Cervical Endoscopic Foraminotomy
Posterior foraminotomy for posterolateral cervical stenosis is a safe and efficacious alternative to anterior surgical procedures. First described by Scoville and Frykholm in the late 1940s, posterior cervical foraminotomy was for many years commonplace among the surgical armamentarium of most neurosurgeons. It allowed for direct decompression of the stenotic foramen and nerve root while minimizing the risks of injury to the visceral and neurovascular structures of the neck. Perhaps even more importantly, posterior foraminotomy does not result in fusion of the cervical spine, which is particularly important to the younger patient. Over recent years, the popularity of anterior approaches has eclipsed the use of classical posterior foraminotomy techniques. As long-term experience with anterior cervical decompression has grown, so too, however, has the recognition of its many limitations and potential complications.
The effectiveness of posterior cervical laminoforaminotomy for decompression of the lateral recess and neural foramen has been well documented in numerous publications over the last 4 decades. When compared with standard anterior cervical techniques, the posterior approach via a “keyhole” type osteotomy may provide better exposure for decompression of the exiting root and for removal of lateral osteophytes and disks. For cases of isolated radiculopathy from either a lateral disk or osteophyte, 93 to 97% of patients experienced symptomatic improvement by simply freeing the nerve root via decompressive laminoforaminotomy and removal of either or both the disk and the osteophyte. Enthusiasm for the operation was tempered by the significant cervical muscular pain and spasm that often followed. The use of wider incisions for adequate visualization and the need for significant paraspinous muscle dissection were blamed for this postoperative pain syndrome that resulted in a slower recovery course.
Microendoscopic foraminotomy (MEF) represents the modern evolution of the classic operation with a minimally invasive approach and high-magnification direct endoscopic visualization. Developments in percutaneous surgical access, optical technology, neuroanesthetic techniques, and noninvasive imaging modalities have brought posterior foraminotomy into a new millennium of spinal surgery. By minimizing the amount of tissue trauma and muscle injury, the MEF procedure overcomes the limited visualization, postoperative pain, muscle spasm, and prolonged disability that served to limit the open foraminotomy operation.
The MEF procedure is also able to accomplish the same degree of bony and soft tissue decompression as open foraminotomy. The average proportion of facet removal and length of nerve root decompression can actually be greater in the MEF than in an open decompression. Scoville, one of the pioneers and early champions of the posterior laminoforaminotomy (LF) operation, reported excellent or good results in 95% of his patients. His contemporaries, Odom et al and Raaf, reported similar good and excellent outcomes of 85% and 94% as well. More recent literature from the era of the operating microscope has since corroborated these earlier works. Henderson et al reported a 96% incidence of pain relief after posterior LF in 846 consecutively operated patients. Our clinical experience with the MEF procedure has yielded symptomatic improvement for ~87% of patients with neck pain and 92% of patients with radiculopathy. Thus MEF yields the same clinical results as open foraminotomy with far less tissue trauma during the approach.
A word of caution is needed. Microendoscopic techniques such as MEF do involve a very steep learning curve that must be diligently overcome. The two-dimensional view and hand–eye spatial separation of the technique can be extremely disorienting at the beginning. The operation should be first learned in the safe confines of a surgical teaching laboratory in cadavers. Only after one has become comfortable with the endoscopic technique should one perform the MEF in the operating theater. As such, a significant amount of time is requisite before any surgeon can gain facility with this procedure. This steep learning curve, however, is well justified when one considers the many benefits to the patient. Compared with open foraminotomy, the MEF technique offers significant reductions in operative blood loss, length of hospital stay, and postoperative pain and disability. Performed safely and correctly, the cervical MEF is a paradigm of outpatient spinal surgical procedures.
Local anesthesia combined with intravenous sedation is inadequate for most cases of MEF because there is a substantial risk of injury to the spinal cord and nerve roots should there be any accidental movement during the procedure.
In our last 13 cases, we adopted a sitting position with a Mayfield headrest, which significantly improved visualization, relieved epidural venous congestion, and decreased operative blood loss (Fig. 1).
The video monitors are typically placed on the patient opposite of the operative side. However, the ultimate arrangement of the video monitor and C-arm monitor should be varied to allow for optimal ergonomic flow during the procedure.
Fig. 1demonstrates an example of this operative arrangement with a closeup view of the endoscopic apparatus in place as it would appear during the procedure (inset).
Ideally, the pin should rest at the spinolaminar junction on the medial edge of the facet complex (Fig. 2).
Fig. 2 Lateral radiographic images demonstrating -- A the placement of the Steinmann pin down to the junction of the lateral mass and lamina over the C4–C5 foramen. -- B Sequential passage of the metal dilators allows for a minimally traumatic spreading of the posterior cervical muscles off the surgical area. -- C The final 18 mm tubular retractor is then put into position to provide the final surgical exposure. -- D Illustration depicting serial dilators in dorsal musculature of cervical spine.
The series of dilators are then sequentially inserted through the neck soft tissues, over which a 16 or 18 mm tubular working channel is then inserted (Fig. 2).
Real-time lateral radiographic images should be obtained as often as needed to insure a proper working trajectory throughout this process (Fig. 2).
We employ the METRx system (Medtronic Sofamor-Danek; Memphis, TN) of endoscopic retractors, camera, and instruments for our MEF procedures (Fig. 3).
Once the tubular retractor is set in the desired position (Fig. 4), a Bovie cautery with a long tip is used to remove the remaining muscle and soft tissue overlying the lateral mass and facet.
Fig. 4 A Illustration demonstrates endoscopic drilling of the lamina. -- B View through the endoscope with the angled curette dissecting beneath the medial edge of the facet. -- C Curette is placed beneath the lamina, and a lateral fluoroscopic image is obtained to confirm the level and position. INF, inferior; LAT, lateral.
With the bone well visualized, a small straight endoscopic curette is used to scrape the inferior edge of the superior lamina and the medial edge of the lateral mass–facet complex (Fig. 4).
Proper placement of the curettes can be confirmed under fluoroscopy to double check that it is indeed under the lamina of the correct level (Fig. 4).
After the plane has been clearly defined, a small angled endoscopic 1 or 2 mm Kerrison rongeur is utilized to begin the foraminotomy (Fig. 5).
Fig. 5 A A small Kerrison rongeur being used to begin the foraminal exposure. -- B Drilling of the facet overlying the axilla and proximal takeoff of the corresponding nerve root is performed. -- C The laminoforaminotomy is continued. -- D A microcurette is utilized to further decompress the nerve root. -- E Nerve hook being passed along the course of the exiting root to ensure adequate decompression. If needed, a diskectomy can be performed. -- F A blunt hook dissector is utilized to confirm the foraminal decompression. INF, inferior; LAT, lateral.
In cases of marked facet arthropathy and enlargement, a drill with a long endoscopic bit (e.g., AM-8 bit with Midas Rex [Medtronic, Minneapolis, MN] or TAC bit with MEDNext drill) can be used to further thin the medial facet and lateral mass (Fig. 5).
Frequent dissection of the soft tissue off the bone with an angled curette facilitates safe use of the Kerrison rongeur (Fig. 5).
In this fashion, the decompression is carefully continued inferiorly and laterally along the course of the neural foramen (Fig. 5).
The adequacy of the decompression should be confirmed by palpating the root along its course with a small nerve hook (Fig. 5).
Paracentral disk herniations or osteophytes can sometimes be decompressed as well. However, it is difficult to address truly central canal pathology through the MEF approach and caution should be exercised not to exert undue medial retraction on the spinal cord.
Upon completion of the diskectomy and decompression, the nerve hook is again passed along the exiting root to confirm its free passage, and a lateral fluoroscopic image is obtained (Fig. 6).
It is important to ensure that the nerve root be palpated along its anterior surface to ensure that there is no residual compression along its course. This is particularly true at the axilla and shoulder where it joins the spinal cord.
Fig. 6illustrates the typical foraminotomy defect that is obtained after MEF with good preservation of the lateral mass integrity.
Either Steri-Strips or Dermabond can then be used to cover the skin. Dermabond is attractive because it keeps the skin edges closely approximated for a 7- to 10-day period as well as providing a waterproof barrier. The patient can thus shower almost immediately after surgery.
For cases where a CSF leak has occurred, direct repair is difficult because the durotomy is small and the access limited. Thus we have routinely employed a lumbar drain for 2 to 3 days postoperatively to help close the small dural tear.
Henderson CM, Hennessy RG, Shuey HM, Shackelford EG. Posterior-lateral foraminotomy as an exclusive operative technique for cervical radiculopathy: a review of 846 consecutively operated cases. Neurosurgery. 1983;13(5):504‐512.
Woertgen C, Holzschuh M, Rothoerl RD, Haeusler E, Brawanski A. Prognostic factors of posterior cervical disc surgery: a prospective, consecutive study of 54 patients. Neurosurgery. 1997;40(4):724‐728, discussion 728–729.