Lumbar Disc Herniations: Comprehensive Guide to Diagnosis and Treatment
Learn about lumbar disc herniations, including definition, anatomy, pathogenesis, natural history, imaging, diagnostic studies, differential diagnosis, nonoperative management, and surgical management. Get the latest information on treatment options and outcomes.”
Lumbar Disc Herniations: Definition, Anatomy, and Classification
Definition
Clinically significant lumbar disc herniations are characterized by a focal distortion of the normal anatomic configuration of discal material. This results in compression and subsequent dysfunction of the lumbar nerve roots.
Anatomy
The functional components of the intervertebral disc include the annulus fibrosus, nucleus pulposus, and vertebral endplates. The annulus fibrosus is made up of fibrous concentric rings of type I collagen, while the nucleus pulposus is gelatinous and contains type II collagen and proteoglycans. The vertebral endplates are made of hyaline cartilage.
The anatomic unit of the lumbar spine consists of the vertebral body, its attached posterior elements, and the disc below it. The nerve roots travel within the common dural sac (the cauda equina) and exit at each level, 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 extraforaminal (far lateral) zone.
Classification
Disc herniations can be classified based on the integrity of the annulus fibrosus and whether there is a connection of herniated discal material with the disc space. They can also be classified based on the anatomic location of the herniated material relative to the disc space, canal, and compressed nerve root.
Accurate anatomic classification of disc herniations is important for 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.
Lumbar Disc Herniations: Pathogenesis and Natural History
Pathogenesis
In a normal disc, the nucleus pulposus imbibes and releases water to balance mechanical loads. The annulus fibrosus converts these loads to hoop stresses, containing the nuclear material. The endplates allow diffusion of nutrition into and waste products out of the nucleus. Together, these components allow for mobility, stability, and protection of nearby neurologic structures.
With early or intermediate disc degeneration, the endplates fail to allow adequate diffusion, the nucleus fails to replace degraded proteoglycans, and annular support weakens. This can result in biomechanical dysfunction and 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
Studies have shown that over 90% of patients with a first-time lumbar disc herniation will improve without surgery with time and nonoperative treatment. Surgery should only be considered with clear indications.
Absolute indications for surgery include bladder or bowel involvement secondary to a massive disc herniation and cauda equina syndrome, which requires immediate surgical intervention. Progressive neurologic deficit is also an indication for surgery, with earlier intervention being better prognostically.
 |
 |
 |
FIG 2 • Classification of disc herniations based on relation to outer annulus: (A) protrusion, (B) subannular extrusion, (C) transannular extrusion, and (D) sequestration.
Lumbar Disc Herniations: Relative Indications for Surgery and History and Physical Findings
Relative Indications for Surgery
Relative indications for surgery include failure of conservative measures for greater than 6 weeks to 3 months, multiple recurrent sciatica, and significant neurologic deficit. In each case, the patient must be properly informed and understand the current best evidence.
Most patients with lumbar disc herniation improve quickly with nonoperative care. For those with significant symptoms that do not improve within 6 weeks, short-term and long-term outcomes are better with discectomy compared to continued nonoperative care.
History and Physical Findings
The most common complaint in patients with lumbar disc herniation 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).
Lumbar Disc Herniations: Imaging, Diagnostic Studies, Differential Diagnosis, and Nonoperative Management
Imaging and Diagnostic Studies
Magnetic resonance imaging (MRI) is the preferred imaging study for diagnosing and classifying lumbar disc herniations. It is highly sensitive and specific and provides detailed information for preoperative planning.
Computed tomography (CT) myelography is 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.” They can be helpful in ruling out unexpected destructive pathology and in delineating bony anomalies that may be important for preoperative planning.
Differential Diagnosis
Differential diagnoses for lumbar disc herniation include intraspinal, extrinsic compression or irritation at the level of the nerve root, such as spinal stenosis, osteomyelitis or discitis, neoplasm, or epidural fibrosis. Other possibilities include intraspinal, extrinsic compression or irritation proximal to the nerve root, such as conus and cauda lesions, or intraspinal, intrinsic nerve root dysfunction such as neuropathy or arachnoiditis. Extraspinal sources distal to the nerve root may also be considered.
Nonoperative Management
Nonoperative management options for lumbar disc herniation include rest, medication, exercise, injections, and time. Bed rest should be limited to 2-3 days and activity or job modification may be necessary. Medications such as analgesics and nonsteroidal anti-inflammatories may provide relief. Physical therapy and epidural or selective root blocks may also provide temporary relief. Nonoperative management should be continued for 6 weeks to 3 months unless there are absolute indications for surgery.
 |
FIG 4 • A. The kneeling position obtained with the Andrews, Wilson, or Jackson frames. B. The marking needle.
Lumbar Disc Herniations: Surgical Management
Overview
Open discectomy and microdiscectomy are the gold standard surgical techniques for lumbar disc herniations, with well-documented short-term and long-term outcomes.
Preoperative Planning
Preoperative planning is vital and should aim to answer three questions: what nerve root is involved, where is the herniated material relative to the disc space, canal, and nerve root, and what approach will provide the best visualization and access 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, Wilson frame, or Jackson table. 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. Shoulders should be abducted less than 90 degrees with some flexion, and the neck should be neutral or gently flexed. Eyes must be protected and elbows, knees, and feet well padded.
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 cases and is appropriate for herniations within the foraminal and extraforaminal zones from L1 to L5.
Techniques
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. The subcutaneous tissues are then gently 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.
For the interlaminar window approach, the dorsolumbar fascia is incised just off the midline on the involved side. 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, with a medial hook for the interspinous ligament and a blade for gentle lateral muscular retraction. An intraoperative C-arm image or lateral radiograph is obtained to confirm the level. A cylindrical retractor, placed transmuscularly using a sequential dilation technique, is an alternative approach.
- Illumination and magnification are gained by the use of an operative microscope or a headlamp and loupes. A laminotomy on the undersurface of the cephalad lamina and minimal medial facetectomy is then performed using a Kerrison rongeur. 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.
- The ligamentum flavum is then addressed using one of two techniques: the Rick Delamarter and John McCulloch flap or the Rob Fraser split. The lateral edge of the traversing nerve root is then identified, readily identified by consistent lateral veins and the root’s association with the pedicle. These veins can be gently mobilized to allow exposure of the underlying annulus.
- For herniations within the canal or subarticular zones, the traversing nerve root is gently mobilized medially, allowing exposure of the herniated disc. If the root is immobile, more bone within the subarticular region (medial facetectomy) should be excised 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).
- 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.
 |
 |
TECH FIG 2 • Root retraction is minimal and intermittent.
- For herniations extending caudally to the third story of the level below, the herniation is usually within the “axilla” of the traversing root. Retraction of the root is not used; rather, the herniation is gently teased out.
- 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 by annulotomy, using a long-handled no. 15 blade facing away from the traversing root. Within the disc space, any loose fragments are removed with the pituitary rongeur and the disc space is irrigated.
- 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 wound is thoroughly irrigated and closed in three layers (fascia, subcutaneous tissue, and skin).
- For the intertransverse window approach, the dorsolumbar fascia is incised 1.5 fingerbreadths off the midline longitudinally. 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 and an intraoperative C-arm image is obtained to confirm the level.
- Gentle blunt dissection is used to identify the exiting nerve root and the underlying herniated material. 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. The wound is irrigated, hemostasis is obtained, and closure is performed as described earlier.
 |
 |
TECH FIG 3 • Discectomy. After annulotomy, the pituitary rongeur is used to remove the herniation and
loose fragments within the disc space.
-
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 interarticularis are exposed with electrocautery and partially resected (TECH FIG 4C,D).
The intertransverse membrane is gently retracted laterally using a ball-tipped probe.
 |
 |
TECH FIG 4 • A. The fascial incision is made 1.5 fingerbreadths from the midline. B. Retraction.
(continued)
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.
P.5228
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 ▪ Using the interlaminar window instead, with resection of the inferior
|
|
via the intertransverse articular process of the cephalad vertebra with or without arthrodesis, is window for foraminal safer and affords excellent visualization. or extraforaminal disc herniations is not recommended as the planes will be distorted and safe surgery is difficult.
Anomalous neural ▪ The surgeon should beware of large, perfectly round soft tissue anatomy can be best masses within the foramen on parasagittal imaging or in the canal on identified axial imaging. If it does not look like the other roots (mimicking a large preoperatively on MRI. round disc herniation) but has their signal intensity, it is likely an anomalous or conjoined root. |
|
|
|
||
Interactive MCQs on Lumbar Disc Herniations