Lumbar Discectomy

 

 

 

DEFINITION

Clinically significant lumbar disc herniations are characterized by a focal distortion of the normal anatomic configuration of discal material resulting in compression and subsequent dysfunction of the lumbar nerve roots.

 

 

ANATOMY

 

The functional components of the intervertebral disc are the annulus fibrosus (fibrous concentric rings, type I collagen) enclosing the central nucleus pulposus (gelatinous, type II collagen, proteoglycans) and the vertebral endplates (hyaline cartilage).

 

The anatomic unit of the lumbar spine is the vertebral body with its attached posterior elements and the disc below (FIG 1A).

 

The nerve roots travel within the common dural sac (the cauda equina) and then exit at each level. They are numbered according to the pedicle beneath which they pass.

 

The spinal canal is divided into zones from medial to lateral: central canal, subarticular zone, foraminal zone, and extra-foraminal (far lateral) zone (FIG 1B).

 

Disc herniations are best classified based on the following ways:

 

 

Based on the integrity of the annulus fibrosus and whether there is a connection of herniated discal material with the disc space (FIG 2)

 

Based on the anatomic location of the herniated material relative to the disc space, the canal, and the compressed nerve root using the nomenclature mentioned earlier (FIG 3)

 

Accurate anatomic classification of disc herniations facilitates preoperative planning and can minimize the risk of surgical complications such as missed pathology and iatrogenic nerve root injury.

 

 

 

FIG 1 • A. Anatomic unit. The first floor is the disc level, the second floor is the foraminal level, and the third floor is the pedicle level. B. Regions of the canal.

 

 

The importance of a complete knowledge of spinal anatomy and understanding of the particular patient's pathoanatomy cannot be overstated.

 

PATHOGENESIS

 

In the normal disc, the nucleus pulposus imbibes and releases water to balance mechanical loads. The annulus fibrosus converts these loads to hoop stresses, thereby containing the nuclear material. The endplates allow diffusion of nutrition into, and waste products out of, the nucleus.

 

 

Together, they allow for the three basic spinal segmental functions: mobility, stability, and protection of the nearby neurologic structures.

 

With early or intermediate disc degeneration (natural aging with or without minor repetitive trauma), the endplates fail to allow adequate diffusion, the nucleus fails to replace degraded proteoglycans, and annular support weakens (failure of cross-linking, development of clefts). Biomechanical dysfunction occurs, with possible herniation of nuclear material.

 

Many disc herniations do not cause pain or neurologic symptoms. A combination of herniation, nerve root compression, and an inflammatory interface is required for nerve root dysfunction and associated radiculopathy and sciatica.

 

NATURAL HISTORY

 

Many studies have shown that with time and nonoperative treatment, over 90% of patients with a first-time lumbar disc herniation will get better without surgery. Accordingly, to propose surgery requires clear indications.

 

 

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FIG 2 • Classification of disc herniations based on relation to outer annulus: (A) protrusion, (B) subannular extrusion, (C) transannular extrusion, and (D) sequestration.

 

 

Absolute indications

 

 

Bladder or bowel involvement secondary to a massive disc herniation and cauda equina syndrome: immediate surgical intervention

 

 

Progressive (ie, worsening) neurologic deficit: the earlier, the better prognostically Relative indications

 

 

Failure of conservative measures greater than 6 weeks to 3 months Multiply recurrent sciatica

 

Significant neurologic deficit

 

 

In each case, the properly informed patient must clearly understand the current best evidence: Most patients get better quickly with nonoperative care. For those with significant symptoms that are not better within 6 weeks, short-term and long-term (8 years) outcomes are better in patients treated with discectomy as compared with continued nonoperative care.

HISTORY AND PHYSICAL FINDINGS

 

The most common complaint is pain with or without associated paresthesias or weakness in a specific monoradicular anatomic distribution.

 

 

 

 

FIG 3 • The patterns of disc migration can be characterized relative to the structures of the anatomic unit (eg, at the disc level or at the pedicle level). The area of root compression can be described relative to the nerve root anatomy (eg, at the shoulder of the traversing root, in the axilla of the exiting root).

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Magnetic resonance imaging (MRI) is the imaging study of choice for the diagnosis and anatomic classification of lumbar disc herniations. It is highly sensitive and specific and provides, along with the clinical picture, adequate information for detailed preoperative planning.

 

Computed tomography (CT) myelography is invasive and less specific than MRI but provides excellent sensitivity when MRI is unavailable or contraindicated.

 

Plain radiographs may show disc space narrowing, early formation of osteophytes, or a “sciatic scoliosis.” Although providing no direct evidence of a herniated disc, they may be helpful to rule out unexpected destructive pathology (eg, infection, tumor, fracture) in patients who have failed to respond to nonoperative intervention or those with red flags. They also allow excellent delineation of bony anomalies that may prove vital to preoperative planning and intraoperative localization, such as transitional lumbosacral articulations or spina bifida occulta.

 

DIFFERENTIAL DIAGNOSIS

Intraspinal, extrinsic compression, or irritation at the level of the nerve root: spinal stenosis, osteomyelitis or discitis, neoplasm, epidural fibrosis (scar)

Intraspinal, extrinsic compression, or irritation proximal to the nerve root: conus and cauda lesions such as neurofibroma or ependymoma

Intraspinal, intrinsic nerve root dysfunction: neuropathy (diabetic, idiopathic, alcoholic, iatrogenic [chemotherapy]), herpes zoster, arachnoiditis, nerve root tumor

Extraspinal sources distal to the nerve root: pelvic or more distal neoplasms with associated sciatic or femoral nerve compression, sacroiliac disease (eg, infection, osteoarthritis), osteoarthritis of the hip, peripheral vascular disease

 

 

NONOPERATIVE MANAGEMENT

 

The evidence base is still a bit unclear, but the following are commonly recommended.

 

 

Rest: bed rest (no more than 2 or 3 days), activity or job modification, weight loss

 

Medication: analgesics (very short term for severe pain only), nonsteroidal anti-inflammatories, tapered doses of oral steroids

 

Exercise: physical therapy (McKenzie program)

 

Injections: epidural or selective root blocks (may provide some temporary relief while the natural history takes over)—no impact on long-term outcomes

 

Time: 6 weeks to 3 months (unless absolute indications for surgery exist as noted earlier)

 

 

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FIG 4 • A. The kneeling position obtained with the Andrews, Wilson, or Jackson frames. B. The marking needle.

 

SURGICAL MANAGEMENT

 

The evidence base is clear: Open discectomy and micro-discectomy are the operative techniques with the best-documented short-term and long-term outcomes and are the gold standards of surgery for lumbar disc herniations.

 

Preoperative Planning

 

This is vital and should aim to answer three questions:

 

What nerve root is involved (answered by history and physical examination)?

 

Where is the herniated material relative to the disc space, the canal, and the nerve root (answered by MRI)?

 

What approach will afford the best visualization and access to the herniated material while minimizing injury to tissues not directly involved in the pathologic process?

 

Positioning

 

A “kneeling” position is generally used, with the patient stabilized on an Andrews frame, a Wilson frame, or the Jackson table (FIG 4A).

 

Some hip and knee flexion will decrease lumbar lordosis and facilitate an approach through the interlaminar window.

 

The abdomen must be free to decrease intra-abdominal pressure and venous backflow through the plexus of Batson into the spinal canal.

 

Shoulders should be abducted less than 90 degrees and with some flexion. The neck should be neutral or gently flexed.

 

Eyes must be protected and elbows, knees, and feet well padded.

 

A needle is passed between and lateral to the spinous processes at the involved level, and C-arm imaging is used to confirm that the proper level will be approached (FIG 4B). The needle is removed, and the level is marked and labeled on the skin.

 

The involved side will be determined preoperatively by patient complaint and location of herniation on MRI but should also be marked on the patient's skin at this point.

 

Approach

 

The interlaminar window approach is used in about 90% of lumbar disc herniations requiring surgery. It is appropriate for herniations within the central canal or subarticular zones from L1 to S1 and for herniations within the foramen at L5-S1.

 

The intertransverse window approach is used in about 10% of lumbar disc herniations requiring surgery. It is appropriate for herniations within the foraminal and extraforaminal zones from L1 to L5.

 

For each step in the procedure, incision, excision, and retraction of tissues should be minimized. The goal is to get the job done completely and safely with minimal trauma to tissues not directly involved in the pathologic process.

 

TECHNIQUES

• Incision and Dissection

  The skin incision is made directly midline posteriorly and extends from the top of the cephalad spinous process to the bottom of the caudal spinous process, about 1.5 inches for single-level pathology.

  The subcutaneous tissues are then gently and bluntly mobilized and retracted to allow visualization of the dorsolumbar fascia.

  From here, one of two windows of approach will be undertaken based on the location of the disc herniation: the interlaminar window or the intertransverse window.

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• Interlaminar Window

The dorsolumbar fascia is incised just off the midline in a gentle curvilinear fashion on the involved side at a length to match the skin incision.

A Cobb elevator is used to gently elevate the muscle (multifidus) from the spinous processes to the midportion of the facet joint laterally.

The degree of muscle elevation should be limited to what is necessary to allow adequate laminar exposure for laminotomy.

 

 

 

 

TECH FIG 1 • A. Muscle retractor. B. Laminotomy. C. Laminotomy and the ligamentum. Bony excision used for the typical disc herniation in the canal or subarticular zones. It may need to be extended cephalad for herniations extending upward into the second story or may need to include the upper portion of the caudal lamina for herniations extending downward into the third story of the level below. The ligamentum is either freed from its insertions on the undersurface of the lamina above and the undersurface of the facet capsule laterally using a sharp curette, creating a flap, or is incised and split as depicted. D. Identifying the lateral edge of the root. The traversing root is readily identified by vessels that travel along its lateral edge longitudinally, rise up onto its shoulder, and form a plexus in its axilla. Further caudally, the root is closely associated with the medial border of the pedicle.

 

 

A retractor is then placed. We prefer a retractor with a medial hook for the interspinous ligament and a blade for gentle lateral muscular retraction (TECH FIG 1A).

 

An intraoperative C-arm image is then obtained to confirm the level. Alternatively, a lateral radiograph can be taken.

 

A cylindrical retractor, placed transmuscularly using a sequential dilation technique, is a reasonable

alternative as long as great care is taken to expose the correct portion of the interlaminar window (there is a tendency to be “pushed” too far laterally).

 

P.858

 

At this point, illumination and magnification are gained by the use of the operative microscope (our preference) or a headlamp and loupes.

 

Outcomes are similar for the two when used properly, and the surgeon should decide on his or her preference based on experience and comfort level.

 

A laminotomy on the undersurface of the cephalad lamina and minimal medial facetectomy is then performed using a Kerrison rongeur (TECH FIG 1B).

 

The degree of laminotomy and facetectomy should be enough to allow full visualization of the underlying nerve root at the area of compression and to allow access for excision of herniated disc material—no more and no less.

 

For small disc herniations in the canal or subarticular zones (the “typical disc herniation”), minimal bony excision is required at lower lumbar levels.

 

For larger disc herniations and those extending cephalad into the second story, a larger laminotomy or even hemilaminectomy may be required. The key in these situations is to preserve at least 5 mm of the lateral pars interarticularis and at least 50% of the medial facet.

 

Laminotomy of the upper surface of the caudal lamina is generally not needed unless the herniated material has migrated caudally to the third story of the level below adjacent to the pedicle.

 

The ligamentum flavum is then addressed. One of two techniques is used: the Rick Delamarter and John McCulloch flap or the Rob Fraser split (TECH FIG 1C).

 

The former preserves the ligamentum flavum as a complete barrier to minimize scar formation from posterior, whereas the latter offers a little less coverage but preserves the ligament's biomechanical integrity.

 

The lateral edge of the traversing nerve root is then identified.

 

This is readily identified by consistent lateral veins and the root's association with the pedicle (TECH FIG 1D).

 

These veins can then be gently mobilized to allow exposure of the underlying annulus.

 

Occasionally, anomalous roots lateral to the traversing root may be present. Again, safety is ensured by identifying the veins directly overlying the annulus and using these to provide a window to access.

Herniation Exposure

 

For herniations within the canal or subarticular zones and in the first or second story (85% of encountered discs), the traversing nerve root is gently mobilized medially, allowing exposure of the herniated disc.

 

If the root is immobile, the surgeon should excise more bone within the subarticular region (medial facetectomy) to afford visualization and palpation of the medial border of the pedicle associated with the traversing root.

 

Access to the disc cephalad to this will be within a safe zone lateral to the traversing root and within the axilla of the exiting root.

 

 

Once larger fragments are teased out, the traversing root will become mobile, allowing greater access. Retraction should be minimal at upper levels (L1-L3 due to presence of the conus) and limited to about

40%—that is, to less than half the width of the unilateral hemilaminotomy below this (TECH FIG 2).

 

 

 

TECH FIG 2 • Root retraction is minimal and intermittent.

 

 

Retraction should be relaxed during periods in which no active work is undertaken in or near the disc space: The nerve is rested while the pituitary rongeur is being cleaned and gently reretracted when it returns. This will minimize trauma to the root.

 

Hemostasis is then obtained by gently tucking small pieces of Gelfoam or thrombin cephalad and caudally to the exposed disc space. These are to be removed at the end of the case.

 

If bipolar cautery is used, it should be done with caution to avoid root injury.

 

Herniations extending caudally to the third story of the level below (uncommon, 5%) are most often within the “axilla” of the traversing root. Retraction of the root is not used; rather, the herniation (usually sequestered) is gently teased out.

Discectomy

 

Once visualized, any free disc material is removed with a pituitary rongeur. A ball-tipped probe is used to tease out any additional free fragments hiding further out in the subarticular zone or under the common dural sac or root.

 

The disc space is then entered (this will be the first step in “contained” herniations) by annulotomy. A long-handled no. 15 blade facing away from the traversing root is used, preferably with a longitudinal orientation.

 

Within the disc space, any loose fragments are removed with the pituitary rongeur (TECH FIG 3), and the disc space is irrigated.

 

More aggressive excision (“complete discectomy”) may slightly decrease the risk of recurrence but at the price of increased back pain and a potential for accelerating the degenerative process.

 

Depth of work should be limited to avoid anterior perforation and potential vascular injury. The surgeon should respect the anterior portion of the annulus and avoid perforating it with an instrument.

 

P.859

 

 

 

TECH FIG 3 • Discectomy. After annulotomy, the pituitary rongeur is used to remove the herniation and loose fragments within the disc space.

 

 

Discectomy is complete when no additional loose fragments can be removed from the disc space and free mobility of the nerve root is confirmed.

 

The root retractor is then removed, along with the pieces of Gelfoam.

 

The wound is thoroughly irrigated. This “washing,” coupled with removing the root retractor, is usually adequate to stop any epidural bleeding.

 

If it persists, temporarily placing Gelfoam again is almost always adequate.

 

Unless there is still a bit of oozing, drains are generally not indicated, and the wound is closed in three layers (fascia, subcutaneous tissue, and skin [absorbable, subcuticular]).

• Intertransverse Window

   

  The dorsolumbar fascia is incised 1.5 fingerbreadths off the midline longitudinally (TECH FIG 4A).

   

  The plane between the multifidus medially and the longissimus laterally is freed by finger dissection, allowing palpation of the facet joint.

   

  A retractor is placed within this plane (TECH FIG 4B) and an intraoperative C-arm image is obtained to confirm the level.

   

  The tip of the superior articular process and the lateral pars inter-articularis are exposed with electrocautery and partially resected (TECH FIG 4C,D).

   

  The intertransverse membrane is gently retracted laterally using a ball-tipped probe.

   

  Gentle blunt dissection is used to identify the exiting nerve root and the underlying herniated material. Gentle technique, patience, and really good lighting and magnification are required here (again, we prefer the operative microscope but outcomes are similar regardless). There is plenty of adipose tissue and a venous plexus surrounding the dorsal root ganglion of the root that must be identified before introducing the pituitary rongeur.

   

  A ball-tipped probe and pituitary rongeur are used to gently tease out the loose fragment, with minimal to no retraction applied to the root. This can be traced back into the disc space as necessary and any loose fragments are removed.

   

  The wound is irrigated, hemostasis is obtained, and closure is performed as described earlier.

   

   

   

  TECH FIG 4 • A. The fascial incision is made 1.5 fingerbreadths from the midline. B. Retraction. (continued)

   

   

  P.860

   

   

   

  TECH FIG 4 • (continued) C. The shaded areas represent the area of bony excision during discectomy. D.

  The intertransverse membrane is then gently mobilized laterally, allowing exposure and excision of the

  herniated disc.

   

   

  PEARLS AND PITFALLS

   

  Wrong-level exposure, exploration, or surgery is always a risk. The level is marked preoperatively and intraoperatively as noted earlier.

• The surgeon should beware of obese patients with a significant lumbar lordosis. It is very common to expose the wrong level despite proper localization of the skin incision. Thus, the correct level must be ensured radiographically before entering the spinal canal.

• The surgeon should also beware of patients with “transitional” lumbar vertebrae (sacralization or lumbarization). Here, it is often best to correlate the level on intraoperative images with the preoperative MRI, which will clearly show the disc herniation as well as the immobile, uninvolved transitional levels (narrow disc space with maintained bright signal intensity on T2 with or without poorly developed facet joints).

   

  Certain differences exist between revision discectomy via the interlaminar window and primary surgery.

  • In revision surgery, the laminotomy and facetectomy should be extended cephalad and laterally to allow exposure of “normal” dura (above and lateral to areas of epidural fibrosis [scar]).

  • Identification of the traversing root may be difficult (scar, loss of characteristic veins), but it will still always be associated with its pedicle. The medial border of the pedicle is readily identified, and tissues medial to it (scar, root) are gently mobilized to identify the fragment and disc space.

  • If the root is completely immobile, further medial facetectomy will be required, and the disc space should be entered in line with the subjacent pedicle to ensure being lateral to the traversing root and medial to the exiting root.

     

    Revision discectomy via the intertransverse window for foraminal or extraforaminal disc herniations is not recommended as the planes will be distorted and safe surgery is difficult.

• Using the interlaminar window instead, with resection of the inferior articular process of the cephalad vertebra with or without arthrodesis, is safer and affords excellent visualization.

   

  Anomalous neural anatomy can be best identified preoperatively on MRI.

• The surgeon should beware of large, perfectly round soft tissue masses within the foramen on parasagittal imaging or in the canal on axial imaging. If it does not look like the other roots (mimicking a large round disc herniation) but has their signal intensity, it is likely an anomalous or conjoined root.

 

 

 

POSTOPERATIVE CARE

 

After surgery, patients may be fitted with a light lumbar corset if desired and are encouraged to walk once anesthesia has worn off and pain permits. About 85% are discharged as outpatients. Fifteen percent who are older (less mobile) or have nausea and vomiting require an overnight stay and 23-hour observation.

 

Once home, patients engage in a program of progressive walking, stretching, and corset use for comfort. For those progressing slowly, physical therapy may be introduced. Heavy lifting and excessive bending and twisting should be avoided in the first few weeks.

 

If all is well, they may drive in about a week and return to light work once they feel up to it. Heavy labor should be avoided for 6 to 12 weeks to ensure proper soft tissue healing (skin, muscle, annulotomy). Long-term activities are not restricted.

 

OUTCOMES

There is an 85% likelihood of an excellent or good outcome 8 years postoperatively.

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Patients with significant medical or social comorbidities (eg, diabetes, heavy smoking), worker's compensation or litigation, and psychological problems (depression) are less likely to do well. The same is true for patients who receive no care for more than 6 months before presentation.

Anatomically, patients with larger disc herniations (sac compression one-third or more) and those at higher levels (L2-L3 or L3-L4) have a better prognosis. Those with a retrolisthesis at L5-S1 do not do as well.

Truly informed consent is mandatory.

 

 

COMPLICATIONS

Surgeon-dependent: wrong level, wrong side, missed pathology, iatrogenic instability, “battered root syndrome,” dural tear, hemorrhage, positioning (eg, eyes, ulnar nerve)

Operative environment or patient-dependent: wound infection, disc space infection, urinary retention, thrombophlebitis, or pulmonary embolism

 

 

SUGGESTED READINGS

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2. Boden SD, Davis DO, Dina TS, et al. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg Am 1990;72(3):403-408.

    

    

3. Lurie J, Weinstein J, Lurie JD, et al. Surgical versus nonoperative treatment for lumbar disc herniation: eight-year results for the spine patient outcomes research trial. Spine 2014;39:3-16.

    

    

4. McCulloch JA. Microdiscectomy. In: Frymoyer JW, ed. The Adult Spine: Principles and Practice. New York: Raven Press, 1991:1765-1783.

    

    

5. McCulloch JA, Weiner BK. Microsurgery in the lumbar intertransverse interval. Instr Course Lect 2002;51:233-241.

    

    

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7. Weber H. Lumbar disc herniation. A controlled prospective study with ten years of observations. Spine 1983;8(2):131-140.

    

    

8. Weiner BK, Dabbah M. Lateral lumbar disc herniations treated with a paraspinal approach: an independent assessment of longer-term outcomes. J Spinal Disord Tech 2005;18(6):519-521.