Spinal Tethering and Growth Modulation for Paediatric Scoliosis

Courtesy: Prof Baron Lonner MD, Professor of Orthopaedic Surgery, Chief of Minimally Invasive Scoliosis Surgery, Mount Sinai Hospital and Icahn School of Medicine, New York, USA

The mainstay of management in AIS patients is categorized into 3 sections.

1. Firstly, Observation restricted to cases with mild curves.
2. Next, Bracing for moderate curves and growing child and
3. lastly, Fusion/Arthrodesis reserved for definitive treatment.

The ultimate priority in the management of scoliosis is preservation of motion followed by deformity correction and minimizing the complications such as pulmonary distress.

 

• In adolescents the natural history of arthrodesis is impacted by the Lowest instrumented vertebra (LIV)
• The milestones in the evolution of surgical intervention dates back more than 100 years ago with some revolutionary and mostly evolutionary changes.
• The first fusion surgery was done in 1911 by Professors Hibbs and Albee.
• Harrington was the first surgeon to use metallic implant used in Scoliosis which was then controversial in 1958. Prof. Suk(Seoul) introduced pedicle screws in Spine.
• Early onset scoliosis is being treated with growing rods which were magnetically controlled (MCGR) and finally, Tethering and posterior dynamic distraction being the latest development.

Arthrodesis, a salvage procedure, has always been the end stage choice in any joint and not just Spine.

• So the focus lies on preserving the flexion as much as possible.
• Studies(1) have shown five times greater complication rate in delayed surgery in skeletally immature adolescents in delayed or letting the natural course of disease to ensue patients have experience higher rates of complications such as nerve pain, larger curves need for extensive procedures.
• In a matched analysis it is evident that more levels have been fused, pelvic fusion, more blood loss etc.
• Arthrodesis is particularly disadvantageous in individuals who are professional swimmers, dancers or gymnasts.
• Young patients who had fusion surgery in their early teens had significantly developed disc degeneration(2) due to the impact of LIV nearly after a decade when they’re in their early twenties when the LIV is deviated from midline requiring revision surgery by fusing further segments distally,
• So the ultimate procedure is the one which corrects deformity, preserves pulmonary function and growth (for stature), preserves flexibility and is highly reliable with least complication rate, which may be achieved by vertebral body tethering.

VBT (vertebral body tethering) is a motion sparing, reversible surgery which promotes early recovery and is done with minimal blood loss by involving fewer segments thereby lesser incidence of degeneration

• The basic science(3) behind VBT is growth modulation taking advantage of the remaining anterior growth, coronal wedging by tethering growth on convexity and allowing growth over the concavity based on Heuter Volkmann principle.
• Historically VBT was done with staples in 1950s and recently Nitinol staples which have shown better results in milder curves.
• Animal Studies(4) were conducted by creating scoliosis and reversing it with untethered, single tether and double tether.
• The latter showed consistent results.
• This helped in understanding etiology of AIS where anterior overgrowth of vertebral body was leading to loss of kyphosis and twisting of spine.
• These studies have also shown biochemical changes such as preserved water content in disc, enhanced proteoglycan content unchanged collagen content with narrowing of disc but preserved disc tissue.
• Studies(5) on Porcine models showed excellent outcome by tethering with respect to axial rotation, coronal and sagittal plane deformities with improved kyphosis.

FDA(USA) has approved VBT with certain indications as follows:
– Skeletally immature patients that require surgical treatment
– Major Cobb angle 30*-65*
– Failed bracing/ intolerant to bracing

• VBT is done in minimal incisions (VATS) minimally invasive in lateral decubitus position under thoracoscopy with pleural dissection and screws(titanium, HA) placed adjacent to rib head and aiming for bicortical purchase and contralateral rib head with fluoroscopic guidance.
• Segmental arteries have to be taken into account and needs to be studied more with appropriate preop evaluation. Timing of procedure is usually set according to the Sanders score of skeletal maturity which is assessed by taking an X-ray of hand(usually left) to avoid risks of overcorrection in cases of peak growth velocity as in Sanders 2.
• More tensioning at apex vertebra and lesser at terminal ends in cases of higher growth potential is beneficial. Contraindications include lesser than 30* and more than 65 degree, significant kyphosis (>50*) & skeletally mature patients.
• Follow up radiographs have shown significantly improved change in the shape of vertebra. However, Long-term follow-ups are required to establish its efficacy.
• The course of surgical outcome by tethering is highly unpredictable but definite improvement over the time has been evident(6) with minimal between first immediate post-op and one year follow-up and higher in 2 year follow-up.
• Thoracolumbar curves have shown best outcome as compared to Thoracic curve which was reported earlier
• In one cohort study(7) done between post VBT and PSF surgeries, it was observed that revision rate was quite higher in very young adolescents who underwent VBT as opposed to better outcome seen in late adolescents.
• In one matched analysis, ( Prof. Baon Lonner et. al, Scoliosis society 2020), VBT has proven to be better with minimal blood loss and has shown improved kyphosis and preserved flexion when compared to PSF
• In conclusion, VBT has the potential to give best results in terms of growth modulation with preserving motion along with correction & growth.
• Long term results will be the key in determining it. There is a lot of scope in this procedure and more studies have to be done to see its efficacy in skeletally mature patients. Posterior dynamic distraction is also being thoroughly studied and put in development for the advancement.

Ref:-
1. Lonner BS, Ren Y, Bess S, Kelly M, Kim HJ, Yaszay B, Lafage V, Marks M, Miyanji F, Shaffrey CI, Newton PO. Surgery for the Adolescent Idiopathic Scoliosis Patients After Skeletal Maturity: Early Versus Late Surgery. Spine Deform. 2019 Jan;7(1):84-92. doi: 10.1016/j.jspd.2018.05.012. PMID: 30587326.
2. Lonner BS, Ren Y, Upasani VV, Marks MM, Newton PO, Samdani AF, Chen K, Shufflebarger HL, Shah SA, Lefton DR, Nasser H, Dabrowski CT, Betz RR. Disc Degeneration in Unfused Caudal Motion Segments Ten Years Following Surgery for Adolescent Idiopathic Scoliosis. Spine Deform. 2018 Nov-Dec;6(6):684-690. doi: 10.1016/j.jspd.2018.03.013. PMID: 30348344.
3. Stokes, I.A., Burwell, R.G. & Dangerfield, P.H. Biomechanical spinal growth modulation and progressive adolescent scoliosis – a test of the ‘vicious cycle’ pathogenetic hypothesis: Summary of an electronic focus group debate of the IBSE. Scoliosis 1, 16 (2006)
4. Newton, Peter & Faro, Fran & Farnsworth, Christine & Shapiro, Gary & Mohamad, Fazir & Parent, Stefan & Fricka, Kevin. (2006). Multilevel Spinal Growth Modulation With an Anterolateral Flexible Tether in an Immature Bovine Model. Spine. 30. 2608-13. 10.1097/01.brs.0000188267.66847.bf.
5. Chay E, Patel A, Ungar B, Leung A, Moal B, Lafage V, Farcy JP, Schwab F. Impact of unilateral corrective tethering on the histology of the growth plate in an established porcine model for thoracic scoliosis. Spine (Phila Pa 1976). 2012 Jul 1;37(15):E883-9. doi: 10.1097/BRS.0b013e31824d973c. PMID: 22333954.
6. Herring JA. Vertebral Tethering for Scoliosis Management: Commentary on an article by Peter O. Newton, MD, et al.: “Anterior Spinal Growth Tethering for Skeletally Immature Patients with Scoliosis. A Retrospective Look Two to Four Years Postoperatively”. J Bone Joint Surg Am. 2018 Oct 3;100(19):e130. doi: 10.2106/JBJS.18.00655. PMID: 30278007.
7. Newton, Peter O. MD1,2,a; Bartley, Carrie E. MA1; Bastrom, Tracey P. MA1; Kluck, Dylan G. MD2; Saito, Wataru MD, PhD3; Yaszay, Burt MD1,2 Anterior Spinal Growth Modulation in Skeletally Immature Patients with Idiopathic Scoliosis, The Journal of Bone and Joint Surgery: May 6, 2020 – Volume 102 – Issue 9 – p 769-777