Anterior Vertebral Body Growth-Modulation Tethering in Idiopathic Scoliosis

Surgical Technique

Stefan Parent, MD, PhD; Jesse Shen, MD, MSc

Disclosures

J Am Acad Orthop Surg. 2020;28(17):693-699. 

In This Article

Abstract and Introduction

Abstract

The management of idiopathic scoliosis in the skeletally immature patient can be challenging. Posterior spinal fusion and instrumentation is indicated for severe scoliosis deformities. However, the skeletally immature patient undergoing posterior fusion and instrumentation is at risk for developing crankshaft deformities. Moreover, bracing treatment remains an option for patients who are skeletally immature, and although it was found to be effective, it does not completely preclude deformity progression. Recently, fusionless treatment options, such as anterior vertebral body growth modulation, have been developed to treat these patients while avoiding the complications of posterior rigid fusion. Good results have been shown in recent literature with proper indications and planning in the skeletally immature patient.

Introduction

The underlying concept of modulating skeletal growth is to alter the mechanical environment of the vertebral physis and to guide its growth. In the seminal study by Stokes,[1] the "Hueter-Volkmann Law" was demonstrated in a rat tail model, which suggests that the same concept could be applied to scoliosis to modulate growth. Under this law, compressive forces stunt physeal growth while distractive forces stimulate growth.[2]

This concept can conceivably be applied to scoliosis because the forces applied to the convex and concave side of each vertebra may differ.[1,3,4] Modulating growth by changing the mechanical environment can thus potentially correct the deformity.[3,4] The idea of compressing the convex side of the scoliotic curve using implants to tether the spine came to fruition.[5–9] This will essentially allow the concave side to "catch up," and the deformity will progressively correct itself. In a retrospective study, Samdani et al[10,11] have shown that this growth-modulating technique can progressively correct deformities without fusion. Samdani et al reported 70% curve correction with anterior vertebral body growth modulation (AVBGM) at the 2 years follow-up.

Although promising, the overall complication rate has not been clearly defined with this new technique. Revision rates from 18% to 41%[10,12] have been described and mainly occur because of tether breakage and undercorrection or overcorrection. There is a need to describe the nature and chronology of complications for AVBGM.

This technique inherently needs a patient to have potential growth for modulation to function. Patients at skeletal maturity are thus poor candidates for growth modulation and should be considered for standard surgical treatment when indicated. The remaining necessary growth and the timing for surgery remain to be defined for this novel technique. However, there are certain clinical and radiologic parameters that may guide the surgeon in planning and selecting the right candidates for this technique.

Predicting progressive scoliosis has been extensively studied.[13–16] The Sanders staging, Tanner-Whitehouse III staging, Risser grading, proximal humerus ossification system, triradiate cartilage, and menarche are all tools that essentially guide the clinician to pinpoint skeletal age of the patient and to understand the amount and velocity of remaining growth. This is a crucial part in planning for surgery because the amount of potential remaining growth is a reflection of the amount of correction that can be progressively induced. This will also allow the clinician to evaluate the likelihood of success for bracing treatment.[17]

The technique of anterior vertebral body growth modulation is a growth-friendly technique[18] consisting of tethering the spine using staple and screw instrumentation with a cable connecting these screws together (Figure 1). This creates a fusionless construct partly correcting the deformity while modifying the local forces acting on each vertebra.

Figure 1.

Radiographs of an example case of anterior vertebral body growthmodulation tethering showing the initial preoperative visit and 1-year followup. This is a premenarchal patient, with Risser 0 with open triradiate cartilage.

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