26: Posterior Far Lateral Disk Herniation

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Procedure 26 Posterior Far Lateral Disk Herniation

Chadi Tannoury, D. Greg Anderson, Alexander R. Vaccaro, Todd J. Albert

Indications

image Intractable radiculopathy resistant to conservative measures

image Unilateral, single-level, nerve root compression lateral to the neuroforamen

image Far lateral disk herniation confirmed by computed tomography (CT) scan or magnetic resonance imaging (MRI): nucleus pulposus herniates beyond the intervertebral foramen, or at least two-thirds lateral to the vertebral pedicle (Papavero and Caspar, 1993).

image Absence of segmental instability, facet incompetence, or additional pathologies, that is, spinal stenosis or associated central disk herniation

image Radiculopathy correlating with radiographic evidence of far lateral disk herniation (FLDH) compressing the symptomatic exiting nerve root

Indications Pitfalls

• Diagnostic process is complex.

• Clinical symptoms alone, without radiographic studies, do not differentiate this type of disk hernia from other entities.

• Radiographic findings may have no clinical correlation, and/or false-positive results may be derived from imaging studies.

Indications Controversies

• A far lateral disk herniation (FLDH) associated with adjacent canal stenosis at the level above

• Monoradicular symptoms (denoting isolated far lateral disk herniation) versus multiradicular symptoms (denoting a far lateral disk associated with medially located pathologies, including degenerative changes, canal stenosis, or central disk herniations)

Examination/Imaging

image Presentation

• Occurs most often in patients greater than 40 years of age
• Slight male predominance
• Most commonly affects upper lumbar roots (e.g., anterior thigh pain) although can affect any level
• Exiting nerve root affected rather than traversing nerve root
• Lower limb pain predominates over low back pain
• Pain referred to the knee can be mistaken for primary hip or knee pathology.

image Physical examination

• Limitation of flexion/extension, lumbar list, antalgic gait
• Neurologic signs (sensory, motor, or both); L2 = groin/medial thigh; L3 = anterior thigh; L4 = anterolateral thigh/medial leg; L5 = dorsal foot
• Diminished or absent deep tendon reflex
• Reproduction of symptoms by lateral bending to the side of the lesion
• Positive nerve tension tests: femoral nerve stretch and the Lasegue sign (depending on level of herniation)
• Muscular atrophy
• Paravertebral point tenderness (intertransverse membrane level)
• Bowel/bladder dysfunction is not typically present.

image Imaging

• Plain radiographs: mainly to rule out other disorders (spondylolysis/listhesis, lumbar stenosis, etc.)
• MRI is the method of choice (most sensitive diagnostic tool); however, one third of FLDH cases may be overlooked (Osborn et al, 1988). Seventy-five percent of FLDH cases occur at L4-5 and above (O’Hara and Marshall, 1997), with 46% occurring at L2-3 and L3-4 levels.
• Most accurate diagnosis offered by CT diskography (Jackson and Glah, 1987)
• Radiologic findings supporting the diagnosis of FLDH include
• Disk fragment lateral to the neural foramen
• Absence of foraminal or paraforaminal fat around nerve root

Treatment Options

• Conservative management

• Local spinal infiltration (anesthetics, corticosteroids, etc.) with or without fluoroscopic guidance

• Surgical

• SPORT study showed beneficial effect of surgery at each follow-up period (Pearson et al, 2008).
• Midline interlaminar approach (partial/complete facetectomy, or removal of the pars interarticularis) (Figure 26-1, arrow A)
• Intertransverse transmuscular approach (Figure 26-1, arrow B)
• Intertransverse muscle-splitting approach (Figure 26-1, arrow C)
• Transforaminal percutaneous approach
image

FIGURE 26-1

Surgical Anatomy

image Anatomic definition: Far lateral, extraforaminal, or extreme lateral disk herniation denotes a disk hernia occurring lateral to the neuroforamen and the facet joint complex (Figure 26-2). The herniated disk fragment usually compresses the exiting nerve root and displaces it superiorly and laterally under tension.

image Because of its anatomic location (Figure 26-3, A), unlike the posterolateral herniated nucleus pulposus (HNP), which affects the traversing nerve root (Figure 26-3, B), FLDH affects the exiting nerve root at the same level.

image The anatomic boundaries of the “operative window” or “surgical corridor” for the intertransverse lateral approach (Figure 26-4) are

• Superiorly: the lower edge of the pedicle and the superior transverse process
• Medially: the pars interarticularis
• Inferiorly: the facet joint and superior border of the inferior transverse process
image

FIGURE 26-2

image

FIGURE 26-3

image

FIGURE 26-4

Positioning

image The prone position with abdomen free hanging is preferred by most surgeons.

image Although both regional and general anesthesia have been described (Reulen et al, 1996), general anesthesia with endotracheal intubation offers more control of the airway and is preferred by the authors.

Positioning Pearls

• Positioning the patient on an Andrews frame in a kneeling position allows flexion of the lumbar spine and opening of the intertransverse space, therefore providing a better access to the neural foramen.

• Clearing the abdomen from any compression during positioning prevents intraabdominal pressure–related venous congestion, thereby reducing the risk of bleeding and helping in lumbar flexion.

Positioning Pitfalls

• All pressure points should be well padded, and arms should be positioned under no tension to avoid brachial plexus and ulnar nerve injuries.

Positioning Equipment

• Various frames and positioning equipments are available (Wilson frame, Jackson table, Andrews frame, Montreal mattress, chest-rolls, etc.)

Portals/Exposures

image Localization and placement of an accurate skin incision is made possible with the use of plain radiographs or C-arm fluoroscopy (anteroposterior and lateral views); following identification of the affected disk level, two horizontal and two vertical lines are marked on the skin.

image Horizontally, the upper line marks the inferior border of the transverse process proximal to the affected disk, and the lower line marks the inferior border of the affected disk space.

image Vertically, one line is placed centrally, marking the midline overlying the spinous processes, and a more lateral line (4- to 5-cm paramedian) marks the lateral borders of the pedicles above and below the affected disk level.

image The site of the skin incision (3 to 4 cm in length, and 4- to 5-cm paramedian) is therefore outlined by these horizontal and vertical lines.

image Muscle-splitting technique: Following skin incision, the thoracolumbar fascia is identified and incised in line with the skin incision to expose the erector spinae aponeurosis, which is cut longitudinally to expose the multifidus and longissimus muscles. A blunt dissection is carried through the cleavage between the latter muscles and a self-retaining (McCulloch or Gelpi) retractor is placed to expose the “working zone.” This zone is located between the lower surface of the superior transverse process proximally, the superior surface of the inferior transverse process distally, the lateral surface of the pars interarticularis medially, and the tips of the transverse processes laterally (see Figure 26-3).

Portals/Exposures Pearls

• True anteroposterior and lateral fluoroscopic views are crucial for accurate surgical site placement.

Portals/Exposures Equipment

• Preoperative and intraoperative use of radiograph and/or C-arm fluoroscopy is valuable to mark the correct level for surgery.

• Modified Caspar speculum and self-retaining lumbar retractors can help with exposure.

• Tubular retractor systems are useful to reach to extraforaminal zone.

Portals/Exposures Controversies

• Transmuscular versus muscle-splitting (intertransverse) approach

• At L5-S1, the exposure of surgical site can be anatomically limited, and therefore the approach can be modified by removal of the L5 transverse process, as required for a better exposure.

Procedure

Step 1

image Surgical site marking, skin incision, and paraspinal muscles dissection (see Portals/Exposures)

Step 1 Pearls

• Blunt finger dissection and palpation of bony landmarks (transverse processes and lateral aspect of the pars) can help localize the “operative window.”

• A Kerrison rongeur can be used to remove part of the facet pars laterally, when necessary for adequate exposure.

• The soft tissue can be cleared off the bony landmarks of the working zone and the intertransverse membrane, using a series of angled (3-0) curettes and no. 2 curettes.

Step 1 Instrumentation/Implantation

• Surgical microscope: useful for magnification and anatomic structures differentiation

• Blunt dissectors

• Self-retaining retractors: Caspar retractor, McCulloch retractor, or Gelpi retractor can be used

• Curettes: no. 2 and angled 3-0

• High-speed burr with angled and long handpiece

• Pituitary rongeur

Step 2

image Exposure of bony landmarks: transverse processes, facet joint, pars, and isthmus

image Exposure of the intertransverse muscle

image High-speed burr, or Kerrison rongeur, can be used to partially remove bony overgrowth and improve exposure, as in cases of facet hypertrophy, at L5-S1 level, and around the lateral aspect of the pars.

Step 3

image The “intertransverse membrane” is exposed after incising the medial half of the intertransverse muscle, which is reflected laterally.

image The posterior primary ramus is then identified, using a microscope as it crosses the medial portion of the intertransverse membrane and before it innervates the paraspinal muscles.

image Using the posterior primary ramus as a reference, the dorsal root ganglion and the spinal nerve are then located underneath the intertransverse membrane surrounded by connective tissue and extraforaminal fat.

image The spinal nerve is then handled very gently to avoid irritation of the dorsal root ganglion.

image Sweeping a ball-tipped probe beneath the nerve root, the herniated fragment can be identified and removed.

image Identification of the pedicle below offers an alternative option to locate the HNP and the exiting nerve root (dorsal to the pedicle).

image Underneath the intertransverse membrane, the nerve root/spinal nerve branches are in close proximity to arterial-venous branches (lumbar artery) and herniated disk material. The lumbar artery is a potential source of vigorous bleeding, and should be spared whenever possible. Meticulous hemostasis using bipolar cautery helps exposing the extruded disk herniation, if obscured by venous bundles.

Step 3 Pearls

• A direct view of the surgical “working zone” can be enhanced by tilting the operating table 15 to 20 degrees away from the surgeon.

• The herniated disk fragment is often sequestrated (50% of cases) and tends to stretch and displace the spinal nerve superiorly and laterally (see Figure 26-2).

Step 3 Pitfalls

• Postoperative anterior thigh burning sensation and dysesthesia may develop secondary to excessive manipulation of the dorsal ganglion during exposure. However, spontaneous resolution is expected.

• Persistent or recurrent leg pain occurs in 21.7% of operated patients, and development of foraminal stenosis or the presence of double herniation (combination of posterolateral and FLDH) should be considered (Chang et al, 2006).

Step 3 Instrumentation/Implantation

• Visualization: microscope (three-dimensional view) versus binocular loupe magnification with fiberoptic headlight source

• Endoscopic or microsurgery: bayoneted instruments

Step 3 Controversies

• Anatomic and surgical landmarks

• Posterior ramus of the spinal nerve (Fankhauser and de Tribolet, 1991)

• Lateral branch of posterior primary ramus (O’Brien et al, 1995)

• Medial branch of the posterior primary ramus (O’Hara and Marshall, 1997)

Step 4

image Neurologic decompression: the extruded disk hernia is removed with a pituitary rongeur, and although, in most cases, this is considered sufficient for symptoms relief, further exploration and probing of the neuroforamen with a blunt probe, searching for any residual sequestered disk material or associated foraminal stenosis (notorious for unfavorable outcomes), may be necessary.

image Following nerve root manipulation and probing, some surgeons prefer to place a steroid-soaked Gelfoam pledget at the site.

Step 5

image A surgical drain is not typically necessary.

image Wound closure in layers: paraspinal muscles are usually reapproximated without sutures, and the fascia/aponeurosis are stitched with absorbable sutures.

image Local anesthetics (e.g., Marcaine [bupivicaine] without epinephrine) can be generously infiltrated into the soft tissues for analgesia. Deep injection of the local analgesics risks anesthetizing the exiting nerve root.

Postoperative Care and Expected Outcomes

image Postoperative care

• Ambulation and light activity are encouraged.
• The operation can be performed on an outpatient basis with most patients.
• Physical therapy promotes progressive mobilization and core strengthening.
• Restrictions are no heavy lifting and twisting/bending for 6 weeks postoperatively to avoid recurrent HNP.
• Return to work is permitted when tolerated.

image Expected outcomes

• Most patients (89%) report neurologic improvement (Chang et al, 2006; Darden et al, 1995; O’Hara and Marshall, 1997; Papavero and Caspar, 1993).
• Complete motor weakness resolution is reported in 78% of patients.
• Complete sensory deficit resolution is reported in 50% of patients.
• Excellent results are reported by 41% to 60% of patients.
• Good results are reported by 30% to 35% of patients.
• Unfavorable results are reported in 21.7% of patients.

Postoperative Pitfalls

• Wrong-level surgery mandates revision exploration and is prevented by use of intraoperative C-arm fluoroscopy or plain radiography.

• Spondylodiskitis should be treated with immobilization and organism-specific antibiotic therapy.

• Spinal instability, caused by excessive pars excision, may promote accelerated degeneration.

• Persistent/recurrent leg pain may complicate a battered nerve root syndrome, an inadequate decompression, or wrong diagnosis (20% of cases).

• Facet distress syndrome is leg pain (pseudoradicular) with low back pain, more often complicating an L5-S1 interlaminar decompression. Complication can be significantly prevented (incidence rate decreased by 50%) with use of a muscle-splitting technique instead.

Evidence

Chang SB, Lee SH, Ahn Y, Kim JM. Risk factor for unsatisfactory outcome after lumbar foraminal and far lateral microdecompression. Spine. 2006;31:1163-1167.

Risk factors for unfavorable outcomes following surgical decompression of far lateral disk herniation were analyzed. Age, gender, duration of symptoms, degree of disk degeneration, presence of associated intracanalicular disk hernia, and presence of instability were investigated. Unfavorable outcomes were reported in 21.7% of patients (persistent or recurrent leg pain). This study concluded that patients with double herniation were almost 3 times more likely to have persistent or recurrent leg pain.

Darden BV2nd, Wade JF, Alexander R, et al. Far lateral disc herniations treated by microscopic fragment excision: techniques and results. Spine. 1995;20:1500-1505.

A series of patients who had been treated with microscopic facet-sparing paraspinal muscle-splitting approach for far lateral disk herniation were evaluated retrospectively using parameters such as history, physical examination, pain questionnaires, visual analog scales, and plain radiographs. The overall clinical results were encouraging, and no radiographic signs of instability were noted. In addition, the paraspinal muscle-splitting approach is thought to minimize manipulation of the dorsal root ganglion, which is responsible for postoperative dysesthesia.

Fankhauser H, de Tribolet N. Extraforaminal approach for extreme lateral lumbar disc herniation. In: Torrens MJ, Dickinson RA, editors. Operative Spinal Surgery (Practice of Surgery Series). Edinburgh: Churchill Livingstone; 1991:145-160.

Using the transmuscular approach for far lateral disk herniation, the authors observed the posterior primary ramus of the spinal nerve during operative dissection. However, its usefulness as an anatomic landmark has been argued because of difficult identification of its branches and time consumption.

Jackson RP, Glah JJ. Foraminal and extraforaminal lumbar disc herniation: diagnosis and treatment. Spine. 1987;12:577-585.

In this study, 10% of patients undergoing lumbar diskectomy for herniated nucleus pulposus were found to have far lateral foraminal or extraforaminal disk herniation. Different diagnostic radiographic evaluations have been proposed; however, diskography-enhanced computed tomography proved accurate diagnosis in more than 90% of cases. In terms of surgical approach, the authors opted for bilateral hemilaminectomy, with partial medial facetectomy and partial internal foraminotomy as most effective for diskectomy and nerve root decompression.

O’Brien MF, Peterson D, Crockard HA. A posterolateral microsurgical approach to extreme-lateral lumbar disc herniation. J Neurosurg. 1995;83:636-640.

O’Brien and colleagues have adopted the posterolateral approach of Watkins for patients with a far lateral disk herniation. The authors recommend the use of the lateral branch of the posterior primary ramus as a key anatomic landmark to direct them to the spinal nerve and the intervertebral foramen.

O’Hara LJ, Marshall RW. Far lateral lumbar disc herniation: the key to the intertransverse approach. J Bone Joint Surg Br. 1997;79:943-947.

In a series of patients with far lateral lumbar disk herniation, an intertransverse muscle-splitting approach has been adopted with encouraging outcomes. A cadaver study describing the anatomic course of the posterior primary ramus within the intertransverse membrane has also been reported. The authors recommend the use of a muscle-splitting intertransverse approach to far lateral herniation, referring to the posterior primary ramus as the anatomic key to safe dissection.

Osborn AG, Hood RS, Sherry RG, Smoker WRK, Harnsberger HR. CT/MRI spectrum of far lateral and anterior lumbosacral disc herniations. AJNR Am J Neuroradiol. 1988;9:775-778.

A radiologic assessment of patients with extraforaminal disk herniations (EFDHs) using CT and/or MRI reported that the most commonly affected level was L4-5; however, 46% of EFDHs were overlooked and located at L2-3 or L3-4 levels. EFDHs can be readily diagnosed on both CT and MRI if appropriate scans are obtained from L2 through S1 and if the neural foramina and paravertebral spaces are carefully examined. Overlooked EFDHs are an important preventable cause of failed intraspinal diskectomy.

Papavero L, Caspar W. The lumbar microdiscectomy. Acta Orthop Scand Suppl. 1993;64:34-37.

Pearson AM, Blood EA, Frymoyer JW, et al. SPORT lumbar intervertebral disc herniation and back pain: does treatment, location, or morphology matter? Spine. 2008;33:428-435.

Patients with sciatica and low back pain secondary to HNP were enrolled in a randomized and controlled cohort. The goal was to determine whether diskectomy benefits low back pain and whether herniation location and morphology affect treatment outcomes. The study concluded that leg pain improves better than back pain, in both the surgery and nonoperative groups, and they suggest that leg pain relief should be the primary aim of surgery.

Reulen HJ, Muller A, Ebeling U. Microsurgical anatomy of the lateral approach to extraforaminal lumbar disc herniations. Neurosurgery. 1996;39:345-350. discussion 350-1

In lumbar spine specimens taken from human cadavers, the relevant distances and proportions of the operative window were measured at the levels L1-2 to L5-S1. The anatomic findings led to important conclusions regarding the microsurgical approach to extraforaminal lumbar disk herniations; at levels L1-2 to L3-4, the midline approach with lateral retraction of the paraspinal muscles allows for efficient exposure of the lateral neural foramen and avoidance of trauma to the facet joint. Often at level L4-5, and nearly always at level L5-S1, a tangential route through a paramedian transmuscular approach offers many advantages.

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