Anterior Thoracic Corpectomy

Sheeraz A. Qureshi

Samuel C. Overley

Morgan N. Chen

Andrew C. Hecht

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
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.