9 Anterior Cervical Discectomy with Arthroplasty or Fusion

Knowledge of the three-dimensional anatomy of the cervical vertebral body is an absolute necessity for mastery of decompressions and instrumentation of the anterior cervical spine. The surgeon must develop an intuitive understanding of the dimensions of the cervical vertebral bodies, including their heights, widths and depths, to achieve a command of the necessary exposure of the bony anatomy and decompression of the neural elements. Panjabi and colleagues offer a comprehensive quantitative three-dimensional analysis of the subaxial spine, and their paper is mandatory reading for surgeons striving to master anterior approaches.1 I summarize some of the key elements of that analysis, but nothing replaces the in-depth understanding achieved by reading and rereading Panjabi’s article (▶ Fig. 9.1 and ▶ Table 9.1 ).¹

The height of each cervical vertebral body provides a sense of the rostrocaudal exposure needed for a single-level arthroplasty or a four-level ACD fusion (ACDF). This knowledge also helps in planning the length of the anterior cervical plate. The width of the vertebral body provides a sense of the medial-lateral exposure needed for placement of an interbody graft, arthroplasty device or anterior cervical plate. Knowledge of the distance between the foramen transversarium provides the confidence needed to achieve a wide decompression of the cervical nerve roots compressed by lateral spurs on the uncovertebral joints. This section presents a brief summary of the key dimensions of the cervical vertebral bodies to begin the process of making the dimensions of the cervical spine intuitive.

Throughout this chapter, I place particular focus on the importance of completely exposing the uncinate processes during the discectomy phase of the operation. These gently sloping joints are the North Star for anterior approaches to the cervical spine. Whether for motion preservation or for arthrodesis, the uncovertebral joints, also known as the joints of Luschka, named after the German anatomist Herbert von Luschka, are the orienting structures whose complete exposure reliably allows the surgeon to establish the midline. Identifying and marking the geometric midline is the sine qua non of an adequate decompression, ideal positioning of an artificial disc or the orthogonal and midline placement of an anterior cervical plate (▶ Fig. 9.2).

The upslope of the uncovertebral joints is the lateral boundary of the decompression. On the other side of that lateral boundary courses the vertebral artery (▶ Fig. 9.3). Absolute certainty of the vertebral artery location provides you with the confidence to completely decompress a nerve root within its foramen. As mentioned previously, reconstruction of the anatomy at depth with anatomic measurements at your mental fingertips is a characteristic of minimally invasive surgery. The cadaveric analysis by Panjabi and colleagues provides a valuable reference regarding the canal width.¹ Vaccaro and colleagues corroborate Panjabi and colleagues’ reported measurements with a radiographic analysis of axial computed tomography (CT) in which the authors measured the intervertebral artery distance throughout the subaxial spine. The range of the intervertebral artery distance is as high as 29 mm at C6 and as little as 25 mm at C3.² As will be discussed in the technique section of this chapter, these measurements, alongside those reported by Panjabi and colleagues, demonstrate the anatomical basis for at least a 20- to 22-mm decompression of the disc space in the majority of patients (▶ Fig. 9.2). It has become part of my preoperative routine to review the foramen transversaria by scrolling through the axial images at the level or levels that I intend to decompress and make note of any potential irregularity, such as an ectatic or tortuous vertebral artery.

9.3 Requisite Anatomy

Bringing together all of the anatomical measurements of the anterior cervical spine leads to a definition of the requisite anatomy for an anterior cervical operation. The mediolateral dimension of an exposure for any particular segment should be a minimum of 20 mm and up to 22 mm of the vertebral bodies. The rostral and caudal exposures should not exceed 5 mm above and below the disc space to mitigate the risk of adjacent segment degeneration. ▶ Fig. 9.4 illustrates the requisite anatomical unit needed for a single-level decompression with arthrodesis or arthroplasty. Logically, a multilevel surgery is the sum of the various requisite anatomical units in need of decompression, all of which should be exposed at the outset of the operation (▶ Fig. 9.5).

9.4 Operating Room Setup

The surgery is performed on a standard operating table that is reversed to shift the base away from the head of the bed. Configuring the operating table in this manner facilitates positioning the fluoroscopic unit. I position the patient’s head in a Caspar head holder to maintain the position of the cervical spine in an ideal orthogonal position. A stable head makes for a stable cervical spine. Furthermore, the head holder achieves and captures the ideal lordotic position with the use of a bolster in the posterior cervical spine. In my estimation, the quest for the geometric midline of the cervical spine begins with positioning the patient. The stability added by the Caspar head holder is a valuable element in identifying and securing the midline. I discuss the merits of this contraption further in the patient positioning section.

The laterality of the approach needs to be determined so that the operating room staff know where to place the microscope and fluoroscope to set up the operating room properly. I prefer to approach the cervical spine opposite the side of the symptoms. For instance, if a patient presents with a left C6 radiculopathy secondary to a large disc herniation that is eccentric to the left, I use a right-sided approach. The rationale is that a right-sided approach provides a direct line of sight onto the contralateral aspect of the disc space and foramen. Applying that same rationale to right-sided symptoms would then prompt a left-sided approach. It is important to clearly communicate the laterality of the approach in advance to the operating room staff to enable them to efficiently set up the operating room. Admittedly, a complete decompression of the entire segment can be achieved from either side. However, I have found that approaching from the side opposite of the symptoms optimizes my visualization into the most symptomatic lateral recess.

The fluoroscope is positioned and remains in the operative field from the outset to optimize the flow of the operation before the patient is prepped and draped. Similar to the previous techniques mentioned in this Primer, the image intensifier of the fluoroscope is always positioned on the side opposite of the side of the incision, whereas the microscope stands ready to roll in on the same side of the incision and opposite of the image intensifier. I avoid any difficulty navigating the bases of the microscope and fluoroscope with this configuration (▶ Fig. 9.6).

9.5 Patient Positioning

When I first started in practice, I positioned the patient with nothing more than a bag of intravenous fluid behind the shoulder blades and the head positioned in a doughnut-shaped gel roll. The shoulders were taped down to facilitate exposure of the lower cervical levels. The problem I encountered with this positioning technique was that there was nothing to stabilize the head. If the head rotated during the operation, I found that it had an impact on putting the cervical plate in a perfectly midline and orthogonal position, or it affected the placement of an arthroplasty device. Maintaining the spine in a perfectly orthogonal position is a principle tenet of instrumentation of the spine at any level.

A stable head makes for a stable cervical spine, and therefore, some sort of head holder is ideal for stabilization of the head and cervical spine for anterior cervical approaches. The headpiece centers the patient’s head on the operating table, the chinstrap captures and holds a midline orthogonal position and the shoulder bolster ensures a lordotic position for the neck. The bolster is helpful when tapping a tight-fitting graft into place, and it is particularly valuable as a counterforce when securing an artificial disc (▶ Fig. 9.7).

An adhesive spray is applied to the shoulders, which are then taped down onto the bed to facilitate visualization of the lower cervical segments. The fluoroscope, which has been parked above the head of the bed, rolls into position to facilitate planning the incision.

9.6 Planning the Incision

For a single-level operation, I plan the incision precisely over the disc space (▶ Fig. 9.8).

For a multilevel operation, I plan the incision over the top of the central vertebral body or disc space. For example, when performing a C5–6, C6–7 ACDF, I plan the incision over the top of the C6 vertebral body, which is the central point of the exposure (▶ Fig. 9.9). For a three-level ACDF, I plan the incision over the top of the central disc space. For example, for a C4–5, C5–6 and C6–7 ACDF, I plan the incision over the C5–6 disc space, which is the central point of the exposure (▶ Fig. 9.10).

Finally, for a four-level ACDF, I use the two-incision technique as described by Riew in Chin et al.³ For example, for a C3–4, C4–5, C5–6 and C6–7 ACDF, I plan one smaller incision over the C4 vertebral body, which provides access to the disc spaces of C3–4 and C4–5, and a second longer incision over the C6 vertebral body, which provides access to the disc spaces of C5–6 and C6–7 (▶ Fig. 9.11). The two-incision technique is described in greater detail in Section 9.8, Operative Technique.

As mentioned earlier, I plan the incision on the side of the neck opposite the symptoms, which provides me an optimal view of the symptomatic lateral recess. I mark the incision by placing a protected Steinman pin perfectly vertical and alongside the sternocleidomastoid muscle. Vertical positioning of the Steinman pin for the fluoroscopic image is important to establish the trajectory of exposure. During the exposure, completing the dissection along the same trajectory of the vertically positioned Steinman pin almost guarantees the exposure of the intended level. One or two fluoroscopic images allow me to confirm an ideal location on the skin to plan the incision. I mark the ideal incision immediately over my intended target and then look for a prominent neck crease in the vicinity of this mark (▶ Fig. 9.12). If I am able to identify two neck creases, I use the higher one because rostral dissection is more restricting than caudal dissection. In the absence of an obvious neck crease, I use the initial mark.

After I mark the incision, I mark a prominent V in the sternal notch as a reference point for the midline (▶ Fig. 9.13). An electrocardiogram lead may be placed on the tip of the nose so that it may be palpated under the sterile drapes. The tip of the nose and the sternal notch become two reference points for the midline, which are of tremendous value when plating. I widely prep and drape the surgical site to include the midline and the V to provide as many visual cues as possible for establishing the midline.

9.7 Historical Vignette

The surgical approach to the anterior spine that I describe in the surgical technique section is known as the Smith–Robinson approach. The story of the evolution of that approach for management of cervical radiculopathy and myelopathy is worthy of a chapter, if not a book, of its own. Although outside the purview of this Primer, it would be impossible for me, given my insatiable penchant for the history of spinal procedures, not to include a comment or two on this topic. The hope is to nudge the reader into reviewing those original papers, both of which make for extraordinarily insightful reading and provide all of us with a greater appreciation of our origins and how far we have come.

The year 1958 was a remarkable year for the anterior cervical spine. Prior to that year, the management of cervical radiculopathy and myelopathy was limited to posterior approaches. Spine surgeons had long recognized the limitations of cervical laminectomies and foraminotomies and began exploring decompression of the spinal cord and nerve roots from an anterior approach, especially for midline compression of the spinal cord. Writing from Honolulu, Hawaii, Ralph Cloward published “Anterior Approach for Ruptured Cervical Disks” in the Journal of Neurosurgery in 1958, while the very same year, writing from Baltimore, Maryland, George W. Smith and Robert A. Robinson published “The Treatment of Certain Cervical-Spine Disorders by Anterior Removal of the Intervertebral Disc and Interbody Fusion” in the Journal of Bone and Joint Surgery.4,5 The Cloward procedure involved a drill that reamed a hole within the disc space for the decompression and then placement of a bone dowel for fusion (▶ Fig. 9.14),⁴ whereas the Smith–Robinson procedure was more in line with the procedure performed today: discectomy and placement of a shaped iliac crest autograft for interbody fusion (▶ Fig. 9.15).⁵

Surgeons had some understandable concerns about the risk involved in drilling with a large drill bit through the disc space and in the direction of the central canal, and the Cloward procedure gradually fell out of favor. The simplicity and reproducibility of the Smith and Robinson approach, on the other hand, allowed for much wider adoption. As a result, the anterior approach to the anterior cervical spine has become known as the Smith–Robinson approach and is the approach I describe in the next section. It is important to recognize that both the Cloward and Smith–Robinson techniques use the same avascular plane medial to the sternocleidomastoid muscle that allows for a bloodless dissection onto the anterior cervical spine. From the standpoint of exposure, these two techniques are indistinguishable.

9.8 Operative Technique

In Jonathan Swift’s novel Gulliver’s Travels, the tiny men from the island of Lilliput tied down the hero, Lemuel Gulliver, with hundreds of tiny ropes, which were no more than threads to Gulliver. Although one rope of the Lilliputians could never hold the enormous Gulliver down, the combination of hundreds of tiny ropes made the giant their prisoner.6 I oftentimes think of Swift’s tale when I am exposing the anterior cervical spine. The exposure can be a painful struggle or an effortless joy; it depends on how much attention I direct toward freeing the tissue planes. The hundreds of tiny ropes holding me back from the cervical spine need only be identified and meticulously spread or divided. The exposure then becomes effortless and the surgery enjoyable. At the same time, whereas one of these tiny ropes alone could not hold me back, the combination of adhesions and fascial bands between the tissue planes can make me their prisoner. The operation then becomes laborious, the exposure becomes suboptimal and everything from the decompression to the plating becomes a struggle. Welcome to Lilliput.

With all of this in mind, the theme for exposure is to dissect the various tissue planes in a manner that allows for near effortless retraction of the esophagus and trachea medially and maximizes the exposure of the requisite anatomical unit(s). The more these tissue planes are identified and freed, the easier it becomes to visualize the requisite anatomy of the operation. Not doing so limits the retractor blades’ capacity to expose the requisite anatomical unit. As illustrated in ▶ Fig. 9.4, the goal is exposure of the inferior 5 mm of the rostral vertebral body and exposure of the superior 5 mm of the caudal vertebral body along with a mediolateral exposure of 20 to 22 mm. By way of example, for a C5–6 ACDF, I expose the inferior half, approximately 5 mm, of the C5 vertebral body and the superior half (5 mm) of the C6 vertebral body. I mobilize the longus muscles and expose the 20 to 22 mm of the anterior vertebral bodies. An identical exposure is needed for arthroplasty. I always make a concerted effort not to expose a segment that is not being operated on to prevent a degenerative cascade from beginning.

All of the exposure that is needed for the entire operation, including plating, should be accomplished before placing the self-retaining cervical retractor blades or Caspar posts. Whether the operation is a single- or a four-level operation, completing the exposure of all the requisite anatomical units at the outset optimizes the flow of the operation. A potential pitfall is placing the Caspar posts into the vertebral bodies too early. The posts become a distraction and end up limiting the exposure. I complete the entire exposure for the decompression and the plating with Cloward handheld retractors between my assistant and myself before beginning the decompression of any segment. In that way, when I complete decompression and interbody graft placement for the final segment, there is no need for additional exposure. Instead, after the final interbody spacer is placed, I know that I can slide the cervical plate into position and fixate it to the anterior cervical spine. The work performed at the beginning of the operation should make plating the easiest part of the operation.

With a plane of dissection below the platysma, I slide the Metzenbaum scissors underneath the thin veil of platysma, spread the scissors open and use cautery to divide the fibers of the platysma along the length of the incision. I use DeBakey forceps again to pick up each limb of the divided platysma and undermine it in the rostral, caudal and medial directions. These fascial adhesions and bands beneath platysma are what contribute to those Lilliputian ropes holding me back from an effortless exposure onto the cervical spine. With the platysma divided and undermined, I can deepen the position of the self-retaining Weitlaner retractor to beneath the divided platysma. The sternocleidomastoid muscle becomes clearly visible as the prominent muscle in the lateral aspect of the exposure when I open the Weitlaner retractor (▶ Fig. 9.16). The trachea and esophagus lie medial to the sternocleidomastoid muscle, whereas the carotid artery and jugular vein lie immediately below the muscle.

With minimal dissection, the corridor that leads directly onto the cervical spine becomes obvious when following the medial aspect of sternocleidomastoid muscle belly along the avascular plane. I use DeBakey forceps to lightly pull the sternocleidomastoid muscle laterally to reveal the medial fascial bands. The action of the Metzenbaum scissors is to spread those fascial bands and develop the avascular plane. With nothing more than spreading the blades of the scissors, the plane of dissection between the sternocleidomastoid laterally and the sternohyoid, sternothyroid and omohyoid muscles medially opens and leads directly to the prevertebral cervical fascia. I routinely use an index finger to confirm that the pulsing carotid artery is lateral to my plane of dissection and the cartilaginous rings of the trachea are medial, precisely the same way Smith and Robinson described their approach in their 1958 landmark paper.⁵

9.10 Recurrent Laryngeal Nerve

Inspection of a right-sided exposure may reveal the recurrent laryngeal nerve (▶ Fig. 9.17). If so, it is a worthwhile endeavor to ensure that the nerve is safely mobilized and that no traction will be upon it when the self-retaining retractors are in place. If I do not see the recurrent laryngeal nerve, I make no attempt to search for it. The literature on the incidence, cause and prevention of injury to recurrent laryngeal nerves is voluminous. There are several studies that suggest a left-sided approach decreases the incidence of such an injury.^7,8 However, that body of literature has been countered with an equal body that does not support this hypothesis.^9,10 Regardless of the side of the approach, deflating the endotracheal cuff after the retractors are in position and reinflating it to less than 20 mm Hg, as recommended by Apfelbaum and colleagues, is a worthwhile routine to incorporate into your technique.¹¹

9.11 Exposure of the Requisite Anatomical Unit

At this point, I pass Cloward handheld retractors into the dissected plane and onto the prevertebral cervical fascia, and I begin to retract the trachea and esophagus as I bluntly dissect my way to the cervical spine with Kittner dissectors. Smith and Robinson described this part of the operation with the following sentence: “The anterior longitudinal ligament glistens over the mid-line of the vertebral bodies even through the prevertebral fascia. It clearly marks the mid-line.”5 That statement is as true today as it was in 1958 and is something I always keep in mind as I begin to identify the midline.

With my assistant retracting medially, I use two Kittner dissectors to bluntly dissect in opposite directions in the rostrocaudal plane against the anterior cervical spine. My goal is to separate the prevertebral cervical fascia without sharp dissection and visualize the glistening anterior longitudinal ligament on the cervical vertebral bodies and disc spaces. Before bluntly dissecting, I inspect the area for traversing veins on the top of the prevertebral cervical fascia. Although these veins are small, they are capable of causing bleeding that can become quite a nuisance during the exposure. To eliminate the risk of tearing these veins, I find it worthwhile to cauterize them and then sharply divide them over the segment to be operated on before proceeding with blunt dissection of the rostrocaudal plane using Kittner dissectors.

Because I have proceeded along the vertical path in line with the Steinman pin that I used to plan my incision, I will reliably reach my intended target. I do not use a spinal needle to confirm the level. Instead, I place a Kittner on the disc space to confirm the location with a fluoroscopic image. I long ago abandoned the practice of using a spinal needle to puncture the presumptive disc space on the off chance that I am off by a level. There is literature to suggest that puncturing an unaffected disc level begins the degenerative cascade that ushers in adjacent segment degeneration.¹² So instead of a spinal needle, I hold the Kittner on the disc space, remove the handheld Cloward retractor, since it is not radiolucent, and bring in the fluoroscope as the operating table rises to the predetermined fluoroscopic height. A lateral fluoroscopic image confirms that I am at the correct level (▶ Fig. 9.18). In the event that I am off by a level, there is no consequence since the annulus has not been punctured; there has not been a disruption in the prevertebral cervical fascia, nor have I used cautery up to this point. I merely extend my dissection either up or down to the correct level by freeing the various fascial bands medial to the sternocleidomastoid muscle. It is only after I have confirmed the correct level that I make a preliminary mark above and below the disc space into the vertebral bodies with cautery and return to completing the exposure.

With the segment confirmed, I return to using the handheld Cloward retractors and ensure that I have bluntly dissected through the prevertebral cervical fascia. The longus colli muscles become readily evident on either side of the disc space. Those vertical columns of muscle provide me with my first opportunity to establish the midline. I hold the Cloward handheld retractor so that I am holding back the soft tissue above the longus colli without actually retracting the longus colli. The objective is to prevent any distortion of the muscular columns. My assistant does likewise on their side. I then visualize the two columns of longus colli muscle coursing over the segment (▶ Fig. 9.19). The midpoint between longus colli pillars is a very close approximation of the midline of the spine. I cauterize a vertical line into the vertebral body just above the disc space and then mark it with a purple marking pen. I do not use black ink, because it is indistinguishable from the anatomy that encountered the tip of the cautery. That purple mark is evaluated again later relative to the exposed uncovertebral joints to further confirm the midline.

With the midline marked, I now expose the lateral aspects of the vertebral bodies by releasing and elevating the medial aspect of the longus colli muscle with cautery. I strive to develop a cuff that the retractor blades can capture with their hooked configuration. Principles that I have embraced in minimally invasive spine surgery are applicable at this point. A measurement that should be at the forefront on every spine surgeon’s mind is the distance between the vertebral arteries, which varies from 24 to 29 mm throughout the cervical spine. Anatomical studies have established that the intervertebral artery distance is the least at C3 and the greatest at C6.² Therefore, exposing up to 22 mm of the transverse dimension of the vertebral bodies is a safe, if not necessary, distance to expose the disc space for an adequate decompression of a cervical segment. If 22 mm of exposure is not accomplished at the time of the initial dissection, it will not be accomplished after the self-retaining retractors are placed. I am cognizant of the sympathetic chain ganglia that course in the lateral aspect of the longus colli and keep my dissection at the interface of the medial muscle belly of the longus colli and lateral vertebral body.

Incorporating yet another element of minimally invasive spinal surgery that we have routinely used in the various other procedures presented in this Primer is helpful in developing the cuff on the longus colli muscle for the eventual hooked blades of the retractors. The larger of the two minimally invasive suction retractors is ideal for this component of the procedure. The minimally invasive suction retractor lifts the insertion point of the longus colli muscle and allows for cautery to dissect the medial insertion off the vertebral body to complete the lateral exposure while simultaneously eliminating the smoke created from the cautery. The cuff that is created can engage and hold the retractor blade.

To ensure the same operation every time, I have the scrub technician trim a plastic ruler to 22 mm, which should fit easily within the exposure. Once I have 22 mm of the disc space exposed, I complete the exposure by exposing the inferior half of the rostral vertebral body to a distance of 5 mm and the superior half of the caudal body to a distance of 5 mm. I extend my dissection 22 mm in the medial-lateral dimension at both levels. Reaching those dimensions, I am now confident that I have the exposure I need for an optimal decompression, interbody graft placement, fixating a cervical plate or placing an arthroplasty device. I repeat the exposure process just described for every segment that I intend to operate on before I place the blades for the self-retaining retractors and secure the Caspar pin posts (▶ Fig. 9.20).

I prefer to perform the exposure for the entire operation and place the first set of Caspar distraction posts under loupe magnification and headlight illumination. I begin a preliminary discectomy and keep the loupes and headlight on until the disc has been almost completely removed and the posterior aspect of the disc space is seen, at which point I bring in the operating microscope. My operating room team knows that, after the Caspar posts are in, it is only a matter of minutes before I ask my team to roll the microscope into position (▶ Fig. 9.21).

9.12 Exposures for Multilevel Anterior Cervical Discectomy and Fusion

The natural tendency when performing a multilevel ACDF is to expose the first segment and then extend either upward or downward from there. That was my routine for years until I stumbled onto a manuscript written by Riew and colleagues, who used two incisions to perform a four-level operation.3 The crux of their manuscript is essentially to have two operative sites above the skin and connect them below the skin and platysma, thereby reducing the amount of exposure and retraction on the esophagus and trachea. The elements of that concept may be applied to a single incision for two- and three-level ACDFs. Instead of exposing one level and then working up or down, I remove the handheld Cloward retractors altogether and begin the dissection anew. The principle is to expose the segments as a series of “silos,” as if each silo were a single-level procedure, and then connect the exposures into one.

With no retractors in the surgical site holding open the previous exposure, I begin descending down the avascular plane medial to the sternocleidomastoid as if my only intent were to expose the level above or below. Once I am onto the prevertebral cervical fascia, I again use Kittners for blunt dissection and invariably connect to the previous exposure. At this point, I identify those fascial bands holding me back from a continuous exposure and divide them. I now have a continuous exposure between the two disc spaces. If I am performing a three-level surgery, then I repeat the process.

What I have found using this technique is that, in the end, it is faster than extending the exposure from the first level. Furthermore, I am more readily able to identify that it is either the platysma holding me up or a fascial band here or there. Connecting three different silos of exposure (in the case of a three-level ACDF) offers an exposure that is vastly superior and almost tension free compared to the exposure that I accomplish by extension from the first level I expose to the third level. In my experience, attempting to extend the exposure with the self-retaining retractors in position blurs the anatomy and hides the very bands that need to be identified and divided. In the end, whether it is a single- or four-level operation, I perform all of the exposures level by level sequentially connecting these silos of exposure until all of the operative levels have been exposed to a width of 22 mm. By adhering to this principle, I am certain that, before I place the self-retaining retractors in position, no further exposure will be needed during the plating phase of the operation.

9.13 Table-Mounted Arm for Self-Retaining Retractor: A Minimally Invasive Surgery Modification

When I was in training, I watched my attendings attempt to anchor the cervical retractor using a Ray-tech sponge and a Kelly clamp, with minimal effectiveness. For years after my training, I did the same—behavioral mimicry. The objective of wrapping these sponges and using these clamps was to create stability, but all these attempts fell short. More often than not, as a resident, I found myself holding the retractor in position to optimize the exposure. The self-retaining cervical retractor represents yet another opportunity to steal a page out of the minimally invasive surgery playbook. By anchoring the cervical self-retaining retractor onto the table-mounted arm, the same table-mounted arm that we use for all of the minimal access ports we work with, all the frustration that comes with using the cervical retractor evaporates. This opportunity presented itself when various types of connectors to the self-retaining cervical retractor became available that allowed the cervical retractor to be anchored onto the table-mounted arm used for minimally invasive approaches. Connecting the cervical self-retaining retractor now fixates the retractor into position and, if needed, allows repositioning with added stability to capture and expose the ideal midline position (▶ Fig. 9.22).

Although I have found the simple use of this minimally invasive table-mounted arm invaluable, it does not take away from the fact that the key component for the self-retaining cervical retractor is the mobilization of the longus colli muscles and the soft-tissue planes. An adequate cuff of longus colli muscle is necessary for the retractor blade to properly engage the edge of the muscle and proficiently retract it. The benefit of having the retractor anchored to the table-mounted frame is that it prevents the temptation to overly open the retractor. Doing so only dislodges the retractor blade from the underside of the longus colli muscle and compromises the exposure. I am careful when I open the retractor to ensure the cuff of the longus colli muscle stays within the confines of the curved aspect of the cervical retractor blade. Downward pressure on the retractor helps maintain its position as I open the blades. But as careful as I am, at times I go one click too far and lose the contact of the muscle on the retractor blade. The mobilized longus colli then flops itself into the lateral aspect of my exposure. Salvaging this without removing the blade is difficult, almost futile. It is a mistake to accept such a field of view. Instead, it is a worthwhile investment in time to simply start over with reengaging the longus colli and positioning the retractor. I apply one less click the second time around.

9.14 Caspar Distraction Posts

Now that the self-retaining retractor is in position, the anesthesiologist raises the bed once again to fluoroscopic height, and I secure the Caspar posts into the vertebral bodies with fluoroscopic guidance. I use my preliminary midline marks as my guide to place the posts in the midline. Based on my 5-mm approximation from the disc space, I place the awl or Caspar post at what I perceive to be 1 to 2 mm shy of the midportion of the vertebral body. A fluoroscopic image confirms the correct position. By doing so, I accomplish one of my ancillary objectives: to cause as little disruption to the adjacent segment as possible. If I am performing arthroplasty with a keel-based device, placement of the post three-quarters of the way from the disc space will be necessary to have room for the keel cut. However, non-keel-based arthroplasty devices allow me to remain shy of the midportion of the vertebral body and therefore have become my preferred implant.

There are two sizes of Caspar posts, 12 and 14 mm. Using the dimensions from Panjabi et al1 as my basis, I use 12-mm posts in women and 14-mm posts in men. Once the posts are secured into position, their appearance on fluoroscopy also becomes a helpful reference point for deciding the length of the cervical screws or the depth of the interbody space or arthroplasty device. These topics are discussed in greater detail in Section 9.22, Interbody Graft Placement, and Section 9.23, Sizing the Interbody Spacer.

I use a fluoroscopic image or two to confirm the location on the vertebral body and set the trajectory for ideal placement of the Caspar posts. First and foremost, I want to ensure that the posts are perfectly perpendicular to the posterior aspect of the vertebral body and, second, that they are a safe distance from the adjacent segment (▶ Fig. 9.23). Since the consensus distance has been demonstrated to be less than 5 mm, I attempt to place my posts just shy of the midpoint of the vertebral body for fusions.^13,14 For a keel-based arthroplasty, the posts need to be positioned a safe distance from the keel cuts. ▶ Fig. 9.24 demonstrates the need to be well beyond the midportion of the vertebral body to accommodate the keel of the arthroplasty device.

In many circumstances, patients have focal kyphosis at the segment of cervical spondylosis (▶ Fig. 9.25). The most effective manner to address the kyphosis is to ensure that the posts are completely perpendicular to the back wall of the vertebral body so that the posts reverse the kyphosis when they are distracted, and a more lordotic geometry of the segment is captured for the arthrodesis. Again, it bears repeating that, for cervical fusions, I make every effort to maintain the distance away from the adjacent segment to minimize the risk of causing adjacent segment degeneration. I have already alluded to the minimum distance from the adjacent disc space being 5 mm, a value that I qualify in Section 9.25, Cervical Plating.

In order to pass the Caspar post distractor over the post, Penfield nos. 3 and 1 dissectors are helpful to prevent the soft tissue from getting caught as the distractor slips over the posts. At times, because the focal kyphosis is so pronounced, the posts converge so greatly that placement of the distractor becomes untenable without separating the posts into a parallel alignment. For these circumstances, I place a handheld Cloward retractor between the posts and turn it enough to alter the convergent trajectories to parallel. The post distractor may now slide into position; using Penfields, hold back any soft tissue that may get in the way. At times, closing the mediolateral cervical retractor just a click or two takes just enough tension off the rostral aspect of the exposure to facilitate passage of the Caspar post distractor onto the posts. I distract the posts with a click or two to reverse the kyphosis and open the disc space and begin the discectomy. The fluoroscope rolls to the head of the bed as the microscope rolls into position for the decompression phase of the operation (▶ Fig. 9.26).

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