Summary of Key Points
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Patient selection is paramount when choosing a lateral approach for a thoracic or lumbar decompression.
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Fluoroscopy or stereotactic navigation is critical to define the anteroposterior and lateral axes prior to incision.
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Mastery of the lateral anatomic constraints of the thoracic and lumbar spine is critical to avoid complications and limit morbidity.
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Continuous neuromonitoring when dilating and docking during a transpsoas approach is essential to potentially avoid or limit injury to the lumbar plexus.
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Stand-alone single and multilevel lateral interbody fusions are still under investigation, and many surgeons still advocate for supplemental instrumentation.
Minimally invasive or minimal access surgery was developed to address the approach-related morbidity associated with open spine surgery. Beginning with the introduction of the microscope by Yasargil to minimize surgical exposure and morbidity, we now use minimal access technology to treat spinal deformity, trauma, degenerative disease, and extradural or intradural tumors. Lateral approaches to the thoracolumbar spine represent an emerging frontier allowing decompression and ventral reconstruction of the thoracolumbar spine while theoretically decreasing morbidity and mortality. This chapter describes minimal access lateral approaches used for decompression of the spinal canal.
Indications for Operative Intervention
Neoplasm
Most neoplastic disorders of the ventral spine are bony metastatic disease. Spinal neoplasms can present with pain, progressive deformity, or neurologic compromise. Operative goals are often to determine histopathologic diagnosis, decompress the neural elements, and provide spinal stabilization. Important considerations for operative intervention include patient age, preoperative functional status, systemic extent of metastatic disease, life expectancy, and medical comorbidities. Nonemergent surgical intervention should be reserved for patients with a life expectancy of greater than 6 months. Urgent or emergent intervention must be considered in the setting of acute or progressive neurologic decline regardless of life expectancy if surgical intervention may significantly improve quality of life. Adjuvant therapy with radiation, chemotherapy, or hormone modulation is often required after surgery; however, in the setting of spinal cord compression, they are often unable to be initiated safely. The surgeon must take all of these factors into consideration when evaluating patients with neoplastic disorders, and minimally invasive approaches can be used to treat these patients while minimizing morbidity and mortality.
Trauma
Thoracolumbar trauma typically occurs at the junction in over 50% of cases involving the levels of T10 to L2. Flexion-distraction and compressive loading forces transmit directly through this transition zone and result oftentimes in vertebral body fractures such as compression or burst fractures with or without traumatic disc extrusions. All traumatic fractures with or without significant loss of height involving the vertebral body in the setting of neurologic injury or when canal compromise is present should be evaluated emergently for surgical consideration. The surgical approach remains controversial and many spine surgeons elect for a dorsal decompression and instrumentation, but minimally invasive reconstruction of the vertebral body through a lateral approach is an emerging option with low morbidity and mortality. Of note in complex fracture patterns where both ventral and dorsal elements are unstable, a ventral construct may be inadequate to resist flexion and distraction forces, and supplemental dorsal stabilization must be considered on a case-by-case basis.
Infection
With advancements in modern medical treatment of infection, patients with discitis and osteomyelitis can be treated effectively without surgery in over 90% of cases. However, surgical strategies must be considered in patients with refractory infections, progressive deformity, intractable pain, or neurologic decline. Operative goals are to aid in identifying the causative organism, debridement of necrotic and infected bone, decompression of neural elements, and spinal column reconstruction and stabilization. Especially above the conus, a dorsal decompression is often inadequate for ventral pathology, and complete evacuation of a ventrally located abscess or phlegmon is not always possible. A lateral minimally invasive approach provides surgeons with direct visualization of the diseased ventral bony elements optimizing decompression while minimizing morbidity. Surgical series have shown anterior instrumentation to be safe in the setting of infection.
Deformity and Degenerative Conditions
Symptomatic deformity of the thoracolumbar spine can occur as a late complication of trauma, previous surgery, infection, or neoplasm. Coronal and sagittal balance can be corrected ventrally with minimal morbidity and mortality through minimally invasive lateral approaches. Multilevel correction will often require supplemental dorsal stabilization. For thoracic disc herniations, studies suggest ventral discectomy is recommended over a dorsal decompression. Whereas laterally located, soft disc herniations can often be approached with a minimally invasive transpedicular strategy, more central, highly calcified disc herniations are unsafe to treat with this approach. Minimally invasive lateral methods represent an excellent approach to this pathology with minimal morbidity.
Minimally Invasive Surgical Approaches for Thoracic Decompression
MIS Transthoracic Approach
Surgical management of thoracic herniated discs, spinal cord compression, or thoracic spine reconstruction can be performed with minimal morbidity through a minimally invasive thoracotomy with or without thoracoscopic assist. Absolute contraindications to this approach would be patients who cannot tolerate one-lung ventilation or complex anatomy of the great vessels. A dual-lumen endotracheal tube is crucial to allow deflation of the lung on the operative side. The patient is placed in the lateral decubitis position with the side of the target pathology up ( Fig. 73-1A ). If pathology is midline, left side up is generally preferred to reduce risk of major vessel injury as the vena cava is much more fragile. An axillary roll is placed to prevent injury to the contralateral brachial plexus during surgery and securing the patient to the operative table ensuring the spine remains perpendicular to the floor at the desired level are critical. Under fluoroscopic guidance, the level of interest should be localized and an incision should be marked out parallel to the contour of the rib cage one to two rib levels above this location to maximize the working angle for surgery. Subperiosteal dissection of the rib should be performed to preserve the neurovascular bundle superiorly. A 3- to 4-cm section of the rib can be harvested if necessary for a wider exposure. At this point, the parietal pleura can carefully be opened with Metzenbaum scissors and the lung deflated, or using blunt dissection along the rib cage, the first dilator can be carefully swept along the rib leading at the level of interest confirmed by fluoroscopy ( Fig. 73-1B ). The dilators can carefully be progressively placed, and a minimally invasive retractor system can be used to create the working space for the procedure ( Figs. 73-1C–E ). A microscope can aid in visualization through the retractor system but is optional according to surgeon preference, as most retractor systems utilize internal fiberoptic lighting systems. For treating pathology within the spinal canal such as a herniated disc ( Figs. 73-2A–D ), the retractor should be opened enough in the anteroposterior plane to visualize the ventral margin of the vertebral body and dorsal elements including the foramen and pedicle. A helpful strategy, especially applicable for large, calcified disc herniations, is to resect a portion of the vertebral bodies on either side of the disc space that is as large craniocaudally as the disc fragment ( Figs. 73-2E and F ), creating a cavity ventral to the herniation. The pedicle can be removed with an osteotome, high-speed drill, or Kerrison rongeurs to visualize the ventral thecal sac ( Figs. 73-2G and H ), and the disc fragment can then be safely mobilized and pushed away from the neural elements anteriorly. For corpectomies, a similar technique can be employed with egg shelling and detaching the dorsal vertebral body ventrally away from the spinal cord to prevent neurologic injury.
Thoracoscopic-Assisted MIS Approach
A multidisciplinary approach to lateral MIS approaches has gained popularity, with access surgeons performing a thoracoscopic-assisted approach. This approach allows the surgeons to gain direct visualization of the thoracic cavity prior to performing critical aspects of tissue dissection and docking of the retraction system. A 1- to 2-cm incision is created typically two to three rib levels below and 5 to 6 cm anterior to the primary working incision. After subperiosteal dissection is performed preserving the neurovascular bundle, Metzenbaum scissors are used to open the pleura. An endoscope can then be introduced and the lung deflated to allow direct visualization. The lung can be inspected and mobilized anteriorly if any scarring is present using this technique. Moreover, under direct visualization the access site for the retractor system can be opened. Then, after careful dissection and hemostasis is achieved, the dilator tubes can be placed one by one directly over the level of interest and confirmed by fluoroscopic and direct visualization with the endoscope. After docking is achieved, the critical aspects of the decompression can be performed in a similar fashion. After removal of the docking system, endoscopic suction, irrigation, and aspiration allow the access surgeon to ensure all bleeding from retractor placement, the surgical site, as well as the retractor access site is addressed. After hemostasis is achieved, a chest tube or pigtail catheter is typically left in place and can be inserted through the access site and placed to suction for 24 to 48 hours postoperatively.
MIS Extracavitary Approach
Surgical management of severe destructive pathologies such as metastatic tumors, trauma, or vertebral osteomyelitis can be a complex endeavor, requiring a corpectomy at the affected level. A minimal access version of the lateral extracavitary approach allows percutaneous pedicle screw instrumentation combined with a minimally invasive corpectomy from a more lateral approach enhancing ventral exposure and decompression while minimizing morbidity. Using fluoroscopic guidance, a 3- to 4-cm vertical incision can be made 4 cm off midline down to the fascia. A K-wire can be percutaneously placed through the posterolateral thoracic musculature docking onto the lateral aspect of the facet joint at the level of interest. Sequential soft tissue dilators can be used to dilate to a 24-mm tubular retractor system secured with a flexible arm. Using a combination of subperiosteal dissection and electrocautery, the transverse process can be identified and removed, exposing the rib head above and below the level of interest. The rib heads can be removed using either an osteotome or a high-speed drill. The pedicle is identified, and for a corpectomy, the pedicle is removed under direct microscopic visualization, exposing the lateral aspect of the thecal sac. The posterior vertebral body wall can then be identified and the corpectomy can be completed in standard fashion. Of note, as with an open approach, pathology involving the contralateral, dorsal aspect of the vertebral body can be impossible to access through this approach unless access is carried out bilaterally. Blood loss may be limited secondary to the small working corridor, but the approach has a steep learning curve with increased operative time and unfamiliarity with a new working angle and retractor system. The use of fluoroscopy or computer-assisted navigation is recommended.
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