5

Anterior cervical diskectomy with or without bony fusion has been the standard treatment for cervical disk protrusions since the 1950s1–4; however, these operations are associated with significant local morbidity^5,6 (e.g., graft collapse, graft extrusion, hardware failure, nonfusion with resultant instability, infections, esophageal perforation with infection, and permanent pain, peripheral nerve injury, or infection at the graft donor site). In contrast, anterior endoscopic cervical microdiskectomy (AECM)^7,8 is a minimally invasive, outpatient procedure with much less morbidity, no graft donor site to cause secondary problems, and a significant decrease in the period of convalescence and costs.

The evolution of spinal surgery is trending toward less-invasive techniques, with clever procedures not thought possible a few years ago.^9–14 Advancements in microinstrumentation, fiberoptics, improved fluoroscopic imaging, and high-resolution digital video imaging endoscopy, along with the accumulation of experience in percutaneous lumbar diskectomy^15–18 and spinal laser applications,^18–20 have facilitated the development of AECM.⁷

In 1995, the use of a Holmium laser at low, nonablative levels of energy to cause contraction of the disk tissue, further reducing the size of the protrusion and hardening the disk (laser thermodiskoplasty) to prevent recurrence, was added to our standard protocol for percutaneous AECM. Anterior cervical fusion (ACF) is associated with a 15% or greater chance of junctional disk herniation at interspaces adjacent to fused levels, presumably because fusion places additional stress on adjacent vertebral segments. Minimally invasive endoscopic diskectomy does not affect the stability of adjacent vertebral segments.

Multiple levels of symptomatic cervical disk disease do occur. ACF is often an unattractive treatment in the presence of multiple symptomatic disk levels in a patient, but AECM, a minimally invasive outpatient spinal surgery, can be safely utilized for these cases.

This chapter will describe the surgical technique of AECM step by step, using current endoscopic equipment, instrumentation, surgical tools, potential surgical complications, and complication avoidance in the treatment of symptomatic herniated cervical disks.

Indications

The AECM approach is indicated in the following clinical situations⁷:

• Neck pain with radiation down the arm (radicular pain)
  
• Symptoms of tingling and numbness, as well as signs of sensory loss, muscle weakness, and/or decreased reflexes in the upper extremities, correlated with the level of involvement
  
• Severe intractable cervicogenic headache associated with neck pain
  
• No improvement of symptoms after a minimum of 12 weeks of conservative therapy
  
• Magnetic resonance imaging (MRI) or computed tomographic (CT) scan positive for disk herniation, consistent with dermatome of clinical symptoms (MRI is the imaging study of choice)
  
• Junctional cervical disk herniation syndrome in postcervical fusion
  
• Positive pre- or intraoperative diskogram and pain provocation test
  
• Positive electromyography is considered helpful
  
• Multiple cervical disks can be treated at one sitting

Contraindications

• Cervical endoscopic diskectomy set (Karl Storz, Tuttlingen, Germany), including 4 mm, 0-degree endoscope (Fig. 5–1A)
  
• Cervical diskectomy sets (2.5 and 3.5 mm) (Blackstone Medical, Inc., Springfield, MA) with short cervical diskectomes (Fig. 5–1B).
  
• Endoscopic tower equipped with digital video monitor, DVT/VHS recorder, light source, and photo printer, with trichip digital camera system (Fig. 5–1C)
  
• Endoscopic grasping and cutting forceps (Fig. 5–1D)
  
• Endoscopic probe, knife, rasp, and burr (Fig. 5–1D)
  
• More aggressively toothed trephines used for spurs and spondylitic ridges at the anterior and posterior disk space (Fig. 5–1D)
  
• 3.5 mm, 6-degree cervical operating endoscope (Fig. 5–1E)
  
• Holmium:YAG laser generator (Trimedyne, Irvine, CA) with right-angle (side-firing) probe (Fig. 5–2A,B)
  
• Digital fluoroscopy equipment (C-arm) and monitor

FIGURE 5–2 Holmium: yttrium-aluminum-garnet (YAG) laser equipment for laser thermodiskoplasty. (A) Holmium:YAG laser generator. (B) Right-angle (side-firing) laser probe.

The patient is placed in a supine position, with the neck extended over a rolled towel under the shoulders, on an adjustable radiolucent surgical table.7 A soft strap is placed over the forehead to stabilize it. The shoulders are distracted gently downward with tape (Fig. 5–3A). Digital C-arm fluoroscopy is used in anteroposterior (AP) and lateral planes to control the placement of all instruments throughout the operation. Electromysgraphy (EMG) needles are placed in 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.

Localization

Initial localizing AP fluoroscopic x-rays are made with Allis clamps attached to the drapes and crossing the neck horizontally at the expected level. The midline, the levels, and the point of entry (operating portal) for surgery are marked on the skin with a marking pen (Fig. 5–3B,C). On the other hand, using sterile technique, the level of the disk can be accurately identified by inserting an 18-gauge needle into a disk under fluoroscopy (Fig. 5–4A–D), as described under Surgical Techniques.

Surgical Techniques

The initial point of entry (operating portal) is adjacent to the medial border of the right sternocleidomastoid muscle, where firm pressure is applied digitally in the space between that muscle and the trachea, pointing toward the vertebral surface (see Fig. 5–4A,B). The larynx and trachea are displaced medially and the carotid artery laterally (see Fig. 5–4A,B). The anterior cervical spine is palpated with the fingertips. An 18-gauge spinal stylette is passed transdermally into the disk space, and its position is confirmed fluoroscopically (see Fig. 5–4C,D). If a pain provocation test and diskogram have not been done preoperatively, they are done now. If results are confirmatory, the operation is performed. A 3 mm skin incision is made, and a narrow guidewire stylette is passed through the needle, which is then removed. A 2.5 mm or 3.5 mm internal diameter cannula/dilator is introduced over the stylette and into the disk interspace.

A standard number 18 guidewire replaces the narrow one. A trephine replaces the dilator and incises the anulus. Under fluoroscopic and endoscopic visualization, minicurettes and forceps (Figs. 5–5A, 5–6) loosen and remove disk fragments prior to introducing the diskectome through the cannula to remove the disk. The diskectome employs a high-pressure irrigation-suction system and a guillotine-cutting blade (Figs. 5–5B, 5–7A). The instruments removing the disk material are moved in a “critical fan sweep maneuver” with a 25-degree “rocking” excursion of the cannula hub from side to side to increase the area of total disk removed up to approximately a 50-degree inverted cone-shaped area within the disk space (Fig. 5–7B).⁷ All maneuvers are closely monitored with fluoroscopy and by endoscopy. Trephines with more aggressive teeth are used to remove bone spurs or osteophytes. Very large bone spurs can be removed with a short cannula system with a burr (Fig. 5–8). The holmium: yttrium-aluminum-garnet (YAG) laser with right-angle (side-firing) probe facilitates removal of disk material further. In addition, it is used at nonablative levels of laser energy (Table 5–1) for laser thermodiskoplasty [i.e., collagen and disk shrinking (Fig. 5–7C) and tightening effect to further decompress and to harden the disk]. Endoscopy is used for direct visualization (Fig. 5–9A,B) and for confirmation of diskectomy and laser thermodiskoplasty. Again, after using the diskectome for laser disk debris removal in the disk space, the probe and cannula are removed. Marcaine (0.25%) is infiltrated subcutaneously around the wound. The tiny incisional wound is closed with a bandage.

FIGURE 5–6 (A,B) Endoscopic views of anterior endoscopic cervical microdiskectomy with forceps removing disk material.

Outcome

Ninety-four percent of surgical patients with single disk problems have good-to-excellent relief of symptoms postoperatively,7,19 resuming usual activity in a few days and full active lives in 3 to 7 weeks.

Infection can be avoided by careful sterile technique, using prophylactic antibiotics IV intraoperatively and the much smaller incisional area. Infection and complications secondary to a donor graft site are obviated. Aseptic diskitis can be prevented by aiming the laser beam in a “bowtie” fashion to avoid damaging the end plates (at 6 and 12 o’clock).

Dysphasia and Postoperative Airway Obstructions Due to Edema

The advantages of AECM are those of minimally invasive spinal surgery7:

• Same-day outpatient procedure (less traumatic, both physically and psychologically)
  
• Small incision and less scarring of the neck
  
• No dissection of muscle, bone, or ligaments, or manipulation of the dural sac or nerve roots
  
• Little or no epidural bleeding
  
• Does not promote further instability of spinal segments or postcervical fusion junctional disk herniation
  
• Early return to activities of daily living
  
• Commonly done under local anesthesia
  
• Costs less than conventional diskectomy
  
• Multiple-level diskectomy feasible and well tolerated
  
• Least challenging to medically high-risk patients (e.g., those with cardiopulmonary problems and the morbidly obese)
  
• Exercise programs begun same day as surgery
  
• Direct endoscopic visualization and confirmation of the efficacy of surgery

Case Illustration

A 62-year-old female patient complained of progressive neck, shoulder, and bilateral arm pain for 3 years, with increasing stiffness of the legs, along with stool and urinary incontinence for 3 months. The left biceps reflex was reduced, and knee and ankle reflexes were 2+. Hypoalgesia was present in the left middle and ring fingers. Babinski’s reflex was equivocal on the right. Mild spastic gait was evident. EMG was abnormal in a left C6–C7 distribution. MRI (Fig. 5–10A) confirmed a large 8 mm herniated C6–C7 disk causing spinal cord compression, a 2 mm disk protrusion at C4–C5, and a 2 to 3 mm protrusion at C5–C6. Provocative diskogram and anterior endoscopic microdecompressive diskectomy with laser thermodiskoplasty were performed. Very brief transient worsening of gait was followed postoperatively by rapid improvement of all symptoms and disappearance of incontinence by the third postoperative day. She was asymptomatic and free of pain at follow-up 1 year later. She had resumed all her normal activities. Comparative pre- and postoperative MRI scans showed complete removal of the large herniated C6–C7 disk (Fig. 5–10B).

Conclusion

Anterior endoscopic cervical microdiskectomy, which represents a new procedure for treating symptomatic herniated cervical disks anteriorly through an endoscope, aims to reduce tissue trauma from conventional open cervical surgery. Low-energy nonablative laser is applied for shrinkage and tightening of the disk (laser thermodiskoplasty). With appropriate endoscopic spinal surgical training, thorough knowledge of the AECM procedure, and surgical experience, AECM is a safe and efficacious procedure. This minimally invasive and less traumatic outpatient procedure results in less morbidity, more rapid recovery, and significant economic savings.

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