis and curves between 35° and 60°
  • At least 50 per cent flexibility or bend to <30°
  • Thoracic kyphosis of <40°
  • Rotational prominence <20°
  • Skeletal maturity is determined using a variety of factors including Risser sign (≤ 2), Sanders score (≤ 4) and menarche status [12].

 

Other factors like parental height, child’s height, secondary sex characteristics, family history and other factors may also affect these general indications [12]. Age is not an absolute measure as it does not fully reflect the remaining growth potential of the patient.

 

Results

Biomechanical basis for tethering was first demonstrated in porcine [13] and goat [14] models. After promising results in animal studies, the first reported human case was an 8.5-year-old patient. The patient’s 40° thoracic curve was initially corrected to 25° after index surgery. The curve progressively corrected to 8° during the follow-up of 48 months [15]. A series of 32 patients with one-year follow-up demonstrated a progressive correction of their major coronal Cobb and rib prominence [11]. For the major curve, 12.5 per cent of patients showed >10° correction during the follow-up, whereas 28 per cent had 5–10° correction, 56 per cent were stable within 5° and 3 per cent had a slight loss of correction [11]. The mean correction in the rib hump was 40 per cent [11]. Only 28 per cent of patients in the first year – and 18 per cent in the second year – had a rib prominence ≥10° compared with 88 per cent of patients pre-op. Later, a larger cohort report demonstrated similar results [12].

The first case was performed in our institute approximately three years ago. To date, there are 12 patients that have completed six-month follow-up. Among those, mean follow-up was 14.9 months (range 7–36). Mean age was 12.2 years (range 11–13). Mean pre-operative thoracic and lumbar curves were 46° (range 35–59°) and 27.6° (range 8–35°), respectively. Post-operative first-erect X-rays revealed a 52 per cent main thoracic curve correction with a mean Cobb of 22° (range 12–26°). An average of 3.9° (range -6–14°) additional correction was attained during follow-up, resulting in an average of 61 per cent correction. Compensatory lumbar curves showed an average of 43 per cent surgical and 7 per cent follow-up correction, adding up to an average of 50 per cent correction (mean 14°, range 2–27°). Mean pre-op kyphosis was 34.8° (15–59°). The mean early post-operative thoracic kyphosis showed a slight decrease (mean 27.1°, range 10–57°), but reached back to initial values during follow-up (mean 30.1°, range 19–49°) (see Figure 1).

Figure 1: (a) Pre-operative AP and (b) lateral radiographs of our first case of anterior VBT. An 11-year-old girl presented to the clinic with a 38° right thoracic curve and a 22° left lumbar curve. Thoracic kyphosis was 32°. (c) Post-operative first-erect AP and (d) lateral radiographs after thoracoscopic anterior VBT show that the thoracic curve corrected to 23° and the lumbar curve to 17°. Thoracic kyphosis was 22°. At age 13, 24 months post-op, the thoracic curve measures 11° and the lumbar 13° on the AP (e) and thoracic kyphosis measures 30° on the lateral radiographs (f). The patient is Risser 5.

Figure 1: (a) Pre-operative AP and (b) lateral radiographs of our first case of anterior VBT. An 11-year-old girl presented to the clinic with a 38° right thoracic curve and a 22° left lumbar curve. Thoracic kyphosis was 32°. (c) Post-operative first-erect AP and (d) lateral radiographs after thoracoscopic anterior VBT show that the thoracic curve corrected to 23° and the lumbar curve to 17°. Thoracic kyphosis was 22°. At age 13, 24 months post-op, the thoracic curve measures 11° and the lumbar 13° on the AP (e) and thoracic kyphosis measures 30° on the lateral radiographs (f). The patient is Risser 5.

 

 

 

 

 

 

 

 

 

 

 

Figure 2: Time-dependent curve magnitude changes of each patient and on average.

 

 

 

 

 

 

 

 

 

Complications

To date, no neurological, infectious or implant-related complications have been reported [11,12]. Atelectasis may require bronchoscopy if not resolved with pulmonary physical therapy. After initial surgical correction, worsening of the deformity can occur, especially in the first few weeks, but is not likely, and there is always the possibility of correction as long as the child has remaining growth potential. Overcorrection is anticipated, especially for younger children. This may require a second thoracoscopic intervention to loosen or cut the tether. Among reported cases, 10–15 per cent of patients were overcorrected [11,12]. With more experience, the ability to judge the amount of correction to impart during the initial surgery is improving, which should decrease the chances of overcorrection [11]. Tether breakage is another possible concern that may need close observation of the segmental angulation changes to identify. Although potentially possible, to date no reported patients have needed a spinal fusion, and all have subjectively retained spinal mobility [12].

 

Conclusions

VBT shows promising early results for non-fusion scoliosis treatment. It is a safe and efficient procedure that may provide substantial advantages over both bracing and definitive spinal fusion in a selected group of patients. Yet, it is not a ‘one and done’ answer for all patients and optimistic scepticism is required.

Growth modulation with anterior convexity vertebral body compression is a promising technique to avoid fusion and related consequences in skeletally immature adolescent idiopathic scoliosis patients. Today, there is some unpublished experience with skeletally mature and adult idiopathic scoliosis that demonstrates that such patients may be future candidates for VBT. Modifications to adopt this non-fusion technique for applicability in early onset scoliosis may be revolutionary.

References 

  1. Nachemson AL, Peterson LE. Effectiveness of treatment with a brace in girls who have adolescent idiopathic scoliosis. A prospective, controlled study based on data from the Brace Study of the Scoliosis Research Society. J Bone Joint Surg Am. Jun 1995;77(6):815-822.
  2. Green DW, Lawhorne TW, 3rd, Widmann RF, et al. Long-term magnetic resonance imaging follow-up demonstrates minimal transitional level lumbar disc degeneration after posterior spine fusion for adolescent idiopathic scoliosis. Spine (Phila Pa 1976). Nov 1 2011;36(23):1948-1954.
  3. Kepler CK, Meredith DS, Green DW, Widmann RF. Long-term outcomes after posterior spine fusion for adolescent idiopathic scoliosis. Curr Opin Pediatr. Feb 2012;24(1):68-75.
  4. Weinstein SL, Dolan LA, Wright JG, Dobbs MB. Effects of bracing in adolescents with idiopathic scoliosis. N Engl J Med. Oct 17 2013;369(16):1512-1521.
  5. Fallstrom K, Cochran T, Nachemson A. Long-term effects on personality development in patients with adolescent idiopathic scoliosis. Influence of type of treatment. Spine (Phila Pa 1976). Sep 1986;11(7):756-758.
  6. Misterska E, Glowacki M, Latuszewska J. Female patients&#39; and parents&#39; assessment of deformity- and brace-related stress in the conservative treatment of adolescent idiopathic scoliosis. Spine (Phila Pa 1976). Jun 15 2012;37(14):1218-1223.
  7. Charles YP, Daures JP, de Rosa V, Dimeglio A. Progression risk of idiopathic juvenile scoliosis during pubertal growth. Spine (Phila Pa 1976). Aug 1 2006;31(17):1933-1942.
  8. Danielsson AJ, Romberg K, Nachemson AL. Spinal range of motion, muscle endurance, and back pain and function at least 20 years after fusion or brace treatment for adolescent idiopathic scoliosis: a case-control study. Spine (Phila Pa 1976). Feb 1 2006;31(3):275-283.
  9. Guille JT, D&#39;Andrea LP, Betz RR. Fusionless treatment of scoliosis. Orthop Clin North Am. Oct 2007;38(4):541-545, vii.
  10. Mehlman CT, Araghi A, Roy DR. Hyphenated history: the Hueter-Volkmann law. Am J Orthop (Belle Mead NJ). Nov 1997;26(11):798-800.
  11. Samdani AF, Ames RJ, Kimball JS, et al. Anterior vertebral body tethering for immature adolescent idiopathic scoliosis: one-year results on the first 32 patients. Eur Spine J. Jul 2015;24(7):1533-1539.
  12. Samdani AF, Ames RJ, Kimball JS, et al. Anterior vertebral body tethering for idiopathic scoliosis: two-year results. Spine (Phila Pa 1976). Sep 15 2014;39(20):1688-1693.
  13. Newton PO, Farnsworth CL, Upasani VV, Chambers RC, Varley E, Tsutsui S. Effects of intraoperative tensioning of an anterolateral spinal tether on spinal growth modulation in a porcine model. Spine (Phila Pa 1976). Jan 15 2011;36(2):109-117.
  14. Braun JT, Ogilvie JW, Akyuz E, Brodke DS, Bachus KN. Creation of an experimental idiopathic-type scoliosis in an immature goat model using a flexible posterior asymmetric tether. Spine (Phila Pa 1976). Jun 1 2006;31(13):1410-1414.
  15. Crawford CH, 3rd, Lenke LG. Growth modulation by means of anterior tethering resulting in progressive correction of juvenile idiopathic scoliosis: a case report. J Bone Joint Surg Am. Jan 2010;92(1):202-209.

 

Authors

Ahmet Alanay

Ahmet is an internationally recognised surgeon, advancing the spinal care specialty and contributing to surgeons’ training around the world. Based at the School of Medicine at Acibadem University, Istanbul, Turkey, he is a recipient of numerous national and international awards, and is a pioneer of many state-of-the-art techniques and new approaches in spinal surgery.

 

Caglar Yilgor

Caglar is assistant professor of orthopaedics and traumatology at Acibadem University School of Medicine. He completed his fellowship on adult and paediatric spinal disorders in the Combined Neurosurgical and Orthopedic Spinal Surgery programme. He is currently working in the Comprehensive Spine Center at Acibadem Maslak Hospital in Istanbul.

 

Gokhan Ergene

Gokhan completed his residency in 2004 at Sureyya Pasa Hospital and worked on endoscopic lung surgeries and lung transplantation at St Louis Washington University. He is currently a doctor in the department of thoracic surgery at Acibadem Maslak Hospital, Istanbul, Turkey.

 

Nuray Sogunmez

Nuray received her Master’s degree from Bosphorus University. She is a PhD candidate in the department of bioinformatics and genetics at Kadir Has University and is currently working as a research coordinator in the Comprehensive Spine Center at Acibadem Maslak Hospital.

 

Barbaros Omer Cebeci

Barbaros is a year 3 student at Acibadem University School of Medicine. He is interested in scoliosis surgery and medical technologies.

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