Anterior Endoscopic Cervical Microdecompression of Disc and Foramen

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Chapter 22 Anterior endoscopic cervical microdecompression of disc and foramen

John Chiu, MD

The standard treatment for cervical disc protrusions and foraminal stenosis ha s been anterior cervical microdecompression of the disc and foramen with or without bony fusion [1–5]. These open operations are associated with significant local morbidity [6,7], such as 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. Anterior cervical fusion (ACF) is associated with a 15% or greater chance of junctional disc herniation or adjacent segment disease at interspaces adjacent to fused levels [8,9].

The evolution of spinal surgery is trending toward less invasive techniques [9–16]. Advancements in microinstrumentation, fiberoptics, improved fluoroscopic imaging, and high-resolution digital video imaging endoscopy, along with the accumulation of experience in percutaneous lumbar discectomy [17–20] and spinal laser applications [20–23], have facilitated the development of anterior endoscopic cervical microdecompression (AECM) and foraminal decompression [9,14,19]. AECM, as minimally invasive surgery, does not affect the stability of adjacent vertebral segments [8–10]. Although ACF is often an unattractive treatment for patients with multiple-level disc symptoms, AECM can be safely utilized for treatment of such patients.

Treatment objectives

The primary objective of AECM is to perform decompression of the herniated cervical disc and foraminal disc. It is a minimally invasive outpatient procedure that aims to reduce tissue trauma with much less morbidity than open cervical spinal surgery [9,10,12]. There is no graft donor site to cause secondary problems, and the period of convalescence and the costs of the procedure are significantly less than those of traditional open operations.

Indications

The indications for AECM are as follows [9,12,19]:

image Symptomatic herniated cervical disc and foraminal disc lesion
image Subjective complaints of neck pain with radiation down the arm (radicular pain)
image Symptoms of tingling and numbness
image Physical findings of sensory loss, muscle weakness, and/or decreased reflexes in the upper extremities that correlate with the level of involvement
image Severe intractable cervicogenic headache associated with neck pain
image No improvement of symptoms after a minimum of 12 weeks of conservative therapy
image Magnetic resonance imaging (the imaging study of choice) or computed tomography findings of disc herniation consistent with the dermatome of clinical symptoms
image Junctional disc herniation syndrome (JDHS) or adjacent segmental disease (ASD) in patients who have undergone cervical fusion
image Positive preoperative or intraoperative discogram and pain provocation test results
image A positive electromyography result can be an indication if other indications are present

Contraindications

Contraindications to AECM are as follows [9,12]:

image Imaging study showing severe cervical spinal canal stenosis.
image Significant migration of a free disc fragment, which is therefore not located at disc level.
image Advanced spondylosis (significant bone spurs) with severe disc space narrowing and with osteophytes blocking entry into the disc space.
image Significant ossification of the posterior longitudinal ligament.

Advantages

The advantages of AECM in comparison with open procedures are as follows [8,9,12,19,22]:

image Excellent pain relief
image Same-day outpatient procedure without need for hospitalization
image Small incision and less scarring of the neck
image No dissection of muscle, bone, ligaments, or manipulation of the dural sac or nerve roots; little or no epidural bleeding
image Does not promote further instability of spinal segments, and preserves spinal motion
image Allows early return of patients to usual activities, including work
image Is commonly performed with the use of local anesthesia
image Costs much less than conventional discectomy and spinal fusion
image Makes multiple-level discectomy feasible and well tolerated
image Is least challenging to medically high-risk patients and the obese
image Allows patients to begin basic exercise programs the same day as surgery
image Is less traumatic, both physically and psychologically

Instrumentation

The following instruments and equipment are needed for AECM (Fig. 22-1) [9,12]:

image Endoscopic tower equipped with digital video monitor, DVT/VHS recorder, light source, photo printer, and tri-chip digital camera system.
image Cervical endoscopic discectomy set (Karl Storz, Tuttlingen, Germany), including 4-mm, 0-degree endoscope.
image Cervical discectomy sets (2.5 and 3.5 mm) (Blackstone Medical, Inc., Springfield, MA) with short cervical discectomes.
image 3.5-mm, 6-degree cervical operating endoscope.
image Endoscopic grasping and cutting forceps.
image Endoscopic probe, knife, rasp, and bur.
image More aggressively toothed trephines used for spurs and spondylitic ridges at the anterior and posterior disc space.
image Holmium:yttrium-aluminum-garnet (Ho:YAG) laser generator (Trimedyne, Inc., Irvine, CA) with right-angle (side-firing) probe (Fig. 22-2).
image Digital fluoroscopy equipment (C-arm) and monitor.
image

Figure 22–1 Video digital endoscopy tower and anterior cervical endoscopic instruments (Karl Storz, Tuttlingen, Germany). (A) Cervical 0-degree endoscopes and endoscopic instruments. (B) Discectomes, working channel sets. (C) Discectomy set: forceps, trephines, and bur. (D) Tri-chip digital camera with cervical 6-degree endoscope and forceps. (E) Video digital endoscopic tower.

image image

Figure 22–2 Holmium:yttrium-aluminum-garnet laser equipment (Trimedyne, Inc., Irvine, CA) for laser thermodiscoplasty. The laser generator (A) and right-angle (side-firing) laser probe (B).

Procedure

Anesthesia

image Local anesthesia with monitored intravenous conscious sedation is used for AECM.
image General anesthesia may be used for restless patients.
image Intravenous injection of 2.0 g cefazolin and 8.0 mg dexamethasone are routinely given.
image The esophagus is made more palpable by insertion of an esophageal or nasogastric tube.
image The pulse of the carotid artery may be augmented with sympathomimetics (e.g., ephedrine) to raise systolic blood pressure to a minimum of 130 mm Hg.

Patient Positioning

Figure 22-3 illustrates patient positioning for AECM [9,12]:

image 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 [12].
image A soft strap is placed over the forehead to stabilize it.
image The shoulders are distracted gently downwards with tape.
image image image

Figure 22–3 A) Patient positioning and localization. (B) Skin marking. (C) Placement of needle and portal entry.

Fluoroscopy and Neurophysiologic Monitoring

Figure 22-3 illustrates the monitoring equipment used for AECM [9,12]:

image Digital C-arm fluoroscopy (see Fig. 22-3) is used in the anteroposterior and lateral planes to control the placement of all instruments throughout the operation.
image Neurophysiologic monitoring with surface electroencephalography (EEG) (SNAP, Nicolet Biomedical, Madison, WI) provides added precision for optimal anesthesia.
image Electromyography (EMG) needles placed in areas of distribution of the nerve roots from the spinal levels being operated on provides continuous neurophysiologic-neuromuscular monitoring throughout the procedure for added safety.

Localization and Point of Entry

1. Initial localizing anteroposterior fluoroscopic images are obtained with Allis clamps attached to the drapes and crossing the neck horizontally at the expected level.
2. The midline, vertebral levels, and point of entry (operating portal) for surgery are marked on the skin with a marking pen (Fig. 22-3).
Alternatively, with sterile technique, the level of the disc can be accurately identified by insertion of an 18-gauge needle into a disc under fluoroscopic guidance (see Fig. 22-4), as described in the next section on surgical technique.

Surgical Technique

The surgical technique for AECM is as follows [8,9,12,19,22]:

1. 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 (Fig. 22-4).
2. The larynx and trachea are displaced medially and the carotid artery laterally (see Fig. 22-4). The anterior cervical spine is palpated with the fingertips.
3. An 18-gauge spinal needle is passed transdermally into the disc space, and its position is confirmed fluoroscopically (see Fig. 22-4).
4. If a pain provocation test and discogram have not been performed preoperatively, they are performed at this point. If results are confirmatory, the operation is performed.
5. A 3-mm skin incision is made, and a narrow guidewire stylet is passed through the needle, which is then removed.
6. A 2.5- or 3.5-mm internal diameter cannula/dilator is introduced over the stylet and into the disc interspace.
7. The narrow guidewire stylet is replaced by a standard No. 18 guidewire.
8. The dilator is replaced by a trephine, which is then used to incise the anulus.
9. Under fluoroscopic and endoscopic visualization, mini-curettes and forceps (Figs. 22-5 and 22-6) are used to loosen and remove disc fragments prior to introduction of the discectome through the cannula to remove the disc.
10. The discectome is then introduced. This instrument employs a high-pressure irrigation-suction system and a guillotine-cutting blade (see Fig. 22-5).
11. The instruments removing the disc 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 disc removed up to approximately a 50-degree inverted cone-shaped area within the disc space (see Fig. 22-7) [9,12]. All maneuvers are closely monitored with fluoroscopy and endoscopy.
12. Trephines with more aggressive teeth are used to remove bone spurs or osteophyte.
13. Very large bone spurs can be removed with a short cannula system with a bur (Fig. 22-8).
14. Use of the Ho:YAG laser with right-angle (side-firing) probe facilitates further removal of disc material. It is used at nonablative levels of laser energy.
See Table 22.1 for the parameters used in laser thermodiscoplasty [i.e., collagen and disc shrinking (first stage) and tightening effect (second stage) to further decompress and to harden the disc].
16. Endoscopy is utilized for direct visualization (see Fig. 22-7) and confirmation of discectomy and laser thermodiscoplasty.
17. After the discectome is used for laser disc debris removal in the disc space, the probe and cannula are removed.
18. For neuroforaminal decompression, the cutting and grasping forceps, microrasp, microcurette, and microtrephine are utilized in addition to the discectome.
The surgeon should be familiar with cervical discectomy before attempting neuroforaminal decompression. Extreme care is to be taken not to injure the cervical nerve root, through close monitoring with fluoroscopy, direct endoscopic visualization, and EMG neurophysiologic monitoring.
20. Bupivacaine (0.25%) is infiltrated subcutaneously around the wound. The small incision is closed with an adhesive bandage.
image image image image

Figure 22–4 Surgical technique for anterior medial cervical approach. (A) Frontal illustration showing needle and stylet placement into the disc with retraction of trachea/esophagus for needle placement. (B) Axial illustration showing retraction of trachea/esophagus for needle placement. Lateral illustration (C) and fluoroscopic view (D) showing placement of the stylet into the disc space.

image image image image image image

Figure 22–5 AECM with forceps (A) curette (B) discectomes (C) trephine (D) bur, (E) and side-firing laser probe (F) under fluoroscopic guidance for microdecompressive cervical discectomy.

image image

Figure 22–6 Endoscopic views of AECM with forceps removing disc material (A) and removed disc material (B).

image

Figure 22–7 Surgical technique of laser thermodiscoplasty. The fan sweep maneuver and endoscopic views of disc shrinkage with side-firing laser probe in action are shown (A). The fan sweep maneuver of the instrument increases disc removal and shrinkage (B) and the laser is used to shrink and tighten the disc beyond the “pursestring” of the disc defect (C).

image image image image image image

Figure 22–8 Foraminal microdecompression with micro–cutting forceps (A) curette (B) discectome (C) trephine (D) rasp (E) and bur (F) (arrow: neural foramen).

Table 22.1 Laser Settings for Cervical Laser Thermodiscoplasty*

Stage Watts Joules
First 8 300
Second 5 200

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

Postoperative managment

Postoperatively, patients are ambulatory within 1 hour and are discharged subsequently. Patients may shower the following day. A soft cervical collar is used for 2 or 3 days or as needed. Ice packs are helpful; mild analgesics and muscle relaxants are required at times. Progressive neck exercise begins on the second postoperative day. Patients are allowed to return to work in 1 to 2 weeks, provided that heavy labor and prolonged sitting are not involved [8,9,12,19,22].

Complications

The complications of AECM, as well as their prevention or treatment, are as follows [12]:

Infection can be avoided by careful sterile technique and intraoperative use of prophylactic intravenous antibiotics. The much smaller incisional area also is associated with a lower risk of infection than with an open procedure. Infection and complications secondary to a donor graft site are obviated. Aseptic discitis can be prevented by aiming the laser beam in a “bowtie” fashion to avoid damaging the end plates (at 6 o’clock and 12 o’clock).

Hematoma (subcutaneous and deep) occurs after ACF and may occur with minimally invasive spinal surgery. It is minimized by (1) avoidance of aspirin and nonsteroidal anti-inflammatory drugs for the week prior to surgery, (2) careful technique, (3) application of gentle digital pressure or placement of an IV bag over the operative site for the first 5 minutes after surgery, and (4) application of an ice pack thereafter.

Vascular injuries are extremely rare when care is taken to locate and protect the carotid artery, jugular vein, and other vascular structures, including the vertebral artery, which is found laterally in the foramen transversarium, and the inferior and superior thyroid arteries. No carotid artery injury has been reported in the United States. The carotid sheath should be identified and protected under the surgeon’s fingers. If carotid arterial pulsation is hard to palpate, it can be augmented with intravenous ephedrine as previously described. No prolonged retraction of the carotid sheath and artery is required as in anterior cervical fusion, and hence, direct trauma and embolic complications involving carotid vessels are unlikely.

Neural injury is extremely rare with minimally invasive approaches. No spinal cord injuries have been reported. Nerve root and spinal cord injury, though possible, can be avoided with continuous intraoperative EMG neurophysiologic monitoring and direct endoscopic visualization. Neural complications of ACF, including hypoglossal, spinal accessory, phrenic, auricular and cutaneous nerves, can be prevented by careful technique. Recurrent laryngeal nerve injury, though a recognized complication of ACF, is extremely rare with AECM. One case of postoperative hiccough and one of postoperative hoarseness have occurred transiently out of 1200 cases of AECM [12].

Sympathetic nerve injury is extremely rare but can occur from injury to cervical sympathetic and stellate ganglions. One case of incidental transient Horner syndrome or oculosympathetic dysfunction lasting 1 day following AECM was noted [12].

Excessive sedation can be avoided with use of surface electroencephalography monitoring, as previously described, which provides more precise estimation of the depth of anesthesia, thereby reducing the amounts of anesthetics required and preventing excessive or insufficient sedation.

A major complication of ACF or AECM is operating at the wrong level and with improper instrumentation. Proper utilization of digital C-arm fluoroscopy for anatomical localization avoids complications caused by poor placement of instruments or operating at the wrong disc level.

Dural tears which is one of the complications of ACF have not been reported after AECM.

Although soft tissue injuries may occur because of prolonged forceful retraction as occurs in ACF operations, they are not an issue with AECM. Similarly, failure of fusion, collapse of the bone plug, migration of the bone plug, and hardware failure cannot occur.

Dysphasia and postoperative airway obstruction due to edema may occur but can be avoided through careful surgical procedures and identification of these organs. Esophageal and tracheal injury due to edema or perforation can be avoided with careful palpation and digital retraction at the site of needle insertion. Having the anesthesiologist place a nasogastric tube into the esophagus helps the surgeon identify and retract that structure by palpation.

Inadequate decompression of disc material can be minimized by using multiple modalities and instruments such as forceps, trephining of the posterior ligament, discectome, bur and rasp, and laser application to both vaporize tissue and perform thermodiscoplasty.

Thyroid gland injury can be avoided by approaching the glands posteriorly and not encountering the parenchyma. Presence of a large goiter requires special care because of its vascularity.

A thorough knowledge of the AECM procedure and surgical anatomy of the cervical spine and neural foramen, careful selection of patients, and preoperative surgical planning with appropriate diagnostic evaluations facilitate AECM and prevent potential complications. All potential complications of open anterior disc surgery are possible but are rare or much less common with AECM.

Conclusion

The minimally invasive surgery involved with AECM and foraminal decompression represents a new procedure for treating symptomatic herniated cervical discs and foraminal disc lesions. The anterior approach through an endoscope aims at reducing tissue trauma from conventional open cervical surgery. Low-energy nonablative laser frequency is applied for shrinkage and tightening of the disc (laser thermodiscoplasty). With appropriate endoscopic spinal surgical training, thorough knowledge of the surgical anatomy of the cervical spine and 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 as compared to traditional open surgery.

CASE STUDY 22.1

A 35-year-old professional musician with increasing and intractable neck and upper extremity pain and numbness of the fingers was unable to perform because of his condition. Magnetic resonance imaging showed a large left foraminal herniated C5-C6 disc compressing the C6 nerve root (Fig. 22-9). AECM and left C5-C6 foraminal decompressive discectomy and foraminoplasty provided immediate relief of all the patient’s symptoms.

image image

Figure 22–9 Case Study 22.1: Preoperative magnetic resonance images showing—a large left foraminal herniated C5-C6 disc compressing the C6 nerve root ((A) axial view; (B) sagittal view).

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