11

Spinal surgeons have long sought to find a procedure of choice by which to treat thoracic disk herniations.1^–12 The threat of spinal cord, neural, vascular, and pulmonary injury has stimulated many attempted approaches, including posterior laminectomy (seldom performed because 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.^{1–6,11–13}

Many clever, minimally invasive surgical endoscopic thoracic procedures have been developed, including video-assisted thoracic surgery (VATS),¹ thoracic sympathectomy, and others attempting to reduce operative trauma.

In the past, surgery was not contemplated unless considerable cord compression and neurologic deficit were present.^5,6,11,12 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 such improved diagnostic methods as MRI scans⁸ (the method of choice), CT myelograms, and CT scans, the diagnosis of these thoracic disk protrusions is now far more common. Such patients usually receive some period of physical therapy, injection therapy, and analgesics, and, if not cured, are expected to live with their discomfort because potential severe postoperative complications are feared if usual surgical treatment is attempted.

PETD with laser thermodiskoplasty^11–13 evolved from minimally invasive techniques used in the lumbar and cervical areas,^10–16 and from the basic approach for performing thoracic diskography.⁹ We also have utilized pre- or intraoperative diskograms and pain provocation tests on almost all cases to confirm the diagnosis and the appropriate levels to treat. This chapter will describe the technique, safety, and efficacy of a method for treating thoracic disk protrusions by outpatient PETD.

Indications

The PETD approach is indicated¹² in the following clinical situations:

• 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 at one sitting17^–21

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

Instruments and Preparation

This surgical equipment and these instruments^11–13 are necessary to perform PETD (similar to anterior endoscopic cervical microdiskectomy):

• Digital fluoroscopy equipment (C-arm) and monitor
  
• Full radiolucent C-arm/fluoroscopic carbon-fiber surgical table
  
• Endoscopic tower equipped with digital video monitor, DVT/VHS recorder, light source, photo printer, with trichip digital camera system (Fig. 11–1)
  
• Thoracic endoscopic diskectomy set (Karl Storz, Tuttlingen, Germany), including 4 mm 0-degree endoscope (Fig. 11–1)
  
• Thoracic operating endoscope, 3.5 mm 6-degree, and diagnostic endoscopes, 2.5 mm 0-degree and 30-degree (Fig. 11–1)
  
• Thoracic diskectomy sets (2.5 and 3.5 mm) (Blackstone Medical, Inc., Springfield, MA) with short and long diskectomes (Fig. 11–1)
  
• Endoscopic grasping and cutting forceps and scissors (Fig. 11–1)
  
• Endoscopic probe, knife, rasp, and burr (Fig. 11–1)
  
• More aggressively toothed trephines used for spurs and spondylitic ridges at the anterior and posterior disk space (Fig. 11–1)
  
• Holmium:YAG laser generator (Trimedyne; Irvine, CA) with and 550 µm holmium bare fiber with flat-tip right-angle (side-firing) probe (Fig. 11–2)

FIGURE 11–1 Posterolateral endoscopic thoracic diskectomy instruments. (A) Thoracic endoscopes (0-, 6-, and 30-degree) and trichip digital camera. (B) Endoscopic working cannula systems, trephines, rasp, and burrs. (C) Various types of forceps and rongeurs.

FIGURE 11–2 Holmium:YAG laser equipment for laser thermodiskoplasty. (A) An 85 W double-pulse holmium:YAG laser generator. (B) A 550 µm holmium bare fiber with flat tip, and right-angle (side-firing) probe. (C) Single-use side-firing probes. (D) Reusable short side-firing probes.

Anesthesia

The patient is treated in an operating room under local anesthesia and monitored for conscious sedation. The anesthesiologist maintains mild sedation, but the patient is able to respond. Two grams of Ancef and 8.0 mg of dexamethasone are given intravenously at the start of anesthesia. Surface EEG (SNAP; Nicolet Biomedical, Madison, WI, USA) provides added precision of anesthesia.

Patient Positioning

The patient is prone on the table with a radiolucent 20-degree angled sponge under the symptomatic side of the chest, angling it into an obliquely up position (Fig. 11–3A). 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.

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.^11–13 The midline, the levels, and the point of entry (operating portal) for surgery are marked on the skin with a marking pen (Fig. 11–3B). Using sterile technique, the level of the disk can be accurately identified by inserting an 18-gauge needle into a disk (Figs. 11–3C, 11–4, 11–5). The portal of entry is to be marked at 4 to 5 cm away from the midline at the midthoracic area (T5–T8 inclusive) at the respective thoracic disk level, 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 neurophysiological EMG monitoring,22 with a ground electrode having been previously placed.

FIGURE 11–3 Patient positioning and localization. (A) Patient positioning. (B) Localization—skin marking. (C) Placement of needle (portal).

FIGURE 11–4 Surgical approach for posterolateral endoscopic thoracic diskectomy for needle and stylette placement into the disk. (A) Axial view illustration for needle placement. (B) Cross-section cadaveric cryomicrotome: posterolateral surgical approach.

Under local anesthesia a beveled 20-gauge, 3.5-inch spinal needle is inserted into the portal of entry, as described under localization and fluoroscopic guidance (Fig. 11–5). The needle is incrementally advanced under C-arm fluoroscopic guidance at a 35- to 45-degree 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. 11–5). During the needle insertion, one must keep the needle tip 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 anulus is punctured, the needle is incrementally advanced to the center of the disk. The stylette of the spinal needle is removed. Isovue contrast (Bracco Diagnostics, Inc., Princeton, NJ) is injected, 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.

A narrow 12-inch plain wire guide is passed into the center of the disk through the spinal needle placed for the diskogram. The needle is then removed. A 3 to 4 mm skin incision is made at the site. The diskectomy cannula containing its dilator is passed over the guidewire and is advanced to the anulus. A trephine replaces the dilator and incises the anulus. The cannula then advances a short distance into the disk space. The disk is decompressed using curettes, trephine, microforceps, diskectome, and the laser (Figs. 11–6, 11–7, 11–8, 11–9). Disk removal is aided by a rocking excursion of the cannula in a 25-degree arc, a “fan sweep” motion from side to side, that creates an oval cone-shaped area of removed disk totaling up to 50 degrees (Fig. 11–7).

During the procedure the endoscope is utilized for visualization, and under magnification additional disk material and osteophytes are removed with microcurettes, rasps, forceps, and diskectomes (Figs. 11–8, 11–9). Large spurs or a rib head obstructing entry to the disk space can be removed or can be perforated by a set of more aggressive-toothed trephines (Fig. 11–6). A holmium:YAG laser (Fig. 11–2) is used to ablate additional disk (500 J at 10 W, 10 Hz, 5 sec on and 5 sec off), then at a lower power setting (300 J at 5 W) (Table. 11–1) to shrink and contract the disk, further reducing the profile of the protrusion and hardening the disk tissue, laser thermodiskoplasty⁹ (Fig. 11–7). This may also cause sinovertebral neurolysis or denervation. The diskectome is again used briefly to remove charred debris. The disk space can be directly visualized by endoscopy for confirmation of disk decompression (Fig. 11–9). The probe and cannula are removed. Marcaine (0.25%) is infiltrated subcutaneously about the wound. A Band-aid is applied over the tiny wound.

Postoperative Care

The patient is checked neurologically prior to leaving the operating room. An upright portable chest x-ray done in the recovery room rules out a pneumothorax. Ambulation begins immediately after recovery, and the patient is usually discharged 1 hour after surgery. The patient may shower the following day. An ice pack is helpful. Mild analgesics and muscle relaxants are required at times. A progressive exercise program begins the second postoperative day. Patients are usually allowed to return to work in 1 to 2 weeks, as long as heavy labor and prolonged sitting are not involved. Most patients found this procedure extremely gratifying.

Ninety-six percent of 150 consecutive patients with a total of 197 herniated thoracic disks demonstrated good to excellent relief of symptoms. Six patients (4%) had persistent thoracic pain, although overall their pain improved. The patients postoperatively resumed usual activity in a few days, and full active lives in 3 to 7 weeks.13

Discussion

PETD is a minimally invasive surgical procedure for treating symptomatic herniated thoracic disks through an operating endoscope with much less tissue trauma and zero mortality. It has numerous advantages, but it requires thorough knowledge of the surgical anatomy, the PETD procedure, specific surgical training, and hands-on experience in a laboratory and working closely with an experienced endoscopic surgeon through its steep surgical learning curve in order for a surgeon to become competent and avoid possible complications.

A thorough knowledge of the procedure and surgical anatomy of the thorax and thoracic spine, careful selection of patients, and preoperative surgical planning with appropriate diagnostic evaluations facilitate the PETD and prevent potential complications.2,3,11,13 All potential complications of open approaches for thoracic disk surgery are possible but are rare or much less frequent^{3,7,10,11,21,23} in PETD, with no rib resection or deliberate collapse of the lung required.

• Pneumothorax, pulmonary injury, and postoperative atelectasis: Pneumothorax is a potential complication in all approaches to thoracic disks, including PETD. The spinal needle should be introduced into the “safety zone” of the disk, with the interpedicular line medially and rib head laterally at the neuroforamen, to protect it from penetrating the pleura. Direct endoscopic visualization helps to avoid pulmonary injury. Atelectasis is not a problem. Chest x-ray is obtained immediately after completing the operation to rule out pneumothorax and to initiate treatment if present.

• Infection: Avoided by careful sterile technique, using prophylactic antibiotics IV intraoperatively, and the much smaller incisional area compared with open posterolateral and transthoracic approaches, as well as the multiport thoracoscopic approaches.
  
• Aseptic discitis: May be prevented by aiming the laser beam in a “bowtie” fashion to avoid damaging the end plates (at 6 and 12 o’clock).
  
• Hematoma (subcutaneous and deep): May occur with PETD but is minimized by careful technique, the small incision (3 mm), not prescribing aspirin or NSAIDs within 1 week prior to surgery, and application of digital pressure or an IV bag over the operative site for the first 5 minutes after surgery, and application of an ice pack thereafter.
  
• Vascular injuries: The thoracic aorta and its segmental branches, the intercostal artery and vein, the azygos, hemiazygos, and accessory hemiazygous veins are at risk in open procedures and lateral, anterior, and posterolateral approaches to thoracic disks. Strict adherence to the technique and knowledge of the applicable surgical anatomy should avoid such injuries. No vascular injury has been reported with PETD.
  
• Neural injury: Extremely rare with PETD; no spinal cord injuries have been reported. Nerve root injury (intercostal nerve) causing intercostal neuralgia, or chest pain, although possible, can be avoided with intraoperative neurophysiologic monitoring (EMG/NCV)22 of intercostal muscles at and immediately below the operated levels. By using direct endoscopic visualization (Fig. 11–9), intercostal injury related to open chest surgery and thorascopic surgery can be avoided. No nerve injuries were noted in 300-plus cases at our center. The initial spinal needle placement can be onto the posterior, superior surface of the rib into the “safety zone” at the neuroforamen, avoiding the intercostal nerve lying in the inferior surface of the rib, in the costal groove. This maneuver and observing the strict boundaries of the interpedicular lines protect the spinal cord.
  
• Sympathetic chain and rami communicantes: Prone position for surgery avoids pressure on the brachial plexus, which can cause compression plexopathy. Complications are only a remote possibility; observing the surgical anatomy of the parathoracic area and keeping needle placement within the “safety zone” should sufficiently guard against this.
  
• Excessive sedation: Avoided by surface EEG monitoring, providing more precise estimation of the depth of sedation and reducing the amount of anesthetics, as well as preventing excessive or insufficient sedation. Patients are able to respond throughout the procedure, and this provides a further means of evaluating their level.
  
• Improper localization: A major complication of all disk surgeries is operating at the wrong level. Proper utilization of C-arm fluoroscopy for anatomical localization avoids complications caused by poor placement of instruments or operating at the wrong disk level. Routine pain provocation test and diskogram give additional verification of the proper level.
  
• Dural tears: These are common in all other approaches to the thoracic disk, but they have not been reported in PETD.
  
• Soft tissue injuries due to prolonged forceful retraction, as occurs in many disk operations, are not an issue with PETD.
  
• Inadequate decompression of disk material: Minimized by using multiple modalities and such instruments as forceps, trephines, diskectome, burr, and rasp, and by application of laser both to vaporize tissue and to perform thermodiskoplasty.

Advantages

The advantages^{7,10–12,14,21} of PETD are numerous. They include:

• No general anesthesia required
  
• Commonly done under local anesthesia
  
• Small incision and less scarring without multiple or large incision
  
• Minimal blood loss
  
• Zero mortality
  
• No need of lung collapse or opening of the pleural cavity
  
• No postoperative pleural effusion, intercostal neuralgia, and pneumothorax
  
• No significant infection
  
• Avoiding injury to blood vessels
  
• No resection of rib
  
• No spinal fusion or fixation needed
  
• No dissection of muscle, bone, ligaments, or manipulation of the dural sac, spinal cord, or nerve roots
  
• Little or no epidural bleeding
  
• Minimal use of analgesics postoperatively
  
• Same-day outpatient procedure
  
• Less traumatic, both physically and psychologically
  
• Does not promote further instability of spinal segments
  
• Early return to usual activities, including work
  
• Costs less than conventional diskectomy
  
• Multiple-level diskectomy feasible and well tolerated^17–21
  
• Least challenging to such medically high-risk patients as those with cardiopulmonary problems, the aged, and the morbidly obese
  
• Exercise programs can begin the same day as surgery
  
• Direct endoscopic visualization and confirmation of the efficacy of surgery, which contribute to a safe and effective outcome

Disadvantages

This technique is useful in select patients and is not appropriate for patients with severe thoracic disk extrusions causing cord compression with severe neurologic deficit (parparesis) and patients with severe congenital or acquired stenosis of the spinal canal. In patients with severe spondylosis and foraminal stenosis, this technique may not be suitable because insertion of the endoscope may not be feasible.

A 24-year-old man had complained for 2 months of intractable midback pain and muscle spasm. Past history was noncontributory. Parathoracic muscle spasm was palpable adjacent to the painful level. Neurologic examination showed hypalgesia in T10 and T12 dermatomes. MRI demonstrated two protruded thoracic disks (at T10 and T12 levels). Physical therapy, analgesics, and epidural steroid injections did not alleviate his discomfort. Chest x-ray demonstrated 13 thoracic vertebrae with 13 ribs, with seven cervical and five lumbar vertebrae. The patient was treated by PETD at T10–T11 and T12–L1. He had total relief of his symptoms postoperatively. Comparative preoperative and postoperative MRI scans showed the disappearance of the protruded disks (Fig. 11–10).

Posterior endoscopic thoracic diskectomy performed for symptomatic herniated thoracic disk with added laser “tightening” of the disk (thermodiskoplasty) is an easier, safe, and efficacious procedure. This minimally invasive, less-traumatic outpatient procedure results in less morbidity, more rapid recovery, and significant economic savings. The mortality rate was zero in a multicenter study²³ of percutaneous endoscopic spinal diskectomy (26,860 cases), and the morbidity rate was less than 1%, with patient satisfaction of more than 92% for thoracic disks. There are no reported spinal cord injuries, intercostal neuralgia, or dural tears, and no significant infection, vascular injury, or pulmonary complications.

PETD requires a knowledgeable and competent surgeon with a thorough appreciation of the surgical anatomy of the thorax and thoracic spine intercostal nerves and vessels, the relationship of the rib heads, pedicles, disk spaces, and spinal cord. To perform the procedure, the spine surgeon must have specific surgical training with hands-on experience in the laboratory, and, most importantly, must spend time working through the steep surgical learning curve with an endoscopic spinal surgeon expert at this procedure.

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