Endoscopic Anterior Cervical Foraminotomy (Jho Procedure)

Overview

The optimal surgical treatment of degenerative cervical spine disease that involves radiculopathy and/or myelopathy would be direct surgical removal of compressive pathology while preserving segmental motion. To achieve these surgical goals, anterior cervical foraminotomy techniques were developed, and these were previously reported by the senior author as the “Jho procedure.” Historically, modern surgical techniques for degenerative cervical spine disease were introduced more than a half-century ago as anterior approach (anterior cervical diskectomy) and posterior approach decompression procedures. Although anterior cervical diskectomy directly targets the compressive pathology, usually soft-disk herniation or spondylotic spurs, the approach itself involves removing structural elements important for segmental motion. In comparison, posterior decompression techniques can usually preserve segmental motion but in many cases do not remove the compressive pathology directly.

The classic anterior cervical approach involves total disk removal, often followed by bone graft fusion. Minor technical modifications have been made over the years that have included various amounts of removal of the vertebral column, various sources of bone substitutes, fusion-enhancing materials, and use of metal implants. Although anterior cervical diskectomy achieves one goal, that of directly removing compressive pathology, loss of segmental motion occurs as a result of complete disk removal at the intervertebral space performed to access the pathology. Bone graft fusion is done to fill the vacant intervertebral space, which also results in loss of segmental motion and sometimes exacerbates degenerative disease at adjacent levels. Reconstruction with spinal fusion and metal implantation is done to compensate for the removal of anatomic structures related to the surgical approach pathway of exposure; it is not because of the focal removal of compressive pathology itself. In attempts to maintain segmental motion, disk arthroplasty has been recently introduced to reconstruction after anterior cervical diskectomy. However, the value of installing a foreign device to maintain motion remains to be established.

From traditional posterior laminectomy techniques in the 1960s a classic posterior approach emerged that involves cervical laminectomy or laminoplasty, with or without posterior foraminotomies. Recently, this approach has been further refined into endoscopic or microscopic posterior foraminotomies. However, posterior approaches often provide indirect compensatory decompression but fail to achieve direct removal of compressive pathology commonly located ventral to the compressed nerve root or spinal cord. Reduction or loss of segmental motion may also occur with some posterior approaches, especially when spinal fusion is used in conjunction with laminectomies to eliminate potential exacerbating dynamic factors and/or delayed kyphotic deformities.

The Jho procedure was developed to overcome the deficits of classic anterior and posterior cervical procedures in selected patients to optimize the achievement of surgical goals. Microsurgical anterior cervical foraminotomy was first reported by H.D. Jho in 1996 under the minimally invasive concept of “functional spine surgery,” in which compressive pathology is directly removed via an anterior approach, and the remaining disk and functioning motion unit is preserved without the use of implants or bone fusion. The technique originally reported for anterior cervical foraminotomy involved removal of the uncovertebral juncture, the most lateral part of the intervertebral disk, to access the compressive pathology. Once the surgical access is made, the soft disk and/or bone spurs that comprise the compressive pathology are excised. This surgical approach directly addresses the compressive pathology with access via the lateral portion of the spinal column, and it results in effective preservation of the integral spinal column structures so that segmental motion remains intact, and bony fusion is not necessary.

Originally, the Jho procedure was performed under the operating microscope; hence the surgery was also called anterior cervical microforaminotomy. Several variations of the surgical technique gradually evolved to achieve surgical goals more efficiently while minimizing surgical impact to the spinal column and functioning motion unit. Further variations on this technique evolved from the concept that the trajectory from the skin incision to the surgical target in the sagittal plane of the cervical spine directs where a bone opening should be made to access the target pathology efficiently and effectively. Thus the surgical technique became tailored, depending on the trajectory, as determined by the nature of the pathology and cervical anatomy. The following four variations of anterior cervical foraminotomy have been progressively developed: transuncal approach, or type 1 Jho procedure; upper-vertebral transcorporeal approach, or type 2 Jho procedure; lower-vertebral transcorporeal approach, or type 3 Jho procedure; and anterior cervical foraminoplasty, or type 4 Jho procedure.

In addition, the use of the operating microscope in anterior cervical microforaminotomy evolved into the utilization of a purely endoscopic technique in anterior cervical foraminotomy. Microscopic visualization has a limited view through the small bony opening because of its straight, tubular viewing access with an inwardly coning configuration. Even if the operating microscope is tilted to visualize the medial, inner aspect of the spinal canal, the view at the surgical target can be limited despite providing a three-dimensional image. An endoscope was adopted to overcome this limitation in surgical view and can provide an outwardly coning viewing configuration with a flask-shaped view that allows for wide, enhanced visualization at the surgical target region, although the image is two dimensional. In this chapter, technical aspects of anterior cervical foraminotomy are described; the term rostral-caudal is used interchangeably with upper-lower or superior-inferior when referencing the vertebral bodies that border the level of target pathology.

Surgical Indications for Anterior Cervical Foraminotomy (Jho Procedure)

Surgical indications are the same as those for conventional anterior cervical diskectomy or corpectomy, and patients often come in for an alternative surgical option after receiving a recommendation for conventional anterior fusion surgery or posterior approaches. However, although most conventional anterior procedures can take care of bilateral radicular symptoms, anterior foraminotomy provides decompression only at the ipsilateral nerve root and, if required, it provides spinal cord decompression further medially. The contralateral nerve root, if symptomatic, must be addressed via a contralateral approach at another time; we have not performed simultaneous bilateral approaches.

Conservative treatment for a minimum of 6 weeks was first attempted, unless profound motor weakness or significant myelopathy was evident. Initial use of anterior cervical foraminotomy was limited to cervical radiculopathy caused by soft-disk herniation or stenosis with bone spur formation. From there, application of the technique and its evolved variations were expanded to include decompression of the spinal cord for spondylotic stenosis, to treat ossification of the posterior longitudinal ligament (OPLL), for removal of extradural or intradural spinal tumors, for syringosubarachnoid shunt placement, or to address any other pathology that required an anterior approach. Because significant improvement was noted in neck pain and/or headaches with this operation, patients with neck pain and/or headaches were also operated on even if they did not have myelopathy or radiculopathy.

All patients had preoperative magnetic resonance (MR) scans, and some patients required myelocomputed tomography or simple computed tomography (CT) scans, particularly when MR scans showed surgical artifact from a previous surgery with anterior fusion and metal implant, or when MR scans were contraindicated. Occasionally, CT scans without myelogram were used as a diagnostic tool when a patient’s symptoms and pathology in a CT scan would match each other well. Intraoperative somatosensory-evoked potential (SSEP) monitoring was used in all patients in the early series; but as experience has grown, the value of intraoperative SSEP or motor-evoked potential (MEP) has been questionable. Now, we do not use intraoperative monitoring in most cases, except for medicolegal considerations.

All patients were kept overnight in the hospital as a standard protocol, except for the earliest patients who received surgery on an outpatient basis and those who insisted on going home on the same day of the surgery. All patients were advised to obtain follow-up MR scans and dynamic cervical spine roentgenograms 6 weeks postoperatively.

Surgical Tools and Techniques

Surgical Instruments

When microscopic surgery was performed, a slender power drill with a 2-mm diamond drill bit and various curettes were used. Once pure endoscopic surgery was adopted, endoscopic equipment and instruments were used. Surgical instruments required for this procedure include endoscopes with 0, 30, and 70 degree lenses and associated appendages, such as the light source plus a video imaging system, an endoscope lens-cleansing device, a rigid endoscope holder, and specifically designed surgical instruments that can accommodate the endoscopic environment.

Endoscopes

The endoscopes we use are rod-lens endoscopes 4 mm in diameter and 18 cm in length. One set consists of five endoscopes: one with a zero-degree lens, one with a 30 degree lens angled toward the light source, one with a 30 degree lens angled away from the light source, one with a 70 degree lens angled toward the light source, and one with a 70 degree lens angled away from the light source ( Fig. 15-1 ). However, a zero-degree endoscope is the basic working configuration used for most applications. Because the endoscope provides a wide-angle view, the zero-degree endoscope usually provides adequate views for exposure at the nerve root and at the spinal cord. However, the 30 degree endoscope angled toward the light source can be used when a more angled view toward the spinal cord is desired, and a 30 degree endoscope angled away from the light source can be used when a more angled view toward the nerve root at the neural foramen is desired. A 70 degree endoscope is usually not necessary for this operation.

Endoscope Lens Cleanser

An endoscope lens-cleansing device is required to keep the lens clear, so the surgeon can continually operate without interruption ( Fig. 15-2 ). The device consists of a disposable irrigation tube that passes through an electric-powered motor. The endoscope is placed through a rigid tubular irrigating sheath connected to the irrigating tube, and the irrigation tube is connected to a saline bag hung on a pole. This motor-powered irrigation device is controlled by a foot pedal to flush saline forward. When the foot pedal is released, the motor reverses its rotary direction and draws the saline back from the tip of the endoscope for 1 to 2 seconds. The forward flow of irrigating saline cleans the lens, and the reverse flow clears away water drops at the tip of the endoscope. Although this device is not yet ideal, it helps the surgeon significantly in the task of keeping the endoscope lens clean without removal of the endoscope from the surgical site.

Endoscope Holder

An appropriate endoscope holder is another piece of essential equipment required to perform this operation bimanually. An endoscope holder is mounted to the operating table not only to provide steady video imaging on a video monitor but also to allow the surgeon to use both hands freely, similar to microscopic surgery. The holder must provide rigid fixation of the endoscope, and its holding terminal must be compact and slender to render adequate operating space around the endoscope shaft for the surgeon to maneuver surgical instruments.

Two types of endoscope holders are currently available, but both are not yet ideal. One is a simple manual holder with multiple joints that can be tightened by hand; the other is a holder with joints powered by nitrogen gas and controlled with a single button. Manual holders are inconvenient to maneuver with releasing, repositioning, and tightening; they also have limitations in flexibility for reaching certain positions. Nitrogen gas–powered devices are more expedient than manual types but are not as smooth as the operating microscope in releasing and locking at various positions. Currently, we use an Aesculap holder for spine applications ( Fig. 15-3 ). We prefer to use the Aesculap holder for spine endoscopy, but holding terminals are not yet ideal for endoscopic spine surgery. We modified the holding terminal to make it more slender and compact. Sagging of a few millimeters after release of the power button is another suboptimal feature of the Nitrogen-powered holders. The power button must be released with the expectation of a few millimeters of sagging and shifting at the endoscope tip.

Endoscopic Surgical Instruments

Because the region of bone removal in anterior cervical foraminotomy requires high precision, a fine drilling device is required. We use a Midas telescoping tubular drill with a 2-mm diamond bit. The drill bit tip can be progressively extended as the depth of drilling advances. Other commercial drill products that have comparable systems also are available. Although an ultrasonic bone cutter is available commercially, we have not actually used it in this procedure; we are concerned with the possibility of impaired endoscopic view from the mist of continual irrigation spray. Bipolar forceps are shaped to accommodate the endoscopic surgical environment, and the blades of the bipolar forceps are parallel to each other, similar to a single-bladed instrument, once the forceps are approximated. Various surgical curettes and other endoscopic instruments were customized and developed to function efficiently within the uniquely curved endoscopic surgical trajectory.

Surgical Technique

Most of the equipment and instruments are similar to those used in conventional cervical spine surgery. Operation was performed under the operating microscope in earlier cases, but it has since evolved to pure endoscopic surgery. A thin-bladed cervical retractor system is used to keep the split longus colli muscle apart to expose the uncovertebral juncture.

Positioning

All operations were performed under general endotracheal anesthesia. In the past, when SSEP was used, baseline SSEP waveforms were obtained before positioning the head, and these were continuously followed until the end of surgery. Now, we usually do not use intraoperative SSEP or MEP. Patient positioning is similar to that for conventional anterior diskectomy, keeping the head straight (without turning) and the neck neutral (without extension). Gentle neck extension with a small bolster under the shoulders may be done only if sufficient spinal canal is demonstrated on MR scans to provide room for the spinal cord. Caution during neck positioning is important to prevent position-induced injury to the spinal cord, especially if patients experience exaggerated symptoms by neck extension preoperatively, or when severe spinal cord compression is noted in MR scans. Cervical traction devices are not used. Significantly obese patients with short, thick necks may require 2-inch adhesive tape for application of gentle skin traction at the chin superiorly and at the anterior chest wall inferiorly.

Surgical Exposure of the Uncovertebral Juncture

The skin incision site is judged by finger palpation of the C6 transverse tubercle, which is typically palpable just medial to the sternocleidomastoid (SCM) muscle. The surgical target area related to the mandibular angle and larynx is reviewed in reference to MR scans of the cervical spine along with the location of the vertebral arteries, being mindful of anatomic variants. The skin incision starts 1 or 2 cm laterally from the midline and extends laterally across the medial margin of the SCM muscle for approximately 3 to 5 cm in total length. Although the center of surgical exposure is usually 3 to 4 cm lateral from the midline, it must be adjusted to the size of the neck. Patients with large necks require a longer skin incision to maintain a 20 degree lateral-to-medial trajectory angle toward the surgical target.

At the anterior portion of the cervical spine, the surgical target anatomy is the uncovertebral juncture covered by the longus colli muscle. Picturing this in axial view, the surgical trajectory angle is determined by an extension line from the very medial margin of the inlet neural foramen to that of the outlet. When this line is extended toward the skin, it is the key exposure point of the skin. The platysma may be split longitudinally along the direction of the muscle fibers or, alternatively, it may be cut parallel to the skin incision.

The medial border of the SCM must then be defined, with clean dissection carried down to the prevertebral fascia just medial to the SCM. The carotid artery on the working side is identified with finger palpation, and a Meyerding retractor is placed just medial to the carotid artery. The tracheoesophageal structure is slightly and gently displaced medially and held with the Meyerding retractor, although not as much exposure of the anterior cervical column is needed as in conventional anterior cervical diskectomy. The perimeter of exposure at the lateral portion of the cervical column is just over the longus colli muscle.

For upper cervical spine surgery, an intraoperative radiograph is obtained to corroborate the correct level of surgery. However, for lower cervical spine surgery, finger palpation of the surgical anatomy at the anterior column of the cervical spine and C6 transverse tubercle is often sufficient for the identification of the correct level of surgery, although a confirmatory radiograph may still be done.

By palpating the transverse tubercles, the extent of the longus colli is identified. The longus colli is split just medial to the transverse tubercles rostral and caudal to the intervertebral disk level, being careful to avoid injury to the sympathetic trunk and to fibers located laterally along the longus colli. A cervical retractor system is applied between the split longus colli muscle fibers to maintain exposure of the uncovertebral juncture. The original description mentioned sectioning of the medial part of the longus colli muscle, but this soon evolved to splitting the longus colli muscle to allow its preservation.

At this point, an endoscope is brought into the surgical site, and the vertebral artery is defined just lateral to the uncinate process under endoscopic visualization. The vertebral artery pulsation is easily visible lateral to the uncinate process, and the proximal transverse processes of the rostral and caudal vertebrae are then defined. Because the surgical site is small, the close-up panoramic endoscopic view often improves surgical visualization compared with the operating microscope.

Original Description of Microsurgical Anterior Cervical Foraminotomy

As previously mentioned, the original technique for microsurgical anterior cervical foraminotomy was reported as a new approach for cervical disk herniation in 1996. In the original description, the lateral 5- to 8-mm portion of the uncovertebral juncture was drilled and removed, which eventually evolved into less bone removal. The vertical dimensions of bone removal originally extended from the inferior margin of the rostral vertebra’s medial transverse process to the superior margin of the caudal vertebra’s medial transverse process, usually measuring 7 to 10 mm in total length. Bone removal is performed using a 2 mm cutting bit in a slender high-speed drill. The intervertebral disk is kept largely intact, and opening of the posterior longitudinal ligament (PLL) is sometimes done to confirm an adequate decompression from the lateral portion of the spinal cord to the nerve exit behind the vertebral artery. It is possible for venous bleeding to be cumbersome while the PLL is open. Once adequate decompression is accomplished, the platysma and subcutaneous tissue are closed with 3-0 absorbable sutures. The surgical incision site is infiltrated with a local anesthetic, and skin is closed with absorbable stitches or adhesive glue.

The original technique involved the removal of a few millimeters of width of the most lateral portion of the uncovertebral juncture in a medial-to-lateral direction as a surgical conduit to the compressive pathology. However, this technique was soon modified, because the end result of bony removal often became more superfluous than required, and concern for potential vertebral artery injury frequently made the start of bone removal farther medial than truly necessary. In addition, bone opening at the uncovertebral juncture did not always produce an optimal access to the target pathology, depending on the surgical trajectory from the skin incision. Technical refinements into four major subtypes of anterior cervical foraminotomy followed. In addition, the use of the operating microscope was changed to the use of an endoscope to maximize the visualization through a tiny bony opening.

Evolution of Anterior Cervical Foraminotomy (Jho Procedure)

Type 1: Transuncal Approach

When the surgical trajectory from the skin incision to the target pathology is perpendicular to the sagittal plane of the cervical spine, a bone opening at the anterolateral spine should be made along this trajectory line. Particularly for C4–C5 or C5–C6 operations, a routine skin incision at the upper or middle portion of the neck will produce such a perpendicular surgical trajectory. In this case, the uncinate process lies directly along the perpendicular surgical trajectory ( Fig. 15-4, A ).