Thoracic Decompression and Instrumented Fusion Techniques (2023)

Considerations

Laminectomy was first described by Smith in 1828 and popularized by Hibb and Albee in the 1900s. This procedure is performed to decompress the thoracic spinal canal and increase the space available for the spinal cord and exiting nerve roots. It is performed via a posterior approach, which also provides access for thoracic instrumentation and fusion, and is the ideal access method for intradural lesions. Dorsal laminectomy through a direct posterior approach is the predominant method for most thoracic spinal decompression. The main advantages of this approach include direct access to the osseous and ligamentous portions of the posterior spine and avoidance of major vascular structures anteriorly. Indications for this approach include any posterior impingement of the spinal canal from stenosis/spondylosis, evacuation of epidural abscess or hematoma, removal of neoplasms of the posterior elements, removal of intra- or extradural tumors, and many traumatic spine injuries.

It is important to note that anterior spinal canal compromise, as may occur in the case of burst fractures or tumors, often require a posterior and anterior decompression. A simple posterior decompression in the setting of anterior compression from tumor or traumatic bone retropulsion will not sufficiently decompress the spinal cord and may lead to increased instability if performed alone without stabilization and fusion. It is important
to identify those patients with preoperative instability or anterior column incompetence who may benefit from fusion to prevent the risk of secondary kyphosis. It is also important to recognize if posterior fusion with pedicle screws may not be feasible because of aberrant pedicle morphology, insufficient bony dimensions, or fracture. All of these may be apparent on preoperative axial imaging.

Positioning and Preparation

Patients are generally positioned prone for this approach and receive general anesthetic at the start of the case. A Jackson frame (or gelatin rolls) is utilized to remove pressure from the abdomen during the procedure. Avoiding compression of the abdomen helps to prevent venous engorgement of the epidural venous plexus and may reduce blood loss. Sterile preparation of the skin is then performed and the surgical area of interest is delineated with sterile drapes. It is important to drape widely to allow for sufficient exposure and possible drain placement. Fluoroscopy can be utilized while marking the surgical incision to confirm the location of the operative level. Wrong-level surgery is a risk in the thoracic spine and great care must be taken to insure the correct level identified. Loupe magnification or the use of a free-standing microscope is beneficial during the decompression. Fusion instrumentation should be available. If a bilateral decompression (i.e., full laminectomy) is deemed necessary, an instrumented fusion is recommended. The thoracic spine is naturally kyphotic and removal of the posterior elements can destabilize the spinal segment and potentiate postoperative iatrogenic kyphosis.

Exposure

After localizing the appropriate spinal level, a longitudinal incision is marked directly over the spinous processes of the affected levels. The dermis and subdermal layers are incised with a scalpel. Electrocautery is utilized to incise the subcutaneous layer and is divided down to the level of the deep fascia. Small blood vessels encountered along the way should be cauterized to allow for a bloodless operative field. The deep fascia is then released on both sides of the spinous processes to expose the superficial back musculature. The trapezius and rhomboid muscle aponeurosis is located in the upper thoracic spine and that of the latissimus dorsi in the lower thoracic spine. A Cobb elevator is utilized to subperiosteally elevate this musculature from either side of the spinous process and retract laterally. Subperiosteal dissection minimizes bleeding. The intrinsic muscles of the erector spinae and transversospinal group are then subperiosteally elevated from the spinous processes and laminae. The subperiosteal dissection can be extended out laterally beyond the facet joints to the tips of the transverse processes if a fusion construct is desired. Self-retaining retractors are used to hold the paraspinal musculature out of the operative field. Caution is exercised to avoid dissecting deep to the ribs and lateral to the pars so as to avoid risk of pleural injury and damage to the neurovascular bundle that runs along the undersurface of the ribs. The facet joint is exposed with electrocautery taking care to avoid stripping of the capsule unless fusion is intended at that spinal level.

Decompression

Following adequate exposure of the laminae, a formal decompressive laminectomy can be initiated (Fig. 31.1). A high-speed burr or drill is utilized to create a trough bilaterally at the junction of the lamina and the facet. After adequate thinning of the lamina with the use of the burr, a 2- or 3-mm Kerrison rongeur is used to complete the trough and remove the lamina. This can be en bloc if possible or in the standard piecemeal technique using the Kerrison rongeur. The ligamentum flavum is released off of the edges of the adjacent superior and inferior laminae using a Woodson or small Kerrison rongeur to enable removal of the laminectomy fragment. Further decompression with removal of portions of the facet joint can be performed if indicated at this time.

Indications

• 
  

  Lateral or posterolaterally located thoracic disk herniations

  
  
• 
  

  Lateral or posterolaterally located focal stenosis, tumor, and fracture fragments

Transpedicular decompression was first described in 1978 and has been used for the excision of herniated thoracic disks primarily. This procedure is particularly useful when ventral spinal cord compression is significant and decompressive laminectomy is thought to be inadequate. The exposure is slightly more extensive than that for standard laminectomy and must be carried out to the lateral aspect of the transverse processes to adequately visualize the facet and pedicle (Fig. 31.2). The medial aspect of the transverse process is excised to allow access to the lateral pedicle wall. Periosteal dissection with a small Cobb or key elevator along the lateral wall is performed. The medial rib can be left intact. The pleura are ventral to the rib and should be protected. A self-retaining retractor can be used to maintain exposure. A hemilaminectomy is then performed initially. This allows palpation of the medial pedicle wall and visualization of the neural elements. Pediculectomy is performed with a high-speed drill through the lateral wall into the central pedicle leaving an “egg-shell” outer cortex medially. Kerrison rongeurs can then be used to resect the remaining cortex. Removal of the pedicle allows surgeon access to the anterolateral thecal sac,
nerve root and dorsal aspect of the vertebral body and disk. The posterolateral aspect of the disk can be safely addressed without thecal sac retraction. If the disk is calcified, a small dorsal portion of the cranial and caudad portions of the adjacent vertebral bodies can be excised with a burr. This allows a cavity for the calcified disk to be pushed ventrally into the defect away from the thecal sac and spinal cord where it can be more safely removed. In the case of trauma, retropulsed bone fragments may be decompressed using the same method.

Figure 31.1 Thoracic laminectomy. A: The spinous processes have been removed, and dorsal cortex of the lamina has been removed. This enables easy identification of the cranial and caudal border of the lamina. It is extremely difficult to do thoracic laminectomy without spinous process removal due to the overhang of cranial levels obscuring the cranial border of the lamina to be removed. The lamina has also been thinned to the ventral cortex. B: Drilling bilateral troughs. The thin lamina facilitates easy identification of ligamentum flavum and dura. The authors start at the caudal border since flavum protects the dura at this level. C: Example of thoracic laminectomy. D: Subdural/intramedullary spinal cord hemorrhage evident on thoracic laminectomy. (Reprinted from Zdeblick TA, Albert TJ. Master Techniques in Orthopaedic Surgery—The Spine. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2014:18.)

Figure 31.2 Transpedicular decompression. A: Bilateral transpedicular decompression. The surgeon is reaching into the vertebral body through the left pedicle, which has been removed. Note that the right pedicle has also been removed and bilateral nerve roots have been sacrificed. B: Example of transpedicular decompression for thoracolumbar burst fracture with incomplete spinal cord injury. Preoperative sagittal view demonstrates significant bony retropulsion. C: Postoperative sagittal view demonstrates reduction of fracture and resection of bony fragment. D: Axial view demonstrates bilateral transpedicular decompression. (Reprinted from Zdeblick TA, Albert TJ. Master Techniques in Orthopaedic Surgery—The Spine. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2014:18.)

Indications

• 
  

  Ventral spinal stenosis/compression secondary to central herniated disk, retropulsed bone fragments, tumor, or infection

  
  
• 
  

  Correction of rigid deformity

Costotransversectomy was first described in 1894 as a posterolateral approach to the ventral spine to treat patients with Pott disease and epidural abscesses. This approach avoids the morbidity associated with ventral approaches. The indications for this approach have expanded over the past few decades as surgeons have perfected the technique. It is now commonly used for diseases affecting the anterior thoracic column that in the past may have been addressed using an anterior approach. It has become the preferred approach to the anterior column in the upper thoracic spine where the anterior approach may be more difficult, often requiring sternotomy or partial sternal resection.

The setup of the patient is typically prone on a radiolucent Jackson frame table. The use of neuromonitoring is highly recommended when performing this procedure. A lateral position and approach has also been described. The table should allow 360-degree fluoroscopic exposure of the spine. The table should also allow rotation in order to “airplane” the patient from the left and right in order to facilitate visualization. The cervical spine can be stabilized with either three-point Mayfield
tongs or Gardner-Wells tongs with 10 to 15 lb of traction. The arms are typically padded and tucked at the patients’ side.

A midline incision is performed through the skin and subcutaneous tissue to the spinous processes and dorsal fascia. Additionally, a semilunar (or J-type) incision can also be utilized, oriented toward the side of the lesion. A T-type incision has also been described for severe kyphotic deformity correction. When working at the cervicothoracic junction and upper thoracic spine, the trapezius is identified. Below the trapezius, the levator scapulae and rhomboids are identified and dissected from the midline in line with the incision. The paraspinals are then divided in a subperiosteal fashion from the midline of the spinous process and over the lamina. Exposure is carried out (unilaterally or bilaterally) past the costotransverse junction.

Figure 31.3 A: Removal of the posterior elements, including spinous process, laminae, facets, and transverse processes at the level(s) to be resected. B: The pedicle and lateral aspect of the vertebral body are then removed using an osteotome, high-speed drill, and/or rongeurs. C: Resection of the vertebral body and intervening disks is then accomplished in a piecemeal fashion, extending toward the medial side and crossing over to the contralateral side. D: A thin shell of bone is left behind to protect the dural tube. E: An Epstein reverse-cutting curette can then be used to remove the shell of bone adjacent to the dural tube. F: An intervertebral support device may be placed in the defect.

Posterior pedicle screw fixation is usually performed following the initial exposure but before decompression. Once placement of the pedicle screws has been performed, a rod is placed on the contralateral side of where the initial decompression will be performed. This will help avoid instability or spinal subluxation as the decompression proceeds.

Next, a laminectomy is usually performed as described in the previous section (Fig. 31.3A). The transverse processes are identified and removed with a rongeur. The costovertebral joint should be identified. Careful dissection of the rib from the underlying pleura is essential. This will limit the amount of bleeding encountered
and decrease the risk of pneumothorax or direct lung injury.

The intercostal bundle is identified at the caudal aspect of the rib. The extent of rib resection is dependent upon the amount of exposure necessary for adequate anterior column exposure (typically 5 to 6 cm). Once the rib is removed, a subperiosteal dissection along the lateral vertebral body and pedicle is performed around to the anterior vertebral body. Malleable retractors are placed to protect and retract the vascular and pleural structures. A high-speed burr is used to resect the lateral pedicle and vertebral body (Fig. 31.3B). The resection is advanced anteriorly, posteriorly, and medially to the midline of the vertebral body or further if it can be safely reached (Fig. 31.3C). The dorsal cortex is thinned with angled curettes and the high-speed burr (Fig. 31.3D). As the exposure progresses, the plane between the posterior longitudinal ligament (PLL) and the dura is developed with a blunt instrument. The PLL can then be divided and removed in order to gain additional access to the vertebral body. If a complete corpectomy/vertebrectomy is needed, the adjacent-level intervertebral disk and cartilaginous end plates are removed with curettes and rongeurs. This is performed bilaterally. A stabilizing rod is placed on the contralateral side during this step as the spine will become unstable. A flat paddled instrument is placed between the dura and the remaining thinned dorsal cortex and ventral pressure is used to displace the fragments anteriorly into the space created by the vertebrectomy (Fig. 31.3E).

Related

Nov 11, 2018 | Posted by drzezo in ORTHOPEDIC | Comments Off on Thoracic Decompression and Instrumented Fusion Techniques