The Role of Anterior Surgery for Thoracolumbar Deformity

Anterior Versus Posterior Approaches to Spinal Deformity

The surgical management of spinal deformity has evolved with the development of surgical techniques and approaches. The evolution of anterior spine surgery has changed significantly regarding surgical invasiveness and approaches. Spinal deformity attributed to developmental pathology and infection has been an important driver of innovation in anterior surgical approaches. Infections of the spine and joints have led to important developments in surgical approaches and techniques. Tuberculosis characteristically affects the anterior column of the spine in the lower thoracic and upper lumbar regions. ^, Kyphosis and spinal cord compression from vertebral body osteolysis have been important surgical challenges in Pott disease. ^, The earliest report of debridement of the anterior column of the spine was in 1894 by Victor Menard, who described assessment of abscess formation in the anterior column of the spine with a costotransversectomy approach. In 1906, Muller described a transperitoneal approach to the lumbar spine for debridement of tuberculosis. In 1934, Ito, Tsuchiya, and Asami reported a series in which they used a retroperitoneal approach to the lumbar spine for debridement and reconstruction. Hodgson and Stock developed an anterior approach to the thoracic spine for tuberculosis, and discovered that the anterior approach is the most thorough method for an effective debridement of caseous material, granulation tissue, and bony sequestra, as well as the most effective approach for loading the bone graft for fusion in a stable reconstruction. For developmental deformity of the spine, Capener described the ventral approach for transosseous fixation in spondylolisthesis in 1932, followed by a description by Burns in 1933. ^, The development of techniques for anterior approaches to the thoracic and lumbar spine and fixation systems for the ventral spinal column have enabled surgeons to effectively achieve deformity realignment and stabilization using an anterior approach.

Advantages of the Anterior Approach to the Spine

The anterior approach to the thoracic and lumbar spine offers significant advantages compared with posterior surgery. The anterior approach facilitates direct access to ventral pathology that may be causing neural compression or deformity, including infection or tumor. Removal of intervertebral disc material and vertebral end plate preparation are more effective with an anterior approach compared with a posterior-based approach. ^, An anterior discectomy with interbody grafting provides a larger surface area for fusion and space for larger implants for structural support, maximizing the biological environment for fusion. ^, Bone graft in the anterior interbody space is loaded in compression, which optimizes the mechanical forces for new bone formation. In contrast, fusion in the posterolateral space is compromised by limited surface area for fusion and less compressive loading.

Structural interbody grafting with autograft, allograft, or synthetic materials is useful in reconstruction of the anterior column of the spine, with restoration of lordosis and correction of vertebral obliquity. Complete discectomy, including release of the anterior longitudinal and posterior longitudinal ligaments and annulus fibrosus, provides significant segmental mobility to the spine. The end plate of the vertebral body consists of dense cancellous bone that is most resistant to compressive forces at the apophyseal regions. Interbody implants are useful for structural support of spinal realignment and for creating segmental lordosis, as well as for indirect decompression of the spinal canal. With complete release of the annulus of the disc anteriorly and posteriorly, the anterior lumbar interbody fusion (ALIF) technique can facilitate indirect compression of the neural elements by significantly improving foraminal space measured by pedicle-to-pedicle distance. The interface between bone and interbody implant is important to maintain realignment of the spine and to avoid subsidence of the implant into the vertebral body. End plates are prepared with care to avoid penetration of the dense cancellous bone of the end plate. Exposure of the trabecular bone within the vertebral body is important in surgical technique. Implant position and surface area are also important in avoiding subsidence and loss of correction, although at physiological loads implant subsidence may be observed even with support of posterior fixation.

The distribution of lordosis is an important consideration in reconstructive surgery for spinal deformity. Burkert and Bridwell described the normal segmental alignment of the spine in asymptomatic volunteers and demonstrated that more than 60% of lumbar lordosis comes from the segments at L4 to S1. Roussouly et al. classified spinal alignment into four distinct patterns based upon sacral slope and apex of lordosis. Restoration of sagittal profiles according to the Roussouly classification of lordosis distribution and apex of lordosis is important to avoid junctional complications in deformity surgery. ^, Yilgor and the European Spine Study Group described the Global Alignment and Proportion (GAP) score as a predictor of complications after spinal reconstruction for thoracolumbar deformity. The distribution of lordosis in the region L4 to S1 relative to the upper lumbar spine is an important radiographic component of the GAP score. Ohba showed that the GAP score correlates with the Oswestry Disability Index (ODI) and with increased proximal junctional angle 2 years after surgery, and concluded that appropriate restoration of lordosis from L4 to S1 is a priority for optimal sagittal spine pelvic alignment and for favorable outcomes of corrective spinal surgery.

The anterior lumbar fusion at L3 or L4 to S1 facilitates effective and appropriate restoration of lordosis in the lower lumbar spine. In contrast, posterior-based techniques for creating lumbar lordosis may be compromised by inappropriate distribution of lordosis. The three-column osteotomy for restoration of lordosis in patients with prior circumferential fusion commonly restored lordosis above L4, and was associated with high rates of rod failure and junctional kyphosis. Restoration of physiological lordosis in spinal deformity surgery is significantly more reliable with ALIF compared with posterior-based transforaminal lumbar interbody fusion (TLIF) or posterior lumbar interbody fusion (PLIF) approaches. In a systematic review of seven studies comparing ALIF with TLIF, the ALIF approach was significantly more reliable in restoring lordosis at L4 to S1. In a comparison of techniques of interbody fusion, Mobbs et al. demonstrate that the ALIF technique is more reliable when considering alternatives, including TLIF, PLIF, and lateral lumbar interbody fusion, in restoring lordosis at L4 to S1. The benefit of anterior and posterior surgery compared with posterior-only surgery for adult deformity has been demonstrated in multiple case comparison studies. ^{, ,} In summary, ALIF is an effective and useful technique for restoration of lumbosacral lordosis and physiological alignment of the lumbar spine in reconstruction for deformity.

Although the ALIF approach has significant advantages compared with posterior-based surgery in terms of restoration of physiological lordosis at L4 to S1, interbody implant loading and subsidence, and indirect decompression of the neural elements, the posterior-based approach to thoracolumbar deformity may be appropriate in some cases. The posterior approach is familiar to all spine surgeons, can be performed in a single stage, and does not require the assistance of a vascular or general surgeon. The use of posterior-based osteotomies permits progressive destabilization of the spinal column, and mobilization of the spine. Schwab et al. classified posterior-based osteotomies based upon the extent of mobilization of the spinal column. Luhmann et al. demonstrated that, using pedicle screw constructs, anterior release was not necessary for correcting coronal or sagittal deformity or enhancing fusion rates in patients with thoracic adolescent idiopathic scoliosis (AIS) deformity with curves ranging from 70 to 100 degrees. Similarly, in the lumbar region of adult spinal deformity, Kim et al. demonstrated that posterior segmental instrumentation without anterior release of the lumbar spine demonstrated better outcomes using Scoliosis Research Society outcome scores, without significant differences in radiographic parameters. Crandall and Revella compared ALIF to PLIF as an adjunct to posterior-based correction for adult spinal deformity and reported no significant difference in clinical outcomes or complication rates. Radiographic, visual analog score, and ODI outcomes amongst both PLIF and ALIF patients were similar as well. Table 146.1 summarizes the advantages of the anterior and posterior approaches to thoracolumbar deformity.

The anterior approach to the thoracolumbar spine may be associated with significant morbidity ( Fig. 146.1 ). Kim retrospectively reported on associated complications and patient satisfaction rates in 62 patients who underwent anterior surgery for deformity treatment. In patients undergoing an open thoracolumbar approach for deformity, with anterior interbody fusion at two to 12 levels (mean 5.6), there was a high rate of dissatisfaction with the anterior approach, with complaints including pain, pseudohernia, and functional limitations related to the approach. The development of minimally invasive direct lateral and antepsoas approaches to the lumbar spine may reduce the morbidity of the anterior approach to the thoracolumbar spine. The sections below provide specific information regarding the spectrum of anterior approaches to the thoracolumbar spine.

Surgical Approaches to the Anterior Thoracolumbar Spine