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Minimally Invasive 2-Level Posterior Cervical Foraminotomy

Preliminary Clinical Results

Holly, Langston T. MD; Moftakhar, Parham BA; Khoo, Larry T. MD; Wang, Jeffrey C. MD; Shamie, Nick MD

Author Information
Journal of Spinal Disorders & Techniques: February 2007 - Volume 20 - Issue 1 - p 20-24
doi: 10.1097/01.bsd.0000211254.98002.80
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Abstract

Posterior cervical foraminotomy was first described over 60 years ago,1,2 and is still a widely accepted method for the surgical treatment of cervical radiculopathy. Although presently anterior cervical discectomy and fusion is the procedure of choice for many surgeons, posterior cervical foraminotomy can provide excellent results in appropriately selected patients. This technique has several advantages over anterior cervical discectomy such as preservation of cervical motion, no need for internal or external bracing, and virtually eliminates the risk of swallowing or voice-related complications postoperatively.

Minimally invasive surgical techniques have become the gold standard in many surgical disciplines, and these principles have become increasingly applied to the field of spine surgery. One of the drawbacks of conventionally performed posterior cervical foraminotomy is the significant muscle stripping and retraction that must be performed to expose the spine. This can result in significant postoperative pain, increased intraoperative blood loss, and impaired muscle function. These undesired consequences of the surgical approach can be magnified in multilevel posterior cervical procedures.

Several authors have previously described the minimally invasive posterior cervical foraminotomy, primarily focusing on the surgical management of single-level radiculopathy.3,4 This novel method seems to be safe and efficacious, without compromising the goals of the procedure. In this manuscript the authors detail our preliminary experience performing the 2-level minimally invasive posterior cervical foraminotomy through a single incision.

MATERIALS AND METHODS

Patient Population

The cohort is composed of 21 consecutive patients with cervical spondylosis who underwent a minimally invasive 2-level posterior cervical foraminotomy at the University of California at Los Angeles Medical Center between 2003 and 2005. A retrospective hospital chart and magnetic resonance imaging review was performed on each patient. The Office for the Protection of Research Subjects at our institution approved the protocol for this study. There were 13 men and 8 women with an age range of 35 to 78 (mean 51).

Signs and Symptoms

All of the patients had radicular symptoms that were referable to 2 adjacent dermatomes located on the same side. Radicular arm pain was the most common presenting symptom, and was encountered in all 21 patients. Fifteen patients complained of numbness or paresthesias in the upper extremities. Eleven patients noted weakness in at least one muscle group in the arms, and 5 patients suffered from hand weakness. Thirteen of the patients had cervical radiculopathies on their left side and 8 patients were symptomatic on their right side.

Physical Examination

Fifteen patients had abnormalities in their sensory examination located in a specific radicular distribution. Eleven patients were determined to have mild unilateral upper extremity weakness. Eleven of the patients were hyporeflexic in the muscle groups associated with the nerve root compression, and 10 had normal upper extremity reflexes. In 4 patients, muscle atrophy and fasiculations were also encountered. Hoffman reflex or any other sign of upper motor neuron disease was not elicited.

Radiographical Imaging

Magnetic resonance imaging was used in each case to evaluate the degree of spinal canal and nerve root compression. Computed tomographic myelography was used in selected patients to inspect the neural foramina for nerve root filling defects. Computed tomographic myelography was particularly helpful in patients who had previous anterior cervical surgery with resultant metallic hardware artifact. The levels that were affected included: C2-3, and C3-4 (1 patient), C3-C4 and C4-C5 (3 patients), C4-C5 and C5-C6 (2 patients), C6-C7 and C7-T1 (1 patient), with most patients presenting at C5-C6 and C6-C7 (14 patients). Preoperative imaging demonstrated either posterolateral disc herniations or foraminal stenosis secondary to osteophyte formation and cervical spondylosis (Figs. 1A–D).

F1-4
FIGURE 1.:
A, Sagittal T2 weighted magnetic resonance imaging of a 58-year-old man demonstrating mild C5-6, C6-7 disc bulging without evidence of a spinal stenosis. B, The parasagittal and axial views demonstrates spondylosis that causes severe left-sided (C) C5-6 and (D) C6-7 foraminal stenosis.

All patients had failed a trial of at least 3 months of nonoperative management. The nonoperative management was not uniform, but consisted of at least two of the following modalities: nonsteroidal anti-inflammatory medication, physical therapy, oral steroids, and epidural steroid injections. Three of the patients had previously undergone anterior cervical discectomy and fusion procedures at another institution. Two of these patients developed a recurrence of their radicular complaints at the level of surgery, whereas the other patient's primary symptoms were at the level adjacent to the fusion.

Operative Technique

After induction of general anesthesia the Mayfield head clamp is affixed to the patient's head, and the patient is carefully turned into the prone position on bolsters. The patient's neck is attached to the bedframe in a slightly flexed position, and all of the pressure points are appropriately padded. The bed is placed in reverse trendelenburg to minimize epidural venous bleeding. A lateral C-arm fluoroscopic image is then obtained to make sure that at least the most rostral of the two operative levels can be adequately visualized. If neither level can be visualized due to patient body habitus, then antero-posterior fluoroscopy is used for localization (Fig. 2). The patient is then prepped and the C-arm unit is drapped into the surgical field.

F2-4
FIGURE 2.:
Intraoperative anteroposterior fluoroscopic image in a patient demonstrating localization of the tubular retractor to the C6-7 level. This level could not be adequately visualized using lateral fluoroscopy secondary to the patient's body habitus.

Under fluoroscopic guidance, a 22-gauge needle is superficially inserted into the paraspinal muscle overlying the lateral mass located between the 2 operative levels (eg, C6 for a C5-6, C6-7 procedure). An 18-mm skin incision is centered on this point, approximately 15 mm lateral to the midline on the operative side. Monopolar electrocautery is used to dissect through the subcutaneous tissue and make a small opening in the cervical fascia. The fasical opening is then slightly enlarged by gently spreading a pair of Metzenbaum scissors. At this point the serial dilators from the Metrx tubular retractor system (Medtronic Sofamor Danek, Memphis, TN) are used to perform the final dilation of the paraspinal muscle and fascia under fluoroscopic guidance. Unlike lumbar procedures in which this system is used, the initial K-wire step is not recommended because of the possibility of inadvertently passing the wire into the spinal canal. The appropriate length (18 mm) tube is then centered over the rostral lamina-facet junction (Figs. 3A, B), and the operative microscope is brought into the field. The tube is then connected to a table mounted flexible arm retractor.

F3-4
FIGURE 3.:
A and B, Lateral fluoroscopic images demonstrating the tubular retractor and sucker localized over the C5-6 and C6-7 levels in the same patient.

At this point the foraminotomy should be performed in virtually the same manner as an open procedure. A 2-mm Kerrison punch is used to remove some of the medial superior and inferior lamina to access the spinal canal. A high-speed drill is then used to thin the medial facet, centered over the joint. The remaining bone overlying the nerve root is removed using angled curettes and small Kerrison instruments. The superior and inferior pedicles represent the rostral-caudal limitations of the bone removal and should be palpated with a small nerve hook. The nerve hook is passed laterally out through the foramen to confirm adequate neural decompression. Epidural venous bleeding is usually well-controlled using gelfoam. In cases in which a soft lateral disc herniation is present, the nerve root can be gently elevated, and a small hook is used to retrieve disc material from the axilla of the root sleeve. After the cephalad nerve root has been decompressed satisfactorily, attention is turned toward the caudal level. The tube is then gently centered over the caudal level using the last dilator, and the same exact procedure is performed. The last dilator has a slightly smaller diameter than the tubular retractor, and with a subtle manipulation the tube can be directed caudally over the area of interest. Epidural steroids can be placed over the nerve roots if desired. The tubular retractor is then removed, and soft tissue hemostasis is achieved using bipolar electrocautery. The incision is closed in anatomic layers using absorbable suture and steri-strips.

RESULTS

The mean follow up for the patients was 23 months (range 12 to 36). Sixteen patients were discharged home the same day of surgery with oral narcotics and muscle relaxants. Four patients were discharged the following day, and 1 patient went home 2 days after surgery. All of the patients who stayed 1 night in the hospital did so because they lived a significant distance from the hospital and preferred to leave the next morning. Nineteen of the 21 patients (90%) had complete resolution of their preoperative radicular pain after their surgery. Patients who presented with only pain noted resolution immediately postoperatively, whereas patients with preoperative pain combined with mild motor weakness or numbness generally noted complete pain resolution by their 2-week visit. By the third month, patients who had prior muscle atrophy and fasiculations, were regaining bulk in the respective muscle and the fasiculations had ceased.

Two patients did not show any improvement in their preoperative pain after surgery. One of these patients had a history of chronic pain and thoracic syringomyelia. A spinal cord stimulator was subsequently placed that did not provide pain relief either. The second patient underwent an anterior cervical discectomy and fusion at the 2 symptomatic levels. The pain resolved after the anterior procedure.

Average blood loss during surgery was 35 mL with a range between 10 and 100 mL. There were no intraoperative or postoperative complications including dural tear, cerebrospinal fluid leak or wound infection. All patients had incisional pain that resolved within several weeks postoperatively.

DISCUSSION

The surgical management of cervical radiculopathy has undergone significant evolution since Semmes and Murphey first described the relationship between unilateral disc rupture and arm pain in 1943.1,5 Initially, this condition was exclusively treated via a posterior cervical approach, pioneered by Frykholm6 as well as Spurling and Scoville.2 This technique yielded excellent results for radiculopathy, however, was suboptimal for treating patients with central disc herniations. The anterior cervical discectomy procedure was first described by Smith and Robinson,7 and provided a safe and effective manner to address central disc herniations. This procedure was later modified by Cloward8 and others, and was performed with or without fusion. Over time, anterior cervical surgery became increasingly popular and, for many surgeons, displaced the posterior cervical foraminotomy as the primary surgical treatment of cervical radiculopathy. However, with the recent advancement of minimally invasive spinal techniques, the posterior cervical foraminotomy has been met with renewed interest.

Minimally Invasive Posterior Cervical Foraminotomy

Minimally invasive posterior cervical foraminotomy via a tubular retractor system was adopted from the microendoscopic system for lumbar microdiscectomy first described by Foley and Smith.9 The rationale for the development of this technique was to reduce the iatrogenic soft tissue injury associated with conventional exposure of the spine.10–14 Although the soft tissue injury is clearly more significant with lumbar fusion procedures, studies have demonstrated that even a smaller procedure such as microdiscectomy is associated with undesired deleterious side effects related to muscle stripping and muscle retraction.15,16 The posterior cervical musculature assumes an important role in the maintenance of spinal alignment and neck posture. These muscles can also be a source of severe pain after posterior cervical surgical procedures. For these reasons, the development of minimally invasive posterior cervical procedures represents an important advancement in the field of spine surgery.

There have been several previous reports of minimally invasive posterior cervical foraminotomy published in the medical literature. Adamson3 described a series of 100 patients who underwent this procedure for single-level unilateral cervical radiculopathy. In his series approximately 97% of patients were significantly improved after the procedure, and the complication rate was only 3%. These study results compared quite favorably to those previously reported for open posterior cervical foraminotomy procedures, and indicated that this procedure could be successfully performed in a minimally invasive fashion. Fessler and Khoo4 reported a series of 25 patients who underwent minimally invasive posterior cervical foraminotomy and compared the results to his last 25 patients who underwent an open procedure. Successful results were obtained in 92% of patients, and the estimated blood loss was significantly lower in the minimally invasive cohort. Furthermore, the hospital stays were significantly shorter and postoperative narcotic use was significantly less in the minimally invasive group.

To our knowledge, there have been no studies of 2-level minimally invasive posterior cervical foraminotomy studies previously published in the medical literature. Ninety percent of our patients had successful outcomes as their pain completely resolved after our procedure. These results are comparable to the aforementioned minimally invasive procedure, and conventionally performed single-level procedure studies that demonstrate a success rate of 90% to 96%.13,14,17–19 Our mean estimated blood loss was 35 mL, and there were no perioperative complications. Our mean hospital stay was quite short as most of the patients went home the same day.

Comparison of Surgical Options

The minimally invasive 2-level posterior cervical foraminotomy is indicated for patients with symptomatic nerve root compression at 2 adjacent levels, and offers advantages over other commonly performed surgical approaches. Anterior cervical discectomy and fusion is certainly preferred over posterior foraminotomy in most patients with a centrally located disc herniation. However, in patients with foraminal stenosis or a formaminal/paracentral disc herniation without spinal cord compression, nerve root decompression can be achieved via a posterior cervical foraminotomy. The posterior approach can virtually eliminate undesired, yet commonly encountered complications of anterior cervical surgery including dysphonia, dysphagia, and odynophagia. Furthermore, normal cervical motion is spared and no prosthetic implants are required. Another surgical option for cervical radiculopathy is the anterior cervical foraminotomy procedure. This procedure eliminates some of the risks associated with cervical plating and fusion, but clearly the approach-related complications still exist. This operation has not become universally accepted among surgeons, as there have been concerns regarding spinal instability and recurrence of symptoms.20 These issues are likely to be only magnified for procedures at 2 adjacent levels.

Although posterior cervical foraminotomy has been proven to be a successful method to treat cervical radiculopathy, there are patients who should not be considered as candidates for this procedure. Patients with evidence of segmental hypermobility on flexion-extension radiographs may develop instability after this procedure, even if it is performed using minimally invasive techniques. Axial neck pain is poorly treated with this technique, and anterior discectomy and fusion may be the optimal surgical procedure in cases where significant axial neck pain and radiculopathy coexist. Lastly, patients who have evidence of both neural foraminal and spinal cord compression are best treated via an anterior cervical approach.

CONCLUSIONS

Two-level minimally invasive posterior cervical foraminotomy is ideal for patients with radicular symptoms caused by posterolateral and foraminal cervical pathology localized to adjacent spinal levels. This technique provides both surgeons and patients with a viable alternative to 2-level anterior cervical discectomy and fusion or open foraminotomy using a midline approach. Our preliminary results indicate that this outpatient procedure can be effectively performed with rates of success and complication equivalent to that of conventional foraminotomy.

REFERENCES

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Keywords:

posterior; cervical; minimally; invasive; foraminotomy

© 2007 Lippincott Williams & Wilkins, Inc.