Indications

The operative indications for minimally invasive laminotomy/foraminotomy/discectomy are (1) unilateral single-root (Fig. 49-1) or multiple-root cervical radiculopathy from lateral disc herniations or foraminal stenosis (single-level or multilevel), without instability, significant kyphosis, or severe axial neck pain; (2) persistent or recurrent root symptoms following anterior cervical discectomy and fusion; (3) cervical disc disease in patients for whom anterior approaches are relatively contraindicated (e.g., ventral neck infection, tracheostomy, prior irradiation); and (4) cervicothoracic disc herniation and radiculopathy, to avoid ventral approach potential complications and when the ventral approach is not feasible (short neck or others). A ventral approach should be considered in case of same-level bilateral radiculopathy, central disc herniation, significant kyphosis, and severe axial neck pain.

FIGURE 49-1 Axial T2-weighted cervical spine MRI demonstrates laterally herniated disc to the left with resultant effacement of the lateral thecal sac and compression of the exiting nerve root.

Most patients who are candidates for a noninstrumented, dorsal cervical decompression are also candidates for a minimally invasive cervical decompression. These are selected patients with clinical myelopathy or myeloradiculopathy, radiographic evidence of spinal cord compression from one to three adjacent cervical levels, and a lordotic cervical spine (Fig. 49-2). Contraindications include loss of the normal cervical lordosis, severe ventral disease (disease that extends for more than three levels), and segmental instability.

FIGURE 49-2 An 80-year-old male presented with chronic myelopathy from cervical stenosis and underwent right-sided approach for C4-5 microendoscopic decompression for stenosis. A, Sagittal T2-weighted MRI demonstrates focal C4-5 spondylotic stenosis with signal change in the spinal cord. B, Axial T2-weighted MRI reveals severe focal compression at C4-5. C, Postoperative axial CT image shows typical extent of bony resection required to achieve adequate decompression of the spinal cord. Note the preservation of the dorsal spinous process and contralateral lamina and facet. Also note the minimal impact on paraspinal soft tissues on the approach side (postoperative air is seen on the approach side and at the site of the laminotomy).

Minimally invasive dorsal cervical fixation could be applied in case of facet dislocation or segmental instability or to support ventral instrumentation. Few clinical reports are available in the literature.^36,37,39 Minimally invasive cervical laminoplasty is still undergoing investigation.

Preoperative Evaluation

The preoperative radiographic evaluation follows a detailed history and physical examination and should include MRI or postmyelographic CT, in addition to anteroposterior (AP), lateral, and dynamic cervical radiographs. Electromyography (EMG) and nerve conduction studies (NCS) may also assist to confirm the localization of radicular compression. Selective nerve root blocks can also be a useful additional therapeutic and diagnostic tool. All patients with pure radiculopathy who go on to surgery have failed conservative therapy, including oral medications, physical therapy, and/or steroid injections. Cervical spondylotic myelopathy patients undergo a careful analysis of their disease progression, physical examination, radiographic studies, and comorbidities. All patients are carefully counseled regarding the risks, benefits, and alternatives to surgery.

Midline Approach

A 3-cm skin incision is made in the dorsal midline with the disc space centered on the incision. Larger incisions extending over several segments may be necessary for multilevel disease. The operative level(s) and entry point are confirmed on lateral fluoroscopy. The superficial fascia is incised in the midline to the level of the ligamentum nuchae. The ligamentum nuchae is incised just off the midline ipsilateral to the site of interest. Care should be taken to avoid penetration into the erector spinae muscles, by staying along the margin of the bloodless deep fascia. After reaching the spinous processes of the site of interest, paraspinous muscles are dissected from the spinous processes, laminae, and facet joint, using a monopolar cautery or subperiostal dissection with a Cobb. A self-retaining retractor is placed to reflect the paraspinous muscles from the interlaminar space of interest. The remaining steps are performed under microscopic magnification or using loops and an endoscope.

Paramedian Approach

The operative level(s) and entry point are confirmed on lateral fluoroscopy with a K-wire. A 1.8-cm longitudinal incision is marked out approximately 1.5 cm off the midline on the operative side and injected with local anesthetic. For two-level procedures the incision should be placed midway between the targeted levels. After an initial stab incision, the K-wire is advanced slowly though the subcutaneous tissue and docked on the cervicodorsal fascia. Once an optimal trajectory is established, the fascia is incised with a scalpel to accommodate dilators. The fascia is retracted, and the smallest dilator is placed through the posterior cervical musculature under fluoroscopic guidance and docked at the lamina-facet junction of the level of interest. A slightly lateral trajectory is advised to avoid the spinal canal and ensure contact with the lateral mass. Successive tubular muscle dilators are carefully and gently inserted, remembering that the axial forces that are routinely applied during muscle dilation in the lumbar spine are hazardous in the cervical spine. After dilation, the final tubular retractor is placed and secured over the junction of the lamina and the facet with a table-mounted flexible retractor arm and the dilators are removed. The following steps are performed under microscopic magnification or using loupes or an endoscope. The endoscope is inserted and attached to the tubular retractor (Fig. 49-4). Monopolar cautery and pituitary rongeurs are used to clear the remaining soft tissue off of the lateral mass and lamina of interest, taking care to start the dissection over solid bone laterally.

FIGURE 49-4 A, Fluoroscopic control verifying the right placement of the table-mounted retractor after removal of the dilators. B, The endoscope and the retractor separately. C, The endoscope mounted on the tubular retractor.

Laminotomy/Foraminotomy/Discectomy

The medial facet/interlaminar space junction is identified. Using a high-speed drill, a partial laminotomy-facetectomy is performed beginning at the medial facet/interlaminar space and going laterally, without exceeding 50% facet removal, to maintain biomechanical integrity. The dorsolateral portion of the superior lamina and the medial part of the inferior articular facet are removed first. This will permit the removal of the lateral corner of the inferior lamina and the medial part of the superior articular facet, exposing the medial border of the caudal pedicle. The nerve root is located directly above the caudal pedicle and anterior to the superior articular facet. The ligamentum flavum can be removed medially after the foraminotomy to expose the lateral edge of the dura and proximal portion of the nerve root. Progressive lateral dissection can then proceed along the root as it enters the foramen. The venous plexus overlying the nerve root should be carefully coagulated with bipolar cautery and incised. With the root well visualized, a fine-angled dissector can be used to palpate ventrally to the nerve root for osteophytes or disc fragments. Should an osteophyte be present, a down-angled curette may be used to tamp the material further ventrally into the disc space or fragment it for subsequent removal. In the case of a soft disc herniation, a nerve hook may be passed ventrally and inferiorly to the root to gently tease the fragment away from the nerve for ultimate removal with a pituitary rongeur. In either case, additional drilling of the superomedial quadrant of the caudal pedicle allows greater access to the ventral pathology and obviates the need for excessive nerve root retraction superiorly (Fig. 49-5).

FIGURE 49-5 Intraoperative endoscopic photographs during left-sided cervical microendoscopic foraminotomy. In all photos, rostral is to the top and medial is to the right. A, Initial exposure reveals lateral edge of lamina (L) joining the medial facet (F) with fine up-going curette inserted under caudal edge of laminofacet junction. B, After initial laminotomy, the ligamentum flavum (LF) is seen with adjacent facet (F). C, After foraminotomy, the lateral edge of dura (D) and decompressed nerve root (NR) in the proximal foramen are revealed.

Decompression for Stenosis

In this case, ipsilateral laminotomy of the levels of interest is performed and the ligamentum flavum is left in place to protect the dura. The tube is then angled about 45 degrees off the midline such that the tube is oriented to visualize the contralateral side. A plane between the ligament and undersurface of the spinous process is gently dissected with a fine curette. The drill with guard sleeve extended is then used to progressively drill the undersurface of the spinous process and contralateral lamina all the way to the contralateral facet. This initial decompression allows greater working space within which to remove hypertrophied ligament while avoiding downward pressure on the dura and spinal cord. Dissection and removal of the ligament with curettes and Kerrison rongeurs may now proceed safely. Any compressive elements of the contralateral facet or the superior edge of the caudal lamina may also be drilled off or removed with Kerrison rongeurs at this time because their impact on the dura is more apparent with the ligament removed. After gently confirming decompression over to the contralateral foramen with a fine probe, the tube is returned to its original position to complete the ipsilateral removal of ligament and bone. This should then reveal completely decompressed and pulsatile dura (Fig. 49-6). If indicated, ipsilateral foraminotomy, as described earlier, also may be performed at this time.

FIGURE 49-6 Intraoperative endoscopic photograph during right-sided approach. The dura is seen to be completely decompressed in this image, following removal of offending bone and ligament. Rostral is to the right and lateral is to the bottom.

Lateral Mass Fixation

After exposure of the facet joint, a hand drill is used to create a pilot hole. The starting point is 1 mm medial to the midpoint of the lateral mass, and the trajectory will be 25 degrees lateral and parallel to the facet joint. Appropriate dimension screws are inserted after taping, and a rod is fixed with set screws. A midline incision is preferred in this case for the transmuscular approach. The same incision could be used for both sides. Also, fluoroscopic guidance is preferred.

Closure and Postoperative Care

Local anesthestic is injected into the fascia and muscles surrounding the incision. The wound is closed using one or two absorbable stitches for the fascia, two or three inverted stitches for the subcutaneous layer, and a running subcuticular stitch and Dermabond for the skin. After awaking from general anesthesia, the patient is brought to the postanesthesia care unit and mobilized as early as possible. No collar is necessary. The patient is discharged the same or next day, if medically stable.

Outcomes and Results

Favorable outcomes were reported in the literature for posterior cervical foraminotomy with a range between 75% and 100%.^{1,3,9,44–48} Krupp et al. separated the outcomes by soft, hard, and mixed pathology, with favorable outcomes of 98%, 84%, and 91%, respectively.⁴⁵ Jodicke et al. reported a significantly better outcome for soft discs compared to hard discs in early follow-up, but no difference was found at long-term follow-up.⁴⁷

The reports of minimally invasive, microscopic, and microendoscopic posterior cervical formainotomy have demonstrated equivalent efficacy to the open technique, but the blood loss, length of stay, and postoperative pain medication usage were reduced with the minimally invasive techniques.^{9,13,20,21,25,26,48} The senior author and Khoo prospectively used cervical microendoscopic posterior foraminotomy in 25 patients and compared the results with another 26 patients treated via open cervical laminoforaminotomy.⁹ The microendoscopic group had a lower overall operative time (115 vs. 171 minutes), less blood loss (138 vs. 246 mL), shorter postoperative hospital stay (20 vs. 68 hours), and fewer postoperative narcotic medications (11 vs. 40 equivalents) when compared with the open technique group.

Ruetten et al. conducted a prospective, randomized, controlled study with lateral cervical herniations, operated either in a full endoscopic posterior foraminotomy (89 patients) or conventional microsurgical anterior technique with fusion/plating (86 patients), with 2 years of follow-up.²⁰ There was no significant difference between the groups in the clinical outcome, revision, or complication rates. Preservation of motion was conserved in the full endoscopic posterior group.

Perez-Cruet and the senior author have reported on five patients undergoing cervical microendoscopic decompression for stenosis at one, two, or three levels.¹⁶ All patients demonstrated improvement in their myelopathy and returned to work with the only complication being one unintended durotomy that sealed spontaneously. Yabuki et al. performed endoscopic partial laminectomy in 10 patients with degenerative cervical compressive myelopathy.²⁸ All patients experienced symptomatic improvement with slight postoperative wound pain. The mean operative duration was 164 ± 35 minutes and the intraoperative blood loss was 45.5 ± 27 mL. Boehm et al. reported the results of 13 patients who were operated on under the microscope through a transmuscular tubular approach.³⁰ Nine of these patients suffered from cervical myelopathy. The average follow-up was 17 months. The neck disability index score and visual analogue scale score were significantly improved. Thirty-three percent showed complete recovery of the preoperative neurologic deficit, while 67% had improvement.

Wang et al. reviewed retrospectively 18 patients treated with lateral mass screws placed in a minimally invasive fashion.³⁷ In two cases, the minimally invasive technique was converted to the standard open technique because of inability to visualize anatomic landmarks on fluoroscopy (bulky shoulders). Successful fusion was documented in all cases, and there were no hardware failures during the minimum 2 years of follow-up. Two patients were lost to follow-up after 6 months.

Complications

The posterior cervical foraminotomy is a safe procedure associated with a low rate of complications (1–15%),^{1,3,9,13,20,21,25,26,44–48} with wound infection and dural tear contributing to the majority of them. The senior author has no infection to date in his microendoscopic series, and the unintended durotomy rate has dropped from 8% in the initial series of patients⁹ to around 1% more recently. Direct suture repair of durotomy is difficult through the narrow-diameter tubes or small incisions. Therefore one technique for handling small defects is to simply cover the durotomy with muscle, fat, hemostatic gelatin (Gelfoam, Baxter Healthcare, Glendale, CA), or dural susbstitute followed by fibrin glue or synthetic sealant such as Coseal (Baxter Healthcare, Glendale, CA). Using this approach, overnight bedrest is usually sufficient to seal the defect. For larger dural tears that cannot be primarily closed, 2 to 3 days of lumbar cerebrospinal fluid (CSF) drainage may prevent a leak. Ultimately, the small opening and relative lack of dead space after minimally invasive procedures have made the incidence of postoperative pseudomeningoceles and CSF49-cutaneous fistulae negligible.