DEFINITION

Anterior thoracic approaches provide a means of decompression, stabilization, and fusion for a variety of spinal pathologies, such as deformity, trauma, infection, tumors, and disc herniations.

 

 

ANATOMY

 

The thoracic vertebral bodies are heart-shaped in the axial plane.

 

 

 

The thoracic pedicles are oval and are larger superoinferiorly than mediolaterally. The T4 pedicle is the smallest in width with a mean10 of just 4.4 mm.

 

The progression of width starts with the largest at T12, decreasing to T4, and increasing again from T3 to

T1.

 

The average height is 8 to 15 mm and the average width is 3 to 10 mm.

 

The medial cortex is the thickest; however, there is no epidural space between the medial cortical edge and the dura.19

 

The facet joints are situated more anteriorly and articulate superiorly and inferiorly with a rib. As the transition from the thoracic to lumbar spine occurs, the thoracic vertebrae begin to resemble the lumbar vertebrae and the facets change from a coronal orientation to one that is more sagittal.

 

PATHOGENESIS

Intervertebral Disc Herniation

 

Thoracic disc herniations are uncommon, making up only 1% of all operable intervertebral disc herniations.16

 

Seventy-five percent of thoracic disc herniations occur between T8 and L1, with T11-T12 being most common. They are classified as central, centrolateral, lateral, or paramedian.

 

 

Most herniations occur central or centrolateral and are often calcified.

 

Bimodal distribution with traumatic etiology (discussed in the following text) is common in acute herniated nucleus pulposus (HNP) in the young and degenerative HNP in the elderly.16

 

The spinal canal in the thoracic spine is relatively small.

 

 

Neurologic consequences occur from direct anterior compression of the spinal cord from a herniated disc. There can be posterior displacement of the cord and local vascular insufficiency.

Infection

 

The mechanism of spinal infections is controversial. Proposed routes of infection include hematogenous spread from other infected foci, local extension from nearby infections, and direct inoculation.

 

The two proposed routes of hematogenous spread are venous and arterial.

 

Advocates of venous hematogenous spread argue that organisms are carried to the spine via the plexus of Batson, similar to the mechanism of tumor metastasis.2

 

Proponents of arterial hematogenous spread note that the metaphyseal bone near the anterior longitudinal ligament is an area where infections typically begin. This region has an end-arteriole network that is susceptible to bacterial seeding.22

Tumor

 

Most spine tumors are of metastatic origin. The spinal column is the most frequent site of skeletal metastasis.21

 

Malignant cells are carried to the spine through the valveless, extradural venous plexus of Batson.2,8 A recent anatomic model suggests that malignant cells can also metastasize through the segmental arteries.23

Trauma

 

 

The articulation of the vertebral column, ribs, and sternum makes the thoracic spine relatively stable.1 High-energy injuries are frequently required to produce injury to the thoracic spine.

 

Forces associated with injury are axial compression, flexion, lateral compression, flexion-rotation, shear, flexion-distraction, and extension.

 

Traumatic herniations are most common at T11-T12 secondary to true costovertebral joint and transition to more sagittally oriented facets, both allowing for increased flexion-extension moments.

 

NATURAL HISTORY

Intervertebral Disc Herniation

 

Surgical indications are similar to lumbar/cervical: myelopathy, intractable radicular pain that has not improved with conservative measures, and progressive neurologic deterioration.

 

Wood et al24 described 20 patients with asymptomatic thoracic disc protrusions followed by magnetic resonance imaging (MRI). All patients remained asymptomatic at an average of 26 months, and most disc herniations were smaller or unchanged on repeat MRI.

 

 

It is unknown how often asymptomatic thoracic herniations become symptomatic.

 

 

Brown et al3 reported on 55 patients with 72 thoracic disc herniations. Fifty-four were treated initially with conservative therapy and 15 eventually required surgery. Nine of 11 patients with lower extremity complaints went on to

 

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have surgery. Two patients had myelopathy and were treated surgically. All 55 patients ultimately returned to their previous level of activity.

 

 

Patients with lower extremity symptoms and myelopathy are likely to require surgical intervention.

Infection

 

Vertebral osteomyelitis is rare and accounts for 2% to 4% of all cases of osteomyelitis.

 

 

Staphylococcus aureus is the most common organism, accounting for almost 50% of pyogenic infections.5

 

The incidence is rising as a result of a growing immunocompromised and elderly patient population, increased intravenous drug abuse, and an increase in invasive diagnostic and therapeutic procedures.

 

Before medical and surgical treatment, spinal osteomyelitis carried a mortality rate of greater than 70%.12 The advent of antibiotics and anterior spinal débridement techniques has reduced mortality to less than 15%.6,15

 

Carragee6 reported on 72 patients treated nonoperatively with antibiotics. Over 33% of them required surgical débridement. Results were related to patient age and immune status.

 

Tumor

 

Over 90% of spinal tumors are metastatic lesions with a distant primary source.

 

Primary tumors from the breast, prostate, lung, kidney, and thyroid are most likely to metastasize to the vertebral column.21

 

Tumors that affect the anterior elements of the spine can be benign or malignant.

 

Benign primary tumors that have a predilection for the anterior elements include giant cell tumors and hemangiomas. Malignant tumors that commonly affect the anterior elements include osteosarcomas,

chondrosarcomas, myelomas, and lymphomas.18

 

 

Improved diagnostics have allowed for more accurate diagnosis and improved staging.11 Chemotherapy and radiotherapy have improved survival and local control.17

 

Treatment goals include preservation of neural function, spinal stability, margin-free tumor resection, and

correction of deformity.

 

Trauma

 

Fractures of the thoracolumbar spine are the most common spinal injuries.

 

 

The thoracic spine configuration of vertebrae, sternum, and ribcage confers an inherent stability.1

 

Injuries to this region require significant force, and unstable injuries are usually a result of high-energy injuries such as motor vehicle accidents, falls from heights, and crush injuries.

 

Patients can have associated injuries such as pneumothoraces, pulmonary contusions, and vascular injuries.

 

Although most thoracic injuries do not involve neurologic deficit, complete neurologic deficits are more common with thoracic spine injuries due to the small neural canal, the tenuous blood supply, and the high

energy needed to cause injury.4

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

Neurologic status is examined.

 

 

 

Manual motor testing of the lower extremities may detect a mass effect on the corticospinal tract. Pinprick and light touch sensory examination may help to localize the cord level of injury based on

dermatome.

 

 

Babinski reflex and clonus are upper motor neuron signs, indicating a potential thoracic cord compression. Reflex examination of the patellar and Achilles tendons: Hyperactivity is an upper motor neuron sign.

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

It is often useful to obtain an MRI and a computed tomography (CT) myelogram preoperatively. MRI is the key radiologic study to confirm the diagnosis and localize pathology. Plain CT scans are helpful in delineating bony anatomy. As with all spinal imaging, it is imperative to correlate imaging with physical examination findings.

 

A plain CT scan should be obtained in concert with MRI on every patient with a destructive bony process, such as tumor or infection, to preoperatively assess the degree of bony loss and determine the optimal strategy for reconstruction.

 

CT myelography may be needed if MRI scans cannot be obtained or if quality of the MRI is suboptimal due to patient movement, metal artifact from prior implants, or other factors.

 

 

CT can detail ossification of the posterior longitudinal ligament (PLL) or ligamentum flavum.

 

CT myelography can also clarify whether cord compression is primarily anterior secondary to a disc fragment or circumferential due to stenosis.

 

 

DIFFERENTIAL DIAGNOSIS

Spinal tumors Infections Transverse myelitis

Ankylosing spondylitis Fractures

Intercostal neuralgia Herpes zoster

Cervical and lumbar herniated discs Disorders of thoracic and abdominal viscera Amyotrophic lateral sclerosis

Multiple sclerosis Arteriovenous malformations

 

 

NONOPERATIVE MANAGEMENT

Intervertebral Disc Herniation

 

In the absence of myelopathy, most patients can be treated conservatively.

 

A conservative treatment plan should include nonsteroidal anti-inflammatories, activity modification, and physical therapy focusing on trunk stabilization.3

 

Other options include selective intercostal nerve blocks and pharmacotherapy such as narcotics, tricyclic

antidepressants, serotonin reuptake inhibitors, and certain antiepileptics.

 

Infection

 

Carragee6 showed that white blood cells (WBC) is normal in over half of patients with vertebral osteomyelitis, whereas

 

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erythrocyte sedimentation rate (ESR) was elevated in all with normal immune status.

 

 

 

Vertebral infections should be treated nonoperatively with culture-specific antibiotics and spinal immobilization. Open or CT-guided biopsy can aid in targeting appropriate antibiotic treatment.

 

 

Treatment frequently involves 6 weeks of parenteral antibiotics followed by a course of oral antibiotics. An infectious disease consultant can help guide the antibiotic regimen.

 

 

External immobilization with an orthosis can help stabilize the spine, decrease pain, and prevent deformity. Bracing is particularly important in patients with greater than 50% destruction of the vertebral body because they are at greater risk for deformity.7

 

Response to treatment can be followed clinically with ESR.

 

Tumor

 

A multidisciplinary approach including a neuroradiologist, pathologist, oncologist, and spine surgeon is used to treat spinal tumors.

 

A CT-guided biopsy can help establish a diagnosis in 76% to 93% of lesions.11,21

 

Metastatic lesions that do not compromise spinal stability and without rapid neurologic progression can be managed nonoperatively.21

 

 

Nonoperative treatment can include radiation, chemotherapy, embolization, and bracing. Most primary spinal tumors require operative treatment.

Trauma

 

Most thoracic and thoracolumbar spine injuries can be effectively treated nonoperatively.

 

Conservative treatment can include recumbency, bracing, and pain management for patients without neurologic deterioration and with a structurally stable injury.13,20

 

Decubitus ulcers, thromboembolism, urinary tract infections, and late pain are complications reported with nonoperative treatment.14

SURGICAL MANAGEMENT

 

Indications for discectomy

 

 

Presence of myelopathy on presentation

 

 

Progressive neurologic symptoms, primarily weakness or paralysis Radicular pain refractory to conservative therapy

 

Deformity correction

 

Indications for corpectomy

 

 

 

 

Fractures with anterior spinal cord compression Metastatic or primary thoracic tumors Osteomyelitis

 

 

Sequestered disc herniations that have migrated behind the vertebral body Ossification of the PLL

 

Indications for bone grafting and cage or allograft placement

 

 

Infection

 

 

Although somewhat counterintuitive, anterior spinal infections can be successfully managed with allograft, cage, or instrumentation reconstruction if a thorough débridement of infected tissues is performed and postoperative antibiotics are administered.

 

 

Tumor Trauma

 

Degenerative disease

 

 

Deformity correction (scoliosis, kyphosis) Indications for polymethylmethacrylate (PMMA) use

 

 

Anterior column reconstruction of tumors in patients with a life expectancy of less than 1 year Patients in whom the use of radiation or chemotherapy is anticipated

 

Indications for plate fixation

 

 

 

 

Anterior and middle column instability Revision of failed posterior fusion Pseudarthrosis

 

Indications for use of solid rod instrumentation

 

 

Patient younger than 30 years of age

 

Thoracic and thoracolumbar curves of less than 65 degrees (Cobb angle)

 

Thoracic or lumbar compensatory curves that correct to less than 20 degrees with side bending

 

Hypokyphosis (<20 degrees from T5 to T12)

TECHNIQUES

• Thoracic Discectomy

After elevating the articular ligaments of the costotransverse and costovertebral articulations, the remaining rib head is excised (TECH FIG 1).

The superior edge of the pedicle of the caudal vertebra is resected with a rongeur to expose the dural tube.

To find the disc herniation, the surgeon follows the superior edge of the pedicle to the vertebral body and

 

disc space.

 

The disc herniation is removed using small-angled curettes and pituitary rongeurs.

 

Discectomy can be facilitated by removing a small portion (1 to 2 cm) of the adjacent vertebral bodies. If the disc is extremely calcified or has migrated behind the vertebral body, it is helpful to perform hemicorpectomies of the adjacent vertebral bodies.

 

The portion of the disc that lies away from the ventral aspect of the spinal cord should be removed first. Once a cavity is created by removing this initial disc and bone, the rest of the disc can be removed into this cavity, ensuring that all forceful maneuvers are directed anteriorly away from the thecal sac.

 

We prefer to keep the PLL intact whenever possible, as its removal often results in substantial epidural bleeding. We will pass an elevator or nerve hook through a rent in the PLL if one is present to ensure adequate decompression from pedicle to pedicle. If the PLL needs to be removed, we use bipolar cautery to cauterize the PLL and then carefully remove it with either a Kerrison or a combination of pituitary rongeur and curette.

 

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TECH FIG 1 • The rib head can be removed with a high-speed burr once the costotransverse and costovertebral articulations are excised.

• Minimally Invasive Thoracic Discectomy

   

  The patient is positioned prone on radiolucent Jackson-type table.

   

  C-arm anteroposterior (AP) localization of desired level with attention to cephalocaudal orientation for flat appearing endplates

   

  A 2- to 3-cm vertical incision is made through skin and fascia lateral to midline, just lateral to facet so that an obliquely oriented working tube may dock with medial third over the lateral facet complex overlying desired disc space (TECH FIG 2).

   

  Blunt dissection may be carried out manually with a finger down to the facet complex or the surgeon may begin initial blunt dissection with progressive tubular dilators such as the METRx port system docking in the desired position described earlier.

   

   

   

  TECH FIG 2 • A. Posterolateral approach to the thoracic disc space. B. The obliquity of the dilator tube allow for bilateral decompression without spinal cord manipulation.

   

   

  Confirmation of appropriate position of the dilator tubes is obtained with AP (medial third of tube over lateral facet) and lateral radiographs (disc space at center of tube with flat endplate appearance).

   

  Lock tube to secure table-mounted flexible arm and bring in microscope.

   

  Insulated unipolar and bipolar cautery along with pituitary and Kerrison are used to dissect remaining overlying tissue until facet complex/transverse process junction is encountered.

   

  Using the high-speed burr, remove the cranial portion of the transverse process and lateral aspects of the facet joint until the ligamentum flavum is encountered.

   

  76

   

  Carefully remove the ligamentum flavum from the underlying nerve root and lateral edged of the spinal cord. The herniated disc should now be visible and may be removed under direct visualization without any retraction of the spinal cord.

   

  The obliquity of the approach provides almost a lateral view of the disc space interface, allowing for bilateral decompression through a single annulotomy.

   

  Using a no. 11 blade with nerve root retractors protecting the cord medially and the exiting nerve root inferolaterally, a cruciate or box annulotomy is made.

   

  The desired amount of degenerative nucleus pulposus is removed; the disc space is pressure-irrigated through the annulotomy and after hemostasis is achieved, the tube is removed.9

• Thoracic or Thoracolumbar Corpectomy

   

  The posterior aspect of the vertebral body is identified.

   

   

   

  Discectomy is performed above and below the level of the corpectomy. The lateral annulus is incised using a no. 10 blade to the anterior midline. An elevator is then used to separate the disc from the endplates.

   

  Discectomy is completed using curettes and rongeurs.

   

  Attention is turned to the vertebrectomy. Using a 4-mm burr, the surgeon removes most of the bone from the vertebral body.

   

  Corpectomy is completed by removing the remaining bone with a rongeur (TECH FIG 3).

   

  Depending on the nature of the pathology, the PLL may need to be removed for the purposes of decompression.

   

  For retropulsed fracture fragments, the fragments are first thinned using a high-speed, 4-mm, ball-tipped burr.

   

  Then a thin, sharp curette is used to peel the fragments away from the dura and into the created trough.

   

  It is important to work quickly but carefully at this point as there can be a significant amount of epidural bleeding.

   

  The posterior cortical fragments are removed from the contralateral (deep) side of the canal first so that the bulging dura will not obscure the rest of the fragments.

   

   

   

  TECH FIG 4 • Application of plate and screws. A. Osteophytes are removed, and a trajectory is planned parallel to the endplate and angled slightly anteriorly to avoid penetration of the canal. B. Nuts secure the posterior bolts, and screws are applied anteriorly. C. It is important for the screws to be a safe distance from the dural covering of the spinal cord.

   

   

   

  TECH FIG 3 • Corpectomy site.

   

   

  Decompression is adequate when the dura can be seen bulging into the corpectomy trough and the spinal canal has been decompressed throughout its complete width.

  Plating

   

  A flat surface is prepared for the plate by removing lateral endplate prominences and rib heads with a high-speed burr.

   

  Using an awl insertion guide, a posterior bicortical thoracic bolt is placed at the cephalad and caudad fixation levels.

   

  The trajectory should be parallel to the endplate and angled slightly anteriorly to avoid penetrating the canal (TECH FIG 4A).

   

  77

   

  If sagittal correction or interbody graft placement is needed, distraction is performed on the endplates using a lamina spreader.

   

  A correct length plate is applied over the bolts without extending into the adjacent disc spaces (TECH FIG 4B,C). Nuts are applied loosely to secure the plate to the posterior bolts.

   

  Using a drill or awl, correct length anterior screws are placed angling slightly posteriorly.

   

  In general, bicortical screws are preferred because the cancellous bone of the vertebral body provides relatively weak purchase, especially in patients with tumors or infections.

• Screw-Rod Instrumentation

   

  Use of an anterior screw-rod construct allows for correction of coronal plane deformity through fusion of fewer spinal motion segments compared with posterior instrumentation.

   

  The entry position for the anterior vertebral screws is determined based on the location of the vertebral foramen, as this identifies posterior body cortex.

   

   

   

  TECH FIG 5 • Application of screw-rod instrumentation.

   

   

  The surgeon inserts the most cephalad and caudal screws first in the midlateral vertebral body at the same distance from the posterior cortex (TECH FIG 5).

   

  The screw tips should engage the far cortex of each vertebra and should be directed toward the posterolateral corner of the vertebra.

   

  The rest of the screws are placed in similar fashion.

   

  The rods are inserted as directed by the particular system, and alignment is corrected before tightening.

• Bone Grafting and Cages

 

 

It is of utmost importance to prepare an adequate fusion bed. A thorough decortication is performed.

 

Although placement of the graft on preserved bleeding subchondral endplates is preserved, creating a slot or peg hole in the adjacent vertebral bodies can help to prevent graft extrusion.

 

Before graft placement, kyphotic deformity can be corrected by distracting adjacent vertebrae.

 

Extreme care must be taken to avoid injury to the adjacent endplates during distraction, especially in patients with osteoporosis or other states with compromised bone quality (tumors, infections).

 

After the graft has been anchored, compression locks the graft in position.

 

 

If tricortical iliac crest bone is used, we prefer to have the cortical smooth surface face the spinal canal. Single-level corpectomy defects can be supported with tricortical iliac crest grafts, whereas larger defects

are better stabilized with autogenous fibular strut grafts or shaft allografts.

 

Depending on the size of the patient, humeral shafts often provide the best fit in the thoracic spine.

 

For cage placement, the ends of the cage can be trimmed to create the necessary cage configuration (TECH FIG 6A).

 

Alternatively, stackable cages (eg, those made of polyetheretherketone [PEEK]) can be measured to fit the space.

 

 

The packed cage is implanted between the distracted adjacent endplates (TECH FIG 6B). The cage is stabilized when the distraction is released.

 

Bone graft should be packed in and around the cage.

 

 

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TECH FIG 6 • A. Titanium mesh cages. B. Cage placement.

 

Polymethylmethacrylate

 

PMMA may be used in patients with spinal tumors who have poor life expectancy or who are unlikely to heal anterior bone grafts due to poor bone quality or healing potential.

 

It provides immediate spinal stability and is strongest in compression.

 

The PMMA can be reinforced and anchored with Steinmann pins drilled into the adjacent vertebral bodies.

 

Bends in the Steinmann pins can prevent pin migration.

 

 

To increase interdigitation of the cement, multiple drill holes are placed in the adjacent vertebral bodies.

 

POSTOPERATIVE CARE
	Thoracic ▪ By keeping the PLL intact until the end of procedure, epidural bleeding can be corpectomy minimized.     Choice of ▪ Patients with short life expectancies and those who will need adjuvant graft chemotherapy or radiation should be reconstructed with PMMA to provide the maximal short-term stability.

 

	Graft sizing ▪ It is important not to undersize the graft, as it is more prone to migration.     Thoracic ▪ When removing herniated disc fragments, the surgeon should always direct the discectomy angled curettes away from the dura.

 

 

POSTOPERATIVE CARE

 

Chest tubes remain until output is less than 150 mL over 24 hours.

COMPLICATIONS

The exiting nerve root can be injured while removing the pedicle. Vascular injury

Intercostal neuralgia Atelectasis Neurologic injury Wrong-level surgery

Significant bleeding can be encountered when entering the epidural space.

 

 

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