Chapter 24 Endoscopy-Assisted Thoracic Microdiscectomy

Historically, spinal surgeons have sought to find a surgical procedure of choice to treat thoracic disc herniations [1–14]. The threat of spinal cord, neural, vascular, and pulmonary injuries has stimulated many attempted approaches, including posterior laminectomy (seldom performed because it is too likely to result in neurologic injury), costotransversectomy, transthoracic, transpleural, posterolateral, transfacet pedicle-sparing, transpedicular, and, more recently, transthoracic endoscopic and posterolateral endoscopic procedures [4,5,11–17].

Many clever, minimally invasive surgical endoscopic thoracic procedures, including video-assisted thoracic surgery (VATS) [1,2,4,5] and thoracic sympathectomy, have been developed in an attempt to reduce operative trauma. Endoscopy-assisted thoracic discectomy (EATD) (i.e., posterolateral endoscopic thoracic discectomy) is an alternative procedure for treating symptomatic herniated thoracic discs through an endoscope to cause less tissue trauma than current conventional thoracic disc surgery and thoracoscopic procedures [5,11–21]. In laser thermodiscoplasty, tissue modulation technology of a lower-energy non-ablative laser is applied for shrinkage and tightening of the disc [5,10–15,18].

A significant number of patients with thoracic disc herniations complain of intractable thoracic spinal and paraspinal pain, intercostal or chest wall pain, upper abdominal pain, and, occasionally, low back pain due to thoracic disc protrusions without severe neurologic deficit. With improved diagnostic methods such as magnetic resonance imaging (the method of choice), computed tomography myelograms, and computed tomography scans, the diagnosis of these thoracic disc herniations or protrusions is now far more common [5,11–15]. Usually, patients with such conditions undergo some period of physical therapy, injection therapy, and analgesics, but if these treatments are not effective, the patients are often expected to live with their discomfort because of the fear of the potentially severe postoperative complications associated with surgical treatment [5,11–15].

Treatment objective of endoscopy-assisted thoracic discectomy

The objective of EATD is the microdecompressive endoscopy-assisted thoracic discectomy of herniated thoracic disc and foraminal disc herniation. It is a minimally invasive, outpatient procedure with minimal tissue trauma and much less morbidity than open thoracic spinal surgery. There is no bone graft or fusion hardware to cause secondary problems, and the is procedure is associated with significantly lower associated convalescence periods and costs. Also, multiple thoracic discs may be treated at one sitting [5,11–15,19–21].

Indications

The indications for EATD are as follows [5,11–16]:

Pain along the thoracic spine, often radiating to the chest wall, with possible numbness and paresthesia in an intercostal distribution related to thoracic disc herniation.

No improvement of intractable symptoms after a minimum of 12 weeks of conservative management.

Magnetic resonance imaging or computed tomography findings positive for disc herniation consistent with the level of clinical symptoms.

Confirmatory preoperative or intraoperative discogram and pain provocation test results.

Contraindications

EATD is contraindicated by the following findings or conditions [5,11–16]:

Demonstration of severe cord compression or total block on radiographic studies secondary to severe thoracic disc extrusions that cause cord compression with severe neurologic deficit (paraparesis).

Advanced spondylosis with severe disc space narrowing or osteophytes blocking entry into the disc space.

Severe congenital or acquired stenosis of the spinal canal associated with significant disc herniation.

Advantages

The advantages of EATD over open procedures are as follows:

Provides excellent pain relief

Is a same-day outpatient procedure

Involves a small incision with less scarring and less trauma

Is commonly performed with use of local anesthesia and intravenous conscious sedation; usually no general anesthesia required

Does not require dissection of muscle, bone, or ligaments or manipulation of the dural sac, spinal cord, or nerve roots

Does not involve resection of rib, so there is no need to collapse the lung or open the pleural cavity

Is not associated with postoperative pleural effusion, intercostal neuralgia, and pneumothorax

Requires no spinal fusion or fixation

Involves minimal or no blood loss

Is less traumatic, physically and psychologically

Does not promote further instability of spinal segments

Permits early return of patient to usual activities, including work

Costs less than conventional discectomy

Makes multiple-level discectomy feasible and well tolerated [17–21]

Enables exercise programs to begin on the same day as surgery

Uses direct endoscopic visualization and confirmation of the efficacy of surgery, which contribute to a safe and effective outcome

Is associated with zero mortality

Instrumentation

The following instruments and equipment are needed for EATD:

Digital fluoroscopy equipment (C-arm) and monitor (see Fig. 24-2)

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

Endoscopic tower equipped with digital video monitor, DVD recorder, light source, and photo printer, with tri-chip digital camera system (Karl Storz, Tuttlingen, Germany) (Fig. 24-2)

Thoracic endoscopic discectomy set (Karl Storz), including a 4-mm 0-degree endoscope

Thoracic operating endoscope (3.5-mm 6-degree) and diagnostic endoscopes (2.5-mm 0-degree and 30-degree) (Karl Storz)

Thoracic discectomy sets (2.5- and 3.5-mm) (Blackstone Medical, Inc., Springfield, MA) with short and long discectomes

Endoscopic grasping and cutting forceps and scissors (Karl Storz)

Endoscopic probe, knife, rasp, and bur (Karl Storz)

More aggressively toothed trephines used for spurs and spondylitic ridges at the anterior and posterior disc space (Karl Storz)

Holmium:yttrium-aluminum-garnet (Ho:YAG) laser generator (Trimedyne, Inc., Irvine, CA) with and 550-μm holmium bare fiber with flat-tip right-angle (side-firing) probe (Fig. 24-3)

Figure 24–1 (A) Patient positioning and localization with the fluoroscope. (B) Localization with skin marking and placement of the spinal needle (portal, or point of entry).

Figure 24–2 (A) Video digital endoscopic tower (Karl Storz, Tuttlingen, Germany). (B) Thoracic endoscope 0-degree and tri-chip digital camera (Karl Storz, Tuttlingen, Germany) (C) Endoscopic working channel system with trephine, burs, and rasp (Karl Storz, Tuttlingen, Germany) (D) Thoracic discectomy set with needle, working channel, trephine, 4-mm 0-degree endoscope and tissue grasping and cutting forceps (Karl Storz, Tuttlingen, Germany). (E) Long and short discectomes, and various types of tissue grasping and cutting forceps (Karl Storz, Tuttlingen, Germany).

Figure 24–3 Holmium:YAG laser generator (A) and right-angle (side firing) laser probe (B) for laser thermodiscoplasty (Trimedyne, Inc., Irvine, CA).

Preoperative preparation

Anesthesia

Local anesthesia with monitored IV conscious sedation is used; restless patients may be given general anesthesia

At the California Spine Institute, 2.0 g of cefazolin and 8.0 mg of dexamethasone are routinely given intravenously at the start of anesthesia.

The anesthesiologist maintains mild sedation, but the patient is able to respond.

Surface electroencephalography (SNAP, Nicolet Biomedical, Madison, WI) provides added precision of anesthesia.

Patient Positioning

The patient is positioned as follows for EATD [5,11–16]:

The patient is positioned prone on the table with a radiolucent 20-degree angled sponge under the symptomatic side of the chest to angle it obliquely upward (Fig. 24-1A). 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 the use of adhesive tape attached to the operating table.

Fluoroscopy and Neurophysiologic Monitoring

The following instruments and equipment are used for monitoring and visualization during EATD [5,11–16]:

Digital C-arm fluoroscopy is used in anteroposterior and lateral planes to control the placement of all instruments throughout the operation (see Fig. 24-1A).

Electromyography needles are placed for neurophysiologic monitoring within the areas of distribution of the nerve roots from the spinal levels being operated on, to provide continuous neurophysiologic-neuromuscular monitoring throughout the procedure for added safety.

As previously described, neurophysiologic monitoring with surface electroencephalography provides added precision for optimal anesthesia (Fig. 24-4).

Figure 24–4 Simple surface electroencephalography monitoring (A) with computerized SNAP monitoring (Nicolet Biomedical, Madison, WI) (B) and neurophysiologic electromyographic/neurophysiologic monitoring (C).

Procedure

Localization and Point of Entry

Localization of structures and point of entry are established as follows [5,11–16]:

1. For upper-level thoracic discectomies, the surgeon identifies levels by counting with fluoroscopy (anteroposterior view) from the 12th rib up and from C7 of the cervical spine down. Radiopaque markers or metal stylets are placed on the skin at appropriate sites [11–13].

2. The midline, levels, and point of entry (operating portal) for surgery are marked on the skin with a marking pen (see Fig. 24-1B).

Alternately, with sterile technique, the level of the disc can be accurately identified by insertion of an 18-gauge spinal needle into a disc under fluoroscopic guidance (see Fig. 24-1B).

3. The point of entry is to be marked 4 to 5 cm away from the midline at the mid-thoracic area (T5-T8 inclusive) at the respective thoracic disc 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).

Surgical Technique

The surgical technique for EATD is as followws [5,11–16]:

1. After administration of intravenous sedation and local anesthesia, a beveled, 20-gauge, 3.5-inch spinal needle is inserted into the portal, as described previously (see Fig. 24-1B).

2. The spinal needle is incrementally advanced under fluoroscopic guidance at a 35- to 45-degree angle from the sagittal plane, targeting toward the center of the disc into the “safety zone”—between the interpedicular line medially and the rib head at the costovertebral articulation—lateral and medial to the costotransverse junction (Figs. 24-5 and 24-6).

3. During needle insertion, the surgeon must guide the needle tip along the medial aspect of the rib head, to avoid entering the spinal canal medially, and must keep the needle medial to the costovertebral junction, to avoid pleural puncture (see Figs. 24-5 and 24-6).

4. After the thoracic anulus is punctured, the needle tip is incrementally advanced to the center of the disc (see Figs. 24-5 and 24-6).

5. The stylet of the spinal needle is removed.

6. A contrast agent (we use Isovue, Bracco Diagnostics, Inc., Princeton, NJ) is injected, with observation of the ease and volume of injection, the fluoroscopic appearance of the contrast medium in anteroposterior and lateral projections, and the patient’s description of the location, concordance, and intensity of any pain produced (Fig. 24-7).

7. If the discogram and pain provocation test results are confirmatory, thoracic disc surgery is to be performed.

8. A narrow, 12-inch, plain guidewire is passed into the center of the disc through the spinal needle placed for the discogram (see Fig. 24-6).

9. The spinal needle is removed.

10. A 3- to 4-mm horizontal skin incision is made along the guidewire at the site.

11. The discectomy cannula with a dilator is passed over the guidewire and is advanced to the thoracic anulus.

12. The dilator is replaced with a trephine, and the anulus is incised (Fig. 24-8B).

13. The cannula is advanced a short distance into the disc space.

14. The disc is decompressed through the use of the curettes, trephine, microforceps, discectome, and laser (Fig. 24-9; see Fig. 24-8). Care is taken not to injure the intercostal nerve (Fig. 24-9C).

15. Disc removal is aided by a rocking excursion of the cannula in a 25-degree arc, a “fan sweep maneuver” from side to side, that creates an oval cone–shaped area of removed disc totaling up to 50 degrees (Fig. 24-10A).

16. During the procedure an endoscope is utilized to provide clear direct visualization under magnification for removal of disc material and osteophytes with microcurettes, rasps, forceps, and discectome.

17. Large spurs or a rib head obstructing entry to the disc space can be removed or perforated by a set of more aggressively toothed trephines.

18. The Ho:YAG laser (see Fig. 24-4) is used in the first stage of the procedure to ablate additional disc material (500 joules at 10 watts, 10 Hz, 5 seconds on and 5 seconds off) and then in the second stage of the procedure it is used to shrink and contract the disc further with laser thermodiscoplasty at a lower power setting (300 joules at 5 watts) (Table 24.1).

Laser thermodiscoplasty reduces the profile of the protrusion and hardens the disc tissue [9]. It also causes sinuvertebral neurolysis or denervation.

19. The discectome is again used to remove charred debris from the laser application.

20. The disc space can again be directly visualized with endoscopy for confirmation of disc decompression.

21. The probe and cannula are removed.

22. Bupivacaine-epinephrine (0.25%) is infiltrated subcutaneously around the wound.

23. A small adhesive bandage is applied over the wound.

Figure 24–5 Surgical approach for endoscopy-assisted thoracic discectomy (EATD) for needle placement (A) and working channel (B).

Figure 24–6 (A) Fluoroscopic 35-degree oblique view for placement of needle/stylet into the “safety zone” between the intrapedicular line and the rib head. Fluoroscopic anteroposterior (B) and lateral (C) views for placement of the needle/stylet into the thoracic disc.

Figure 24–7 (A and B) Fluoroscopic lateral views of abnormal thoracic discogram.

Figure 24–8 (A) Endoscopy-assisted thoracic discectomy (EATD) with forceps. (B) EATD with trephine. (C) EATD with laser probe. (D) Endoscopic thoracic discectomy with rasps. (E) EATD with discectome.

Figure 24–9 Intraoperative edoscopic view of EATD (A) Initial endoscopic view upon insertion of the endoscope. (B) Thoracic disc fragment removal. (C) Thoracic disc fragment removal below the intercostal nerve. (D) Thoracic disc fragment removed. (E) Laser ablation and thermodiscoplasty.

Figure 24–10 Disc removal is aided by a rocking excursion of the cannula in a 25-degree arc, a “fan sweep maneuver” from side to side (A) that creates an oval cone–shaped area of removed disc totaling up to 50 degrees. The laser is used to shrink and tighten the disc to facilitate wound closure at the disc defect (B).

Table 24.1 Laser Settings for Thoracic Laser Thermodiscoplasty*

Stage	Watts	Joules
First	10	500
Second	5	300

* Nonablative levels of laser energy are used—at 10 Hz for 5 seconds on and 5 seconds off.

Postoperative Management

Patients should receive a neurologic examination prior to leaving the operating room; upright portable chest radiographs are obtained in the recovery room to rule out pneumothorax. Ambulation begins immediately after recovery, and patients are usually discharged 1 hour after surgery. Patients are told that they may shower the following day; also that it may be helpful to apply an ice pack and that mild analgesics and muscle relaxants are required at times. A progressive exercise program is begun the second postoperative day. Usually patients are allowed to return to work in 1 to 2 weeks, provided heavy labor and prolonged sitting are not involved. Most patients found this procedure to be beneficial [5,11–16].

Complications

The complications of EATD, as well as their prevention or treatment, are as follows [5,11–17]:

Pneumothorax is a potential complication in all approaches to thoracic discs, including EATD. Introducing the spinal needle into the “safety zone” of the disc, with the interpedicular line medial and rib head lateral to the neuroforamen, keep it from penetrating the pleura. Direct endoscopic visualization helps avoid pulmonary injury. Atelectasis is not a problem. Chest radiographs are obtained immediately after completion of the operation to rule out pneumothorax or to initiate treatment if it is present.

Infection is avoided through careful sterile technique as well as through the intravenous administration of prophylactic antibiotics intraoperatively. Also, the risk of infection is lower because EATD involves a much smaller incisional area than open posterolateral and transthoracic approaches as well as 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 or deep, may occur with EATD, but the risk is minimized by (1) careful technique, (2) the small incision (3 mm) used, (3) avoidance of aspirin and nonsteroidal anti-inflammatory drugs for the week prior to surgery, (4) application of digital pressure or an IV bag over the operative site for the first 5 minutes after surgery, and (5) application of an ice bag thereafter.

No vascular injuries have been reported with EATD. In open procedures, however, including lateral, anterior and postero-lateral approaches to thoracic discs, the thoracic aorta and its segmental branches, the intercostal artery and vein, and the azygos, hemiazygos, and accessory hemiazygos veins are at risk. Strict adherence to the technique and knowledge of the applicable surgical anatomy should avoid such injuries.

Neural injury is extremely rare with EATD; no spinal cord injuries have been reported. Nerve root injury (intercostal nerve) causing intercostal neuralgia, or chest pain, though possible, can be avoided with the use of intraoperative electromyographic/neurophysiologic monitoring [22] of the intercostal muscles at and immediately below the operated levels. With use of direct endoscopic visualization, intercostal injuries 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 to avoid 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.

Prone positioning for the 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 injury to the sympathetic chain and rami communicantes.

Excessive sedation can be avoided with the use of surface electroencephalographic monitoring, which provides a more precise estimation of the depth of sedation and reduces the amount of anesthetics used, thereby preventing excessive and insufficient sedation. Patients are able to respond throughout the procedure, providing a further means of evaluating the sedation level.

A major complication of all disc operations is operating at the wrong level (improper localization). Proper utilization of fluoroscopy for anatomical localization avoids complications caused by poor placement of instruments and operating at the wrong disc level. A routine pain provocation test and discogram give additional verification of the proper operating level.

Dural tears are common in all other approaches to the thoracic disc but have not been reported in EATD.

Soft tissue injuries due to prolonged forceful retraction, as occurs in many disc operations, are not an issue with EATD.

The risk of inadequate decompression of disc material is minimized by the use of multiple modalities and instruments such as forceps, trephines, discectome, bur, and rasp and by application of laser ablation and thermodiscoplasty.

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 EATD and prevent and avoid potential complications. All the potential complications of open approaches for thoracic disc surgery are possible but are either rare or much less frequent in EATD, in which no rib resection or deliberate collapse of the lung is required [5,11–17].

CASE STUDY 24.1

As the result of an auto accident, a 39-year-old man experienced intractable thoracic spinal pain and right T8 radiculopathy along the right lower chest wall radiating anteriorly. Neurologic examination revealed moderate parathoracic T8 and T9 vertebral muscle tenderness and muscle spasm as well as a moderate decrease in pain and touch sensation along the right T8 dermatome. Magnetic resonance imaging of the thoracic spine demonstrated a large (4-mm) T8-T9 disc herniation toward the right (Fig. 24-11). Endoscopy-assisted thoracic T8 microdiscectomy gave the patient immediate relief of all pain and symptoms.

Figure 24–11 Case Study 24.1: Magnetic resonance images showing a large (4-mm), right-sided T8-T9 disc herniation. (A) T2-weighted sagittal image. (B) T2-weighted axial image.