7 Minimally Invasive Posterior Cervical Foraminotomy
Keywords: cervical spine, decompression, discectomy, foraminotomy, herniation, radiculopathy, spinal cord, thecal sac
He who sees through an open window sees less than he who looks through a closed window.
Charles Baudelaire
7.1 Introduction
Throughout the span of my entire residency, I participated in a total of five posterior cervical foraminotomies. The anterior cervical discectomies and fusions that I assisted with or performed, on the other hand, were too many to count. All that would change within my first several weeks at the Naval Medical Center in San Diego where I landed immediately after I completed my residency. I was struck by how many patients were better candidates for a posterior cervical foraminotomy than an anterior cervical approach. Service member after service member presented to my clinic with a unilateral radiculopathy from a cervical disc herniation that was purely within the cervical foramen and nowhere near the spinal cord. Their only symptoms were due to compression of a single cervical nerve root. Although all these patients were candidates for anterior approaches, they all appeared to be even better candidates for a unilateral posterior cervical foraminotomy with discectomy.
A confounding factor that I had to consider in the decision for the surgical approach was the unique patient population with very specific needs. In contradistinction to the older patient population with multiple levels of degeneration seen during residency in Atlanta, the vast majority of my patients in the Navy were young and healthy, with a single symptomatic segment and high motivation to return to unrestricted duty in the military. Surgical approaches in the Navy had consequences regarding timely return to unrestricted duty. If a cervical fusion was recommended, in most cases the service member could not return to unrestricted duty until arthrodesis could be confirmed. Waiting for a radiographic fusion to occur in order to be able to return these service members to full duty did not seem like the best course of action. Furthermore, to take an entire healthy disc and fuse a segment for such a focal problem in a 20- or 30-year-old who presented with a unilateral radiculopathy from a lateral disc herniation without compression of the spinal cord and no significant spondylosis did not play to the strengths of the various surgical options available. Although arthroplasty was a wonderful alternative, I reserved that operation for more central disc herniations, which were out of the reach of the posterior cervical foraminotomy approach.
It became clear working with my colleagues that from a clinical, practical and military standpoint, a posterior cervical foraminotomy was the most logical path forward.1 However, I had to balance this perspective with my ability to adequately perform the operation given my limited experience. In reality, at that time in my career, I felt more comfortable clipping a posterior communicating artery aneurysm than performing a posterior cervical foraminotomy, much less a minimally invasive one. I have discovered this to be a common theme in the residents and fellows with whom I now work. The posterior cervical foraminotomy is becoming a lost art. The anterior versus the posterior trend is certainly nothing new in the treatment of cervical disc disorders. As long ago as 1990, a concerned Francois Aldrich wrote, “This trend toward anterior discectomy for all types of cervical discs has tended to obscure the progressive development of the posterolateral approach to these lesions.”2
Of course, there was a reason behind my dearth of experience with the posterior cervical foraminotomy and the decreasing frequency of that operation in clinical practice. The simple answer lay in the fact that the anterior approach is so well tolerated by patients in comparison to an open midline posterior cervical approach. The various things I remember about those five foraminotomies during my residency was the blood loss, the muscle dissection, the inability to see anything clearly and the degree of pain that patients experienced during the postoperative course. It was no wonder my mentors avoided that operation. As I look back at it now, it is a marvel that I saw as many as five of these procedures.
The rise of minimally invasive techniques in the lumbar spine introduced a potential equalizer in this cervical equation of posterior versus anterior. If these same techniques that limited the surgical exposure and thereby postoperative discomfort in the lumbar spine could be applied to the cervical spine, there was the potential for even greater benefit. The question of whether to address a nerve root compression syndrome from a posterior approach or anterior approach would become more balanced. The minimally invasive technique could single-handedly buck the trend of the decreasing application of posterior cervical foraminotomies identified by Aldrich.2 All of a sudden, all that blood loss, poor visualization and postoperative pain could be replaced by a small incision, a focal area of exposure in a same-day outpatient operation with minimal discomfort for the patient.
A few short years after surgeons began wanding exposures in the lumbar spine with minimal access dilators for microdiscectomies and laminectomies, they ventured with them into the cervical spine. In 2000, Fessler and his colleagues3 published a cadaveric feasibility study of a transmuscular approach using minimal access ports, effectively translating the techniques from the lumbar spine to the cervical spine. In reading Fessler’s statements regarding hemostasis in the discussion of that manuscript, I found his concern to be quite prescient. In 2001, Adamson4 published the first clinical series in the neurosurgical literature using a minimally invasive approach to access the posterior cervical foramen in 100 consecutive individuals. Perhaps the most important aspect of Adamson’s publication4 was the same-day discharge of 90 of the 100 patients. That data alone demonstrated that the putative benefits of the minimally invasive approach were, in fact, realized. Since Adamson’s 2001 publication, the experience reported in the literature regarding the minimal access approach to the posterior cervical foramen has eclipsed that of its open counterpart.
Although some experts may argue that there is little difference between an open and a minimally invasive lumbar microdiscectomy, few would maintain that argument in the cervical spine, where the complex network of insertions in the posterior cervical musculature have to be detached for the exposure in an open approach. The differences between open and minimally invasive exposures for a foraminotomy in the cervical spine are oceans apart.
It was adopting minimally invasive techniques immediately after residency that allowed me to perform more posterior cervical foraminotomies within my first several months in practice as an attending neurosurgeon at the Naval Hospital in San Diego than I did in my entire residency. It is now an operation that I routinely perform several times a month on an outpatient basis. As always, it was the learning curve with the minimally invasive approach that I needed to tackle in order to fully embrace the technique. I emphasize that the minimally invasive posterior cervical foraminotomy is not the operation to begin your conversion to minimally invasive spine surgery. You will need expertise with the skill set that is built by performing the minimally invasive microdiscectomy and laminectomy in the lumbar spine. Comfort with the minimally invasive attachments to the drill and the bayoneted instruments through a minimal access port is imperative since the diameter of the minimal access port with this procedure is even smaller.
Once you have developed a facility with minimally invasive surgery on the lumbar spine, you will be able to readily translate those skills to the posterior cervical foraminotomy, the gateway procedure to managing posterior cervical pathology minimally invasively. Handling the instruments through minimal access ports is only one element of the skill set. Minimally invasive approaches to the posterior cervical spine have their specific learning curve. The posterior cervical fascia is very different to traverse than the lumbar fascia. The posterior cervical muscular planes are more complex and not as distinct as with the lumbar musculature. Docking onto the lamina in the cervical spine is a different experience for the surgeon than docking onto the lumbar lamina. There is something about the cervical spinal cord residing on the other side of the lamina that changes that experience. Although these skill sets are similar, there are nuances specific to the posterior cervical approach.
This chapter began with a quote from Charles Baudelaire who made the comment that individuals peering through an open window see less than individuals who peer through a closed window. Baudelaire’s statement, which can be applied to the context of the minimally invasive posterior cervical foraminotomy, resonates with me. The minimal access port that I peer through on the cervical spine forces my mind to reconstruct the anatomy at depth. I have to see the pedicle, the superior articular process (SAP) and the cervical nerve root in my mind’s eye before I ever make an incision. The very nature of the limited exposure mandates that I see more through a 14-mm diameter “closed window” than I would otherwise see through a midline “open window.” Baudelaire may not have had minimally invasive spine surgery in mind when he wrote these words, but no statement better describes the workings of the minimally invasive mindset.
The goal of this chapter is to describe the anatomical basis, techniques and operative nuances of the minimally invasive posterior cervical foraminotomy. My hope is that you find a greater understanding of the cervical foramen through a limited diameter than you ever would have achieved through a traditional midline exposure. Mastery of this procedure will serve as a platform for the management of other posterior cervical pathologies covered in the next chapter. As always, understanding the anatomical basis for the approach and having at your fingertips the precise measurements serves as the foundation to increase the slope of your learning curve. Once you grasp the nuances of dilatation and exposure, it will be surprising to you how quickly the minimally invasive posterior cervical foraminotomy will become a valuable asset in your armamentarium. But first, given the remarkable and fascinating history of this procedure, it would be difficult not to highlight certain elements of its evolution.
7.2 Evolution of the Posterior Cervical Foraminotomy
Once Mixter and Barr5 enlightened the world that a lumbar disc herniation can cause radicular leg pain and that surgical removal of that herniation had the potential to alleviate the symptoms, it did not take long before surgeons turned their eyes to the cervical disc as the menacing cause of brachial neuritis. The logical surgical solution to cervical radiculopathy would be to transpose the lumbar operation to the cervical spine. Such a transposition was not a unique idea, and several surgeons went about exploring this possibility. Soon after the publications on the surgical management of lumbar disc herniations made their way into the literature, Love and Camp,6 Semmes and Murphey,7 and Spurling and Scoville8 began reporting their preliminary experience with the clinical diagnosis and surgical treatment of cervical radiculopathy.
In 1943, Semmes and Murphey described their experience in the management of four patients with unilateral radiculopathy treated with posterolateral decompression. Remarkably, these authors report the procedure to have been done under local anesthesia, something I would never entertain even in this day and age.7 Soon thereafter, two medical officers, a US Army Lieutenant Colonel and a US Army Captain serving on active duty during World War II, published a manuscript in 1944 titled “Lateral rupture of the cervical intervertebral disc: A common cause of shoulder and arm pain.”8 In that manuscript, Spurling and Scoville described the diagnosis and treatment of cervical radiculopathy. The technique they described required a small dental chisel to remove the lamina and facet to enlarge the cervical foramen before retracting the nerve root and removing the disc herniation ( ▶ Fig. 7.1).8 As I read the “Technique” section of this manuscript, I could not help but admire with awe the proficiency these surgeons must have possessed with a chisel and the courage to employ such a technique over the top of the nerve root and spinal cord. The skills that Spurling and Scoville possessed in 1944 far exceed the skill and courage currently in my possession in 2020.
Fig. 7.1 Illustration from Spurling and Scoville8 demonstrating the foraminotomy created with a small dental chisel. A nerve hook retracts the C6 nerve root downward to reveal a disc herniation. (Reproduced with permission from Spurling RG, Scoville WB. Lateral rupture of the cervical intervertebral disc: a common cause of shoulder and arm pain. Surg Gynecol Obstet. 1944; 78:350358.)
Writing from Stockholm, Sweden, in 1947, Frykholm9 expressed the same concern I had regarding the use of a chisel over the top of the cervical nerve root and spinal cord. Frykholm’s honest assessment of his suboptimal surgical outcomes led him to believe that his surgical technique may have either damaged the nerve by decompression or had resulted in an incomplete decompression. He sought to address the shortcomings of the chisel technique at the time and introduced a dental drill with a cutting drill bit.9▶ Fig. 7.29 demonstrates Frykholm’s technique with a “spherical vulcanite cutter” drill bit. The change from chiseling to drilling of the bone over the top of the nerve root made the decompression safer and allowed for a more comprehensive decompression. Needless to say, the drill is now the method of choice for this procedure. With advancements in fluoroscopy for localization and general anesthesia, the modern posterior cervical foraminotomy awaited the development of minimal access ports for its next step in evolution. By the early 2000s, surgeons accustomed to wielding minimal access ports in the lumbar spine began applying them to the cervical spine, just like their predecessors in the 1930s transposed Mixter and Barr’s discectomy from the lumbar to the cervical spine. Minimal access ports decreased the surgical exposure relative to the surgical target. The transposition of minimal access ports from the lumbar spine to the cervical spine optimized the Caspar ratio to almost 1:1. Achieving such a Caspar ratio is the essence of a minimally invasive approach.
Fig. 7.2 Illustrations of Frykholm’s technique9 for the posterior cervical foraminotomy. Frykholm sought a safer way to remove the lamina and facet and turned to a dental drill to replace the chisels he had used previously. (Reproduced with permission from Frykholm R. Deformities of dural pouches and strictures of dural sheaths in the cervical region producing nerve-root compression; a contribution to the etiology and operative treatment of brachial neuralgia. J Neurosurg. 1947; 4:403413.)
7.3 Minimally Invasive Posterior Cervical Foraminotomy versus Anterior Cervical Discectomy and Fusion
In this Primer, I have made every effort to make the contents more about technique than about indications for surgery. However, in the case of posterior cervical foraminotomy, it would be difficult not to discuss the topic. An operation like the posterior cervical foraminotomy merits comment regarding the selection of this procedure over an anterior approach. Although an anterior approach tends to be an option for treatment of almost all degenerative pathologies of the cervical spine, the posterior cervical foraminotomy has a much narrower focus.
In my practice, I consider the posterior cervical foraminotomy in patients with unilateral radiculopathy whether from a herniated disc or a disc–osteophyte complex. The ideal patient for this operation is an individual with no significant neck pain, a unilateral radiculopathy with normal lordosis and no significant spondylosis. Magnetic resonance imaging (MRI) should demonstrate compression of the cervical nerve root, whether by foraminal compromise from an osteophyte or a disc herniation. However, patients seldom present in such a clearly delineated category. As such, I apply some additional criteria to further guide my selection. As I review the MRI, I assess whether there is any contact of the disc or disc–osteophyte complex with the spinal cord. The presence of any contact on the ventral aspect of the spinal cord prompts me to consider an anterior approach. Contact by a disc herniation on the lateral aspect of the dura of the spinal cord, provided there is no significant displacement of the spinal cord, is still amenable to a posterior decompression.
As I review the cervical radiographs, focal loss of the cervical lordosis or significant cervical spondylosis, especially at the level where I am considering a foraminotomy, may give me pause. A posterior cervical foraminotomy may not be the best approach in these patients, especially when they present with significant neck pain.
There are three clinical scenarios in which I find the posterior cervical foraminotomy especially valuable. The first is in the patient with multilevel disc degeneration, who is symptomatic at only one level. In this clinical scenario, an anterior approach may mandate a two- or three-level operation, whereas a posterior cervical foraminotomy addresses the symptomatic root. The second clinical scenario involves the patient who has undergone a previous single-level or multilevel cervical fusion and now presents with a unilateral radiculopathy at an adjacent segment. A posterior cervical foraminotomy vastly facilitates the management of such a patient who would otherwise require an anterior approach with exploration of the previous fusion, possible explantation of the cervical plate and, finally, extension of the fusion to decompress the symptomatic root. With that management strategy, the patient has lost another motion segment. Instead, a posterior minimally invasive approach addresses the symptomatic root and avoids the potential complications of anterior revision surgery while preserving motion. Although a posterior foraminotomy is not a comprehensive solution, it may adequately address the radicular symptoms and potentially delay for years, if not avoid altogether, the need for an anterior approach.
7.4 Patient Education
When considering one of two procedures for the same condition, setting expectations for the patient is perhaps the most invaluable element of patient education. For a soft disc extrusion causing a unilateral radiculopathy in a patient without spondylosis, preoperative counseling is relatively straightforward. I review the objectives of the procedure and explain the rationale and technique. In the context of spondylosis, I go into greater depth to discuss the natural history of cervical spondylosis in the context of a cervical radiculopathy. I always explain to patients that the most comprehensive way to address a degenerative cervical disc process is to remove the entire disc, restore the disc height and stabilize the segment through an anterior approach. It is the anterior approach that allows for restoration of the disc height and segmental lordosis with decompression of the neural elements while preventing any further degeneration with immobilization. I emphasize to the patient that a minimally invasive posterior cervical foraminotomy is a motion-preserving procedure intended to relieve the compression of the nerve root. It forgoes the need for an implant, whether an arthroplasty device, interbody graft or cervical plate. As a consequence, however, it does not restore foraminal height and does not prevent further degeneration from occurring. I emphasize to the patient that the objective is to decompress a nerve that goes to the arm and, therefore, does not reliably alleviate neck pain. Finally, I specifically mention the potential need for definitive management with an anterior approach in the years or decades to come. I have found that these statements help patients begin to formulate what to expect in the postoperative period and even consolidate their thinking behind their selection of the type of procedure they wish to undergo.
The end of this chapter includes a series of cases regarding the nuances of patient selection, along with a review of the preoperative and postoperative images, to emphasize that careful patient selection is vital to a good outcome. Ultimately, minimally invasive posterior cervical foraminotomy holds a unique place in the armamentarium of a minimally invasive spine surgeon for well-selected patients.
7.5 Anatomical Basis for the Minimally Invasive Approach
In the cervical spine the nerve root exits above its like-numbered pedicle; that is, the C6 nerve roots exit above the C6 pedicle. Thus, the C6 pedicle forms the floor of the foramen for the C6 nerve root, and the C5 pedicle forms the roof. The anterior boundary of the foramen is formed by the disc space (C5–6 disc in this case) and the lateral uncinate process ( ▶ Fig. 7.3). It is from this aspect of the foramen that the compressive pathology often arises. Discs may herniate and compress the nerve root. The uncovertebral joint may develop osteophyte complexes that result in symptomatic compression of the nerve root.
Fig. 7.3 Illustrations of the C6 cervical neural foramen showing the contributions from C5 and C6. (a) An exploded version of the cervical foramen demonstrates the contributing boundaries. The components of the magenta ring represent the contribution to the foramen by the C5 vertebra. The superior aspect of the foramen is made up of the inferior aspect of the C5 pedicle. The posterior aspect of the C5 vertebral body contributes to the anterosuperior aspect of the foramen. The components of the turquoise ring represent the contribution by the C6 vertebra. As can be seen from the illustration, the majority of the C6 neural foramen is made up by elements of the C6 vertebra. The posterior aspect of the vertebra makes up the anteroinferior wall. The superior aspect of the pedicle of C6 makes up the inferior border of the foramen. The superior articular process (SAP) of C6 makes up the majority of the posterior boundary of the neural foramen. (b) This illustration demonstrates the main target of the bone work. The emphasis in the posterior cervical foraminotomy is the posterior wall of the foramen (turquoise). Therefore, the SAP of C6, in this case, is the main target of the bone work. In this illustration, the foramen transversarium has been removed to demonstrate the contribution of the SAP to the neural foramen.
The posterior wall of the foramen is formed by the SAP of the like-numbered segment; that is, the posterior wall of the C6 nerve root is made up of the SAP of C6. The SAP may also be a source of compression of the nerve root in circumstances of advanced facet arthropathy ( ▶ Fig. 7.4).
There are three measurements that are of tremendous value when performing a minimally invasive posterior cervical foraminotomy. The first is the interpedicular distance. Depending on the disc height, the interpedicular distance ranges from 9 to 12 mm. It will seldom be more than 12 mm. The second measurement is the anteroposterior (AP) dimension, which is measured from the posterior aspect of the disc space to the anterior aspect of the SAP. This AP dimension ranges from 4 to 6 mm.10 The final measurement is the lateral dimension of the foramen. This dimension is measured from the lateral aspect of the disc space to the medial aspect of the mid-SAP as it projects forward; this measurement consistently ranges from 8 to 10 mm ( ▶ Fig. 7.5).
Fig. 7.5 Illustrations showing the dimensions of an average cervical foramen. (a) Isolating the boundaries of the cervical foramen (magenta). The interpedicular distance is dependent on the disc height. (b) The magenta ring shows the average dimensions of a cervical foramen. The rostrocaudal dimension is typically less than 12 mm. The medial-lateral dimension ranges from 8 to 10 mm. Osteophytes from the uncinate processes may encroach on the medial aspect of this dimension.
With these measurements in mind, the necessary exposure to perform the operation becomes evident. The rostrocaudal exposure should be from pedicle to pedicle, a distance of at least 12 mm. The mediolateral exposure should be from the medial aspect of the pedicle to the middle of the facet–lateral mass complex, a distance of at least 10 mm. The inherent nature of a posterior approach makes the AP dimension irrelevant for the exposure. Using both of these measurements defines the surgical target as 12 × 10 mm. Applying the principle of the ideal Caspar ratio (surgical target to surgical exposure as 1:1) using a 14-mm-diameter access port fulfills that criterion. It is through a sophisticated understanding of these measurements that it becomes evident how a well-positioned 14-mm-diameter minimal access port can adequately provide the surface area needed for a comprehensive decompression of the cervical nerve root, without exposing unnecessary anatomy ( ▶ Fig. 7.6).
With this review of the anatomy of the cervical foramen and its anatomical measurements, we have established the anatomical basis of the minimally invasive approach to the cervical spine. Before describing the techniques of the procedure, I want to underscore the words “well positioned” in the previous paragraph. A minimal access port positioned over the lateral aspect of the lateral mass will not allow you to perform an adequate decompression of the cervical root, and it carries a risk of destabilizing the segment. A minimal access port positioned over the lamina does not destabilize the segment, but it exposes the cervical spinal cord to unnecessary risk as you make your way laterally to the nerve root. The ideal placement of the minimal access port is precisely over the cervical nerve root, and this placement is the central element of this procedure ( ▶ Fig. 7.7).
Fig. 7.7 Illustrations of the ideal placement of the minimal access port for a minimally invasive posterior cervical foraminotomy. (a) Lateral view of the cervical spine with a 14-mm access port in position, which demonstrates the placement of the minimal access port parallel to the disc space. The inferior and superior articular processes fall within the field of view. (b) The posterior view through the access port showing the minimal access port positioned over the midpedicular line to access the medial and lateral aspects of the foramen. The pedicles are demarcated in blue.
7.6 Patient Positioning
There are several elements to positioning a patient for a posterior cervical foraminotomy to optimize visualization of the segment with fluoroscopy, the ergonomics for the surgeon and the comfort of the patient. From the placement of the skull clamp to the position of the chest rolls, this section covers the various nuances of patient positioning.
7.6.1 Application of the Skull Clamp
The ideal position of the skull clamp offers rigid stabilization of the head and cervical spine without causing any significant postoperative discomfort. The key to both is avoiding the temporalis muscle ( ▶ Fig. 7.8). Pins secured into the temporalis muscle have the potential to cause bleeding once the skull clamp is removed and postoperative discomfort for the patient long after their radiculopathy has resolved. Nonetheless, good purchase into the cranium is an absolute necessity for stability since the dilators exert downward pressure onto the cervical spine. There should never be a circumstance where a patient slips out of the pins because of suboptimal placement. Therefore, the ideal position is to have all the pins at the superior temporal line, which by definition places them above the temporalis muscle.
Fig. 7.8 Illustrations of the ideal placement of skull clamp pins in the cranium showing the temporalis muscle, which should be avoided. The pins should be placed above the superior temporal line, which is defined by the rostral insertion point of the temporalis muscle. (a) View of the right side of the head with the single pin in line with the external auditory canal and above the temporalis muscle. (b) View of the left side of the head with the pin sites denoted as fiducials on either side of the tragus.
The clamp should be positioned on the skull so that the pin on one side is in line with the tragus, and the two pins on the opposite side are positioned on either side of the tragus ( ▶ Fig. 7.8). I apply 60 pounds of pressure onto the skull clamp after confirming the optimal positioning of the pins. As I hold the head of the pinned patient, my operating team rolls the patient onto their chest, and we position the patient in the center of the operating table on chest rolls so that the components of the skull clamp system that connect to the table do not obstruct the eventual AP image I must take to confirm the position of the access port relative to the cervical pedicle. As I hold the patient’s head in a neutral position, my assistant secures the articulating arm and locks the skull clamp into position ( ▶ Fig. 7.9).
Fig. 7.9 (a) Illustration and (b) photograph of patient positioning. Once the skull clamp has been placed, the patient is rolled onto chest rolls and into the center of the operating table. The skull clamp is then secured to the bed with the articulating arm with the cervical spine positioned in a neutral configuration.
7.6.2 Positioning the Patient
Fessler3 made a very sound argument for performing this operation with the patient in the seated position. The supposition is that the surgeon is more likely to encounter vigorous venous bleeding with the patient in the prone position because of the increased epidural venous pressure that accompanies that position. The greatest advantage of the sitting position is the decrease in epidural venous pressure and, therefore, a decrease in venous bleeding. Even as I type this, certain cases jump immediately to my mind where I was dealing with a venous deluge in patients positioned prone. During those early cases I whispered to myself, “Perhaps I should be doing these operations with the patient in the seated position.” At the same time, this argument may be countered by a risk of an air embolism, which, at least in theory, is elevated when the patient is in the seated position. The proponents of the seated position deny this risk is relevant, as they have not seen this entity in the hundreds of cases they have performed.
Acknowledging both the advantages and disadvantages of both the seated and prone position, I perform this operation with the patient in the prone position, but I make a point to place the patient in the reverse Trendelenburg position. In that manner, the head is higher than the heart, which decreases the epidural venous pressure, even if only slightly.
My decision to position patients prone is a practical one. The seated position is not a very popular one among our anesthesia colleagues, and I have found the added struggle to place the patient routinely in the seated position is not worth the putative benefits, which, in large part, may be accomplished in the reverse Trendelenburg position. Although epidural venous bleeding may be less in the seated position, the reality is that bleeding will occur regardless of the patient’s position. I have experienced considerable blood loss with the patient in both the seated and prone positions. However, the tipping point for me is the visceral response that is brought about just by alluding to the seated position to our anesthesia colleagues. Even the mention of it appears to decrease the efficiency of the anesthesia and thereby, the entire operation. Thus, I have exchanged the potential benefit of decreased cervical epidural venous pressure for the efficiency of positioning and a welcoming and enthusiastic anesthesiologist. I have found that this concession has decreased the time under anesthesia and optimized my time in the operating theater. I seldom have blood losses that exceed 50 mL, but admittedly, on occasion, I do encounter vigorous epidural venous bleeding that once again makes me reconsider the seated position. Fortunately, that type of bleeding does not occur with enough frequency to change my practice.
7.7 Operating Room Setup and Workflow
I set the operating room up to optimize the flow of the operation. I position the operating table well away from the anesthesiologist, almost in the middle of the room, so that I may perform the dilatation and docking of the minimal access port at the head of the bed. The microscope is set on the symptomatic side of the patient. I position the image intensifier of the fluoroscope on the opposite side of the patient’s symptoms ( ▶ Fig. 7.10). Over the years, I have come to realize that the ideal ergonomic position for positioning the access port is at the head of the bed ( ▶ Fig. 7.11) and not at the side of the patient. Working at the head of the bed optimizes the efficiency of the operation. For this reason, I position the fluoroscope tower with its video screens at the foot of the bed, which provides me with a direct line of sight to the screens as I dilate the muscle and dock the access port.
Fig. 7.11 Illustration and intraoperative photograph of patient positioning and operating room set up. (a) An illustration of the view over the shoulder of the surgeon. The surgeon stands at the head of the bed with a direct line of sight for the incision, dilatation and docking of the minimal access port. (b) Intraoperative photograph with a view from the head of the bed of the operating room setup and patient in a skull clamp positioned on chest rolls. Fluoroscope is in position with the image intensifier opposite the side of the symptoms. The monitors of the fluoroscope are at the foot of the bed. The microscope (not seen) is on the patient’s symptomatic side (in this case, the right side), draped and ready to be rolled into place. This photograph is taken from the vantage point of the surgeon working to dock the minimal access port. Working at the head of the bed prevents any obstruction by the fluoroscope when making the incision and securing the minimal access port into position, while optimizing an ergonomic position for the surgeon to work.
I place the clamp for the table-mounted arm opposite the side of the symptoms just above the level of the patient’s elbow, which is the ideal position for the table-mounted arm to hold the minimal access port for the procedure. By working at the head of the bed, I am not climbing over the fluoroscopy unit to make an incision or position the access port. Instead, I am in the ideal ergonomic position to complete the first phase of the operation.
7.8 Fluoroscopy
The objective of patient positioning is to place the patient in the geometric center of the bed where there is minimal metallic interference with AP fluoroscopic imaging. I make every effort to keep the neck neutral as my assistant tightens the articulating arm of the skull clamp. The first potential positioning pitfall occurs at this moment. The chest rolls need to be high enough on the chest to maintain the neutral position of the neck. If the rolls are positioned too low, the chest settles and the cervical spine goes into extension, with the downward pressure of dilators pushing down against the spine. It is also invaluable to ensure there is no tilt to the head when the skull clamp has been secured into its final position. Any tilt in the position of the head complicates lining up the facets on the lateral fluoroscopic image, which is essential for ideal positioning of the minimal access port. When I keep the anatomy in line without any tilt, the anatomy at depth is predictable for the dissection. When all one has is a 14-mm-diameter exposure, minimizing the variability of the anatomy at depth is crucial to maintain orientation.
Once the patient is positioned, I flex the patient’s knees to prevent the patient from sliding down the bed, and then I place the patient in the reverse Trendelenburg position ( ▶ Fig. 7.12). The shoulders are taped down to facilitate visualization of the level. The fluoroscope rolls into the field for planning and confirming the incision ( ▶ Fig. 7.13).
Fig. 7.13 Intraoperative photographs of patient positioning and operating room setup. (a) The fluoroscope rolls into the operative field for planning the incision before prepping and draping the patient. (b) Intraoperative photograph of the operating room setup for a C7–T1 posterior cervical foraminotomy below the level of a C6–7 anterior cervical discectomy and fusion. Once the ideal image is captured, the fluoroscope will stay in position until the access port is docked to prevent the need to recapture the ideal lateral image.
A special circumstance arises for visualization for the decompression of the eighth cervical nerve root, given the inherent difficulties of a lateral image at this level. The anatomists of old named the spinous process of C7 vertebra prominens because of its long characteristic spinous process that was reliably palpable through the skin. So, I begin by palpating the vertebra prominens (C7) and palpate up or down, depending on the level, and approximate the location of the incision by placing a Kelly clamp or a blunted Steinman pin with a protective cover, so as not to puncture the skin ( ▶ Fig. 7.14). I strive for an ideal lateral fluoroscopic image, with the facets perfectly aligned in the image. The fluoroscope may need to be wagged and the bed slightly rotated to achieve the ideal image. Unlike the previous procedures described thus far in this Primer, where I defer any imaging until after draping the patient, the time to obtain the perfect image is before prepping and draping the patient. Perfect orthogonal positioning of the patient greatly facilitates radiographic imaging.
Fig. 7.14 (a) Planning the incision. A Kelly clamp or a protected Steinman pin is used to plan the incision. (b) Lateral fluoroscopic image showing a Steinman pin (with the tip covered by tape to prevent puncture of the skin) at the C6–7 level for planning the incision. The lateral image needs to be adjusted until the facets are perfectly aligned. Note that in this image, the facets of the segment to be operated upon (C6–7) are aligned.
Once I have captured the perfect lateral image, I keep the fluoroscope in position until I have secured the minimal access port into position. I may move the table up and down for prepping and draping the patient, but I do not move the base of the fluoroscope. The goal is to save the time of trying to obtain the same image again but only moments later.
I adjust the blunted Steinman pin according to the fluoroscopic image and mark the level ( ▶ Fig. 7.15). I plan the incision 1.5 cm off the midline. I add 2 mm to the diameter of the port that I will use; that is, for a 14-mm port, I plan a 16-mm incision. I then prep and drape the posterior cervical spine widely. I incorporate the midline markings into the draped field in order to help keep my bearings.
Fig. 7.15 Planning the incision. The midline is marked by palpating the spinous processes as shown in this photograph by the dots in the midline. The spinous process of C7 (vertebra prominens) is readily palpated and marked (denoted in the image as a cross at inferior-most aspect of the markings). A 16-mm incision is planned 1.5 cm off the midline and over the top of the area confirmed by fluoroscopy. The surgeon’s mind needs to begin to reconstruct the anatomy at depth at this point in the operation.
7.9 Localization
Admittedly, I find localization and positioning the minimal access port more harrowing in the cervical spine than in the lumbar spine. The consequences of having any instrument enter the spinal canal at this phase of the operation are dire, a topic that is covered in greater depth in Chapter 8 on the minimally invasive posterior cervical laminectomy. At the same time, I have confidence in my knowledge of the anatomy at depth. As long as I know where the midline is, I know I can safely dock laterally on the facet–lateral mass complex. Knowledge and certainty of the midline is imperative. Based on the anthropometric measurements reported by Panjabi et al,11 the distance from the geometric center of the canal to the lateral aspect of the canal is approximately 12 mm. I know that with an incision planned 15 mm lateral to midline, I will safely dock onto bone, provided I do not overly converge.
All the prepping and draping are done around the fluoroscope. To optimize the operative flow, it is essential that I do not move the fluoroscope after the ideal image has been captured during the preoperative localization process. As mentioned in Section 7.7, Operating Room Setup and Workflow, I stand at the head of the bed facing the monitors of the fluoroscope ( ▶ Fig. 7.16) when I begin the operation. Thus, I am out of the way of the fluoroscope, and I am not craning my neck trying to look at the images while the radiology technologist intermittently and inadvertently irradiates parts of my body, which invariably get in the way when standing at the side of the patient. The fluoroscope monitors are at the foot of the bed, which allows me to look directly at the images and the operative site simultaneously. Because I do not move the fluoroscope after localization, I know that the first image I take will be the ideal image.
Fig. 7.16 Photograph of surgeon positioned at the head of the bed for the placement of the minimal access port. Standing at the head of the bed optimizes the ergonomics of positioning the access port while avoiding the path of the fluoroscope. With the fluoroscope monitors at the foot of the bed, the surgeon has a simultaneous, direct line of sight to the fluoroscopic images and the optimal working space.
Related posts:
Minimally Invasive Decompressions for Metastatic Spinal Disease
Minimally Invasive Posterior Cervical Laminectomy
Minimally Invasive Far Lateral Microdiscectomy
Minimally Invasive Lateral Transpsoas Interbody Lumbar Fusion
Anterior Cervical Discectomy with Arthroplasty or Fusion
Minimally Invasive Transforaminal Lumbar Interbody Fusion
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