In the last post we discussed the posterior cervical foraminotomy (PCF) in which a pinched cervical nerve is decompressed via small hole in the lamina at the back of the spine. The main benefit of the PCF is that the nerve can be directly decompressed without significant alterations in the biomechanics of the spine (i.e. no alterations to the disc and no need for a fusion). Most of the pathology that compresses nerves in the cervical spine, though, occurs in front of the nerve at the disc space and uncovertebral joint (see figure 1). Thus, a major drawback of the PCF is that you only indirectly treat the cause of the nerve compression; you can’t remove the disc bulge or bone spur that is actually compressing the nerve. Because of this and other limitations of posterior approaches, an anterior (i.e. from the front of the spine) approach was sought.
Figure 1: axial view of the spinal cord in the cervical spinal canal. Note the left side of the image where the nerve root is compressed from a herniated disc and overgrowth of the uncovertebral joint. Notice how this pathology is found anterior to the nerve root. (Source: Carette S, Fehlings MG. Clinical practice. Cervical radiculopathy. N Engl J Med. Jul 28 2005; 353(4): 393-399.)
In the 1950s Cloward as well as Smith and Robinson described similar techniques for an anterior approach to the spine for removal of herniated discs or bone spurs. Both Cloward’s and Smith/Robinson’s techniques involved the insertion of bone into the disc space after removal of the disc (i.e. discectomy) to promote a fusion across the disc space (the term fusion refers to the formation of bone that causes two bones, in this case vertebral bodies, to fuse into one.) Thus, this technique came to be known as an anterior cervical discectomy and fusion, or ACDF. Shortly thereafter other surgeons altered the technique such that it only involved the discectomy without the additional step of inserting the bone graft. This technique is referred to as an anterior cervical discectomy without fusion (ACD.) Since then, there have been several decades of controversy in the literature about which of these therapies (ACD versus ACDF) is superior. The advent in the 1980s of plating the front of the spine during an ACDF (the plate acts as an internal brace to theoretically promote more rapid bony fusion) only added to the controversy.
Figure 2: Image from Cloward’s 1958 article describing his ACDF technique. Label c indicates the path of the large-bore drill used to drill away the disc en route to the spinal cord and nerve root. This hole was then filled with a bone plug. (Source: Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg. 1958; 15: 602–17.)
Despite the controversy, what is certain is that the modern ACDF, with its plate, spacer and bone graft materials (see figure 3) is much costlier than the simple ACD. While the surgical approach hasn’t varied much, the materials definitely have. For example, these days more exotic materials are used to make the spacers to try to make them promote fusion. Also, because of pain associated with harvesting bone graft from the hip many surgeons today will use manufactured graft products rather than the patient’s own bone. The cost of all of these new materials starts to add up.
Figure 3: Side view of cervical spine after modern 2-level ACDF. Removed discs have been replaced with spacers and bone graft (red arrows). A plate is attached to the front of the vertebral bodies with screws. (Source: Medtronic.com)
Why incur the cost then? Why not just offer patients the ACD, which by most studies in the literature is just about as effective as ACDF? First, most surgeons believe that by using a spacer they can provide more structural support to the spine to restore disc height (degenerated discs often collapse which can exacerbate narrowing around the nerves). Also, some studies found that after ACD (without the spacer and fusion) there was a significantly higher rate of kyphosis (a deformity in which the spine bends forward over time) when compared to ACDF. Is it worth the extra cost of the spacer to avoid this potential complication down the road? Second, regarding the plate, many surgeons, myself included, believe that the extra stability of the plate promotes fusion more rapidly and effectively. This, in my practice at least, allows the patient to go home without having to wear a neck brace. What is it worth to the patient to not have to wear a brace for 2 months? Finally, all of these modern devices are supposed to make the bones fuse together more effectively. Again, there has never been any strong evidence to suggest that fusion is mandatory for the patient to feel better after a cervical discectomy. That said, most surgeons believe that movement at the disc space causes bone spur formation and disc bulging and that by performing a fusion the surgeon arrests this degenerative process (at that level of the spine at least; see my post on adjacent segment degeneration). If the goal is to maximize the patient’s chances of fusion is it worth the cost of all of these implants to increase the rate of fusion from, say, 90% to 95%? These are difficult questions that we’ll never be able to answer in a blog post. It is always worth considering, though, that just because a treatment is more modern and more costly doesn’t necessarily mean that it is better than the treatment that’s been around for decades.
Wow, I got off on a healthcare economics rant there… In the next post we’ll discuss the steps involved in an ACDF.