Role of Minimally Invasive Cervical Spine Surgery in the Aging Spine

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33 Role of Minimally Invasive Cervical Spine Surgery in the Aging Spine

Woo-Kyung Kim

KEY POINTS

• The anatomic and pathophysiologic changes of the aging spine are discussed.
• Techniques of various minimally invasive surgical procedures in the cervical spine include anterior cervical microforaminotomy, percutaneous cervical discectomy, microendoscopic discectomy, and percutaneous cervical nucleoplasty.
• The controversies of current minimally invasive surgical procedures are presented.

Introduction

The aging of the population in industrialized nations appears to be an inevitable situation. It does not simply mean an increase in life expectancy owing to the improvement of medical science and health care, but additionally a significant decrease in birth rates has led to this situation. Back and neck pain are most frequently occurred presentations of older people, and the unique nature of the spine makes those problems highly complex to evaluate and to manage. The spine is a very specific anatomic and functional unit. The findings of radiological degenerative changes of the cervical spine in aging population are common. By the fourth decade of life, 30% of asymptomatic subjects show degenerative changes of the intervertebral discs, whereas by the seventh decade, up to 90% have developed degenerative alterations.1,2 Thus, it is always important to interpret such radiological features in the light of the clinical presentation. If symptoms and findings are not correlated, the presence of a different pathology should be suspected, and appropriate evaluations are required. In order to assess the spine unit of patients (clinical, radiological; and laboratory findings; neurophysiology, etc.), cooperation between the orthopedic surgeon, the neurosurgeon, and the neurologisted is needed. Based on the present illness and physical examinations, a proper neurological workup should be performed. In addition to the neurological assessment, additional laboratory evaluations and other studies may be helpful in the differential diagnosis, including electromyography (EMG), electroneurography (ENG), sensory evoked potentials (SEP), and motor evoked potentials (MEP).

The aging of the spine induces considerable alterations in anatomical structures: discs, facet joints, ligaments, muscles, and bones. The degeneration of some of these structures can be responsible for the injury to the neural structures by herniated disc, spinal stenosis, and other degenerative disease.1

Although various surgical treatments for spinal disorders have been proposed for years, the current concept in the evolution of all spinal surgical procedure is mostly concerned with minimally invasive techniques. The advantages of minimally invasive procedures include less postoperative pain, shorter hospital stays with faster recovery, and decreased surgical morbidity, mortality, and long-term sequelae. These benefits are the result of reduced damage to surrounding spinal structures.

Basic Science

As a flexible, multisegmental column, the functional role of the spine is to provide stabilization and upright position. The spine is composed of a static, changeless component, the vertebral bodies, and an elastic mobile component, the three joint complexes, consisting of the intervertebral disc and the two posterior facet joints. As mentioned earlier, the aging spine experiences considerable changes in anatomy (the structural components, biomechanics, etc.).2

The quantity of water present in the nucleus pulposus (contains a high proportion of hydrophilic glycosaminoglycans) decreases and both spinal height and the cushioning effect are reduced with aging. Gaps and fissures may develop in the discs, and with the time they may become desiccated and even ossified. As the disc height decreases, there may be a buckling of both anterior and posterior longitudinal ligaments. The buckling posterior ligaments may project into the spinal canal, reducing the space available for the spinal cord. Bony osteophytes may develop in the region of the vertebral bodies; endplate osteophytes may expand across the disc spaces and merge with osteophytes of adjacent vertebrae to form bridging osteophytes. If the osteophytes involve posterior endplates, they may protrude into the spinal canal, compressing the dural sac. People with congenitally narrowed spinal canals have greater risk for spinal cord compression as a result of these changes. Large bridging osteophytes on the anterior endplates may lead to severe problems in gastrointestinal, respiratory, or vascular systems. The size of the neural foramen, which the spinal nerves pass through, may be decreased both with the loss of spinal length and ossification and hypertrophy of these soft tissues around the vertebral column. Such age-related changes demonstrate the symptomatology in most patients presenting for cervical spine surgery.1,2

Surgical Indications and Preparation

The indications for surgery include (1) persistent or recurrent upper extremity pain or numbness not responsive to a conservative treatments for more than 3 to 6 months, (2) progressive or profound neurological deficit, (3) static neurological deficit associated with radicular pain, and (4) imaging studies confirming pathoanatomic features consistent with clinical features.

All patients should have routine cervical spine radiographs, including dynamic views, computed tomography (CT) scanning, and magnetic resonance imaging (MRI) preoperatively. Intraoperative somatosensory evoked potentials are useful for monitoring the sensory neurological pathway continuously during the surgery and have been very effective for monitoring the dorsal columns of the spinal cord. This decreases the risk of an obstructed blood vessel, accidental removal of the breathing tube, or a patient becoming conscious during the procedure. Also, the patient may be monitored with motor evoked potentials (MEP) and electromyograms (EMG) intraoperatively.

Radiological Evaluation

Routine cervical spine radiographs, including anteroposterior, lateral, flexion, extension, and both oblique views, are taken for the evaluation of degenerative disc disease. The narrowing of the intervertebral disc space and neural foramen, formation of osteophytes or bony spurs, subluxation of facet joints, and segmental instability are commonly shown in degenerative cervical diseases. Although cervical radiographs and CT scanning are useful for visualizing bony anatomy and overall alignment of the spine, they are limited in the evaluation of neural structures, such as neural foramen, spinal cord or nerve roots, and the presence or absence of neural compression.

Magnetic resonance imaging provides excellent images of spinal structures, such as discs, neural elements, bony structures, muscles, and ligaments. It is the preferred method for confirmatory diagnosis and is generally recognized in published studies.

Surgical Techniques

Anterior Cervical Microforaminotomy

Transuncal Approach

Under general anesthesia, the patient is placed in a supine position. Under fluoroscopic guidance, the incision site is marked at the medial border of the sternocleidomastoid (SCM) muscle perpendicular to the disc space angle. A 2-cm transverse skin incision is made from the medial border of the SCM muscle. The surgical trajectory from skin incision to pathologic lesion is perpendicular to the sagittal plane of the cervical spine, so the bone must be opened at the anterolateral spine along the line of the trajectory. In this case, the uncinate process lies along the perpendicular surgical trajectory. Especially in procedures at C4-C5 or C5-C6 level, a skin incision at the upper or mid portion of the neck produces such a perpendicular surgical trajectory. Skin incision to bone exposure is performed as in the previously discussed approach. The medial 1 to 2 mm of the most medial transverse processes at the upper and lower vertebrae are removed, and the vertebral artery is identified. Then, the lateral uncinate process is dissected from the vertebral artery. The most lateral 2-mm portion of the uncinate is drilled just medial to the vertebral artery toward the posterior longitudinal ligament. Once the posterior longitudinal ligament is exposed, compressive lesions, such as herniated soft disc or bone spurs, are excised. Often the posterior longitudinal ligament is opened to expose the dura mater at the most lateral portion of the spinal cord and proximal nerve root to detect hidden migrated disc fragments. The thin bone wall of the medial uncinate must not be damaged to maintain the integrity of the intervertebral disc.

Upper Vertebral Transcorporeal Approach

This approach uses bone opening at the most inferolateral portion of the upper vertebral body, because the anteroposterior surgical trajectory is inclined caudally. It is usually used for C6-C7 and C7-T1 cervical surgery, but it is also used for other levels by placing the skin incision more cephalad. The vertebral artery is slightly exposed, and a 2-mm medial portion of the transverse process of the upper vertebra is removed. The bone is opened at the inferolateral 2- to 3-mm portion of the upper vertebra by drilling toward the posterior longitudinal ligament. The intervertebral endplate, at the anterior two thirds of the intervertebral disc, must not be damaged. The surgical trajectory is directed toward the pathological lesion only through the most posterior portion. The rest of the procedure is the same as described previously.

Lower Vertebral Transcorporeal Approach

This technique refers to the location of the bone opening at the lateral portion of the lower vertebra of the intervertebral disc. When an operation is at a high level such as C3-C4, this surgical technique is required to expose the pathologic lesion, because the surgical trajectory from the skin incision to the target site is inclined cephalad.

The transverse skin incision about 1 to 2 inches then the platysma can be split longitudinally or dissected transversely. Blunt dissection proceeds medially to the sternocleidomastoid muscle and internal carotid artery toward the anterior aspect of the cervical vertebrae.

The longus colli muscle is split longitudinally to expose the lateral portion of the cervical spine. An anterior cervical retractor system (e.g., Thompson retractor) is applied before the operating microscope. Endoscopic surgery has been performed for this operation. The medial portion of the transverse process at the rostral and caudal vertebrae are identified. The most medial, upper 1- to 2-mm portion of the transverse process at the lower vertebra is removed, and the vertebral artery is identified. Using a 1- or 2-mm cutting drill bit, the superolateral 2- to 3-mm portion of the lower vertebra is drilled posteriorly just medial to the vertebral artery.

A cephalically inclined surgical trajectory leads the drilling toward the target pathologic lesion posteriorly. Compressive herniated soft disc or bone spurs are removed with microdissectors and various curettes. The nerve root and most lateral portion of the spinal cord are released. Surgical closure is made as in other anterior cervical surgery.

Case Studies

A 67-year-old woman had continuous radiating pain into her left arm. During 6 months of conservative treatment and physiotherapy, the symptoms were not relieved. Plain radiographs showed decrease in the height of disc space at the level of C5-C6 (Figure 33-1 ). Cervical MRI demonstrated narrowing and obstruction of neural foramen at the levels of C5-C6 and C6-C7 (Figure 33-2 ). The decision was made to perform a microsurgical decompression with anterior foraminotomy at both cervical segments. Transuncal approach at C5-C6 and upper vertebral transcorporeal approach at C6-C7 were performed, respectively. Plain and dynamic radiographs and three-dimensional (3-D) cervical CT were done postoperatively (Figure 33-3). The radiculopathy was significantly improved after the operation. The patient was symptom free, and 3-D CT and dynamic radiographs showed no instability of operated levels at follow-up.

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FIGURE 33-1 The plain and dynamic radiographs show decreased disc space at C5-C6 level, preoperatively. A: AP view, B: lateral view, C: flexion view, D: extension view.

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FIGURE 33-2 A: Cervical MRI sagittal view shows narrowing the neural foramen at C5-C6 and C6-C7 levels. B: Cervical MRI axial view shows narrowing the neural foramen by the compressive pathologic lesion at C5-C6 level. C: C6-C7 level.

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FIGURE 33-3 Postoperative cervical CT. A: The 3-D image shows two bony openings that were drilled via transuncal approach and upper vertebral transcorporeal approach respectively. B and C: Axial CT images also demonstrate the bone openings and decompression of the pathologic lesion at C5-C6 and C6-C7 levels.

Percutaneous Cervical Nucleoplasty

Percutaneous disc decompression, regardless of technique, has been based on the concept that a small reduction of volume in a closed hydraulic space results in a disproportionately large drop of pressure in the intervertebral disc space. Percutaneous cervical discectomy (PCD) has been developed as an effective treatment method for soft cervical disc herniation. Percutaneous cervical nucleoplasty (PCN) is one of the new minimally invasive techniques that uses radiofrequency energy to ablate the nucleus pulposus (Figure 33-4).

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FIGURE 33-4 Intraoperative PCN procedures in different levels. A: C3-C4, B: C4-C5, C: C5-C6, D: C6-C7.

Inclusion criteria are the same as those of other conventional anterior cervical foraminodiscectomy. Exclusion criteria are extruded disc fragment, hemorrhagic diathesis, spondylolisthesis, spinal canal stenosis, ossification of posterior longitudinal ligament (OPLL), previous surgery at the indicated level, and cases of myelopathy.

Under local anesthesia, the patient is placed in a supine position as for other anterior cervical approaches. The anterior cervical spine is palpated with the fingertips, and a spinal needle is used to puncture the right side of the neck and is then passed into the indicated disc space under fluoroscopic control. The fiber of the Perc-D SpineWand (ArthroCare Corporation, Austin, Tex.) is inserted through the 18-gauge needle. The wand is connected to the standard ArthroCare power generator. The power for nucleoplasty ablation is set at 3 W with a setting of 1 second for coagulation. If there is no syndrome of pain, the SpineWand is placed in the right space on the disc and then the Coblation device is activated for 14 seconds with fluoroscopic monitoring. When the SpineWand is returned to the annulus, coagulation is applied for 1 second to shrink the surrounding collagen and widen the channel. This process is repeated four to six times during the surgical procedure.

Percutaneous Endoscopic Discectomy

Under local or general anesthesia, the patient is positioned and other surgical preparations are performed as for other cervical surgery. The exact target level is confirmed fluoroscopically.

A 2- to 3-mm skin incision is made, a spine needle is placed in the target disc using fluoroscopic guidance, and a narrow guide wire is passed through the needle. The needle is removed. A blunt trocar is introduced over the guide wire down to the interspace, followed by the cannula, and the central elements are removed. A trephine is inserted through the cannula and the annulus is cut in a circular fashion. Minicurettes are used to loosen and remove disc material before a suction-irrigation system is introduced and the discectomy is performed with a guillotine cutting blade. The instruments included a probe, grasper forceps, and laser fiber. Movement in a fan sweep maneuver is critical; a 25-degree rocking excursion of the cannula hub from side to side increases the removal up to a 50-degree cone-shaped area within the disc space. The procedure is closely monitored with the fluoroscope and endoscope. The holmium:yttrium-aluminum-garnet laser with right angle or side-fire probe facilitates this discectomy. In addition, nonablative levels of holmium laser energy or thermodiscoplasty causes shrinking of the collagen and fibrocartilage; this tightening effect further decompresses and hardens the herniated cervical disc.

Microendoscopic Discectomy

Microendoscopic discectomy (MED) (Figure 33-5) is used when there is a need to visualize across the spinal canal and an operating microscope is insufficient. Positioning and anesthesia are the same as those for a posterior cervical microendoscopic foraminotomy. Single level and multilevel decompression can be performed with the standard fixed-aperture tubular retractor. For two-level decompression, the tube can be angled rostrally or caudally. The incision should be centered on a point between the two interspaces. For a three-level grated decompression, a longer incision can be used. A longer incision allows better visualization and decreases the amount of soft tissue resection required. For multilevel decompression, an expandable working channel can be used. Generally, it is easiest to begin with the most caudal level first, minimizing the amount of blood running into the field. After the level has been confirmed with fluoroscopy, soft tissues are cleared off the level of interest and the lateral edges of the lamina are defined. To minimize the risk of injury to the spinal cord, a high-speed drill is used to remove the lateral aspect of the lamina. If an ipsilateral foraminotomy is not needed, take care not to injure the facet capsule. Otherwise, the high-speed burr and Kerrison punches can be used to perform foraminotomy. The tube is then angled medially, exposing the base of the spinous process. The high-speed burr is used to drill away the base of the spinous process. It is usually necessary to angle the working channel rostrally to resect the remainder of the spinous process. Fluoroscopy can be used to confirm the rostrocaudal extent of the decompression. The ligamentum flavum is initially left intact to protect the underlying dura mater. But, to get adequate visualization of the contralateral aspect of the spinal canal, the ligamentum flavum is resected with the aid of curettes and Kerrison punches. The undersurface of the contralateral lamina should be drilled away to provide better visualization. Decompression is complete when a nerve hook can be passed along the lateral aspect of the dura mater contralaterally. Once a single level has been decompressed, further levels can be decompressed with a high-speed burr or a Kerrison punch. Bone bleeding should be waxed as soon as possible to reduce the risk of venous air embolism. The operative wound is then repaired in layers like other cervical spine procedures.

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FIGURE 33-5 A: A guide pin (arrow) is inserted into the inferior aspect of the facet of C4 to access the neural foramen at C4-C5. B: And the Serial dilator (arrow) is docked.

Discussion

In recent years the general trend in spinal surgery has been one of reductionism and minimization. The concept of minimally invasive cervical spine surgery is ideal for the management of cervical aging disease. The extensive muscle dissection required for the traditional posterior approaches leads to significant postoperative pain and the potential for postoperative deformity. By minimizing the extent of muscular dissection and by preserving the contralateral soft tissue, the less invasive approaches may lead to shortened hospital stays, decreased narcotic use, and better outcomes.

Stookey3 described the clinical symptoms and anatomic location of cervical disc herniation in 1928. Subsequently, the landmark paper by Mixter and Barr4 clearly established the relationship between herniated discs and sciatica, and provided evidence that laminectomy and disc excision could successfully relieve pain associated with radiculopathy. Bailey and Badgley5, Cloward6, and Robinson and Smith7 popularized the anterior approach with interbody fusion in the 1950s. Hirsch8 and Robertson9 recommended cervical discectomy without fusion. Fukushima10 introduced the ventriculofiberscope in 1973 and further enhanced the foundation for percutaneous endoscopic cervical discectomy.3,4

Minimally invasive treatments aimed at removing nuclear materials and lowering intradiscal pressure through devices inserted percutaneously into the intervertebral disc space have been shown to be safe and effective. A number of techniques have recently been developed that are applicable in the treatment of degenerative disorder on the cervical spine.

Microsurgical Anterior Cervical Foraminodiscectomy

In the 1930s, Spurling and Scoville11, and Frykholm12 pioneered the posterior cervical approach for the treatment of cervical radiculopathy. But the posterior approach was limited in dealing with central compressive pathology and the open approach was associated with significant muscle morbidity. Subsequently, in the 1950s, the anterior approach was described and popularized. Compared to the open posterior approach, the anterior approach is generally associated with shorter recovery times but has a greater potential for complication. Anterior cervical discectomy and fusion (ACDF) results in a loss of mobility at the operated level, and increases rates of degenerative disc disease in adjacent levels. In addition, the compressive pathological factors are located anteriorly, and the immediate surgical outcomes of anterior discectomy are fairly good. However, the consequences of anterior disc-ectomy are obvious. Conventional anterior discectomy and fusion requires complete removal of the remaining disc in the intervertebral disc space, which results in loss of the functional motion unit.13

Microsurgical anterior cervical foraminodiscectomy (MACF) is a minimally invasive technique and one that permits anatomic and functional preservation of the functional motion unit of the cervical spine. Therefore this technique was named functional cervical disc surgery. This method avoids osteoarthrodesis or arthroplasty with disc prosthesis. This technique is efficient with good results and low morbidity, especially in an aging spine.

Percutaneous Cervical Nucleoplasty(PCN)

Percutaneous disc decompression, regardless of technique, has been based on the principle that a small reduction of volume in a closed hydraulic space, like an intact disc, results in a disproportionately large reduction of pressure. Percutaneous cervical decompression has been developed as an effective treatment option for soft disc herniation. PCN is a minimally invasive technique that uses radiofrequency energy to ablate the nucleus pulposus in a controlled manner for disc decompression.

Treatment of cervical disc hernia with PCN is safe to perform, and the efficacy of this technique is good in patients. The advantage of PCN is that it reduces the volume and pressure of the affected disc without damaging other spinal functional units. Ablation of a relatively small volume of the nucleus pulposus results in a significant reduction in intradisc pressure. Histologic examination revealed no evidence of direct mechanical or thermal damage to the surrounding tissues in human cadavers. Given these radical thermal penetrations, high temperatures and lethal thermal doses do not occur in small regions outside of the nucleus or within the bone endplates in human cadavers.14

A small number of complications are associated with PCN. With the approach from the anterior neck to disc space, it is important to monitor the distance from the tip of the needle to the spinal canal. Therefore monitoring of the needle is essential during this procedure. X-ray fluoroscopy is used to confirm the correct position of the needle tip during placement of the needle, permitting accurate nucleoplasty of the intervertebral disc. Vascular injury can occur if the device contacts an artery or a vein. Particular care should be taken to avoid puncture of the anterior annulus. But, according to Chen’s study15 in human cadavers, intradiscal pressure was markedly reduced in the younger, healthy disc cadaver. In the older, degenerative disc cadavers, the change in intradiscal pressure after nucleoplasty was very small. There was an inverse correlation between the degree of disc degeneration and the change in intradiscal pressure. Their conclusion is that pressure reduction through nucleoplasty is highly dependent on the degree of spine degeneration. Nucleoplasty markedly reduced intradiscal pressure in nondegenerative discs, but had a negligible effect on highly degenerative discs.

Percutaneous Endoscopic Cervical Discectomy

Since the first description of cervical percutaneous discectomy by Tajima and colleagues16 in 1981, percutaneous endoscopic cervical discectomy (PED) may be considered a good alternative to the standard anterior cervical discectomy and fusion for treating soft cervical disc herniation. The goal of this procedure is to decompress the spinal nerve root through percutaneously removing the herniated mass and shrinking the nucleus pulposus while the patient is under local anesthesia.

Most patients who have cervicobrachial neuralgia caused by disc herniation experience good response to medical treatment. However, symptoms related to perineural cicatricial fibrosis caused by prolonged pressure on the nerve root could become irreversible. Therefore the occurrence or aggravation of a neurologic deficit, even after an adequate period of conservative treatment, requires consideration of surgical decompression. PED is indicated in the surgical treatment of soft cervical disc herniation not contained by the posterior longitudinal ligament, which includes central, lateral, and foraminal disc herniation.

Minimally invasive PED under local anesthesia can prevent such complications as epidural bleeding, perineural fibrosis, graft-related problems, dysphasia, hoarseness, and so on. It also maintains the stability of the intervertebral mobile segment and provides patients with excellent cosmetic effect and early recovery. Moreover, it does not preclude further open procedures even after treatment failure. But PED is contraindicated in patients presenting with a severe neurologic deficit, segmental instability, acute py-ramidal syndrome, progressive myelopathy, and other pathologic conditions, such as tumor, fracture, infection, and nerve entrapment with scar tissue from previous surgery. This procedure is also contraindicated in patients who have migrated discs, calcified disc protrusion, ossification of the posterior longitudinal ligament, marked spondylosis with disc space narrowing, and neurologic or vascular pathologies mimicking disc herniations.17

Microendoscopic Discectomy

Many studies have described the effectiveness of the anterior approach for the treatment of cervical disc prolapse and spondylotic stenosis. Although the anterior approach is more commonly performed for the treatment of cervical disc disease, the posterior approach has distinct advantage in selected cases of foraminal stenosis and posterior-lateral disc herniation.

Frykholm and Scoville described posterior foraminotomy through partial resection of the medial part of the facet joint to relieve the compression of the cervical nerve root in radiculopathy patients. Conventional posterior approaches have the disadvantage of detaching the extensor cervical muscles from the laminae and the spinous process. This operative trauma to the cervical paraspinal muscles is a major cause of postoperative complications in the form of persistent neck and shoulder pain, and sometimes spinal instability may result.18

Roh et al19 described the use of microendoscopic posterior cervical foraminotomy in a cadaveric study, and Burke and Caputy20 reported on the use of the same technique. The microendoscopic technique has the advantage of providing a minimally invasive approach through transmuscular dilatation. However, the disadvantage of this procedure is that it only allows two-dimensional visualization, and the view often gets blocked by bleeding or obscured by fragments during removal. The main limitation of this procedure is in the treatment of severe bony stenosis that necessitates laminectomy to decompress the spinal cord.

Conclusions

These surgical options for the treatment of cervical spinal degenerative disorders in the aging spine provide good relief of the patient’s symptoms, such as radiculopathy. It is evident that PCN, MACF, PED, and MED are varied methods of minimally invasive surgery resulting in short-term recovery and return to full functions.

In addition, in MACF there is the special potential for the problems in the long term. First, the disc resection is limited to its lateral part, and the facet joint is not damaged. As a result, the risk of postoperative instability is very low in MACF. No osteoarthrodesis or arthroplasty by disc prosthesis is necessary. Second, the nerve root decompression is perfectly achieved regardless of whether the pathology is soft disc or canal stenosis, and it can be addressed under direct visual control. As with other anterior techniques, however, this procedure is applicable only if the compressive lesion is located anterior to the spinal cord.

Although these microsurgical procedures are technically demanding in executing adequate decompression of the spinal cord, substantial anatomic knowledge is required, and the technique should be mastered thoroughly with cadaveric dissection. This technique can be a favorable anterior surgical procedure in older people with various degenerative pathologies that cannot be treated with other minimally invasive techniques in the aging spine.

References

1. Szpalski M., Gunzburg R., Mélot C.M., et al. The aging of the population: a growing concern for spine care in the twenty-first century. Eur. Spine J.. 2003;12(Suppl. 2):S81-83.

2. Benoist M. Natural history of the aging spine. Eur. Spine J.. 2003;12(Suppl. 2):S86-S89.

3. Stookey B. Compression of the spinal cord due to ventral extradural cervical chondromas. Arch. Neurol. Psychiatry. 1928;20:275-278.

4. Mixter W.J., Barr J.S. Rupture of the intervertebral disc with involvement of the spinal canal. N. Engl. J. Med.. 1934;211:210-215.

5. Bailey R.W., Badgley C.E. Stabilization of the cervical spine by anterior fusion. J. Bone. Joint. Surg. Am.. 1967;42-A:565-594.

6. Cloward R.B. The anterior approach for removal of ruptured cervical disks. J. Neurosurg.. 1958;15(6):602-617.

7. Smith G.W., Robinson R.A. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J. Bone. Joint. Surg .Am.. 1958;40-A(3):607-624.

8. Hirsch C., Wickbom I., Lidstroem A., Rosengren K. Cervical-disc resection: A follow-up of myelographic and surgical procedure. J. Bone. Joint. Surg. Am.. 1964;46:1811-1821.

9. Robertson J.T., Johnson S.D. Anterior cervical discectomy without fusion: Long-term results. Clin. Neurosurg.. 1980;27:440-449.

10. Fukushima T., Ishijima B., Hirakawa K., Nakamura N., et al. Ventriculofiberscope: a new technique for endoscopic diagnosis and operation. Technical note, J. Neurogurg.. 1973;38(2):251-256.

11. Spurling R.G., Scoville W.B. Lateral rupture of the cervical intervertebral discs. A common cause of shoulder and arm pain. Surg. Gynecol. Obstet.. 1944;78:350-358.

12. Frykholm R. Deformities of dural pouches and strictures of dural sheaths in the cervical region producing nerve root compression. J. Neurosurg.. 1947;4:403-413.

13. Jho H.D. Spinal cord decompression via microsurgical anterior foraminotomy for spondylotic cervical myelotomy. Minim. Invasive Neurosurg.. 1997;40:124-129.

14. Onik G.M., Kambin P., Chang M.K. Minimally invasive disc surgery. Nucleotomy versus fragmentectomy. Spine. 1997;22:827-828.

15. Chen Y.C., Lee S.H., Chen D. Intradiscal pressure study of percutaneous disc decompression with nucleoplasty in human cadavers. Spine. 2003;28(7):661-665.

16. Tajima T., Sakamoto H., Yamakawa H. Discectomy cervicale percutanee. Rev. Med. Orthoped.. 1989;17:7-10.

17. Ahn Y., Lee S.H., Chung S.E., et al. Percutaneous endoscopic cervical discectomy for discogenic cervical headache due to soft disc herniation. Neuroradiology. 2005;47(12):924-930.

18. Krupp W., Muke R. Clinical results of the foraminotomy as described by Frykholm for the treatment of lateral cervical disc herniation. Acta Neurochir. (Wien). 1990;107:22-29.

19. Roh S.W., Kim D.H., Cardoso A.C., Fessler R.G. Endoscopic foraminotomy using MED system in cadaveric specimens. Spine. 2000;25(2):260-264.

20. Burke T.G., Caputy A. Microendoscopic posterior cervical foraminotomy: a cadaveric model and clinical application for cervical radiculopathy. J. Neurosurg.. 2000;93 (Suppl. 1):126-129.

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