# Lumbar Disc Herniation and Sciatica

## Overview

Lumbar disc herniation is the most common cause of sciatica (lumbosacral radiculopathy), with a lifetime prevalence of symptomatic disc herniation of approximately 2-3%. Peak incidence occurs between 30 and 50 years of age. The most common levels are L4-L5 and L5-S1, which account for over 90% of herniations. The natural history is favorable, with 70-90% of patients improving within 6-12 weeks with conservative care.

## Anatomy

### Lumbar Disc

The lumbar disc consists of an annulus fibrosus (outer concentric collagen layers with oblique inner fibers), a nucleus pulposus (gelatinous hydrated center that absorbs axial loads), and cartilaginous endplates that permit nutrient diffusion to the avascular disc. The posterior annulus is the thinnest and weakest, predisposing to posterolateral herniations. The posterior longitudinal ligament is strongest centrally, which further directs herniations posterolaterally.

### Neural Anatomy

Unlike the cervical spine, lumbar nerve roots exit below the correspondingly numbered pedicle. The traversing root crosses the disc space and exits one level below (for example, the L5 root traverses the L4-L5 disc). The exiting root exits at the foramen at the disc level (for example, the L4 root exits at the L4-L5 foramen). A standard posterolateral herniation at L4-L5 typically compresses the traversing L5 root, while a far lateral (foraminal) herniation at L4-L5 compresses the exiting L4 root. The spinal cord ends at L1-L2 (conus medullaris), and below this level the thecal sac contains only nerve roots (cauda equina).

### Types of Herniation

A bulge is a broad-based, symmetric disc extension beyond the vertebral body margin. A protrusion is a focal herniation with the base wider than the dome while the annulus remains intact. An extrusion has the dome wider than the base and extends through the annulus while remaining connected at the base. A sequestration is a free fragment separated from the parent disc that may migrate cranially or caudally.

## Clinical Presentation

### Symptoms

Patients present with radicular leg pain (sciatica) that is sharp, shooting, or burning and follows a dermatomal distribution. Leg pain is typically worse than back pain. Symptoms are exacerbated by sitting, Valsalva maneuvers, and forward flexion. Numbness and tingling follow a dermatomal pattern, and weakness occurs in specific myotomes.

### Root-Specific Syndromes

The L3 root (L2-L3 disc level) produces anterior thigh pain, hip flexion and knee extension weakness, and diminished patellar reflex. The L4 root (L3-L4 disc level) causes medial leg and shin pain, knee extension and tibialis anterior weakness, and diminished patellar reflex. The L5 root (L4-L5 disc level) produces lateral leg, dorsum of foot, and great toe pain, with weakness of the extensor hallucis longus, tibialis anterior, and hip abduction; there is no reliable reflex (though the medial hamstring may be affected). The S1 root (L5-S1 disc level) causes posterior calf, lateral foot, and sole pain, gastrocnemius/soleus (plantarflexion) and peroneal weakness, and diminished Achilles reflex.

| Root | Disc Level | Pain Distribution | Motor Weakness | Reflex |
|------|-----------|-------------------|----------------|--------|
| L3 | L2-L3 | Anterior thigh | Hip flexion, knee extension | Patellar |
| L4 | L3-L4 | Medial leg, shin | Knee extension, tibialis anterior | Patellar |
| L5 | L4-L5 | Lateral leg, dorsal foot, great toe | EHL, tibialis anterior, hip abduction | None reliable |
| S1 | L5-S1 | Posterior calf, lateral/sole of foot | Gastrocnemius (plantarflexion), peroneals | Achilles |

### Physical Examination

The straight leg raise (SLR) is positive at 30-70 degrees when it reproduces radicular leg pain below the knee (sensitivity ~80%, specificity ~40%). The crossed SLR (raising the contralateral leg reproduces ipsilateral leg pain) is less sensitive but much more specific (~90%). The femoral nerve stretch test (hip extension with knee flexion reproducing anterior thigh pain) identifies L2-L4 radiculopathy. Perianal sensation, rectal tone, and bladder function must be assessed to screen for cauda equina syndrome.

### Cauda Equina Syndrome (Surgical Emergency)

A large central disc herniation compressing the cauda equina presents with bilateral leg pain, saddle anesthesia, urinary retention (the most specific symptom), and fecal incontinence. This requires emergent MRI and surgical decompression ideally within 24-48 hours. Delayed treatment results in permanent bladder, bowel, and sexual dysfunction.

## Diagnostic Imaging

### MRI (Study of Choice)

T2 sagittal and axial images best demonstrate disc herniation and root compression. The study assesses location (central, paracentral, foraminal, far lateral), size, and root displacement. Approximately 30% of asymptomatic 30-year-olds have disc herniations on MRI, making clinical correlation essential. The physician must treat the patient, not the MRI.

### CT

CT is useful for bony detail and calcified disc herniations. CT myelography is used when MRI is contraindicated.

### Electrodiagnostics

EMG/NCS is helpful when the clinical picture is unclear or multiple levels are involved. Positive findings (fibrillation potentials, reduced recruitment) appear more than 3 weeks after onset and differentiate radiculopathy from peripheral neuropathy or plexopathy.

## Conservative Management

First-line treatment includes activity modification (avoiding prolonged sitting), NSAIDs, and acetaminophen. A short course of oral corticosteroids may provide short-term relief. Physical therapy employs core strengthening, McKenzie exercises (extension-based), and aerobic conditioning. Epidural steroid injections (transforaminal or interlaminar) provide short-term relief and are most effective as a bridge to recovery or to identify the symptomatic level. Gabapentinoids address the neuropathic pain component. At least 6 weeks of conservative management is recommended before considering surgery, unless red flags are present.

## Surgical Management

### Indications

Cauda equina syndrome is an emergent indication. Progressive motor deficit warrants urgent surgery. Failure of adequate conservative management (typically 6-12 weeks), intractable pain despite conservative therapy, and recurrent disabling episodes are standard elective indications.

### Microdiscectomy (Gold Standard)

Microdiscectomy is the most commonly performed spinal procedure. The approach uses a midline posterior incision with subperiosteal dissection to the lamina-facet junction. A laminotomy (partial removal of the inferior edge of the superior lamina) or hemilaminectomy is performed. The ligamentum flavum is incised and retracted. The thecal sac and traversing nerve root are retracted medially to identify and remove the herniated disc fragment. The foramen is inspected for residual compression. A nerve hook is used to palpate for residual fragments and to explore under the root and into the axilla. The operating microscope or loupes provide magnification.

### MIS Tubular Microdiscectomy

This technique is performed through a tubular retractor (METRx system) with microscope or endoscope. It uses a smaller incision with less muscle dissection and achieves similar clinical outcomes to open microdiscectomy, though with longer operative time, a steeper learning curve, and increased radiation exposure.

### Endoscopic Discectomy

Full-endoscopic technique (transforaminal or interlaminar) uses the smallest incision with potentially the fastest recovery. Outcomes are comparable in experienced hands, but technical demands and the learning curve are significant.

### Far Lateral Disc Herniation

Herniation lateral to the pedicle compresses the exiting root one level higher than expected. This requires a different approach (lateral extracavitary, far lateral, or transforaminal endoscopic) because a standard interlaminar approach will miss the pathology.

## Key Evidence: SPORT Trial

The Spine Patient Outcomes Research Trial (Weinstein et al., JAMA 2006) compared surgery versus non-operative care in randomized and observational cohorts. The as-treated analysis (accounting for crossover) showed that surgery provided significant benefit for pain and function at 2 years. The intent-to-treat analysis showed no significant difference due to a high crossover rate (40% of the non-operative group crossed to surgery). At 8-year follow-up, the surgical group maintained its advantage in pain relief and function. The conclusion is that surgery provides faster and more complete relief, but many patients improve without surgery.

## Outcomes

Microdiscectomy achieves 85-95% good-to-excellent outcomes for leg pain relief. Return to work occurs typically within 2-6 weeks. The recurrence rate is 5-15% at 10 years, with most recurrences within the first 2 years. Risk factors for recurrence include younger age, male sex, smoking, heavy labor, and larger annular defects.

## Complications

Recurrent herniation occurs in 5-15% of cases. Dural tear with CSF leak occurs in 1-7% and is managed with primary repair or fibrin sealant. Nerve root injury occurs in less than 1%. Wound infection occurs in 1-2%. Epidural hematoma is rare. Wrong-level surgery is preventable with intraoperative imaging/fluoroscopy. Discitis/spondylodiscitis is rare but serious, presenting with severe back pain 2-6 weeks postoperatively.

<image>Sagittal T2-weighted MRI of the lumbar spine demonstrating a large L4-L5 disc extrusion with caudal migration of the sequestered fragment, compressing the traversing L5 nerve root, with the free fragment visible posterior to the L5 vertebral body</image>

<image>Axial T2-weighted MRI at the L5-S1 level showing a left posterolateral disc herniation compressing the left S1 nerve root in the lateral recess, with displacement and flattening of the nerve root against the lamina and effacement of the epidural fat</image>

<image>Intraoperative photograph during lumbar microdiscectomy showing the operating microscope view after laminotomy and flavectomy, with the traversing nerve root retracted medially by a nerve root retractor, exposing a large extruded disc fragment beneath the root</image>

## Clinical Pearls

Always check for cauda equina syndrome red flags: urinary retention, saddle anesthesia, bilateral symptoms, and progressive weakness constitute a surgical emergency. A posterolateral L4-L5 disc herniation compresses the traversing L5 root, while a far lateral L4-L5 herniation compresses the exiting L4 root; knowing this distinction prevents incorrect surgery. The crossed straight leg raise is the most specific bedside test for disc herniation. Asymptomatic disc herniations are common on MRI, so imaging must be correlated with clinical findings. Disc resorption can occur naturally, especially with extrusions and sequestrations, which often have the best prognosis with conservative care. After microdiscectomy, early mobilization is encouraged and prolonged bed rest is counterproductive. Smoking cessation is associated with lower recurrence rates and better outcomes.

## References
- Weinstein JN, et al. "Surgical vs Nonoperative Treatment for Lumbar Disk Herniation: The Spine Patient Outcomes Research Trial (SPORT)." *JAMA*. 2006;296(20):2441-2450.
- Kreiner DS, et al. "An Evidence-Based Clinical Guideline for the Diagnosis and Treatment of Lumbar Disc Herniation with Radiculopathy." *Spine J*. 2014;14(1):180-191.
- Lurie JD, et al. "Surgical versus Nonoperative Treatment for Lumbar Disc Herniation: Eight-Year Results for the SPORT." *Spine*. 2014;39(1):3-16.
- Overdevest GM, et al. "Tubular Discectomy versus Conventional Microdiscectomy for Lumbar Disc Herniation." *Cochrane Database Syst Rev*. 2015;(2):CD010036.
- Ahn Y. "Endoscopic Spine Discectomy: Indications and Outcomes." *Int Orthop*. 2019;43(4):909-916.