Chapter 21 Anterior endoscopic cervical discectomy
As with most other aspects of medicine and surgery, the understanding, care, and treatment of cervical disc injury has progressed. In the early days of surgical intervention, operating around the cervical spine and spinal cord did not often have satisfactory results, and it was not until the early part of the 1920s that surgery for cervical disc abnormalities became a reasonable option. The treatment of cervical disc injury started out with posterior decompression, and by the late 1940s, decompression with more of an anterior approach became more common and fusion was accepted fairly rapidly. The mainstream or “gold standard” technique for treatment of cervical disc injury for most of the past half century has consisted of anterior decompression and arthrodesis. Throughout this time, decompression without fusion was explored, but not until later have minimally invasive techniques, such as anterior endoscopic cervical discectomy (AECD), been able to make decompression without fusion a viable option. The next horizon in the development of spinal care will likely include percutaneous disc augmentation technologies that one hopes will reduce the need for subsequent surgical intervention and limit the reliance on implant survivability (Fig. 21-1).
Figure 21–1 Algorithm showing progression of types of spinal care from conservative through pump implantation.
The relatively early realization that anterior cervical disc decompression led to instability and often fusion or arthrodesis in kyphosis led to the common practice of performing fusion at the time of anterior cervical decompressive surgery. In comparison with the lumbar spine, posterior decompression of a cervical disc could be accomplished through a small enough entry zone that instability did not result regularly. It is these types of concepts that have allowed for the evolution of cervical disc surgery to the minimally invasive stage, with the realization that decompression of a cervical disc that does not remove too much of the surrounding structure can in fact be performed without resulting in instability. This procedure can even be performed in a minimally invasive fashion, and the advent of endoscopic technology allows for cervical decompression without the usual requirement for index fusion (Fig. 21-2).
Considering the history of the understanding of the cervical spine, it is no surprise that surgery for cervical disc abnormalities has had difficulties since its very beginning. The reasons are not only the technical difficulties with regard to operating on the cervical spine but also the lack of diagnostic tools and proven successful surgical experience. Differentiating between cervical disc herniations and other diseases, such as multiple sclerosis and amyotrophic lateral sclerosis, was often difficult because commonly there were few or nonspecific symptoms, pointing early clinicians to cervical pathology, and because results of simple radiographic examinations were often inconclusive, in that the neurologic signs and symptoms seemed to predominate in the motor system [1].
As early as 1911, Bailey and Casamajor discussed osteoarthritis of the cervical spine and suggested that the primary pathologic change is thinning of the intervertebral discs with resultant trauma to the vertebral end plates and osteophyte production, which causes symptoms. This narrowing of the disc space decreases the size of the neural foramen and compresses the facet joints. The spurs that then develop in response to this compression increase joint stress [2]. The primary cause of disc degeneration is generally assumed to be deficient nutrition, desiccation progressing with aging. The wear and tear of everyday activities and, occasionally, acute trauma are often additive to other, predisposing factors. Herniations of the cervical intervertebral discs with compression of the spinal cord have been described since 1928, when Stookey and other clinicians pointed out the similarities between the symptoms that arise as a result of a medial herniation and the more commonly associated symptoms of degenerative disease of the cervical spine [3,4]. That there is difficulty in diagnosing cervical disease is nothing new. It was a constant challenge for early clinicians to evaluate both the clinical symptoms and the radiologic findings in patients complaining of cervical and/or radicular symptomatology.
The majority of the anterior minimally invasive cervical discectomy procedures are based on small anterior anulotomy with cannula supported instrumentation, fluoroscopy and often endoscopy assisted intradiscal positioning. Then mechanical as well as laser or radiofrequency assisted disc removal and anular modulation is often added. Chiu and colleagues [5] substantiated their pursuit of minimally invasive cervical discectomy by stating that “fusion caused local inflammation, pain at the graft donor site, and a long recuperation compared to minimally invasive surgery without fusion which negates these complications.” As early as 1994, Chiu [6] had reported on 400 patients with nonextruded cervical disc herniations who had been treated with cervical endoscopic discectomy and laser thermodiscoplasty. With careful selection of patients and the use of lasers and microendoscopic equipment, a near 95% success rate was achieved. Table 21.1 shows the details of the international multicenter patient grouping treated with AECD [7].
The reduction in operative time, cost, and recuperation time with similar if not better outcomes and decrease in the need for fusion have indeed been successful at bringing minimally invasive cervical spine surgery to the 21st century. The commonplace use of lasers in spine surgery has also been a beneficial component of discectomy procedures. Prior to the use of lasers, an assortment of instruments were used with little or no side effects but none was able to satisfactorily remove the posterior disc and the displaced or herniated nuclear material [8]. In Korea, Lee began using holmium:yttrium-aluminum-garnet (Ho:YAG) laser with soft cervical disc herniations as early as 1993. His technique utilized the laser to remove the nucleus pulposus and to shrink down the protruded disc herniation in patients who had not experienced improvement with conservative therapy. It was noted at this time that the added benefit of the minimally invasive surgery was that it could be performed with use of local anesthesia, making monitoring of neurologic function readily evident. In 2001, Lee [8] wrote an article confirming his success with the percutaneous discectomy, stating that the combination of manual disc removal techniques with endoscopically directed Ho:YAG laser discectomy was a safe and effective surgical procedure.
Chemonucleolysis, the use of intradiscal chymopapain, has been out of favor in the United State for a number of years now. However, some surgeons have combined the use of low-dose chemonucleolysis with endoscopic discectomy procedures. In 1995, Hoogland and Scheckenbach [9] in Germany reported a new anterior cervical discectomy procedure with no complications. They performed low-dose chemonucleolysis utilizing 500 IU chymopapain followed by automated percutaneous nucleotomy of the cervical spine. The use of chymopapain remains quite limited, although the results of its use in association with minimally invasive surgery does seem to be improving. The use of lasers in this fashion is becoming more prominent, and with regard to the U.S. markets, lasers seemed to be more accepted than intradiscal chymopapain.
