Anterior Cervical Foraminotomy (Jho Procedure): Microscopic or Endoscopic

Introduction

The optimal surgical treatment for any disease process involves the direct removal of the offending pathology with minimal disruption of the surrounding, natural environment and preservation of functionality. This applies to the treatment of degenerative cervical spine disease involving radiculopathy and/or myelopathy. Cervical spine surgical techniques were introduced almost a century ago consisting of a posterior approach (posterior decompression procedures), later followed by the development of the anterior approach (anterior cervical discectomy). Posterior decompression techniques can preserve segmental motion but do not target the compressive pathology directly. Anterior cervical discectomy evolved to directly remove the compressive pathology whether it be a soft disc herniation or spondylotic stenosis, but the approach also requires the removal of nonpathologic, structural elements important for segmental motion such as the anterior longitudinal ligament and nonherniated portions of the discs for the sake of surgical exposure. To optimize the surgical goals of directly removing the compressive pathology with minimal disruption of normal anatomy as well as maximizing the preservation of segmental motion, anterior cervical foraminotomy techniques were developed and previously reported by the senior author as the “Jho procedure.” ^,

Posterior decompression techniques were first described in 1934 by Mixter and Barr who described 19 cases of ruptured intervertebral discs, 4 cases of which were cervical levels. The posterior techniques started out involving a cervical laminectomy, then evolved to a laminectomy or laminoplasty with or without posterior foraminotomies. It has been further refined into endoscopic or microscopic keyhole foraminotomies, with or without discectomy. Although posterior approaches often provide indirect compensatory decompression, they fail to achieve direct removal of compressive pathology that is commonly located ventral to the compressed nerve root or spinal cord. There may also be reduction or loss of segmental motion with some posterior approaches, especially when spinal fusion is used in conjunction with laminectomies to eliminate potential exacerbating dynamic factors or delayed kyphotic deformities, or both.

The classic anterior cervical approach involves the direct surgical decompression of neural structures by removing the entire cervical disc followed by placement of a bone graft. In the 1950s, the anterior cervical approach was first described and became the foundation of the modern-day anterior cervical discectomy and fusion. ^, Since then, minor technical modifications have been made over the years, such as removing various amounts of the vertebral column and using different sources of bone substitutes, fusion-enhancing materials, and metal implants. Although the anterior cervical discectomy achieves the direct removal of compressive pathology, the entire disc is removed and a bone graft is placed to fill the vacant intervertebral space, resulting in loss of segmental motion and even exacerbating degenerative disease at adjacent levels. Reconstruction with metal implants and spinal fusion are done to compensate for the removal of anatomic structures related to the surgical approach pathway of exposure and not due to the focal removal of the compressive pathology itself. More recent motion-preservation techniques such as placement of an artificial disc have developed in an attempt to minimize the amount of motion loss. However, the value of installing a foreign device in maintaining motion remains to be established.

The Jho procedure was developed to overcome the deficits of classic anterior and posterior cervical procedures 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. The compressive pathology is directly removed via an anterior approach while the remaining disc and functioning motion unit is preserved, eliminating the necessity of placing an implant or bone fusion. The originally reported technique for anterior foraminotomy involved removing the uncovertebral junction (the most lateral part of the intervertebral disc) to access the compressive pathology. Once the surgical access is made, the soft disc and/or bone spurs that compose the compressive pathology are excised. This surgical approach directly addresses the compressive pathology with access via the lateral portion of the spinal column and effective preservation of the anatomic 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 initially 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. Anterior cervical foraminotomy underwent further surgical evolution for refinement over time, and the senior author (HD Jho) wished to coin the term surgiology to describe the process of surgical technique refinement, which resulted in four basic variations and favoring of the endoscope over the original use of the microscope.

In the original report, the approach to the nerve root was made through a surgical entry hole at the lateral portion of the uncovertebral juncture. To minimize the risk of injury to the vertebral artery, this approach began by making a small hole at the medial portion of the uncovertebral juncture. Then the anterior foraminotomy hole was enlarged laterally up to the medial margin of the vertebral artery. The technique of medial-to-lateral bone removal soon evolved to a lateral-to-medial approach, with bone removal starting just medial to the vertebral artery. By doing so, bone removal was minimized at the bony access, often only requiring 2-mm thickness in width. Because the surgical approach pathway is made at the very lateral aspect of the spinal column, the stability of the spinal column is still preserved.

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 surgical technique became tailored depending on the trajectory as determined by the nature of the pathology and cervical anatomy. The result was the progressive development of the following variations: (1) transuncal approach; (2) upper-vertebral transcorporeal approach; (3) lower-vertebral transcorporeal approach; and (4) anterior cervical foraminoplasty.

In addition, the use of the operating microscope in anterior cervical microforaminotomy evolved into the use of a purely endoscopic technique in endoscopic anterior cervical foraminotomy. Microscopic visualization has a limited view through the small bony opening owing to its straight tubular viewing access with an inwardly coning configuration. Even if the operating microscope it 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 wide enhanced visualization at the surgical target region although the image is two dimensional. In this chapter, technical aspects of the anterior cervical foraminotomy are described, with the term rostral-caudal being used interchangeably with upper-lower or superior-inferior when referencing the vertebral bodies bordering the level of target pathology.

Surgical Indications and Preparation

The surgical indications for an anterior cervical foraminotomy are the same as those for conventional anterior cervical discectomy or corpectomy. Often times, patients will present for an alternative surgical option rather than undergo a fusion procedure or a posterior approach. The treatment algorithm first attempts to use conservative measures for a minimum of 6 weeks unless a profound motor weakness or significant myelopathy is evident. All patients had preoperative magnetic resonance imaging (MRI) scans. Occasionally, patients required a myelogram with computed tomography (CT) scans, particularly when MRI scans showed surgical artifact from previous surgery with an anterior fusion and metal implants. Intraoperative somatosensory evoked potential (SSEP) monitoring was used in all patients in the early evolution, but as experience grew, SSEP was used more selectively. All patients were kept 1 night 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 surgery. Follow-up MRI scans and dynamic cervical spine roentgenograms were obtained from all patients 6 weeks after surgery.

Initial use of the anterior cervical foraminotomy was limited to cervical radiculopathy caused by soft disc herniation or stenosis with bone spur formation. Variations of the technique have evolved and expanded to allow for decompression of the spinal cord for spondylotic stenosis or ossification of the posterior longitudinal ligament (OPLL), removal of spinal tumors (extradural or intradural), placement of a syringosubarachnoid shunt, or treatment of any other pathology that requires an anterior approach.

Surgical Tools and Techniques

Endoscopes

The endoscopes that we currently use are rod-lens endoscopes that are 4 mm in diameter and 18 cm in length. One set consists of five endoscopes: a 0-degree-lens endoscope, a 30-degree lens angled toward the light source, 30-degree lens angled away from the light source, a 70-degree lens angled toward the light source, and a 70-degree lens angled away from the light source ( Fig. 134.1 ). The 0-degree-lens endoscope is the basic working configuration used for most applications. Because the endoscope provides a wide-angle view, the 0-degree-lens endoscope usually provides adequate views for exposure at the nerve root as well as the spinal cord. However, the 30-degree-lens endoscope angled toward the light source can be used when a more-angled view toward the spinal cord is desired, and a 30-degree-lens 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.

Endoscope Lens-Cleaner

An endoscopic lens-cleaning device is required to keep the lens clear so that the surgeon can continually operate without interruption ( Fig. 134.2 ). The device consists of a disposable irrigation tube that passes through an electric-powered motor. The endoscope is placed through the rigid tubular irrigating sheath, which is connected to the irrigating tube. The irrigation tube is connected to a saline bag, which is 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 bubbles 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 removing 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. It not only provides steady video imaging on a video monitor, but it also allows a 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 needed for the surgeon to maneuver surgical instruments.

Two different types of endoscope holders are available, but neither is ideal. One is a simple manual holder with multiple joints that can be tightened by hand, and 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 a Mitaka endoscope holder (distributed by Karl Storz) for cranial applications and an Aesculap holder for spine applications ( Fig. 134.3 ). The Mitaka holder is relatively bulky at the attachment shaft and has very narrow accessibility at the holding terminal; thus the endoscope holding terminal has to be appropriately positioned at the surgical area before tightening at the shaft joint. Because the holding terminal maneuverability of the Mitaka holder is superior to Aesculap, we like to use the Mitaka holder for cranial endoscopic surgery. The Aesculap holder has longer flexible arms compared with the Mitaka, but its holding terminal has a limited range of motion, even with custom modifications. We prefer to use the Aesculap holder for spine endoscopy, but the holding terminals of both types of holders are not yet ideal for endoscopic spine surgery. Sagging of a few millimeters after release of the power button is another suboptimal feature of the nitrogen-powered holders.

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