History

Mixter and Barr first provided the description of a herniated disk causing sciatica in 1934. The surgical technique outlined the treatment of lumbar disk herniation at that time, which involved an intradural approach and extensive laminar removal. In the 1970s, however, focus on a less invasive surgical approach with decreased surgical manipulation and trauma to the paraspinal muscles, ligamentum flavum, and affected nerve root began to take shape. Outcomes of decreased morbidity, shorter hospital stay, and faster recovery were widely recorded.

Yasargil and Caspar were the first to document their separate experiences with microdiskectomy technique using an operating microscope. Williams followed shortly thereafter with a description of a microlumbar diskectomy in a series of 532 patients that popularized the technique in the United States.

The past decade has brought advances in fluoroscopy, image-guided techniques, and high-resolution endoscopy. These advances, along with widespread use of tubular retractors, have provided a minimally invasive form of lumbar diskectomy. Early data from a randomized, controlled study from the Netherlands to compare minimally invasive tubular microdiskectomy with standard techniques suggests no differences in functional outcome and less favorable outcomes for minimally invasive treatment at 1 year in regard to leg pain, back pain, and recovery.

Prospective Studies

Over the past three decades, several prospective trials have compared surgical intervention for lumbar disk herniation with conservative management. In 1983, Weber and coll­eagues first compared outcomes of patients receiving disk­ectomy with conservative management. It is important to note that the trial was not blinded, and 26% of patients initially assigned to conservative management subsequently crossed over to receive surgery. Diskectomy was found to be superior to conservative therapy by observer rating at 1 year, although statistically it had not improved significantly at 4 or 10 years.

The Maine Lumbar Spine Study is a large, nonrandomized, observational cohort study of 507 patients from community practice settings. Almost all patients in the surgical cohort received open diskectomy for disk herniation. Followed at intervals of 1, 5, and 10 years, surgically treated patients reported a statistically significant improvement in primary symptoms at 1 and 5 years. At 10 years, no significant difference was reported between groups when polled for any improvement. However, significance was noted: with surgical patients, more reported initial symptoms “much better” or “completely gone,” and more reported satisfaction at 10 years. Limitations of the study included the nonrandomized design, because surgically treated patients had more notable baseline radiologic and clinical findings. Also, not all patients had imaging available to be reviewed by a neuroradiologist, and up to 25% of patients received additional lumbar surgery at 10 years in both groups.

In 2006, the Spine Patient Outcomes Research Trial (SPORT) provided the first multicenter, prospective, randomized, controlled trial that included 501 patients with lumbar disk herniation confirmed by magnetic resonance imaging (MRI) and signs and symptoms of at least 12 weeks’ duration. Open diskectomy was compared with nonoperative management, and study groups were assessed using a 36-item short-form bodily pain and physical function scale and the Modified Oswestry Disability Index. Results of this study were limited, because 50% of patients initially assigned to the surgery group and 30% of the nonoperative group crossed over. Although intention-to-treat analysis was not statistically significant, as-treated analysis did show statistically significant advantages for patients in primary outcomes in addition to self-reported improvement, satisfaction with symptoms, and reduction in the bothersomeness of back pain. Improvements were noted at time points that spanned from 6 weeks to 4 years in most recent study updates. Cost evaluations of the same patient cohort have suggested surgery to be at least moderately cost-effective compared with nonoperative management.

Lumbar Spine

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  There are five lumbar vertebrae.

  
  
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  L5 is sometimes “sacralized” (with L5 fused to the sacrum), or the S1 vertebral body may be “lumbarized” (with a well-developed disk seen between S1 and S2).

  
  
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  When counting from L5, rather than from T12, ensure agreement on the level.

Spinal Canal

The anterior vertebral body, lateral pedicles and posterior bony elements comprise the spinal canal. ( Fig. 41-1 )

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  Anterior vertebral body

  
  
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  Lateral pedicles

  
  
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  Posterior bony elements

  
  
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  Cartilaginous base covers the end plates of adjacent vertebral bodies.

  
  
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  The intervertebral disk is composed of the annulus fibrosis and nucleus pulposus. The nucleus pulposus is semigelatinous.

  
  
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  The annulus fibrosis resists lateral forces of axial compression.

  
  
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  The posterior longitudinal ligament (PLL) attaches to the disk space posteriorly and to the margins of the vertebral bodies above and below the disk space.

  
  
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  The PLL is thin laterally and is thickest at the midline.

A coronal cross-section of the bony spinal canal.

Posterior Elements

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  These include the pedicles, transverse and spinous processes, facet surfaces, laminae, and the pars interarticularis ( Fig. 41-2 ).

  
  

  
  

  
  

  

  
  

  
  

  Posterior elements, lumbar spine.

  
  
  
  
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  Each facet has two superior and two inferior surfaces.

  
  
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  The superior facet surface lies dorsal to the disk space above the vertebral segment, and it articulates with the inferior facet surface of the next superiorly placed vertebral body.

  
  
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  The inferior facet lies dorsal to the disk space below the vertebral segment, and it articulates with the superior facet of the next inferiorly placed vertebra (see Fig. 41-2 ).

  
  
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  Pedicles extend from the dorsolateral surface of the vertebral body just below the superior end plate.

  
  
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  Pedicles are oriented ventral and slightly inferior to the superior articular facet surface.

  
  
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  The pars interarticularis or isthmus is a bony bridge that connects the superior and inferior facet surfaces and is continuous medially with the hemilamina of the vertebral segment (see Fig. 41-2 ).

  
  
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  The spinous process is the convergence of two hemilaminae that converge in the midline.

  
  
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  The transverse process projects from the dorsolateral surface of the pedicle.

  
  
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  The mammillary process is a raised bony prominence on the proximal dorsal aspect of the transverse process.

  
  
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  The mammillary process may serve as an external landmark for the long axis of the underlying pedicle.

  
  
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  The intertransverse ligaments connect adjacent transverse processes.

  
  
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  Ligamentum flavum (yellow ligament) attaches from the dorsal surface of the lamina at the inferior level to the ventral surface of the lamina at the superior level of the interspace. It overlies the spinal epidural space at the interspace.

  
  
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  The ligamentum flavum ends laterally at the level of the facet joint.

  
  
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  The ligamentum flavum is often hypertrophied in degenerative diseases of the lumbar spine.

Nerve Roots

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  The nerve roots exit the spinal canal at the level of the corresponding pedicle.

  
  
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  The L4 nerve root crosses the L3–L4 disk space and exits the spinal canal beneath the L4 pedicle before crossing the L4–L5 disk space.

  
  
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  After exiting the foramen, the L4 nerve root crosses the L4–L5 disk space at its lateral margin (see Fig. 41-1 ).

  
  
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  Paramedian disk herniations affect the lower spinal nerve root, so an L4–L5 disk herniation would result in compression of the L5 nerve root.

  
  
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  A foraminal disk herniation or an extraforaminal or far-lateral disk herniation at L4–L5 would compress the L4 nerve root.

  
  
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  In far-lateral disk herniation, extruded disk lies beyond the lateral intervertebral space, outside the facet.