Intervertebral discs cushion and tether the vertebrae, providing both flexibility and stability. The normally gelatinous nucleus pulposus is surrounded by the ligamentous annulus broses. In the young and healthy disc, the nucleus and annulus blend. Degenerative or pathologic changes can cause separations of the two entities, as well as compromise the integrity of the annulus, such that a sufficient load can cause nuclear fragments to migrate and impinge on neural elements.15 This pathophysiology is reflected in a clinical presentation of acute sciatica pain with a prior history of back pain. Lumbar disc herniations may occur with little or no trauma, although patients frequently report a bending or twisting motion as the inciting event, causing the onset of symptoms. Common causes of lumbar herniations include falls, car accidents, repetitive heavy lifting, and sports injuries of all types.

It is important to understand that most patients with symptomatic herniated lumbar discs will get better over time, regardless of the type of treatment. Weber’s classic study16 reported that sciatica from HNP would improve 60% of the time with nonsurgical methods and 92% of the time with surgery at 1 year. By 4 years out, no statistical difference was found (51% improvement in conservative group versus 66% in the surgical group), and no difference was found at 10-year follow-up. The 5-year outcomes from the Maine Lumbar Spine Study are similar to the 4-year results of the Weber study. At 1-year follow-up, 71% of surgical patients reported relief of leg symptoms compared with 43% of conservatively managed patients.¹⁷ They reported long-term follow-up at 5 years, with 70% of patients in the operative group describing improvement versus 56% in the nonoperative group.¹⁸ More recently, the Spine Patient Outcomes Research Trial results have contributed to the favorable opinion of surgical outcomes as well. Treatment effects were statistically significant at 2 years and maintained at 4-year follow-up for primary outcomes in favor of surgery.¹⁹

In the absence of cauda equina syndrome or progressive or significant neurologic deficits, most practitioners attempt conservative care before suggesting surgical intervention.

The attempt to improve visualization and illumination has led many spine surgeons to use loupes and a headlight. We believe the magni cation and illumination built into the microscope offer many surgical advantages, the most important of which is reduced wound size and decreased tissue manipulation (Fig. 15-2). The surgeon can limit the amount of tissue dissection by working through a small exposure directly over the pathology to be removed. Microsurgical techniques can also be used to preserve the ligamentum flavum and epidural fat to minimize postoperative epidural broses and improve clinical results by preserving natural tissue planes.^8,34 With this approach, the disc herniation can be easily removed, lateral recess stenosis can be decompressed, and nerve root manipulation is kept to a minimum. The senior author has used this technique since 1986 for most lumbar disc herniations and has found the approach to be safe, with fewer dural tears and nerve root injuries and less postoperative epidural broses than with standard discectomy.^5,8,10,35

However, the microscope is not without its disadvantages. Peripheral vision is lost, with the field of vision limited to approximately 4 to 5 cm. Because of this, the surgeon needs to know detailed anatomy of the spine. The line of vision is axed through the microscope. To look over structures (to overcome tissue overhang), the patient or microscope has to be adjusted during the surgery. This can be avoided by proper retraction or dissection of tissue away from the line of vision. Researchers reported increased disc space infection after microsurgery.^36,37 This was most likely caused by contamination from unsterile parts of the microscope during surgery, although no one has looked at the potential for an increased infection rate when two surgeons with loupes and headlights bump heads over the wound! Recent reports by those who have experience with the microscope do not show any increased infection rates.^5,10,14,38,

Microscopic discectomy (microdiscectomy) has become the gold standard for operative treatment of lumbar disc herniations, and the latest minimally invasive percutaneous techniques have not been shown to be more effective.8,39,40 Although no statistical differences can be shown in the ultimate long-term outcomes of microscopic versus standard open discectomies,^{11,13,14,32,41–43} the microscope provides improved illumination and magni cation, and patients have less morbidity and earlier hospital discharge when compared with standard discectomies.

Spinal Canal Entry

After exposure of the interlaminar space and placement of the retractor, a high-speed burr is used to remove several millimeters of the cephalad lamina and 2 to 3 mm of the medial aspect of the inferior facet, taking care to leave at least a 6-mm bridge of bone at the level of the pars (Fig. 15-3). Once the cephalad lamina and medial aspect of the inferior facet have been removed, the ligamentum flavum is easily seen because its bony attachments are exposed. The ligamentum attaches at the very cephalad edge of the lower lamina, but approximately halfway up the upper lamina, and it attaches to the medial aspect of the superior facet. Thus the high-speed burr can be used relatively safely on top of the bottom half of the superior lamina, as well as the medial aspect of the inferior facet.

Free Ligamentum Flavum

The ligamentum flavum is then released from the medial edge of the superior facet with a forward-angled curette. It can also be released from the undersurface of the upper and lower lamina (Fig. 15-4). It is safest to start the curette inferolaterally toward the superior aspect of the pedicle (caudal aspect of the foramen).

A ligamentum and epidural fat-sparing approach, performed by creating a flap of the ligamentum as described previously, decreases postoperative epidural broses and can improve results.^8,34 However, this can make it more difficult to get a good view of the nerve root. Certainly this is easier with a microscope than without one. The less-experienced surgeon may perform partial removal of these tissues. The ligamentum flap is also not recommended for large midline disc herniations (with or without cauda equina syndrome) and severely stenotic canals because the ligamentum itself occupies more room in the already severely compromised spinal canal and would also interfere with direct visualization for the delicate manipulation of the thecal sac.

Lateral Recess Exposure

After release of the ligamentum flavum, the medial edge of the superior facet is resected with 2- to 4-mm Kerrison rongeurs. This resection goes from the lower pedicle to the tip of the superior facet (Fig. 15-5). This medial facet resection decompresses any lateral recess stenosis at the level of the pedicle and up into the foramen, and it allows easy access to the lateral disc space. If needed, some of the lateral ligamentum flavum, particularly into the foramen, can be removed with the Kerrison rongeurs.

Nerve Root and Ligamentum Retraction

Bipolar cautery can be used at this time to cauterize any epidural bleeding over the lateral disc space, directly cephalad to the pedicle. We recommend finding the pedicle and then using it as a guide to release the epidural nonneural tissues above the disc space. At this point a nerve root retractor can be placed on the disc space, and the ligamentum flavum, epidural fat, and nerve root are retracted toward the midline, generally exposing the herniation (Fig. 15-6). Again, the bipolar cautery can be used to cauterize any epidural veins over the disc herniation. Any free large fragments of disc can now be removed (Fig. 15-7). If needed, a forward-angled curette can be used to scrape the inferior and posterior bony margins of the foramen, using a unidirectional pulling motion. Using the bony pedicle as a starting point ensures that the end of the curette does not include any neural tissue before scraping.

Closure

Once the decompression is complete, the entire surgical wound is thoroughly irrigated with antibiotic-containing irrigant. Any final bleeding is controlled with bipolar cautery, thrombin-soaked gel foam, or FloSeal hemostatic gel. After complete hemostasis and removal of all gel foam, the closure is performed in layers. Many attempts have been made to design substances to seal the laminotomy defect and prevent scar formation, including fat grafts, hydrogel, silicone, Dacron, and steroids.49 We simply prefer the ligamentum flap (Fig. 15-8).^5,8,25 The dorsal lumbar fascia is closed with No. 1-0 sutures, the subcutaneous layer with 2-0 sutures, and the skin with 3-0 subcuticular sutures. Using this ligamentum flavum–sparing approach, blood loss should be no more than 10 to 20 ml. With good hemostasis, drainage of the surgical wound is not necessary.

Dural tears occur in 1.0% to 6.7% of cases, although the incidence decreases with experience.5,16,38,65–67 If possible, repair should be done by direct suture (5-0 to 7-0 silk, nylon, or polypropylene) with or without a dural patch.⁶⁵ The patient should be kept flat for a few days after surgery to lower the hydrostatic pressure in the lumbar thecal sac while the repair seals.

Neural injuries are rare, although the risk is greater with unusual disc herniations as described previously. Visceral injuries occur when an instrument penetrates the anterior annulus. Among these, vascular injuries are the most common.^65,68 If these are recognized, then immediate laparotomy for surgical repair is indicated.

Postoperative discitis occurs in 1% of cases or less in experienced hands, although clearly a learning curve exists in developing facility with the microscope. Higher infection rates (up to 7%) have been reported with the use of a microscope during surgery, although in experienced hands this has been shown not to be true.⁶⁵ An MRI is the best diagnostic imaging tool. An image-guided needle biopsy may be performed to assist in organism-specific antibiotic selection. Reoperation may not be necessary unless the patient develops root compression, cauda equina syndrome, or an epidural abscess.

The literature reports recurrent HNP at a previously operated site occurring anywhere from 2% to 5% after lumbar discectomy.^25,69 When reoperating for a recurrent HNP, it is important to get adequate exposure of the dural sac above and below the disc space. Then using a combination of blunt (nerve hook, Penfield, bipolar) and sharp (Kerrison) dissection, the dural sac and nerve root are exposed and mobilized above the HNP.

Iatrogenic mechanical instability is fortunately a rare occurrence after discectomy, even if a decompressive laminectomy was required for a stenotic canal or to excise a large disc.⁶ Symptomatic mechanical treatment may require surgical stabilization. Suboptimal results after discectomy can be the result of several other problems that, unfortunately, do not have a straightforward medical or surgical treatment. Although very rare, these can include epidural broses, arachnoiditis, and complex regional pain syndrome.⁶⁵

Most modern studies using microscopic techniques for treatment of herniated lumbar discs report 90% to 95% success rates.* A multicenter, prospective trial has proved what cannot be repeated often enough: If the therapist selects patients with dominant radicular pain (compared with back pain), with neurologic changes and painful SLRs, and with a study confirming a disc rupture, then he or she can anticipate a high level of success for discectomy, with or without a microscope.⁴¹ The rate of successful outcome drops significantly as more of these inclusion criteria are not met. Persistent back pain occurs in up to 25% of patients who undergo microdiscectomy.^66,67 This has led to the opinion that it is important to save the supraspinous and intraspinous ligament complex, remove as little lamina as possible, save the ligamentum flavum as a flap, and do a limited discectomy. These steps theoretically reduce iatrogenic instability, epidural broses, sterile discitis, and loss of disc height. All of these steps are facilitated by the use of a microscope, but no proof exists that these steps reduce the incidence of back pain.

The most frequent cause of poor result from lumbar disc surgery is faulty patient selection because of erroneous or incomplete diagnosis. Technical errors, such as wrong-level surgery, incomplete decompression, and intraoperative complications, explain a small percentage of failures. A 1981 study assigned the following frequency of missed diagnoses as sources of failure: lateral spinal stenosis, 59%: recurrent or persistent herniation, 14%; adhesive arachnoiditis, 11%; central canal stenosis, 11%; and epidural broses, 7%. Finally, the results of repeat surgery are not as good as primary surgery, regardless of the reason or whether a microscope was used, because of scar tissue, higher incidence of complications, or larger dissections. In the past decade, a substantial increase in interest in minimally invasive procedures has occurred in all areas of medicine, particularly for spinal disorders. Several methods to remove HNP have been proposed as alternatives to standard open discectomy. Injected chymopapain can dissolve much of the central nucleus, but is not likely to act on extruded or sequestered fragments, which are often heavily collagenized.^24,57,62 Likewise, percutaneous suction discectomies and removal of nucleus (either mechanically or by laser from the center of the disc) may reduce intradisc pressure but are unlikely to influence the effects of extruded or sequestered disc material. Therefore although alternative minimally invasive techniques hold considerable promise, lumbar microdiscectomy is still the gold standard for surgical treatment of lumbar HNP with radiculopathy. However, the skills and technology to remove herniated discs by such alternatives are evolving.^{24,39,40,71–73}

GOALS: Protect the surgical site to promote wound healing, maintain nerve root mobility, reduce pain and inflammation, educate patient to minimize fear and apprehension, establish consistently good body mechanics for safe and independent self-care (Table 15-1)