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Sitting

Prone b

Sitting

Prone

Fig. 3. Operative blood loss (a) and time (b) when performing the CMED procedure in all patients combined, in the semisitting position, and in the prone position.

procedure and to rule out secondary gain or psychological issues that may result in a poor surgical outcome.

Anesthesia and Operative Setup

After appropriate preoperative evaluation and medical clearance, patients were brought to the operative suite. Following the induction of general endotracheal anesthesia, adequate intravenous access was secured. An arterial line is placed to enable continuous blood pressure monitoring and control. Adequate blood pressure is maintained to assure spinal cord perfusion during this procedure. During the initial experience with the CMED technique, patients were placed in the prone position. However, this led to bleeding that often obscured the endoscopic image during the operative procedure and resulted in increased operative times and blood loss (fig. 3). A change to the semisitting position using a Mayfield head holder (fig. 4) has resulted in significantly improved operative visualization, relieved epidural venous congestion, and decreased operative blood loss and operative times (fig. 3). The advantage of this position is that blood does not accumulate at the bottom of the tubular retractor. Blood loss was found to be substantially less and the procedure can be preformed with the tubular retractor positioned at a comfortable height for the surgeon (fig. 5). Because of the slightly increased risk of air embolism, precordial Doppler as well as end tidal pCO2 are measures. We do not routinely place a central venous line. Adequate intraoperative measures taken in the event of an air embolism should be familiar to the operative team prior to undertaking this procedure.

Before final patient positioning, utmost care is directed at ensuring that the cervical spine and neck musculature are not kinked or held in an unfavorable

Fig. 4. Patient positioned in a semisitting position with head affixed in a Mayfield head holder (a) with lateral C-arm in place (b).
Fig. 5. The position of the surgeon, while standing behind the patient, viewing the endoscopic image on the operative monitor. Note the ergonomically favorable position of the surgeon's hands and body posture.

position. The neck is placed in a neutral or slightly flexed position to ensure adequate jugular venous drainage and the head is secured in the Mayfield holder to assure direct midline positioning. In most instances a Foley catheter is not placed except in instances where more than one level is performed.

Somatosensory evoked potentials, as well as EMG recordings, are measured to further ensure the safety of the procedure. After the initial induction of anesthesia, we have refrained from the use of neuromuscular paralytics to allow for improved feedback from the nerve root(s) during the operation. A single preoperative dose of either Ancef or vancomycin is used. We do not routinely employ Solumedrol or other glucocorticoids for neural protection.

The fluoroscopic C-arm is brought into the surgical field and positioned with the arc over the patient so that real-time lateral fluoroscopic images can easily be obtained (fig. 6). Although we have not typically use anteroposterior images, they can also be utilized to facilitate docking of the initial K-wire and tubular retractors on the facet complex. The surgeon generally stands directly behind the neck of the patient with the video and fluoroscopic monitors placed within direct view of the surgeon to allow optimal ergonomic flow during the procedure (fig. 5).

Surgical Technique

We employed the METRx system (Medtronic Sofamor-Danek, Memphis, Tenn., USA) of endoscopic retractors, camera, and instruments for the procedures (fig. 1). As this system was initially designed for lumbar discectomy, several modifications have been made to better optimize its use in the CMED procedure. These include lengthening of the table-mounted retractor as well as a better selection of smaller profile curettes and Kerrison punches for use in the more delicate cervical spine. An initial stab incision was made approximately 1-2 cm off midline ipsilateral to and at the level of the pathology. Under fluoroscopic guidance, a K-wire was inserted through the posterior cervical musculature and fascia down to the facet complex or lateral mass of the operative level. Particular caution was taken at this point to insure that the guidewire was docked on bone to avoid inadvertent dural penetration medially or slipping off the facet complex laterally (fig. 6). Once the guidewire is docked on the facet complex in question, the skin incision was extended above and below the K-wire for a total length of approximately 2.0 cm. The skin edges are retracted with a small retractor and the cervical fascia incised using either a Metzenbaum scissors or Bovey cautery. Care should be taken not to cut muscle fibers during this procedure as this can cause unnecessary blood loss. Due to the relative thickness of the posterior cervical fascia, this sharp opening of the fascia is required to allow for easier and safe passage of the sequential dilating cannulas with a minimum use of force. If a skin-covering barrier such as ioband was placed, it should be circumferentially removed from around the skin incision to prevent plastic sequestra that can occur during placement of the percutaneous

Fig. 6. Lateral fluoroscopic images showing docking of the K-wire on the facet complex (a), first dilator (b), second dilator after K-wire is removed (c), third dilator (d), fourth dilator (e), and tubular retractor in place with curette-identifying facet f).

soft tissue dilators. It is important to remove the K-wire after the initial dilator is passed. A series of dilators are then sequentially inserted using a gentle downward rotating maneuver through the posterior neck musculature, over which an 18-mm tubular retractor was inserted. Real-time lateral fluoroscopic images were obtained throughout the above procedure to insure proper docking of the sequential dilators and tubular retractors on the facet complex (fig. 6a-f). The working channel (tubular retractor) is then attached to a flexible arm affixed to the operating table side rail and locked in position. The retractor arm is positioned to avoid obscuring the lateral fluoroscopic image. The endoscope is then attached to the tubular retractor via a circular plastic friction couple. Additionally, the endoscopic camera used today has far superior resolution and clarity than the cameras used during our previous cadaveric studies and initial operative cases. Further modifications of the instruments are ongoing to improve the safety, efficacy, and ease of this procedure.

Once the tubular retractor is set in the desired position, a Bovey cautery with a long insulated tip is used to remove the remaining muscle and soft tissue overlying the facet complex. A small straight or up-going curette in conjunction with lateral fluoroscopic imaging can further define the bone anatomy and localization of surgical anatomy (fig. 6f). The dissection is initially started laterally where the bone is easily palpated with the Bovey tip. Once the bone of the lateral facet complex in exposed, the dissection of muscle off the facet complex continues medial to expose the laminofacet junction with care not to enter the interlaminar space with the Bovey tip. To prevent Bovey cautery smoke from obscuring the endoscopic image during this procedure a frequent on/off technique is used that allows smoke to clear from the tube before proceeding. A suction tubing is also attached to the endoscopic device. If the tubular retractor is properly placed initially only a small piece of muscle tissue needs be removed to expose the facet complex. Often the ligamentum flavum is thinned or altogether absent near the lateral edge of the interlaminar space thereby placing the dura and spinal cord at higher risk. With the bone well visualized the inferior edge of the superior lamina and the medial edge of the lateral mass-facet complex are identified with a small straight or up-going endoscopic curette. The facet complex at the proper level is clearly identified before proceeding. Bleeding from epidural veins is controlled using a long tipped endoscopic bipolar cautery. For bleeding underneath the edge of the lamina, angled bipolar forceps with a 45° angle are often useful. After the medial facet plane has been clearly defined, a small angled 1- or 2-mm Kerrison rongeur is used to begin the foraminotomy (fig. 7a). Periosteal and bone bleeding is addressed with bone wax and cautery. In cases of marked facet arthropathy and enlargement, a drill with a long endoscopic bit (e.g. AM-8 bit with Midas Rex or TAC bit with MEDNext drill) can be used to further thin the medial facet and lateral mass.

Fig. 7. Intraoperative images showing Kerrison punch initiating medial facet removal (a), nerve probe passing out of the foramen once foraminotomy is performed with underlying nerve root exposed (b), lateral fluoroscopic image with down-going curette on disc under nerve root (c), and endoscopic image showing removal of disc fragment (d).

Fig. 7. Intraoperative images showing Kerrison punch initiating medial facet removal (a), nerve probe passing out of the foramen once foraminotomy is performed with underlying nerve root exposed (b), lateral fluoroscopic image with down-going curette on disc under nerve root (c), and endoscopic image showing removal of disc fragment (d).

Frequent dissection of the soft tissue off the bone with an angled curette facilitates safe use of the Kerrison rongeur. In this fashion, the decompression is carefully continued inferiorly and laterally along the course of the neural foramen. The laminoforaminotomy is completed when the nerve root had been well exposed along its proximal foraminal course. The adequacy of the decompression should be confirmed by palpating the root along its course with a small nerve hook (fig. 7b).

In cases where a herniated cervical disk or free disc fragment is present, additional exposure is obtained by drilling a small portion of the superomedial pedicle directly below the exiting nerve root. As the nerve root lies directly against this portion of the pedicle, removing a small portion of the pedicle will create enough space for passing a down-going curette (fig. 7c) under the nerve root to remove a disc fragment without traumatizing the nerve root (fig. 7d). Additionally osteophytes encountered in this region can also be drilled or curetted as needed. Prior to closure the nerve root is palpated along its anterior surface to ensure that no residual compression exists along its course.

Far lateral foraminal stenosis or disc herniations can also be decompressed through this approach. As the nerve root often passes in close proximity to the vertebral artery laterally, particular attention should be paid during decompression in this area. Inadvertent passage of instruments beyond the bone defining the posterior margin of the foramen transversarium should be avoided. Brisk dark bleeding is often encountered from the rich venous plexus, which typically surrounds the space around the vertebral artery. When encountered, such bleeding should serve as a useful warning to limit further dissection and thus prevent inadvertent arterial injury. Unnecessary excessive decompression of the facet should be avoided to prevent iatrogenic instability of the cervical motion segment. Raynor et al. [15] concluded that the integrity of the majority of the facet joint is essential for stability and that no more than 50% of the facet should be removed to maintain its integrity.

Wound Closure

After inspection of the nerve root, meticulous hemostasis should be obtained by a combination of bipolar cautery and gentle tamponade with thrombin-soaked gel-foam pledgets. The area is then copiously irrigated with lactated ringers impregnated with bacitracin antibiotics. Although optional, we have usually placed a small piece of gel-foam soaked with Solumedrol gently over the laminoforaminotomy defect. Use of epidural morphine paste or similar cocktails is reasonable if there is no evidence of dural erosion or tear. Alternatively, Marcaine (0.25%) can be injected around the incision. Such agents may help to reduce postoperative pain and allow for more rapid recovery and ambulation. The tubular retractor and endoscope are then removed and a routine closure of the fascia and skin performed. As the defect is typically quite small, only a limited amount of closure need be performed and a drain is not needed. A 0-Vicryl-type reabsorbable stitch is used to close the lumbodor-sal fascia in a figure of 8. Inverted 2-0 Vicryl stitches are used to reapproximate the subcutaneous layer. Dermabond is used to reapproximate the skin edges and no dressing is applied as the Dermabond will adhere to it. Dermabond is attractive as it keeps the skin edges closely approximated for a 7- to 10-day period as well as providing a waterproof barrier. The patient can thus shower almost immediately after surgery.

Postoperative Care

The patient was then awakened from anesthesia and taken to the postanesthesia recovery unit. Most patients have the procedure on an ambulatory basis; therefore, long-acting inhalational and intravenous agents should be avoided to allow for rapid awakening of the patient postoperatively. Additionally, use of only short-acting muscle relaxants for initial induction will allow for better monitoring of nerve root function as well as quicker extubation of the patient after surgery. This procedure performed on an outpatient basis requires thorough perioperative patient education [14].

Once in the postanesthesia recovery area, the patients are allowed to rapidly mobilize and ambulate as tolerated. Arterial and intravenous lines are removed early on. If a Foley catheter was placed it is generally removed before the patient leaves the operative suite. Done correctly, this procedure does not result in either instability or fusion of the operated cervical motion segment. Therefore no cervical collar is required. Soft collars and other comfortable semirigid collars can be given to patients for their comfort if desired. It is important to emphasize to patients, however, that chronic dependence on such orthosis will only lead to further deconditioning of the cervical musculature. Depending on their preoperative medications, patients are typically discharged on a combination of muscle relaxants (e.g. baclofen or Flexeril), nonsteroidal antiinflammatories (e.g. Toradol, Vioxx, or Celebrex), and an oral opioid for breakthrough pain (i.e. Vicodin or Darvocet). When we compared our patients with patients treated via open cervical foraminotomy, we found that the microendoscopic foraminotomy (MEF) group used significantly less pain medications postoperatively than did the open group [11]. Patients undergoing this procedure typically recovered rapidly with only mild to moderate discomfort upon discharge. Of our last 30 cases, the majority of patients were discharged in 6 h or less.

Complication Avoidance

Complications can be avoided by having a thorough understanding of cervical anatomy, proper training in endoscopic spinal techniques and a knowledge of possible complications. Adamson [1] retrospectively reviewed 100 cases of patients undergoing endoscopic posterior cervical laminoforaminotomy

(MEF) and reported complications in 3 patients; 2 cases of dural puncture required no intervention other than gel-foam and 1 case of superficial wound infection was reported. In a series by Khoo et al. [11] three complications occurred in 25 patients and were attributable to surgical technique. These included two small cerebral spinal fluid (CSF) leaks and 1 case of partial-thickness dural violation. For the 2 cases where a CSF leak occurred, no direct repair was required as the durotomy was very small. After 2-3 days of routine lumbar drainage for patients with CSF leaks, none of these patients went on to have long-term clinical sequelae of chronic CSF leak or symptomatic pseudomeningocele. Thus we have routinely employed a lumbar drain for 2-3 days postoperatively to help closure of the small dural tear. Additional adjuncts such as fibrin glue, fat or muscle grafts can also be used. Spinal headaches and nausea associated with the lumbar drainage were treated symptomatically with nonsteroidal anti-inflammatory medications and bed rest. If a large durotomy occurs, direct dural repair can be attempted if specialized instruments are available for use through the endoscopic tube. Castro-Viejo-type needle holders and long forceps are particularly useful in this regard. In rare instances, conversion to an open procedure may be necessary to close large dural violations. To date, we have not had problems with delayed pseudomeningoceles or continued CSF leaks. The risk of dural injury can be reduced with experience in performing this technique with most durotomies occurring on initial patients undergoing this procedure. Patients should be advised of this potential complication and informed that with appropriate management durotomy results in no adverse clinical result.

A potential complication, which has not been reported, is iatrogenic injury during the surgical approach and muscle dilatation portion of this operation. Unlike the thoracodorsal fascia, the posterior cervical fascia is very thick and must be cut under direct visualization to prevent hyperextension of the neck during insertion of the dilators. The initial K-wire or smaller dilators can be inadvertently pushed between the cervical lamina resulting in nerve root or spinal cord injury; therefore, this portion of the procedure is performed under lateral fluoroscopic guidance. An anteroposterior fluoroscopic image can also help in safely docking the K-wire and subsequent dilators on the facet complex. Additionally, lateral displacement of the K-wire or dilators can result in nerve root or vertebral artery injury. Brisk venous bleeding can also result if the dilators inadvertently slip lateral to the facet complex during placement. This is controlled with gentle gel-foam packing and/or bipolar cautery. The K-wire is removed after the first dilator is passed and subsequent dilators securely docked onto the laminar facet junction.

To help reduce intraoperative bleeding the CMED procedure is performed in the semisitting position (fig. 4). A series of patients comparing cervical laminoforaminotomy performed in the open prone position, microendoscopic prone position, or microendoscopic sitting position revealed reduced operative times, estimated blood loss, postoperative length of stay, and pain medication requirements in the microendoscopic sitting position group [11]. The sitting position significantly reduces epidural venous engorgement, thus decreasing blood loss. In addition, this position allows blood to flow out of the tubular retractor, rather than accumulating and obscuring the endoscopic view of the operative field. Although none of the sitting position patients experienced an air embolism the potential increased risk for air embolism precludes the use of a pericardial Doppler even though the incidence of clinically significant embolic event remains extremely low.

Conclusion

The endoscopic posterior cervical laminoforaminotomy and discectomy technique is a safe and effectively treatment of posterior lateral cervical disc herniation and/or foraminal stenosis. The learning curve associated with this technique requires additional training and we recommend that this training be performed under the guidance of an experienced endoscopic minimally invasive spine surgeon. Cadaveric training can further familiarize the surgeon with this technique. The clinical results are very satisfying since patients experience less postoperative pain and can be discharged on the same operative day.

References

1 Adamson TE: Microendoscopic posterior cervical laminoforaminotomy for unilateral radiculo-pathy: Results of a new technique in 100 cases. J Neurosurg 2001;95(1 suppl):51-57.

2 Aldrich F: Posterolateral microdiscectomy for cervical monoradiculopathy caused by postero-lateral soft cervical disc sequestration. J Neurosurg 1990;72:370-377.

3 Baba G, Furusawa N, Imura S, et al: Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine 1993;18:2167-2173.

4 Brayda-Bruno M, Cinnella P: Posterior endoscopic discectomy (and other procedures). Eur Spine J 2000;9:S24-S29.

5 Fager CA: Posterolateral approach to ruptured median and paramedian cervical disc. Surg Neurol 1983;20:443-452.

6 Foley KT, Smith MM: Microendoscopic discectomy. Tech Neurosurg 1997;3:301-307.

7 Henderson CM, Henney RG, Shuey HM, et al: Posterolateral foraminotomy as an exclusive operative technique for cervical radiculopathy: A review of 846 consecutively operated cases. Neurosurgery 1983;13:504-512.

8 Herkowitz HN, Kurz LT: Surgical management of cervical soft disc herniation: A comparison between the anterior and posterior approach. Spine 1990;15:1026-1030.

9 Hilibrand AS, Yoo JU, Carlson GD, et al: The success of anterior cervical arthrodesis adjacent to a previous fusion. Spine 1997;22:1574-1579.

10 Hunter LY, Braunstein EM, Bailey RR: Radiographic changes following anterior cervical fusion. Spine 1980;5:399-401.

11 Khoo LT, Perez-Cruet MJ, Laich DT, Fessler RG: Posterior cervical microendoscopic foramino-tomy; in Perez-Cruet MJ, Fessler RG (eds): Outpatient Spinal Surgery. St. Louis, Quality Medical Publishing, 2002, pp 71-93.

12 Krupp W, Muke R: Clinical results of the foraminotomy as described by Fryholm for the treatment of lateral cervical disc herniation. Acta Neurochir (Wien) 1990;107:22-29.

13 Perez-Cruet MJ, Smith M, Foley K: Microendoscopic lumbar discectomy; in Perez-Cruet MJ, Fessler RG (eds): Outpatient Spinal Surgery. St. Louis, Quality Medical Publishing, 2002, pp 171-183.

14 Perez-Cruet MJ, Rice-Wyllie L, Pieper DR: Patient education; in Perez-Cruet MJ, Fessler RG (eds): Outpatient Spinal Surgery. St. Louis, Quality Medical Publishing, 2002, pp 35-47.

15 Raynor RB, Pugh J, Shapiro I: Cervical facetectomy and its effect of spine strength. J Neurosurg 1985;63:278-282.

16 Roh SW, Kim DH, Cardoso AC, Fessler RG: Endoscopic foraminotomy using microendoscopic discectomy system in cadaveric specimens. Spine 2000;25:260-264.

17 Simeone F, Dillin W: Treatment of cervical disc disease: Selection of operative approach. Contemp Neurosurg 1986;8:1-6.

18 Tomaras CR, Blacklock JB, Parker WD, Harper RL: Outpatient surgical treatment of cervical radiculopathy. J Neurosurg 1997;87:41-43.

19 Williams RW: Microcervical foraminotomy. A surgical alternative for intractable radicular pain. Spine 1983;8:708-716.

Mick J. Perez-Cruet, MD, MS

Institute for Spine Care, Department of Neurosurgery Chicago Institute of Neurosurgery and Neuroresearch, Rush-Presbyterian-St. Luke's Medical Center, 1725 West Harrison Street Suite 970, Chicago, IL 60612 (USA)

Tel. +1 708 250 3194, Fax +1 312 942 2176, E-Mail [email protected]

Haid RW Jr, Subach BR, Rodts GE Jr (eds): Advances in Spinal Stabilization. Prog Neurol Surg. Basel, Karger, 2003, vol 16, pp 266-276

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