Lumbar Laminectomy and Microdiscectomy

Samuel C. Overley, MD

Sheeraz Qureshi, MD

Dr. Qureshi or an immediate family member has received royalties from Zimmer; is a member of a speakers’ bureau or has made paid presentations on behalf of Globus Medical, Medtronic Sofamor Danek, and Stryker; serves as a paid consultant to Medtronic, Orthofix, Stryker, and Zimmer; and serves as a board member, owner, officer, or committee member of the American Academy of Orthopaedic Surgeons, the Cervical Spine Research Society, Clinical Orthopaedics and Related Research, Contemporary Spine Surgery, Global Spine Journal, the Musculoskeletal Transplant Foundation, the North American Spine Society, the journal Spine, and The Spine Journal. Neither Dr. Overley nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article.

Introduction

Lumbar disc herniation is one of the most common degenerative pathologies that the orthopaedic spine surgeon encounters in practice. A herniated disc or herniated nucleus pulposus is a seemingly simple problem with an equivalently simple definitive surgical treatment. However, there is much controversy regarding how long a herniated disc should be observed and treated conservatively prior to addressing the pathology surgically. Much of the consideration of operative versus nonoperative treatment of herniated discs lies in individual patient factors. Global considerations that must be taken into account when considering any spinal procedure—such as patient age, associated comorbidities, and subjective patient evaluation by the surgeon—are integral to appropriate patient selection, which is paramount.

Once a disc herniation is identified with correlative physical examination findings, a discussion of the natural history of the disease should ensue. This is an area of much controversy and conflicting opinions among experts, though most can agree that a course of nonoperative treatment is a reasonable and necessary step for the first-time presenter, the cornerstone of which is physical therapy and rehabilitation. A commonly quoted study by Saal and Saal found a 90% good or excellent outcome in patients with a symptomatic herniated disc treated nonoperatively. Subsequent studies have not been able to reproduce as high of a success rate; however, more recent highly powered, long-term prospective trials such as the Maine Lumbar Spine Study and the Spine Patient Outcomes Research Trial (SPORT) show good results in over 50% of patients treated nonoperatively. The authors’ preferred time frame for nonoperative treatment of radicular pain without motor impairment, cauda equina syndrome, or progressive neurologic symptoms is 3 months.

After failure of nonoperative treatment in a patient with a single-level symptomatic herniated disc with correlative physical examination and imaging findings, the treating surgeon may offer the patient a microdiscectomy or laminectomy. There are two basic ways to perform such a procedure: through a mini-open approach or through a minimally invasive surgical technique. Each procedure accomplishes the same goal of removing the offending disc bulge/herniation with minimal osseous disruption and neural tissue manipulation. The mini-open approach does, however, involve a subperiosteal muscle dissection, whereas the minimally invasive technique employs a muscle-sparing approach. The salient points of each surgical procedure, primarily as they relate to postoperative rehabilitation implications, will be discussed further in the surgical procedure section.

Lumbar spinal stenosis is another common disease process in the adult spine. We will primarily reference the congenital form of stenosis, though there are acquired etiologies that are beyond the scope of this chapter. The presentation, patient population, and etiology of spinal stenosis differs from that of a single-level herniated disc, thus necessitating a different approach by the surgeon. Congenital spinal stenosis is an anatomic diagnosis by definition, primarily affecting the elderly population. It is the result of degenerative changes in the lumbar spine that ultimately lead to a stenotic canal. It is postulated that varying degrees of spinal stenosis take place in everyone as they age by virtue of its degenerative nature. However, it is uncertain why certain individuals have accelerated rates of stenosis compared to others, though it has been shown that genetics play a large role in the disease process. Additionally, not all patients with spinal stenosis are symptomatic, and there is no direct objective correlation to degree of stenosis and symptomatology. Those who are symptomatic typically present with vague, ill-defined lower back pain that radiates to
the gluteal region and, in some cases, to the lower extremities. This phenomenon, referred to as neurogenic claudication, is typically exacerbated by standing and activities such as walking uphill or up stairs, causing hyperextension of the lumbar spine. Symptoms are relieved by flexion of the lumbar spine, which translates into a patient’s description of relief when sitting or leaning forward onto an object, such as a walker or shopping cart.

Similar to that of herniated discs, there is a wealth of literature that aims to determine the optimal treatment for patients with spinal stenosis. Many recent long-term prospective studies, including the two previously mentioned (Maine Lumbar Spine Study and SPORT) have looked at both operative and nonoperative treatment of spinal stenosis. The results are not conclusive but are tangible and powered sufficiently to permit the North American Spine Society to conclude in their evidence-based guidelines that in one-third to one-half of patients with mild to moderate lumbar spinal stenosis, nonoperative treatment may be favorable.

In patients who fail nonoperative treatment, the primary surgical goal is to increase the space of the stenotic canal. Lumbar spinal stenosis is the most common reason for spinal surgery in the elderly population (age >65 years). In the absence of instability, laminectomy remains the gold standard for definitive treatment of adult spinal stenosis. As with microdiscectomy, a laminectomy may be accomplished via both a mini-open exposure and a minimally invasive approach.

Surgical Procedure

Microdiscectomy

Indications

The most commonly encountered absolute indication for a lumbar microdiscectomy is a progressive neurologic deficit. Contrary to most patients’ perception, radicular pain is the least worrisome symptom relevant to patient safety and potential long-term irreversible nerve damage. Such pain is the most common indication for a trial of nonoperative treatment. However, a progressive deficit that affects motor function, commonly a footdrop (L4–L5 nerve root), is a serious matter that deserves urgent attention. In this scenario, operative treatment is indicated in lieu of conservative treatment to prevent potential permanent nerve damage or progression to cauda equina syndrome.

Other relative indications are typically unique to each patient but universally revolve around a case of severe radicular pain that has not responded adequately to nonoperative treatment. One absolute prerequisite for discectomy is radiologic identification (usually in the form of MRI or CT myelogram) of a compressive disc pathology that is concordant with patient symptomatology and physical examination findings. It is on the onus of the surgeon and patient to develop a strategy for treatment of such conditions that takes into account the risks and benefits of surgery with the expectations of the patient. Generally speaking, a radicular pain pattern and physical examination findings that correlate with imaging have the highest predictability of success when treated surgically.

Contraindications

While there are not true absolute contraindications to lumbar microdiscectomy, the central theme of both peer-reviewed literature and anecdotal evidence is to avoid microdiscectomy in patients with primarily mechanical low back pain. Other factors that are by no means absolute contraindications—but that have been shown to be associated with worse outcomes after microdiscectomy—are work-related injury, absence of correlative findings on physical examination, lack of radicular pain distribution, and central disc bulges.

Laminectomy

Indications

As is true of microdiscectomy for lumbar disc herniations, the one absolute indication for laminectomy is the presence of a progressive neurologic deficit or, more commonly seen with spinal stenosis, cauda equina syndrome. In the absence of these alarming and potentially permanent disease states, a combination of patient desire for surgery and a failed course of nonoperative treatment will be the driving forces for ultimate surgical treatment of lumbar spinal stenosis. Attempts to demonstrate objective outcomes measures have been helpful to aid in the decision-making process for both patient and surgeon; however, definitive prognostic indicators have still not been determined. Deen et al showed that the most common causes of early failed laminectomy was the absence of classical symptoms of neurogenic claudication in combination with lack of objective radiographic evidence of stenosis.

Contraindications

Instability must be assessed and considered when contemplating a laminectomy for spinal stenosis. Instability is a dynamic process that may not always be overtly present on static imaging studies. A thorough and dynamic radiographic examination is often required to diagnose instability. The diagnosis of instability is paramount in any patient with spinal stenosis because, if present, a laminectomy will likely require augmentation with a stabilizing procedure such as a fusion. For this reason, it is generally accepted that patients with spinal stenosis and evidence of lumbar instability should not be treated with an isolated laminectomy, as their failure rates are significantly higher than those without objective instability.

Procedure

Microdiscectomy

Anatomy

The functional components of the lumbar intervertebral disc are the outer fibrous layer known as the annulus fibrosus, the inner gelatin-like layer of the nucleus pulposus, and the hyaline cartilage endplates of the vertebral bodies abutting the cranial and caudal ends of the disc. The annulus fibrosus acts a barrier to the inner nucleus pulposus, converting axial loads through
the spine into hoop stresses. The hyaline cartilage endplates allow for diffusion of nutrients into the inner nucleus pulposus while also serving to absorb metabolic waste products. In early disc degeneration, the endplates lose diffusion capacity, metabolic waste products accumulate in the nucleus pulposus, and annular support weakens, allowing herniation of the nucleus pulposus. Integrity of the pars interarticularis is critical to stability of the posterior elements. This is important to keep in mind when removing os to create adequate exposure in the interlaminar window. The ligamentum flavum is the final layer encountered before the epidural space. This ligament may have adhesions to the dura; therefore, extreme caution must be used when resecting the ligament. The dural sac contains the spinal nerve roots that collectively comprise the cauda equina after termination of the spinal cord at or around L1. Understanding the anatomic relation of the exiting and traversing nerve roots is critical during any spinal procedure. The exiting nerve root of a level exits out of the infrapedicular foramen of that level, while the traversing nerve root of the level below passes the disc space just lateral to the dural sac. Close attention must be paid to the traversing nerve while performing a microdiscectomy to avoid damaging it.

Technique

When performing a mini-open microdiscectomy, a midline incision is made over the spinous processes of the desired intervertebral disc. Subcutaneous dissection is carried down to the spinous processes and interspinous ligament with care to not disrupt the ligament, as it contributes stability to the posterior elements. The paravertebral musculature, comprised of the multifidus and erector spinae, are dissected subperiosteally unilaterally on the side of the disc herniation. The lamina, pars, and facets of the vertebrae on the side of the pathology are exposed without disrupting the facet joint capsules. The interlaminar space is identified and limited bony resection of the laminae with a Kerrison rongeur will provide adequate exposure of the compressed nerve root. The ligamentum flavum is resected carefully, revealing the traversing nerve root and the intervertebral disc below. The nerve root is retracted medially and protected with a nerve root retractor, while the remaining annulus surrounding the disc bulge is incised with an 11-blade scalpel. The pathologic nucleus pulposus is resected with a micropituitary. After the diseased nucleus pulposus is removed, hemostasis is achieved. Closure of the fascia overlying the spine is critical to prevent dehiscence and deep wound infection. The subcutaneous tissue is closed with an absorbable suture and the skin is closed with either a running subcuticular absorbable suture or interrupted nylon sutures.

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