summary Lumbar Disc Herniation is a very common cause of low back pain and unilateral leg pain, known as radiculopathy. In rare cases a large disc herniation can lead to Cauda Equina Syndrome which requires emergent diagnosis and treatment. Diagnosis is made clinically and confirmed with an MRI studies of the lumbar spine. Treatment for radicular leg pain is initially nonoperative with oral medications and physical therapy. Surgical microdiscectomy is only indicated for severe pain and/or motor deficit that have failed to respond to nonoperative management. Treatment for Cauda Equina Syndrome in contrast is emergent microdiscectomy within 48 hours. Epidemiology Incidence peak incidence is 4th and 5th decades lifetime prevalence of 10% only ~5% become symptomatic Demographics 3:1 male:female ratio Location L5/S1 most common level 95% involve L4/5 or L5/S1 levels Etiology Pathoanatomy recurrent torsional strain leads to tears of the outer annulus which leads to herniation of nucleus pulposis lateral edge of posterior longitudinal ligament weakest region common site for posterolateral/paracentral disc herniations sinuvertebral nerves provide pain innervation to the posterior annulus mediate vertebrogenic back pain that precedes or accompanies disc herniation Pathophysiology cellular senescence of fibrochondrocytes leads to loss of proteoglycan production leading to disc height loss loss of height causes increased strain on the annulus fibrosus increased strain leads to fissures of the annulus fibrils annular tears compromise hoop stresses that act against the deforming forces of the nucleus pulposus nucleus pulposus herniates through tear younger, well-hydrated discs more likely to herniate pediatric patients may have Salter-Harris II fracture of the ring apophysis older, desiccated discs less likely to herniate sciatica symptoms result from combined mechanical compression and associated inflammation not all patients with mechanical compression develop symptoms TNF-α, MMP, NO, PE2, and IL-6 are implicated in nerve irritation leading to radiculopathy weak evidence to support DMARDs for treatment Anatomy Complete intervertebral disc anatomy and biomechanics Disc composition annulus fibrosis composed of type I collagen, water, and proteoglycans 15-25 sheets of lamellae characterized by extensibility and tensile strength high collagen / low proteoglycan ratio (low % dry weight of proteoglycans) nucleus pulposus composed of type II collagen, water, and proteoglycans characterized by compressibility low collagen / high proteoglycan ratio (high % dry weight of proteoglycans) proteoglycans interact with water and resist compression a hydrated gel due to high polysaccharide content and high water content (88%) disc height dependent on the degree of hydration avascular structure nutrients supplied by diffusion from the end plates Nerve root anatomy key difference between cervical and lumbar spine is pedicle/nerve root mismatch cervical spine C6 nerve root travels under C5 pedicle (mismatch) lumbar spine L5 nerve root travels under L5 pedicle (match) extra C8 nerve root (no C8 pedicle) allows transition horizontal (cervical) vs. vertical (lumbar) anatomy of nerve root because of vertical anatomy of lumbar nerve root a paracentral and foraminal disc will affect different nerve roots because of horizontal anatomy of cervical nerve root a central and foraminal disc will affect the same nerve root Classification Location Classification central prolapse often associated with back pain only may present with cauda equina syndrome which is a surgical emergency posterolateral (paracentral) most common (90-95%) PLL is weakest here affects the traversing/descending/lower nerve root at L4/5 affects L5 nerve root foraminal (far lateral, extraforaminal) less common (5-10%) affects exiting/upper nerve root at L4/5 affects L4 nerve root herniated disc material directly compresses dorsal root ganglion can manifest with more severe pain than traditional posterolateral disc herniation axillary can affect both exiting and descending nerve roots Morphology classification protrusion eccentric bulging with an intact annulus extrusion disc material herniates through annulus but remains continuous with disc space sequestered fragment (free) disc material herniates through annulus and is no longer continuous with disc space prone to proximal or distal migration Containment classification contained disc material is contained beneath the posterior longitudinal ligament uncontained disc material passes dorsal to the posterior longitudinal ligament Timing classification acute herniations present < 3-6 months important consideration given surgical outcomes are associated with chronicity chronic herniations present >6 months Presentation History sudden onset of pain after lifting a heavy object occupational exposure prolonged sitting with lateral bending and rotation in the presence of vibrational energy symptomatic improvement lying supine with knees and hips flexed especially with lower lumbar disc herniations Symptoms can present with symptoms of axial back pain (low back pain) this may be discogenic or mechanical in nature can precede herniation radicular pain (buttock and leg pain) often worse with sitting, improves with standing symptoms worsened by coughing, valsalva, sneezing pain not worsened with ambulation cauda equina syndrome (present in 1-10%) bilateral leg pain LE weakness saddle anesthesia bowel/bladder symptoms Physical exam inspection limited lumbar range of motion often the pain is the limiting factor patient leaning away from side of radiculopathy effort to increase the size of the neuroforamen palpation spasms of the paraspinal musculature nonspecific associated tenderness in the paraspinal musculature nonspecific motor exam & reflexes see lower extremity neuro exam L3 radiculopathy hip adduction weakness knee extension weakness dermatomal pain in the anteromedial thigh L4 radiculopathy ankle dorsiflexion weakness (L4 > L5) decreased patellar reflex dermatomal pain in the lateral thigh, crossing the knee, to medial foot L5 radiculopathy EHL weakness (L5) manual testing ankle dorsiflexion weakness (L4 > L5 contribution) test by having patient walk on heels ankle inversion weakness hip abduction weakness (L5) have patient lie on side on exam table and abduct leg against resistance dermatomal pain in anterolateral leg and dorsum of foot S1 radiculopathy ankle plantar flexion weakness (S1) have patient do 10 single leg toes stands decreased Achilles tendon reflex dermatomal pain in posterior calf and lateral foot provocative tests straight leg raise (Lasegue's sign) a tension sign for L4, L5 and S1 nerve root technique can be done sitting or supine reproduces pain and paresthesia in leg at 30-70 degrees hip flexion sensitivity/specificity most important and predictive physical finding for identifying who is a good candidate for surgery contralateral SLR crossed straight leg raise is less sensitive but more specific femoral nerve stretch test (Wasserman sign) tension sign for L2 and L3 performed in prone position knee flexed and hip exteneded reproduction of pain in anterior thigh is considered positive Braggard's sign perform SLR to the point of exacerbation lower leg just to the point where pain recedes ankle dorsiflexion causes exacerbated pain Bowstring sign SLR aggravated by compression on popliteal fossa Kernig test pain reproduced with neck flexion, hip flexion, and leg extension Naffziger test pain reproduced by coughing, which is instigated by lying patient supine and applying pressure on the neck veins Milgram test pain reproduced with straight leg elevation for 30 seconds in the supine position gait analysis Trendelenburg gait due to gluteus medius weakness which is innervated by L5 Imaging Radiographs recommended views AP and lateral radiographs helpful for surgical localization identify anomalous vertebrae (sacralized L5 or lumbarized S1) optional views flexion-extension identifies instability if present can changes surgical plan to involve fusion findings most often normal abnormal findings loss of lordosis (spasm) loss of disc height especially at the involved level lumbar spondylosis (degenerative changes) facet hypertrophy disc space collapse peridiscal osteophytes sciatic scoliosis convex or concave list to the ipsilateral side of herniation sensitivity poor sensitivity for identifying disc herniation more often used as a screening tool for other pathology prior to proceeding with MRI CT myelogram indications patients unable to obtain MRI pacemaker views sagittal and coronal reconstructions demonstrate compression of the thecal sac findings myelography filling defect at the level of herniation a calcified disc may be visible sensitivity 93% accurate at detecting associated surgical pathology unable to detect foraminal or extraforaminal herniations MRI without gadolinium indications for obtaining an MRI pain lasting > one month and not responding to nonoperative management or red flags are present infection (IV drug user, h/o of fever and chills) tumor (h/o or cancer) trauma (h/o car accident or fall) cauda equina syndrome (bowel/bladder changes) modality of choice for diagnosis of lumbar disc herniations highly sensitive and specific helpful for preoperative planning useful to differentiate from synovial facet cysts however high rate of abnormal findings on MRI in normal people need to correlate MRI findings with symptoms and physical exam findings views sagittal and coronal T2 reconstructions localize the level and side of the herniation location anatomic location (central vs paracentral vs foraminal vs extraforaminal) MRI with gadolinium indications useful for revision surgery findings allows to distinguish between post-surgical fibrosus (enhances with gadolinium) vs. recurrent herniated disc (does not enhance with gadolinium) Treatment Nonoperative rest and physical therapy, anti-inflammatory medications, and limited narcotics indications first line of treatment for most patients with disc herniation new-onset radicular pain no significant motor weakness absence of cauda equina syndrome no bowel/bladder incontinence outcomes 90% improve without surgery positive predictors of good outcomes with nonoperative treatment higher level of education selective nerve root corticosteroid injections indications second line of treatment if therapy and medications fail usually after 6 weeks outcomes leads to long lasting improvement in ~ 50% (compared to ~90% with surgery) results best in patients with extruded discs as opposed to contained discs no difference in pain relief using lidocaine with and without steroids Operative laminotomy and discectomy (microdiscectomy) indications persistent disabling pain lasting more than 6 weeks that have failed nonoperative options (and epidural injections) timing of appropriate nonoperative treatment varies better surgical outcomes if addressed within 2 months progressive and significant weakness cauda equina syndrome rehabilitation patients may return to medium to high-intensity activity at 4 to 6 weeks outcomes outcomes with surgery compared to nonoperative improvement in pain and function greater with surgery early and sustained pain relief out to 2 years equal likelihood of receiving disability at 5 years positive predictors for good outcome with surgery leg pain is chief complaint positive straight leg raise weakness that correlates with nerve root impingement seen on MRI married status progressively worsening symptoms prior to surgery professional athletes younger age, greater number of games played prior to injury paracentral and foraminal herniations central and extraforaminal associated with worse outcomes herniation at caudal levels L5-S1 results in better outcomes than L2-3 negative predictors for good outcome with surgery worker's compensation WC patients have less relief from symptoms and less improvement in quality of life with surgical treatment smokers chronic headaches depression far lateral microdiskectomy indications for far-lateral disc herniations Techniques Rest and physical therapy, anti-inflammatory medications, and limited narcotics bedrest followed by progressive activity as tolerated historical treatment most modern protocols involve immediate activity with modification to avoid pain exacerbation medications NSAIDS muscle relaxants (more effective than placebo but have side effects) oral steroid taper modest but significant improvement in function, no significant improvement in pain narcotic medications typically avoided due to complication profile dependence difficult post-op pain control worse outcomes following surgical treatment if used, usually for a short period (2-3 days) in the acute setting physical therapy typically initiated three weeks after symptom onset extension exercises are extremely beneficial traction chiropractic manipulation should be performed with care Selective nerve root corticosteroid injections epidural selective nerve block can be therapeutic and diagnostic useful in case of diagnostic dilemmas Laminotomy and discectomy (microdiscectomy) various techniques available most techniques can be performed in a "minimally invasive" fashion can be done with small incision or through "tube" access open technique using a crank (McCulloh) retractor discectomy performed through microscope or loupe magnification no difference in outcomes between the two endoscopic techniques available provide smaller incisions similar outcomes between all techniques surgical techniques fragment excision vs extended disc space curettage (subtotal discectomy) lower long term back pain with fragment excision higher reherniation rates with fragment excision at 2-years follow-up Far lateral microdiskectomy utilizes a paraspinal approach of Wiltse can also be done with tubular or crank retractors Complications Dural tear occurs in 0-4% of cases treatment if have tear at time of surgery then perform water-tight repair has not been shown to adversely affect long term outcomes Recurrent HNP defined as recurrent sciatica at the same operated level pain-free interval of 6 months prior to recurrence of symptoms pathology can be ipsilateral to contralateral to the index presentation recurrence rate 5-15% revision rate at 8-year follow-up is 15% according to the SPORT trial risk factors protective against recurrent herniation discrete herniations small annular defects (<6 mm) treatment can treat nonoperatively initially revision microdiscectomy in patients with persistent symptoms outcomes for revision discectomy have been shown to be as good as for primary discectomy Wound infections occurs in up to 3% of cases epidural abscess in 0.3% of cases risk factors microscope usage proposed as a source of infection some date refutes this claim treatment superficial infections treat with local wound care and antibiotics deep infections surgical I&D Epidural fibrosis scarring the compresses the dura leading to radicular symptoms associated with poor outcomes following revision surgery persistent back pain patients 3.2 times more likely to suffer from recurrent radiculopathy MRI may demonstrate retraction of the dura on the side of the lesion Pyogenic discitis occurs in 2.3% of cases treatment IV antibiotics +/- surgical I&D Chronic low back pain not completely understood but central sensitization may be a factor amplification of neural signaling within the central nervous system (CNS) that elicits pain hypersensitivity. Modic changes on MRI imaging are associated with post-operative back pain Pain diagrams may be useful in identifying patients with an increased likelihood of pain sensitization, psychosocial load, and utilizing pain management resources Vascular catastrophe exceedingly rare caused by breaking through anterior annulus and injuring vena cava/aorta treatment immediate recognition of complication followed by coordinated repair by vascular service Instability due to over resection of lamina and pars interarticularis not all patients are symptomatic treatment instrumentation and fusion of the affected segment Prognosis Natural history 90% of patients will have improvement of symptoms within 3 months without substantial medical treatment patients less likely to improve if still symptomatic after 6 weeks factors associated with good outcomes with nonoperative treatment lack of radiculopathy factors associated with worse outcomes with nonoperative treatment obese patients (BMI >30) symptoms present >6 months prior to starting treatment Size of herniation decreases over time (reabsorbed) sequestered disc herniations show the greatest degree of spontaneous reabsorption macrophage phagocytosis and enzymatic degradation is the mechanism of reabsorption Factors associated with favorable surgical outcomes severe preoperative leg pain shorter symptom duration younger age increased preoperative physical activity Surgical treatment is equivalent to nonsurgical treatment in the long term surgery provides faster pain relief