Introduction

Cervical radiculopathy is a common problem typically encountered by spinal surgeons. It is defined as a syndrome of pain and/or sensorimotor deficits due to compression of a cervical nerve root. Common causes of the syndrome include cervical disc disease, spondylosis, instability, trauma, and tumors. Typical symptoms of cervical radiculopathy include arm pain typically in a dermatomal distribution, neck pain, numbness, and weakness [1].

Most patients (75–90%) with cervical radiculopathy will have symptomatic improvement with conservative, nonoperative management, which includes treatments such as physical therapy, cervical traction, and epidural steroid injections. However, when patients either fail conservative management or begin to experience progressive neurologic deficits, surgical intervention is warranted. Numerous techniques from both anterior and posterior approaches have been investigated in the treatment of cervical radiculopathy, each having its own distinct advantages and disadvantages. The two most common procedures are anterior cervical discectomy and fusion (ACDF) and posterior cervical foraminotomy (PCF).

History of Procedure

PCF was first described by Spurling and Scoville [2], and Frykholm [3]. This procedure became the preferred technique in the treatment of herniated cervical discs until Smith and Robinson introduced the anterior approach [4], modified later by Cloward in 1958 [5]. Over the following decades, the anterior approach became much more commonly used. Although the PCF remained a viable procedure, after this time, there was a paucity of quality data in the literature for the next several decades [6]. Using minimally invasive lumbar discectomy as a model, the minimally invasive technique for PCF was first described in cadaver studies in 1998 [7] and 2000 [8]. In 2001, Adamson described the MIS PCF endoscopic technique and results in his first 100 consecutive patients, showing 97% of patients with good or excellent outcome [9]. In 2002, Fessler and Khoo further described the technique, demonstrating equivalent results of microendoscopic PCF to traditional open PCF, with 87–92% symptomatic improvement in both groups [10].

Indications

The posterior cervical foraminotomy is indicated in patients with a lateral soft disc herniation or foraminal stenosis causing nerve root compression and subsequent progressive or intractable radiculopathy [11, 12]. While indications are narrow, in a carefully selected patient, the complications associated with ACDF can be avoided. Relative contraindications to ACDF, including previous surgery, history of radiation, or history of infection, may influence the decision to perform PCF.

Although the anterior approach has become popular, it is associated with potential complications such as tracheal or esophageal injury, injury to the carotid or vertebral arteries, injury to the jugular vein, or injury to the recurrent laryngeal nerve. Additionally, removal of disc material and subsequent fusion of the spine limits spinal motion, leading to stress on adjacent levels. Subsequent adjacent segment disease as well as pseudarthrosis, graft subsidence and kyphosis can all occur as a result [13, 14].

The procedure is contraindicated in primary axial neck pain, central disc herniation, diffuse spondylotic disease causing central stenosis, or bilateral radicular symptoms. The procedure is also contraindicated in patients with evidence of cervical spine instability or deformity [13].

Surgical Technique

In the operating room, general endotracheal anesthesia is induced. A Mayfield head holder is affixed to the patient’s head. Neuromonitoring should be utilized throughout the procedure with somatosensory evoked potentials (SSEPs) to monitor the integrity of the spinal cord. Electromyography can also be used when manipulating the involved nerve root to monitor for any potential damage to the nerve. The procedure can then be performed in either of two positions: prone or sitting.

For positioning into the prone position, the patient is carefully turned onto the open Jackson table with C-flex head positioning system (Allen Medical). The arms are then tucked at the patient’s side. SSEPs should be checked after positioning to confirm that neurologic function has not been compromised. Advantages of prone positioning include decreased risk of intraoperative hypotension and air embolism. Disadvantages include greater blood loss and more blood in the operative field, although using reverse Trendelenburg position may prevent pooling of blood in the field.

Sitting position is performed when using the endoscope. Potential advantages of the sitting position include decreased operative time and blood loss compared to prone position. Disadvantages include risk of venous air embolism and intraoperative hypotension.

Regardless of positioning, fluoroscopy is then brought into the field for lateral x-ray to localize the appropriate level. Once the appropriate level is marked, the patient is then prepped and draped in the standard fashion. A 2 cm incision is then made approximately 1.5 cm lateral from midline, extending through the fascial layer. Under fluoroscopic guidance, sequential dilators from a tubular retractor system are passed and the final tubular retractor system (between 16 and 21 mm) is held in place with the attachment secured to the operative table. The microscope or endoscope is then brought into the field.

Soft tissues are then removed from the operative field using Bovie electrocautery and pituitary rongeurs, moving cautiously, in order to avoid penetrating through the interlaminar space. After soft tissue removal and bony visualization, a curved currete is used to define the anatomy of the lamino-facet complex and remove ligamentum flavum from the underside of the lamina. 1 or 2 mm Kerrison punch is then utilized to perform the laminotomy and the procedure extends laterally to perform the foraminotomy. Often, a high-speed drill will need to be utilized for appropriate bony removal. It is crucial to avoid >50% of facet removal in order to maintain mechanical stability. The ligamentum flavum can then be removed to visualize the dura and proximal nerve root. Epidural bleeding from the nerve root venous plexus is to be expected during this portion of the procedure. It can be controlled with Gelfoam and cotton patties. If identified, the venous plexus can be coagulated using the bipolar electrocautery on low setting, and then divided.

Once the nerve root is visualized, a 45-degree-angled nerve hook is used to palpate the neural foramen to assess if decompression is adequate and to identify any disc fragments or osteophytes. To facilitate removal of disc or osteophyte and minimize nerve root retraction, approximately 2 mm of the superior medial portion of the rostral pedicle can be drilled.

In the case of soft disc herniation, once identified, the posterior longitudinal ligament can be incised with a #11 blade. Fragments can then be mobilized using a micro nerve hook and removed using a pituitary rongeur. In the case of osteophyte, a down-angled curette can be used to reduce them or break them apart to facilitate their removal.

Once satisfactory nerve root decompression has been achieved, the wound is then copiously irrigated with antibiotic-soaked saline, hemostasis is achieved, and the tube retractor system is removed from the field. The fascial, subcutaneous, and skin layers are then closed with absorbable sutures, and a skin glue is used as the final layer.

Literature Review

Overall, PCF is an effective procedure. The literature reports good-excellent relief of radiculopathy symptoms in 85–100% of patients [15–18]. Several studies have shown statistically significant improvements in Neck Disability Index, Visual Analog Scale for Neck, and Visual Analog Scale for Arm scores at both 1- and 2-year follow-up [19, 20].

Minimally invasive posterior cervical foraminotomy has been shown to be a viable alternative to anterior cervical discectomy and fusion in a select patient population, notably those with a lateral soft disc herniation or foraminal stenosis. A meta-analysis by McAnany et al. in 2015 comparing the effectiveness between open and minimally invasive techniques demonstrated that outcomes were not statistically different between the two procedures [21]. However, in a systemic review by Clark et al., which included the only reported randomized clinical trial [22], which compared outcomes between MIS and open PCF, the authors found that blood loss, pain medication use and hospital length of stay were reduced in patients who underwent MIS PCF over open PCF [23].

In a retrospective review of patients undergoing ACDF or PCF at a single institution between 2005 and 2011, Lubelski et al. reported that both procedures have a statistically equivalent 2-year reoperation rate [24]. Another retrospective review by Ruetten et al. comparing ACDF vs PCF in unilateral single-level radiculopathy in posterolateral or foraminal disc herniation showed no significant difference between the groups in terms of the overall outcome, complication rate, or revision rate [25]. Several studies have also shown a significantly higher cost of ACDF over PCF (one study showing an average cost of $8192 for ACDF and $4320 for PCF), largely related to cost of surgical implants [26, 27].

A long-term follow-up study by Bydon et al. investigating 151 patients who underwent PCF found a reoperation rate of 9.9% an average of 2.4 years after initial surgery, with a rate of 16.4% reoperation in patients with at least 2-year follow-up. It was noted that patients with preoperative neck pain had a higher incidence of reoperation. Reoperation of the same level was statistically more significant over surgery at adjacent/distant level. A majority of these patients (80%) underwent ACDF as the reoperation procedure, with cervical laminectomy and fusion (13.3%) and PCF (6.7%) behind [16]. Skovlrj et al. also showed similar results, with a reoperation rate of 7.1% in patients undergoing ACDF after PCF at index level an average of 55 months after initial procedure [20].

Lastly, PCF has been shown to lead to significant improvements in overall patient mobility, ability to perform daily activities and self-care, relief of pain, and decrease in anxiety/depression [28].

Minimally invasive posterior cervical foraminotomy has been shown to be a safe, and cost-effective treatment for patients with lateral disc herniation or foraminal stenosis, achieving similar long-term outcomes to that of ACDF, while avoiding both potential complications seen in anterior procedures and spinal fusion that could disrupt normal spinal biomechanics.