Chapter 21 Anterior endoscopic cervical discectomy

As with most other aspects of medicine and surgery, the understanding, care, and treatment of cervical disc injury has progressed. In the early days of surgical intervention, operating around the cervical spine and spinal cord did not often have satisfactory results, and it was not until the early part of the 1920s that surgery for cervical disc abnormalities became a reasonable option. The treatment of cervical disc injury started out with posterior decompression, and by the late 1940s, decompression with more of an anterior approach became more common and fusion was accepted fairly rapidly. The mainstream or “gold standard” technique for treatment of cervical disc injury for most of the past half century has consisted of anterior decompression and arthrodesis. Throughout this time, decompression without fusion was explored, but not until later have minimally invasive techniques, such as anterior endoscopic cervical discectomy (AECD), been able to make decompression without fusion a viable option. The next horizon in the development of spinal care will likely include percutaneous disc augmentation technologies that one hopes will reduce the need for subsequent surgical intervention and limit the reliance on implant survivability (Fig. 21-1).

Figure 21–1 Algorithm showing progression of types of spinal care from conservative through pump implantation.

Advances in cervical disc surgery have paralleled, though often lagged behind, those in lumbar disc surgery. For many years, cervical fusion was the standard because of failure to gain satisfactory results with anterior decompression alone. Even in the lumbar spine, it was ultimately determined that decompression could be accomplished without fusion in many situations. Certainly the cervical and lumbar anatomies are not identical, although many similarities can be drawn, and knowledge and techniques can be applied from each area to the other, with special attention to the obvious anatomical differences.

The relatively early realization that anterior cervical disc decompression led to instability and often fusion or arthrodesis in kyphosis led to the common practice of performing fusion at the time of anterior cervical decompressive surgery. In comparison with the lumbar spine, posterior decompression of a cervical disc could be accomplished through a small enough entry zone that instability did not result regularly. It is these types of concepts that have allowed for the evolution of cervical disc surgery to the minimally invasive stage, with the realization that decompression of a cervical disc that does not remove too much of the surrounding structure can in fact be performed without resulting in instability. This procedure can even be performed in a minimally invasive fashion, and the advent of endoscopic technology allows for cervical decompression without the usual requirement for index fusion (Fig. 21-2).

Figure 21–2 Anterior endoscopic cervical discectomy. Transverse incision is made in right anterior neck region (left top), The tracheo-esophagus complex is pushed by the nail of the finger simultaneously the anterior part of the cervical vertebra is felt (left middle), Schematic drawing of flexible laser discoplasty (left bottom), Neural injury by herniated disc (right A), Needle insertion for discography procedure (right B), Drilling of the disc to creating anulotomy (right C), Disc material suctioned out through probe (right D), Flexible laser discoplasty (right E).

Endoscopic surgery has been growing in popularity over the years, notably in areas of joint arthroscopy focusing on the knee and shoulder, and, to some extent, the ankle and wrist. Endoscopic techniques have also enabled the development of abdominal and pelvic laparoscopy, cystoscopy, and ureteroscopy as well as endoscopic gastrointestinal interventions and otorhinolaryngologic applications. In fact, endoscopic techniques are being developed for the non–spine-related aspects of the cervical spine as well, even in the presence of the treacherous anatomy present.

Considering the history of the understanding of the cervical spine, it is no surprise that surgery for cervical disc abnormalities has had difficulties since its very beginning. The reasons are not only the technical difficulties with regard to operating on the cervical spine but also the lack of diagnostic tools and proven successful surgical experience. Differentiating between cervical disc herniations and other diseases, such as multiple sclerosis and amyotrophic lateral sclerosis, was often difficult because commonly there were few or nonspecific symptoms, pointing early clinicians to cervical pathology, and because results of simple radiographic examinations were often inconclusive, in that the neurologic signs and symptoms seemed to predominate in the motor system [1].

As early as 1911, Bailey and Casamajor discussed osteoarthritis of the cervical spine and suggested that the primary pathologic change is thinning of the intervertebral discs with resultant trauma to the vertebral end plates and osteophyte production, which causes symptoms. This narrowing of the disc space decreases the size of the neural foramen and compresses the facet joints. The spurs that then develop in response to this compression increase joint stress [2]. The primary cause of disc degeneration is generally assumed to be deficient nutrition, desiccation progressing with aging. The wear and tear of everyday activities and, occasionally, acute trauma are often additive to other, predisposing factors. Herniations of the cervical intervertebral discs with compression of the spinal cord have been described since 1928, when Stookey and other clinicians pointed out the similarities between the symptoms that arise as a result of a medial herniation and the more commonly associated symptoms of degenerative disease of the cervical spine [3,4]. That there is difficulty in diagnosing cervical disease is nothing new. It was a constant challenge for early clinicians to evaluate both the clinical symptoms and the radiologic findings in patients complaining of cervical and/or radicular symptomatology.

The majority of the anterior minimally invasive cervical discectomy procedures are based on small anterior anulotomy with cannula supported instrumentation, fluoroscopy and often endoscopy assisted intradiscal positioning. Then mechanical as well as laser or radiofrequency assisted disc removal and anular modulation is often added. Chiu and colleagues [5] substantiated their pursuit of minimally invasive cervical discectomy by stating that “fusion caused local inflammation, pain at the graft donor site, and a long recuperation compared to minimally invasive surgery without fusion which negates these complications.” As early as 1994, Chiu [6] had reported on 400 patients with nonextruded cervical disc herniations who had been treated with cervical endoscopic discectomy and laser thermodiscoplasty. With careful selection of patients and the use of lasers and microendoscopic equipment, a near 95% success rate was achieved. Table 21.1 shows the details of the international multicenter patient grouping treated with AECD [7].

The reduction in operative time, cost, and recuperation time with similar if not better outcomes and decrease in the need for fusion have indeed been successful at bringing minimally invasive cervical spine surgery to the 21st century. The commonplace use of lasers in spine surgery has also been a beneficial component of discectomy procedures. Prior to the use of lasers, an assortment of instruments were used with little or no side effects but none was able to satisfactorily remove the posterior disc and the displaced or herniated nuclear material [8]. In Korea, Lee began using holmium:yttrium-aluminum-garnet (Ho:YAG) laser with soft cervical disc herniations as early as 1993. His technique utilized the laser to remove the nucleus pulposus and to shrink down the protruded disc herniation in patients who had not experienced improvement with conservative therapy. It was noted at this time that the added benefit of the minimally invasive surgery was that it could be performed with use of local anesthesia, making monitoring of neurologic function readily evident. In 2001, Lee [8] wrote an article confirming his success with the percutaneous discectomy, stating that the combination of manual disc removal techniques with endoscopically directed Ho:YAG laser discectomy was a safe and effective surgical procedure.

Chemonucleolysis, the use of intradiscal chymopapain, has been out of favor in the United State for a number of years now. However, some surgeons have combined the use of low-dose chemonucleolysis with endoscopic discectomy procedures. In 1995, Hoogland and Scheckenbach [9] in Germany reported a new anterior cervical discectomy procedure with no complications. They performed low-dose chemonucleolysis utilizing 500 IU chymopapain followed by automated percutaneous nucleotomy of the cervical spine. The use of chymopapain remains quite limited, although the results of its use in association with minimally invasive surgery does seem to be improving. The use of lasers in this fashion is becoming more prominent, and with regard to the U.S. markets, lasers seemed to be more accepted than intradiscal chymopapain.

Much of the acceptance and growing U.S. popularity of minimally invasive spine surgery is credited to Drs. Chiu and Young and the development of endoscopic spine systems that allow for visualization while exploring the spinal anatomy for surgery. These procedures use techniques similar to those employed in discography; however, for the endoscopic cervical procedures, general endotracheal anesthesia with intraoperative spinal monitoring seems to be the safest approach. The safe zone for surgical intervention is identified by applying digital pressure over the anterolateral aspect of the cervical spine and displacing the carotid sheath and sternocleidomastoid musculature laterally and the paratracheal tissues medially. It is through this zone that a small incision is made in the skin and the instrumentation is placed into the central posterior portion of the disc. With this technique, success rates for AECD have ranged from 75% to 95%. As discussed later, these results can in fact be longstanding, and the techniques can serve as the basis for additional disc augmentation or even injectable disc replacement technology.

Instrumentation

Figure 21-3 displays the instruments used for AECD.

Figure 21–3 Instrumentation for anterior endoscopic cervical discectomy. (A) Micro-grabbers that can be used under direct vision through the working channel of the endoscope; (B) the working channel of a cervical endoscope; (C) trephine; (D) small cervical grabbers; (E) large cervical grabbers; (F) dilator; (G) working cannula; (H) fluid adapter; (I) stylet; (J) introducer needle.

Procedure

The operating room setup for AECD requires a radiolucent table, a C-arm (fluoroscope), and radiographic and endoscopic monitors, as shown in Figure 21-4. General anesthesia with intraoperative spinal monitoring is used. The patient is then placed in the supine position with a cervical roll for gentle neck extension and the arms at the sides with gentle wrist traction. After mechanical disc decompression, 800 to 1200 kilojoules total with the Ho:YAG laser or radiofrequency delivery with a Disc-FX System (Elliquence, LLC, Oceanside, NY) is used to modulate the injured posterior anulus so as to encourage stabilizing tissue ingrowth. Careful consideration is given to avoiding collapse with excessive tissue modulation.

Figure 21–4 Diagram showing the operating room setup for cervical discectomy.

The selection criteria for performing AECD are based on symptoms being consistent with radiologic findings for longer than 3 months. Discography is performed for difficult or multilevel cases, and a favorable response to traction is consistent with a good outcome for AECD.

1. The patient’s written informed consent is obtained.

2. General anesthesia is given with intraoperative spinal monitoring.

3. The patient’s neck is extended and supported on roll.

4. Digital pressure is applied in the avascular interval between the carotid sheath and the paratracheal fascia (Fig. 21-5).

5. The operative level is identified with fluoroscopy.

6. Skin infiltration of ropivacaine with epinephrine is performed (Fig. 21-6).

7. A transverse stab incision is made within the digital pressure area, and blunt dissection is completed with a hemostat (Fig. 21-7).

8. The needle is placed into the disc under fluoroscopic guidance (Fig. 21-8).

9. Discography with mixture of indigo carmine and contrast medium is performed (Fig. 21-9).

10. The stylet is placed, and the needle is removed (Fig. 21-10).

11. A dilator is introduced over the stylet (Fig. 21-11).

12. The cannula is inserted over the dilator to the center of the disc (Fig. 21-12).

13. Digital pressure is released.

14. The disc is decompressed manually with grabbers under fluoroscopic guidance (Fig. 21-13).

15. Completion of intradiscal decompression is confirmed through endoscopic evaluation (Fig. 21-14).

16. Fluoroscopically directed paraforaminal trephination is performed as needed.

17. Posterior fragments are removed endoscopically as needed (Fig. 21-15).

18. The posterior anular tissue is modulated with the laser (Fig. 21-16).

19. A specimen of approximately 1 to 2 mL is collected for pathologic examination if desired (Fig. 21-17).

20. Digital pressure on the instrument is resumed, and the cannula is removed.

21. A 4-0 synthetic nylon nonabsorbable (ETHILON, ETHICON, INC., Somerville, NJ) simple skin suture is used for closure, and a gauze dressing, ice pack, and firm Philadelphia collar are put in place.

Figure 21–5 Application of digital pressure in the avascular interval between the carotid sheath and the paratracheal fascia. The tracheo-esophagus complex is pushed by the nail of the finger simultaneously the anterior part of the cervical vertebra is felt (A) Schematic drawing of pathway of needle toward pathologic herniated disc. (B).

Figure 21–6 Infiltration of the skin with ropivacaine and epinephrine.

Figure 21–7 Transverse stab incision within the digital pressure area, which is followed by blunt dissection with a hemostat.

Figure 21–8 Needle placement into the disc under fluoroscopic guidance. The tracheo-esophagus (T-E) complex is pushed by the nail of the finger while inserting the needle (A) The shift of the T-E complex is confirmed under fluoroscope (B). The proper insertion of needle is observed at fluoroscopic AP view (C) and lateral view (D).

Figure 21–9 Discography with mixture of indigo carmine solution and contrast medium.

Figure 21–10 Placement of the stylet and removal of the needle.

Figure 21–11 Dilator over the stylet.

Figure 21–12 Cannula over the dilator to the center of the disc. The cannula is inserted over the dilator on intraoperative photography (A)The proper position of cannula is confirmed at fluoroscopic lateral view (B).

Figure 21–13 Manual decompression with grabber under fluoroscopic guidance.

Figure 21–14 Endoscopic evaluation and completion of intradiscal decompression.

Figure 21–15 Endoscopic removal of posterior fragments as needed.

Figure 21–16 Laser modulation of the posterior anular tissue.

Figure 21–17 A specimen of approximately 1 to 2 mL can be collected for pathologic examination if desired. This material was collected from the patient described in Case Study 21.1.

Related anatomy and physiology

Figure 21-18 illustrates the most common clinical presentations of cervical herniated nucleus pulposus, the indication for AECD.

Figure 21–18 The most common clinical presentation of cervical herniated nucleus pulposus (HNP) at different levels.

Complications

Of the 349 patients included in the case series since 1998, 3 patients had complications, all of which were intraoperative. One patient had breathing difficulty due to a reaction to anesthesia, but the procedure was successfully performed with general anesthesia on a subsequent date. Two patients had a vascular complication needing emergency airway and hematoma evacuation without the need for vascular repair. There were no instances of the other possible complications: neurologic compromise, cerebrospinal leak, infection, visceral injury, sympathetic dystrophy, and deep vein thrombosis.

Minimally invasive AECD without fusion has a low complication rate, involves short operation to discharge times, and yields satisfactory functional results. The procedure is easily done in an outpatient surgical facility, which involves lower costs than traditional hospital settings. More importantly, there was only a 4% fusion rate after the initial discectomy in the case series, making this paradigm shift in cervical disc surgery good for patients and payers.

CASE STUDY 21.1

The patient is a 39-year-old white woman who was referred for a second opinion evaluation after sustaining a neck injury in a motor vehicle accident 6 months before. She had experienced worsening rather than improvement in symptomatology over that time. She had been seen by a number of physicians who recommended multiple courses of intervention, including physical therapy, multifaceted medical management, and even surgical reconstruction with open fusion. The cervical magnetic resonance imaging evaluation identified disc herniation at C5-C6 with additional disc bulging from C3 through C7 as seen in Figure 21-19.

Figure 21–19 Case Study 21.1: Magnetic resonance images showing disc herniation at C5-C6 (A) with additional level disc bulging from C3 through C7 (B).

The patient’s complaints were primarily neck pain and radiating symptoms into the right upper extremity as well as down into the hand with associated numbness and tingling in the radial digits. She also had weakness in her right upper extremity with associated neck pain and headaches. Her pain was worse with sleeping and also with lifting things over her head, especially with her right arm. The pain did not worsen with coughing, sneezing, or straining, and there were no changes in bowel or bladder function.

On physical examination, the patient had satisfactory posture with no apparent deformities or surgical scars. Palpation of the cervical spine demonstrated tenderness and spasm in the paracervical musculature extending into the trapezial and periscapular region as well as into the right upper extremity and down into the distal arm and then into the thumb area of the right hand with associated dysesthesia. Motor examination found some weakness in the right wrist extensors as well as a slight decrease in the sensation in the C6 distribution. The patient had no clonus or any other pathologic reflexes, although the brachioradialis reflex was slightly diminished on the right in comparison with the left.

Because of the multilevel nature of the magnetic resonance imaging abnormalities, a discogram was performed to confirm symptomatology at C5-C6. Concordant pain elicited was with epidural leak at the C5-C6 level and no leak, and no pain was elicited at the adjacent levels. Figure 21-20 shows the fluoroscopic and post-injection computed tomographic images of the discogram study. It was decided to proceed with AECD at C5-C6.

Figure 21–20 Case Study 21.1: Post-injection computed tomographic (A) and fluoroscopic (B) images from the discogram study.

Figure 21-17 shows the removed disc material sent for gross inspection. The patient did well intraoperatively. Postoperatively, a firm Philadelphia collar was placed, and once the stitch was removed, the patient was told to utilize the soft collar at night for a total of 2 weeks.

Then, 4 weeks of soft collar use during the day during the subsequent rehabilitative program was instituted. The patient worked on extension range of motion and modalities during this time. At 4 weeks, she progressed to a MedX extension strengthening program for 4 more weeks. (Figure 21-21 depicts the use of the MedX cervical extension strengthening machine.) The patient gained significant relief of the arm pain shortly after the surgery, and the neck pain diminished over the subsequent 2 months with progressive rehabilitative therapy.

Figure 21–21 Case Study 21.1: MedX Cervical Extension Machine (MedX Medical, Orlando, FL), which the patient in 4-week strengthening program.

Slight disc space narrowing was evident on radiography at 3 months, although the patient had minimal cervical complaints at that time. Figure 21-22 shows the lateral cervical radiographs obtained before and 3 month after surgery, demonstrating the slight postoperative disc space narrowing at C5-C6. At 1 year, the patient was evaluated for some increase in low back pain, but no significant neck pain was identified.

Figure 21–22 Case Study 21.1: Lateral cervical radiographs obtained preoperatively (A) and 3 months postoperatively (B) demonstrate the slight postoperative disc space narrowing at C5-C6.