Dual-Rod Instrumentation Via the Anterior Approach for Thoracolumbar and Lumbar Adolescent Idiopathic Scoliosis

Abstract

Background: Posterior spinal fusion with pedicle screw instrumentation is currently the standard technique for spinal surgery. However, the anterior approach remains useful for thoracolumbar and lumbar (TL/L) lesions, such as in adolescent idiopathic scoliosis (AIS) 1–4 and spinal injuries 5,6 . We previously documented that long-term radiographic findings and clinical measures were satisfactory in patients with TL/L AIS treated with anterior dual-rod instrumentation 1 . Description: This surgical technique is indicated for single TL/L (Lenke 5) curves and is performed with use of extrapleural retroperitoneal approaches. The extrapleural cavity is connected to the retroperitoneal space by diaphragmatic transection. The lateral aspect of the vertebral bodies is exposed by retracting the psoas major muscle posteriorly from the intervertebral discs. Segmental vascular bundles are divided with coagulation and/or ligation. Care should be taken to reflect the psoas in its entirety and avoid an intramuscular approach to prevent bleeding injury to nerves, including the femoral, ilioinguinal, and genitofemoral nerves, as well as ureteral injury. After the intervertebral discs and cartilage plates are removed to the vertebral end plates, 2 screws are inserted in each vertebral body through a vertebral staple 1,4 . The anterior rod is then placed in the screw heads and rotated anteriorly, providing 3-dimensional correction of kyphotic deformities with lordosis production 1,4 . After the posterior rod is applied in the same manner as the anterior rod, compression forces are applied between the screws to correct scoliosis 1,4 . The compression force is first applied to the posterior rod so that kyphosis can be corrected more effectively 1,4 . Alternatives: Posterior pedicle screw instrumentation techniques are widely utilized for TL/L AIS curve correction. However, anterior techniques have frequently also been applied to the curve. Dwyer et al. 7 first reported the use of anterior spinal fusion (ASF) with a single braided cable connecting vertebral screws for the treatment of TL/L AIS, and Zielke et al. 8 modified that procedure by replacing the cable with a threaded rod. Although these instrumentation techniques and other single anterior rod techniques such as the Texas Scottish Rite Hospital System effectively correct scoliosis in the coronal plane and improve vertebral derotation 1,9 , poor sagittal and rotational plane deformity correction, implant weakness, and high incidence of pseudarthrosis remain unresolved issues 1 . Rationale: The fundamental advantages of the anterior approach in dual-rod instrumentation are the ability to achieve 3-dimensional correction with extremely low rates of pseudarthrosis and implant failure 1,10–12 . Furthermore, the fusion is expected to include fewer motion segments than with posterior systems (usually 1 level less distally and proximally). However, low skeletal maturity and a TL/L to thoracic Cobb ratio of <1.25 appeared to be important factors for postoperative curve progression of the thoracic coronal deformity following ASF for the treatment of Lenke 5 curves 1,13 . In addition, subjacent disc wedging may occur when the subjacent disc is nearly parallel before surgery 1,14 . Expected Outcomes: The described technique is expected to provide 3-dimensional spinal correction. In a previous study, 30 patients with Lenke 5 AIS were followed for a mean of 17 years 1 . The mean TL/L Cobb angle correction rate and correction loss were 79.8% and 3.4°, respectively, at the time of the latest follow-up 1 . The average percent of predicted forced vital capacity and of forced expiratory volume in 1 second were 91.8% and 81.8%, respectively 1 . The average total score on the Scoliosis Research Society-30 outcome instrument was 4.21. No instrumentation failure, pseudarthrosis, or clinically relevant neurovascular complications were observed 1 . Important Tips: This technique is applicable to Lenke 5 AIS curves. However, the anterior approach can also be utilized for other TL/L lesions.The anterior procedure is accomplished via extrapleural retroperitoneal approaches with diaphragmatic transection.Care should be taken to reflect the psoas in its entirety and avoid an intramuscular approach to prevent bleeding and nerve and ureteral injuries. Acronyms & Abbreviations: SRS-30 = Scoliosis Research Society-30