Percutaneous and Minimally Invasive Approaches to Decompression and Arthrodesis of the Cervical Spine

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Chapter 49 Percutaneous and Minimally Invasive Approaches to Decompression and Arthrodesis of the Cervical Spine

Degenerative disease of the cervical spine can cause compression of neural elements through disc herniation, ligament and facet joint hypertrophy, and the formation of vertebral body end-plate osteophytes. The effects of these changes can be exacerbated by a congenitally narrow spinal canal, segmental instability, and deformity. These dynamic processes can contribute to radiculopathy, myelopathy, or both, depending on the degree to which nerve roots and/or the spinal cord are affected. Surgical decompression is indicated for selected patients with neurologic signs and symptoms of radiculopathy and/or myelopathy with corresponding radiographic evidence of neural compression. The cervical spine can be decompressed through an anterior or a posterior approach, each of which has relative advantages and disadvantages. Although the choice of approach is sometimes relatively clear, often the problem can be addressed from either direction, with the ultimate decision balancing the risks and benefits of each method. In the past 2 decades, the minimally invasive and percutaneous techniques have been shown to preserve healthy tissues, shorten hospital stays, cause less postoperative pain, and enable faster patient recovery. This chapter discusses these different techniques (anterior and posterior approaches) with descriptions of the procedures and outcomes.

Dorsal Minimally Invasive Approaches for the Cervical Spine

Dorsal decompressive procedures are fundamental tools in the surgical treatment of symptomatic cervical degenerative spine disease.¹^–⁴ Even as ventral cervical procedures have gained prominence, posterior cervical laminoforaminotomy still provides symptomatic relief in 92% to 97% of patients with radiculopathy from foraminal stenosis or lateral herniated discs.^3,⁵ Similarly, dorsal cervical decompression for cervical stenosis achieves neurologic improvement in 62.5% to 83% of myelopathic patients undergoing either laminectomy or laminoplasty.^4,⁶^–⁸ Moreover, these operations avoid the complications attendant to ventral approaches to the cervical spine, namely, esophageal injury, vascular injury, recurrent laryngeal nerve paralysis, dysphagia, and accelerated degeneration of adjacent motion segments after fusion.⁹^–¹¹

However, open dorsal approaches to the cervical spine require extensive subperiosteal stripping of the paraspinal musculature that leads to postoperative pain, spasm, and dysfunction and can be persistently disabling in 18% to 60% of patients.^4,^9,^12,¹³ Furthermore, preoperative loss of lordosis and long segment decompressions increase the risk for postoperative sagittal plane deformity,¹⁴^–¹⁷ a complication that frequently prompts instrumented arthrodesis at the time of laminectomy. Employing these extensive posterior fusion techniques increases operative risks, time, and blood loss; exacerbates early postoperative pain; and potentially contributes to adjacent-level degeneration.

The fundamental tenet of minimal access techniques is reduction of approach-related morbidity. To that end, the advent of muscle-splitting tubular retractor systems and the use of endoscopic technology or the microscope have allowed for the application of minimally invasive techniques to dorsal cervical decompressive procedures ^13,¹⁸^–³⁵ and fixation.³⁶^–⁴⁰

Spurling, Scoville, and Frykholm were the first to describe the open cervical foraminal decompression between 1944 and 1947.⁴¹^–⁴³ In 1983 Williams reported the first microsurgical technique for dorsal cervical foraminotomy.⁴⁴ Several minimally invasive dorsal cervical techniques were described after that.¹⁸^–⁴⁰ To avoid confusion, and to simplify the description of all these techniques, we divided them into two main approaches: (1) the minimally invasive midline cervical approach, and (2) the minimally invasive paramedian (transtubular or transmuscular) cervical approach. An endoscope or microscope could be used in either approach. These approaches are used to perform laminotomy/foraminotomy/discectomy, laminectomy, laminoplasty,^34,³⁵ and lateral mass fixation.³⁶^–⁴⁰

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.

Operative Setup

General endotracheal anesthesia is induced on a standard electric operating table. A neurophysiologic monitoring array with capabilities for somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), and free running electromyography (EMG) is put in place. In cases of myelopathy, a fiberoptic intubation may be elected and evoked potentials are compared before and after positioning to identify positioning-related cord ischemia. Maintenance of normotension to avoid spinal cord hypoperfusion is best directed with continuous blood pressure measurements afforded by an arterial line. Measures to detect and treat air embolism, such as a precordial Doppler and a central line, are options but have not yet proven necessary. Given the small exposure, the risk of air embolism is low. A urinary catheter is generally not necessary for one- or two-level procedures. Routine perioperative antibiotics are administered. Relaxants are minimized after induction to allow for effective neurophysiologic monitoring.

Posterior cervical approaches might be performed with the patient in the prone or sitting position. With the prone position, the head is held with a Mayfield pin-holder or a well-padded horseshoe-shaped headrest, with slight flexion. The operating table is tilted in a reverse Trendelenburg position to ensure that the cervical spine is parallel to the floor. The senior author (RGF) prefers the sitting position (Fig. 49-3) because it confers advantages of decreased epidural bleeding, decreased pooling of blood in the operative field, decreased anesthesia time, and gravity-dependent positioning of the shoulders for better lateral fluoroscopic images. The table is turned 180 degrees relative to the anesthesiologist. The patient’s head is fixed in a Mayfield head holder. The table is manipulated to place the patient in a semisitting position with the head flexed and the neck straight and perpendicular to the floor.

FIGURE 49-3 Sitting position with C-arm in place.

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.

Potential neurologic complications include radicular injury from manipulation within the tight foramen or direct mechanical spinal cord injury during dilation or decompression. Vertebral artery injury can be avoided by early detection of dark venous bleeding from the venous plexus surrounding the artery that may arise from accidental dilation lateral to the facet or during overly aggressive dissection laterally in the foramen. This type of bleeding can typically be controlled by packing with Gelfoam or another hemostatic product.

Postoperative muscular pain and spasm from subperiosteal dissection are minimized with the transmuscular miscroscopic and microendoscopic techniques.

Ventral Minimally Invasive Approaches for the Cervical Spine

Anterior cervical discectomy and fusion (ACDF) was first described by Smith and Robinson and then by Cloward in the 1950s.⁴⁹^–⁵¹ Orozco introduced anterior plating in 1970 as adjunctive treatment in cervical fractures.⁵² Since then, several types of plates and grafts were developed. ACDF has now developed as a standard procedure in the treatment of cervical radiculomyelopathy. It is described as a safe and efficacious procedure with good fusion rates. However, several problems can occur, mainly because of access complications and adjacent segment degeneration as a disadvantage of fusion. Hilibrand et al. postulated that up to 25% of the patients who undergo a ventral cervical fusion could require treatment for degenerative changes of the adjacent segments within 10 years.⁵³ With the fascination of minimally invasive techniques and the intent to preserve motion and prevent adjacent segment disease, several anterior alternative approaches have been reported: (1) ventral cervical foraminotomy (microsurgical and endoscopic); (2) percutaneous ventral cervical procedures for discectomy, anuloplasty, and stabilization; and (3) cervical arthroplasty. The final approach is not discussed in this chapter.

Ventral Cervical Foraminotomy (Microsurgical and Endoscopic)

In 1968, Verbiest described a ventrolateral approach to the cervical neuroforamen, which involved sectioning of the longus colli muscle, exposure of the transverse process, mobilization of the vertebral artery, and performing discectomy with and without fusion.⁵⁴ In 1976, Hakuba described the transuncodiscal approach. In his approach the vertebral artery was not displaced, and a complete discectomy was performed with and without fusion.⁵⁵ In 1989, Snyder and Bernhardt published a new anterior cervical fractional interspace decompression technique, which consisted of a 6-mm-wide cylindric bur hole in the lateral third of the intervertebral disc, and fragmentectomy. They reported minimal disc space collapse and a 4% rate of spontaneous fusion.⁵⁶ In 1996, Jho described the anterior cervical foraminotomy with resection of the uncus process, lateral portion of the rostral end plate, and lateral portion of the intervertebral disc. This technique required cutting of the longus colli muscle and exposure of the vertebral artery along its medial surface.⁵⁷ In 2002, Saringer proposed a modification of Jho’s technique by preserving a thin piece of cortical bone of the lateral wall of the uncinate process, avoiding exposure of the vertebral artery,⁵⁸ and he added the endoscope to his procedure in 2003.⁵⁹ Again in 2002, Jho reported an upper vertebral transcorporeal foraminotomy technique. The hole in this technique was drilled at the most lateral and inferior 4 to 5 mm of the upper vertebral body.⁶⁰ The cartilage end plate was exposed and entered in its posterior third. In 2007, Choi et al. described a modification of the upper vertebral transcorporeal Jho’s approach, made by drilling the hole more medially, to avoid cutting the longus colli muscle and exposing the vertebral artery.⁶¹ The evolution of this technique has led to (1) having less disc disruption, (2) avoiding exposure of the vertebral artery, and (3) avoiding cutting the longus colli muscle, which could result in the injury of the sympathetic chain.

Transuncal Approach

The medial border of the longus colli muscle is cut perpendicularly and retracted or excised to expose the medial aspect of the transverse process and the uncinate process of the lower vertebrae. Care should be taken when exposing the C6-7 level because the vertebral artery lies between the transverse process of C7 and the longus colli muscle. The next steps are performed under microscopic magnification or using the endoscope as described by Saringer in his 2003 technique modification.⁵⁹ According to Jho, in his first description,⁵⁷ the uncinate process is undertaken with a 2-mm high-speed drill, leaving a thin dorsolateral rim of cortical bone that limits the vertebral artery laterally and the nerve root dorsally. The thin cortical bone is removed with a curette and a Kerrison rongeur. The posterior longitudinal ligament is exposed, which covers the nerve root posteriorly. At this point, the foraminotomy is completed and the uncovertebral osteophyte is removed. In case of a herniated disc, the posterior longitudinal ligament should be excised with a curette and Kerrison rongeur and the disc fragment removed. Epidural bleeding could be troublesome and should be controlled with bipolar cauterization or by application of Gelfoam and cottonoid. Saringer, in his microscopic⁵⁸ and endoscopic⁵⁹ techniques (Figs. 49-7 and 49-8), described two essential modifications to Jho’s transuncal approach: (1) leaving the lateral cortical rim of the uncinate process to protect the vertebral artery, and (2) extending the foraminotomy by removing more bone from the caudal dorsolateral aspect of the rostral vertebrae.

FIGURE 49-7 Left, Under the endoscope, the medial portion of the longus colli muscle (LCM) is excised and the lateral portion of the disc (D) and the uncus process (UP) are exposed. The UP is drilled up. A thin piece of the lateral wall of the UP is left, serving as a landmark and protective layer for the underlying vertebral artery (VA). Periosteum covers the nerve root, disc fragments, and lateral portion of the posterior longitudinal ligament (PLL). The intervertebral disc is maintained in its form. The VA is intentionally not exposed. Right, The periosteum and cartilaginous and degenerative fibrous tissue between the tip of the UP and the rostral end plate and osteophytes at the dorsolateral cephalad end plate are removed using a 1- or 2-mm thin-foot Kerrison rongeur. Disc fragments (DF), parts of the nerve root (NR), and lateral parts of the PLL are exposed.

(Modified from Saringer WF, Reddy B, Nöbauer-Huhmann I, et al: Endoscopic anterior cervical foraminotomy for unilateral radiculopathy: anatomical morphometric analysis and preliminary clinical experience. J Neurosurg 98[2 Suppl]:171–180, 2003.)

FIGURE 49-8 Left and right, Transtubular and axial depiction of the last step of the operation shown in Figure 49-7. To improve visualization, the endoscope is positioned with its tip inside the drilled canal. Herniated disc fragments are mobilized with a microhook.

Transcorporeal Approach

In his technique modification of the transcorporeal approach, Jho describes drilling a hole through the ventral caudolateral portion of the rostral vertebrae ⁶⁰ that extends dorsally to reach the dorsal portion of the uncinate process. Only this dorsal portion is removed. The uncovertebral osteophyte is removed, and as described earlier, the posterior longitudinal ligament should be opened if a disc fragment has to be removed. This approach reduced the disc disruption comparatively with the transuncal approach. Choi et al. more recently described a modification of this technique made by starting the hole more medially on the upper vertebrae, to avoid cutting the longus colli muscle and its related possible complications.⁶¹ They also stated that a transcorporeal approach through the inferior vertebrae could be feasible, especially for the upper cervical levels (Fig. 49-9).

FIGURE 49-9 Photograph of a cervical spine model demonstrating bone entry sites: Transuncal approach as originally discribed by Jho (A); upper transcorporeal approach as described by Jho (B); lower transcorporeal approach (C); and upper transcorporeal approach as described by Choi et al. (D).

Once the decompression is completed, the platysma is closed as usual with 3-0 absorbable sutures. The skin is closed with a subcuticular suture. No cervical collar is necessary postoperatively, and activity is advanced as tolerated.

Outcomes and Results

The microscopic or endoscopic ventral cervical foraminotomy for unilateral cervical radiculopathy has been shown to be an effective and safe procedure. Johnson et al. reported their series of 21 patients operated on by Jho’s original technique and followed between 6 and 36 months.⁶² Nineteen patients (91%) had improved or resolved radicular symptoms, and two (9%) had persistent radicular symptoms necessitating further surgery. No patients had evidence of instability or loss of disc height on lateral radiographs at 3 months postoperation. Tascioglu et al. reported their result of the same technique for three patients with long-term follow-up.⁶³ The three patients were symptom free in the immediate postoperative period, and their follow-up examinations demonstrated findings within normal limits at 37, 36, and 36 months, respectively, after surgery. Saringer et al. reported in 2002 his results of 34 patients operated with microscopic uncoforaminotomy.⁵⁸ The follow-up period varied from 2 to 17 months with a mean of 8.2 months. The large majority (97%) of patients were pleased with the results of their operation. The relief of neck pain and redicular pain in the affected dermatome was immediate in all patients. Motor weakness and sensory deficit improved dramatically immediately postoperatively, and improved to normal in the majority of patients within 3 to 6 months. One of the patients had a repeat herniation on the second postoperative day but recovered completely after reoperation and continued to do well at the 6-month follow-up. In 2003, Saringer et al. reported their results from 16 patients operated on with endoscopic uncoforaminotomy.⁵⁹ During a mean follow-up period of 13.8 months, an average absolute improvement of 44% (P > .05) in the neck disability index score and of 96% (P > .05) in the visual analogue scale score for radicular pain (compared with the preoperative score) was observed. Jho et al. reported their results for 104 patients.⁶⁰ Ninety-nine percent experienced excellent or good results. One patient developed discitis, which resulted in bony fusion. All other patients maintained their motion segments. Lee et al. reported their results for 13 patients operated on with the transuncal approach⁶⁴; the mean follow-up was 19 months. All patients experienced complete relief of their radiating pain. The mobility was conserved, and no instability was detected on neuroimaging follow-up. Choi et al. also reported their results from 20 patients operated on by their technique.⁶¹ The maximum follow-up was 1 year. All patients experienced immediate postoperative relief of their radicular symptoms and recovery of their neurologic symptoms. The percentage change in disc height was only 6% from the baseline value, but the difference was statistically significant (P = .005). They noted that the loss in disc height seemed to stabilize after 3 months postoperation. Balasubramanian et al. also reported 94% good to excellent results in 34 patients.⁶⁵

Hacker and Miller are the only researchers to report a significant number of poor outcomes (poor 35% and fair 13%) and a high reoperation rate (30%).⁶⁶

Hong et al. compared the results of the transuncal approach (40 patients) and the transcorporeal approach (20 patients).⁶⁷ The mean follow-up period was 9.5 months. They analyzed postoperative changes of disc height, the spinal instability, the average length of hospital stay, the degree of patients’ satisfaction, and complications from each approach. They stated that the transcorporeal approach is a better surgical technique than the transuncal approach, considering the preservation of disc height, spinal stability, length of hospital stay, degree of satisfaction, and complications.

Complications

Possible complications are mostly the same as for a standard anterior cervical approach. As in some of these techniques when the longus colli muscle is cut, risk of injury of the sympathetic chain could be higher. This outcome is true especially at the lower cervical levels, where the sympathetic chain becomes more medial on the longus colli muscle. Jho reported 2 transient Horner syndromes in his 104-patient series.⁶⁰ With Choi’s technique, this complication could be avoided. Injury of the vertebral artery is another concern of these techniques. Meticulous review of the anatomy of the vertebral artery on the imaging studies and good knowledge of the anatomy of this region should help to avoid this complication.

Percutaneous Ventral Cervical Procedures for Discectomy, Nucleoplasty, and Stabilization

In 1963 to 1964, Smith introduced the chemonucleolysis with chymopapain to treat herniated discs.^68,⁶⁹ In 1975, Hijikata developed the percutaneous lumbar discectomy and reported his series of 136 cases 12 years later.⁷⁰ In 1986, Ascher reported the laser discectomy.⁷¹

The percutaneous ventral cervical approach was first described by Smith and Nicole in 1957, as the cervical discographic technique for the diagnosis of discogenic pain.⁷² Despite its low complication rates (0.16–2.48%),⁷³^–⁷⁵ its use was limited due to the catastrophic consequences that can occur if a complication developed. Although controversies still exist, several reports of related percutaneous cervical discectomy (PCD) procedures have been reported: (1) PCD with chemonucleolysis,⁷⁶ (2) automated/coblation PCD,⁷⁷^–⁸² (3) PCD with laser,⁸³^–⁹⁰ (4) PCD with endoscopic manual and laser,^83,⁹¹^–⁹⁵ and (5) PCD with stabilization.⁸³

Indications and Contraindications

Patients who present with new onset of cervicobrachial neuralgia, due mainly to recent soft disc herniation (contained), and who are nonresponsive to conservative treatment and without severe neurologic deficit could be considered for PCD with laser, coblation, or chemonucleolysis. In case of the same scenario, but with noncontained herniated disc, PCD with endoscopic manual and laser is recommended. Percutaneous stabilization is indicated when axial symptoms predominate, in case of angular instability (kyphosis), and when cervicoencephalic pain is reproduced by discography.⁸³

These procedures are contraindicated in patients with migrated or calcified discs, advanced spondylosis, significant anterior bony spurs that could block the entry into the disc, cervical canal stenosis, myelopathy, or evidence of instability, and in those who had previous neck surgery.^83,^92,⁹⁴

Surgical Technique

The procedures could be performed under local or general anesthesia. The patent is placed in the supine position, as for a conventional ventral cervical approach. A roll is placed under the shoulders, and the shoulders are taped down for better visualization of the lower cervical levels as needed. Preparation and draping are completed as usual. The choice of the side of approach depends on the surgeon’s preference, but an approach contralateral to the side of the lateral herniated disc is preferable. Fluoroscopic guidance is used through the procedure for anatomic orientation and avoidance of complications. The level of work is identified with fluoroscopy, using a K-wire. The point of skin entry will be at the medial border of the sternocleidomastoid muscle. Firm pressure is applied digitally at this level between the sternocleidomastoid muscle and the trachea, and pointed toward the cervical spine. The larynx and esophagus are displaced medially, and the carotid artery is displaced laterally (Fig. 49-10). The esophagus could be made more prominent with the insertion of a nasogastric tube, and the carotid pulse is augmented with sympathomimetics. After palpation of the anterior cervical spine, an 18-gauge spinal needle is placed in the disc space of concern under fluoroscopic guidance. A guidewire is passed through the spine needle and then removed. A 3- to 5-mm skin incision is made, depending on the procedure and instruments to be used. To assist the placement of the endoscope or the working cannula, 3- to 5-mm dilators are passed through the K-wire. Specific instruments are then used to perform the discectomy, with papain (chemonucleolysis), loop-shaped electrode (automated PCD), laser, microcurette, and microforceps, as well as graft for fixation (Figs. 49-11 to 49-14).

FIGURE 49-10 Illustration of needle insertion (A) and intraoperative view of serial dilation (B). The tracheoesophagus is displaced medially, and the carotid artery is displaced laterally with the surgeon’s finger. An 18-gauge spinal needle is then inserted into the disc space under fluoroscopic monitoring and percutaneous approach using sequential dilation is performed.

(Modified from Lee SH, Ahn Y, Choi WC, et al: Immediate pain improvement is a useful predictor of long-term favorable outcome after percutaneous laser disc. Photomed Laser Surg 24:508–513, 2006.)

FIGURE 49-11 Minimally invasive spine surgery instruments. Left: minicurettes (A), discectome (B), discectomy dilator/cannula/trephine (C), cutter forceps (D), grasper forceps (E), and endoscopes (F). Right: Loop-shaped electrode.

(Left, Modified from Chiu JC, Clifford TJ, Greenspan M, et al: Percutaneous microdecompressive endoscopic cervical discectomy with laser thermodiskoplasty. Mt Sinai J Med 67:278–282, 2000. Right, Modified from Bonaldi G, Baruzzi F, Facchinetti A, et al: Plasma radio-frequency-based diskectomy for treatment of cervical herniated nucleus pulposus: feasibility, safety, and preliminary clinical results. AJNR Am J Neuroradiol 27:2104–2111, 2006.)

FIGURE 49-12 Intraoperative view (A) and C-arm view (B) of manual discectomy using microforceps.

(Modified from Lee SH, Ahn Y, Choi WC, et al: Immediate pain improvement is a useful predictor of long-term favorable outcome after percutaneous laser disc decompression for cervical disc herniation. Photomed Laser Surg 24:508–513, 2006.)

FIGURE 49-13 Schematic diagram of percutaneous endoscopic cervical discectomy. A, Cross-sectional view through the disc level. The disc fragment is removed by microforceps under high-resolution endoscopic visualization. B, Cross-sectional view through the uncovertebral joint level. The side-firing Ho:YAG laser can safely ablate the osteophytes.

(Modified from Ahn Y, Lee SH, Shin SW: Percutaneous endoscopic cervical discectomy: clinical outcome and radiographic changes. Photomed Laser Surg 23:362–368, 2005.)

FIGURE 49-14 The cervical B-Twin with its delivery system (A), in its reduced form (B) and its expanded form (C). After its proper positioning in the cervical disc space (D), manual rotating leads to expansion of the implant and then the implant is released from the delivery system (E).

(Modified from Lee SH, Lee JH, Choi WC, et al: Anterior minimally invasive approaches for the cervical spine. Orthop Clin North Am 38:327–337, 2007.)

Outcomes, Results, and Complications

Good-to-excellent clinical outcomes were reported in the literature, ranging from 80% to 85% for automated PCD,⁷⁸^–⁸¹ 75% to 94.5% for laser PCD,^86,^87,^89,⁹⁰ 80.2% to 94.5% for PCD with manual resection and laser,⁹¹^–⁹⁴ and 86.36% for chemonucleolysis.⁷⁶ Predictors of good outcome were found to be related to radiating arm pain, lateral disc location herniation, and immediate postoperative pain relief.^91,⁹³ Radiographically, Ahn et al. showed a significant decrease in the disc height by 11.2%, with maintenance of overall and focal sagittal alignments.⁹² There was no segmental instability or spontaneous fusion noted. Interestingly, complication rates were less than 1%, without any catastrophic ones.^76,^80,^81,^86,^87,⁸⁹^–⁹¹ ^,94 Most serious complications were infection⁸¹ and postoperative hematoma due to rupture of the inferior thyroid artery,⁸⁰ not of major vessels. Good knowledge of the cervical anatomy, understanding the safety zone of work for each level,⁹⁶ and frequent fluoroscopic checking will help to avoid complications in these procedures.

Li et al. compared retrospectively the percutaneous cervical disc nucleoplasty (42 patients) with the percutaneous cervical discectomy (38 patients).⁹⁷ The average follow-up was 12 ± 4 to 5 months. There was no significant difference of the clinical outcomes for the two groups, but operative time was significantly lower for the nucleoplasty group.

Ruetten et al. conducted a prospective, randomized, controlled study to compare the results of full-endoscopic anterior cervical discectomy (FACD) (60 patients) with those of ACDF (60 patients) in mediolateral soft disc herniations.⁹⁸ Patients were followed for a period of 2 years. Operative time and blood loss were less in the FACD group. There was no significant difference in the clinical outcomes, the progression of preexisting adjacent disc degeneration, or the increase of the postoperative kyphotic angle at the operated segment between the two groups. Revision rates were 6.1% for the ACDF group and 7.4% for the FACD group.

The clinical outcomes of these techniques seem promising, but they are not widely accepted because of the doubt that the clinical success could be due to the natural history of the disease, rather than the therapeutic effect.