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Chapter Summary
• Context: The treatment of neuromuscular scoliosis in pediatric and adolescent patients represents a major challenge in spine surgery. Early-onset deformities show rapid progression during the pubertal growth spurt and continue to deteriorate in adulthood. Conservative approaches show limited efficacy, resulting in severe, progressive curves associated with pelvic obliquity. These changes compromise trunk balance in the seated position, reduce functional autonomy of the upper limbs, impair respiratory function, and alter bowel transit. Although long posterior arthrodesis with pedicle screws is the gold standard in mature patients, its early use limits thoracic expansion and spinal growth. Conversely, traditional growing rod (TGR) systems present high complication rates ranging between 40% and 73%, such as hardware failure, implant loosening, and infections, in addition to requiring multiple reoperations for periodic distraction. In this setting, the bipolar fixation technique emerges as a modular, less invasive alternative, allowing three-dimensional deformity control while preserving growth.
• Chapter Objective: This chapter aims to train spine surgeons, orthopedists, and neurosurgeons in the theoretical and practical understanding of the bipolar fixation technique for neuromuscular scoliosis. The reader will learn to select appropriate candidates, recognize indications and contraindications, understand the biomechanical concepts of proximal and distal poles, master the surgical technique steps with and without the self-distracting connector (New Expandable Mechanically Operated Sliding Tool – NEMOST), prevent and manage mechanical or infectious complications, and identify the role of emerging technologies, such as robotic navigation.
• Biomechanical Concepts and Implant StructureBipolar fixation is based on a modular assembly without fusion of the intermediate spinal segment, anchored at two main poles interconnected by two 5.5 mm longitudinal rods (titanium or cobalt-chromium) and transverse connectors (FIGURE 1). The proximal pole consists of supralaminar and pedicle thoracic hooks arranged in a "double claw" configuration across two levels separated by a free vertebra, providing high resistance to pull-out and rotational forces. The distal pelvic pole employs cannulated iliosacral screws (TANIT system) inserted via a minimally invasive technique, transfixing the iliac bone into the S1 body through multidirectional connectors. The construct acquires an "Eiffel Tower" geometry, optimizing load distribution. For skeletally immature patients, the system can incorporate the NEMOST self-distracting connector (FIGURE 2), composed of a toothed rod and a unidirectional sliding domino that advances approximately 1 mm progressively with patient growth, eliminating repeated reoperations for lengthening.
• Indications and ContraindicationsThe technique is indicated for immature patients (> 18 kg) with progressive scoliosis (> 50°) of neuromuscular, syndromic, or complex congenital etiology, aiming to preserve pulmonary and thoracic development. It is also highlighted in low-weight, malnourished, or severely compromised neuromuscular patients considered inoperable for conventional long arthrodesis due to high surgical risk and bleeding. It is further applied as a salvage procedure in mechanical failures of traditional growing rods. Absolute contraindications include rigid deformities with prior bony fusion or ankylosis, complex congenital deformities with extensive segmentation failures (e.g., Klippel-Feil or Jarcho-Levin syndromes), active infection, weight below 18 kg (high risk of implant prominence, pain, and skin breakdown), and extremely reduced life expectancy.
• Technical Details and Individual VariationsSurgery is performed under general anesthesia and neuromonitoring in the prone position. Two posterior midline incisions (thoracic and lumbosacral/pelvic) are utilized with muscle-sparing intramuscular dissection (Wiltse approach distally). Rods are contoured and passed in the submuscular plane, correcting the deformity through cantilever maneuvers and asymmetric traction/compression. In non-ambulatory patients with pelvic obliquity, pelvic fixation with iliosacral screws is prioritized to reestablish spinopelvic alignment and sitting balance. In ambulatory patients, distal lumbar fixation with pedicle screws (2 to 3 levels) is used, preserving lumbosacral mobility and gait.
• Clinical Outcomes, Complications, and PerspectivesStudies with follow-up exceeding 5 years show Cobb angle reduction greater than 50%, pelvic obliquity correction between 70% and 77%, and spinal height gain of up to 1.5 mm/month with the automatic connector. Lower complication rates and lower blood loss occur compared to traditional fusion. Progressive peri-implant ankylosis frequently renders scheduled final arthrodesis unnecessary. Complications include superficial infections, implant loosening, symptomatic hardware prominence, and jamming of the self-distraction mechanism resulting from sagittal alignment errors, axial rod rotation, or bony impingement. The future points toward 3D navigation and robotics for precise iliosacral screw and hook placement, optimized metal alloys, and biocompatible surfaces.
• Clinical Application: Clinical application of bipolar fixation requires rigorous screening of the neuromuscular patient. Planning should be grounded in full-length radiographs and computed tomography to map pedicular, laminar, and iliac anatomy. In decision-making, distal pole definition correlates with functional capacity: ambulatory patients should receive distal lumbar fixation to preserve pelvic function during gait, whereas non-ambulatory patients require pelvic anchorage with iliosacral screws to correct obliquity and optimize seated posture. During technical execution, the surgeon must use continuous fluoroscopy or navigation to ensure safe iliac transfixation into S1 and verify the absence of spinal canal impingement during proximal hook insertion. When using the NEMOST self-distracting connector, testing free mechanical sliding of the domino before closure is mandatory, ensuring that sagittal contouring and rod rotation do not generate excessive friction. Postoperative follow-up must monitor spinopelvic alignment evolution, skin integrity in emaciated patients, and continuous self-lengthening progression.
