31 Posterolateral Endoscopic Thoracic Diskectomy

Historically, spinal surgeons have long sought a procedure for treating thoracic disk herniations.1,2,3,4,5,6,7,8,9,10,11,12 The threat of spinal cord, neural, vascular, and pulmonary injury has stimulated many approaches, including posterior laminectomy (seldom performed, as it is too likely to result in neurologic injury), costotransversectomy, and transthoracic, transpleural, posterolateral, transfacet pedicle-sparing, transpedicular, and, more recently, transthoracic endoscopic and posterolateral endoscopic procedures.^{1,2,3,4,5,6,11,12,13}

As a result, many clever minimally invasive endoscopic thoracic procedures have been developed, including video-assisted thoracic surgery (VATS),¹ thoracic sympathectomy, and others attempting to reduce operative trauma. Usually, in the past, surgery was not contemplated unless considerable cord compression and neurologic deficit were present,^5,6,11,12 yet a significant number of patients complain of thoracic spinal and paraspinal pain, intercostal or chest wall pain, upper abdominal pain, and occasionally low back pain due to thoracic disk protrusions without severe neurologic deficit or dramatic radiological abnormalities. With improved diagnostic methods like MRI⁸ (the method of choice), CT myelography, and CT, the diagnosis of thoracic disk protrusions is now far more common. Such patients usually receive some period if not cured, are expected to live with their discomfort because potential severe postoperative complications are feared if usual surgical treatment is attempted.

With the advent of laser thermodiskoplasty,^11,12,13 PETD has evolved from a minimally invasive technique used in the lumbar and cervical areas,10,11,12,13,14,15,16 and from the basic approach for performing thoracic diskography.⁹ The author has utilized pre- or intraoperative diskograms and pain provocation tests in almost all cases to confirm the diagnosis and the appropriate levels to treat. This chapter describes the technique, safety, and efficacy of the method for treating thoracic disk protrusions by outpatient PETD.

31.2 Indications

The surgical indications for PETD are:¹²

• Pain in the thoracic spine, often radiating to the chest wall, with possible numbness and paresthesia in an intercostal distribution due to thoracic disk herniation

• No improvement of symptoms after a minimum of 12 weeks of conservative management

• MRI or CT scan positive for disk herniation, consistent with the level of clinical symptoms

• Confirmatory pre- or intraoperative diskogram and pain provocation test

• Multiple thoracic disks may be treated in one procedure.^{17,18,19,20,21}

31.3 Contraindications

The PETD approach is contraindicated in the following clinical situations:

• Severe cord compression or total block on radiographic studies

• Advanced spondylosis with severe disk space narrowing or osteophytes blocking entry into the disk space

31.4 Instruments and Preparation

The equipment and surgical instruments^11,12,13 necessary to perform PETD (similar to anterior endoscopic cervical micro-diskectomy) are:

• Digital fluoroscopy equipment (C-arm) and monitor

• Full radiolucent C-arm/fluoroscopic carbon-fiber surgical table

• Endoscopic tower equipped with digital video monitor, digital imaging documentation/recording device, light source, photo printer, and high-definition (HD) digital camera system (Fig. 31.1)

• Thoracic endoscopic diskectomy set (Karl Storz, Tuttlingen, Germany), including 4-mm 0° endoscope (Fig. 31.1)

• Thoracic 3.5-mm 6° operating endoscope, and 2.5-mm 0° and 30° diagnostic endoscopes (Fig. 31.1)

• Thoracic diskectomy sets (2.5- and 3.5-mm) (Blackstone Medical, Inc., Springfield, MA) with short and long diskectomes (Fig. 31.1)

• Endoscopic grasping and cutting forceps and scissors (Fig. 31.1)

• Endoscopic probe, knife, rasp, and bur (Fig. 31.1)

• More aggressively toothed trephines used for spurs and spondylitic ridges at the anterior and posterior disk space (Fig. 31.1)

• Holmium:YAG laser generator (Trimedyne, Irvine, CA) and 550 µm holmium bare fiber with flat-tip right-angle (side-firing) probe (Fig. 31.2)

The patient is positioned prone on the table with a radiolucent 20° angled sponge under the symptomatic side of the chest, angling it into an obliquely up position (Fig. 31.3a). The arms are supported on arm boards over the head. Because only local anesthesia and mild sedation are used, the extremities, buttocks, and shoulders are restrained from sudden motion with adhesive tape.

31.7 Localization

Levels are identified by counting under C-arm fluoroscopy from the twelfth rib up, and from C7 of the cervical spine down for upper-level thoracic diskectomies. Radiopaque markers are placed on the skin at appropriate sites.^11,12,13 The midline, the levels, and the point of entry (operating portal) for surgery are marked on the skin with a marking pen (Fig. 31.3b). Using sterile technique, the level of the disk can be accurately identified by inserting an 18 G needle into a disk under fluoroscopic guidance (Fig. 31.3c, Fig. 31.4, Fig. 31.5).

The portal of entry is marked 4 to 5 cm away from the midline at the midthoracic area (T5–T8 inclusive) at the respective thoracic disk level, and 6 to 7 cm from the midline at the lower thoracic area (T9–T12 inclusive) and at the upper thoracic area (T1–T4 inclusive). Positioning of the instruments is checked throughout the procedure by C-arm fluoroscopy in two planes as needed. After the involved levels are identified, sterile needle electrodes are placed in the intercostal muscles innervated from those levels for continuous neurophysiologic EMG monitoring,22 with ground electrodes having been previously placed.

Under local anesthesia, a beveled, 20 G, 3.5-inch spinal needle is inserted into the portal of entry, as described under localization and fluoroscopic guidance (Fig. 31.5). The needle is incrementally advanced under C-arm fluoroscopic guidance at a 35° to 45° angle from the sagittal plane, targeting toward the center of the disk, into the “safety zone,” between the interpedicular line medially and the rib head at the costovertebral articulation laterally,^11,12 and medial to the costotransverse junction (Fig. 31.5). During needle insertion, the needle tip must be kept immediately along the medial aspect of the rib head to avoid entering the spinal canal medially, and medial to the costovertebral junction to avoid pleural puncture. After the annulus is punctured, the needle is incrementally advanced to the center of the disk. The stylet of the spinal needle is removed. Isovue contrast (Bracco Diagnostics, Inc., Princeton, NJ) is injected, with the surgeon observing the ease and volume of injection, the fluoroscopic appearance in AP and lateral projections, and the patient’s description of the location, concordance, and intensity of any pain produced. Surgery is performed if the diskogram and pain provocation tests are confirmatory.

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