Sciatica

Etiology

Any condition structurally impacting or compressing the sciatic nerve may cause sciatica symptoms. The most common cause of sciatica is a herniated or bulging lumbar intervertebral disc. In older patients, lumbar spinal stenosis may cause these symptoms as well. Spondylolisthesis or a relative misalignment of one vertebra relative to another may also result in sciatic symptoms. Additionally, lumbar or pelvic muscular spasms or inflammation may impinge a lumbar or sacral nerve root, causing sciatic symptoms. A spinal or paraspinal mass, including malignancy, epidural hematoma, or epidural abscess, may also cause a mass-like effect and sciatica symptoms.[4][5]

Epidemiology

Sciatica has some unique epidemiologic characteristics:[6]

• There appears to be no gender predominance.
• Peak incidence occurs in patients in their fourth decade.
• Lifetime incidence is reported to be between 10% to 40%.
• An annual incidence of 1% to 5%.
• No association with body height has been established except in patients aged 50 to 60.
• It rarely occurs before age 20 unless secondary to trauma.
• Some studies do suggest a genetic predisposition.
• Physical activity increases incidence in those with prior sciatic symptoms and decreases in those with no prior symptoms
• Occupational predisposition has been shown in machine operators, truck drivers, and jobs where workers are subject to physically awkward positions.[6]

Pathophysiology

The sciatic nerve is comprised of the L4 through S3 nerve roots. These nerve roots fuse to create the large sciatic nerve in the pelvic cavity. The sciatic nerve then exits the pelvis through the sciatic foramen posteriorly. After leaving the pelvis, the nerve courses inferior and anterior to the piriformis and posterior to the gemellus superior, gemellus inferior, obturator internus, and quadratus femoris. Then the sciatic nerve enters the posterior thigh and courses through the biceps femoris and terminates at the knee posteriorly in the popliteal fossa, giving rise to the tibial and common fibular nerves. Sciatica symptoms occur when there is pathology anywhere along this course of the nerve. This pathology can be any of the conditions listed in the differential diagnosis.[7]

History and Physical

Patients with sciatica usually experience unilateral pain in the lumbar spine; however, a common characteristic is pain radiating to the ipsilateral affected extremity. Patients may also describe pain or a burning sensation with accompanying paresthesia deep in the buttocks. Less commonly, there is associated ipsilateral leg weakness, where patients may describe the affected leg as "feeling heavy." 

A straight-leg raise has variable sensitivity and specificity and may or may not be present depending on the underlying cause. The straight-leg test is a passive examination where the patient first lies in a relaxed, supine position. The examiner then lifts the leg from the posterior aspect, flexing at the hip joint and keeping the knee in full extension or keeping the leg straight. Typically, pain that is reproduced between 30° to 70° of hip flexion and experienced primarily in the back is likely due to a lumbar disc herniation. Pain and parenthesis felt in the leg are possible due to lateralizing compression of a peripheral nerve. While not absolute, musculoskeletal causes of the pain usually reproduce pain above 70° of flexion and below 30° of flexion.

Further, a straight leg raise (SLR) test is a neurological maneuver performed while examining a patient presenting with lower back pain. This test is conducted with the patient lying supine while keeping the symptomatic leg straight by flexing the quadriceps. The examiner elevates the leg progressively at a slow pace. The test is deemed positive if it reproduces the patient's symptoms (pain and paresthesia) at an angle lower than 70° with radiation below the knee (Lasegue sign). This test is most helpful in diagnosing L4, L5, and S1 radiculopathies. The patient is asked to dorsiflex the foot while the examiner raises the leg (Bragaad sign) to increase the test's sensitivity. When executing the straight leg raise test, the examiner will slightly bend the patient's knee by 20° to 30°, which will lessen the pain. Then, manual pressure is applied in the popliteal fossa. The Bowstring sign is considered positive if it causes the same level of discomfort that the patient feels during a straight leg raise.[8] The Naffziger test involves reproducing pain via coughing.[9]

Another maneuver is the crossed straight leg test, similar to the straight leg raise test but is conducted on the asymptomatic leg instead. The crossed straight leg test is considered positive if the patient reports pain in the symptomatic leg while the asymptomatic leg is at a 40° angle, representing a central disc herniation with severe nerve root irritation. L3 radiculopathy includes weakness of hip adduction, knee extension, and sensory pain in the anteromedial dermatome of the thigh. Ankle dorsiflexion weakness and absent patellar reflex are present in L4 radiculopathy. Hip abduction and big toe extension weakness show L5 radiculopathy. S1 nerve root compression presents as absent ankle reflexes.

Evaluation

Sciatica is a clinical diagnosis, so a thorough history and physical examination are necessary for a complete evaluation and diagnosis. Imaging is initially of little value; if warranted, plain lumbosacral spine films may be evaluated for fracture or spondylolisthesis. A non-contrast computerized tomography scan may evaluate fracture if plain films are negative. Additionally, pain that has been persistent for 6 to 8 weeks and not responding to conservative management should be imaged. In this case, magnetic resonance imaging is the modality of choice. In cases where the neurologic deficit is present, or mass effect is suspected, immediate magnetic resonance imaging is the standard of care in establishing the cause of the pain and ruling out pressing surgical pathology.[10][11]

Treatment / Management

The following recommendations can help patients manage sciatica pain:

Patient Education [12]

• Use hot or cold packs for comfort and to decrease inflammation
• Avoid inciting activities or prolonged sitting or standing
• Practice good, erect posture
• Engage in exercises to increase core strength
• Gently stretch the lumbar spine and hamstrings
• Participate in regular light exercises such as walking, swimming, or aqua-therapy
• Use of proper lifting techniques

Medical Therapies [13][14]

• A short course of oral nonsteroidal anti-inflammatory drugs, NSAIDs
• Opioid and nonopioid analgesics
• Muscle relaxants
• Anticonvulsants for neurogenic pain
• If oral NSAIDs are insufficient, oral corticosteroids may be beneficial
• Localized corticosteroid injections
• Spinal manipulation
• Deep tissue massage may be helpful
• Physical therapy consultation
• Surgical evaluation and correction of any structural abnormalities such as disc herniation, epidural hematoma, epidural abscess, or tumor
• Acupuncture [15]
(A1)

Differential Diagnosis

A thorough differential list is essential in considering a diagnosis of sciatica and should include the following:

• Herniated lumbosacral disc
• Muscle spasm
• Nerve root impingement
• Epidural abscess
• Epidural hematoma
• Tumor
• Pott disease, also known as spinal tuberculosis
• Piriformis syndrome

Piriformis Syndrome

Piriformis syndrome is a specific condition of special mention as this is often misdiagnosed and unrecognized. The piriformis muscle connects the sacral spine to the upper portions of the femur and aids in hip extension and leg rotation. Due to the proximity of the sciatic nerve, any injury or inflammation of the piriformis muscle can cause "sciatica symptoms." Overuse injuries, particularly in runners or other endurance athletes, cause inflammation of the piriformis muscle, and the ensuing symptoms mimic sciatica. Freiberg (forceful internal rotation of the extended thigh) and FAIR (flexion, adduction, internal rotation) maneuvers help diagnose this piriformis syndrome. Patients with overuse injuries tend to have increased pain when applying direct pressure to the piriformis muscle, increased pain when walking up inclines or stairs, and decreased range of motion of the hip joint. Piriformis-specific and hamstring stretches help release this muscle tension and treat this painful condition. Lumbar and sacroiliac manipulation may also prove beneficial for some patients.[16] In addition, rest from the activity causing the pain is helpful.[17]

Herniated Lumbosacral Disc

A careful and thorough neurological examination can help localize the level of lumbar disc herniation if causing radiculopathy. The radiculopathy associated with lumbar disc herniation varies based on the herniation type and the level at which the herniation occurred. In paracentral or lateral herniation, the transversing nerve root is usually affected. A lateral herniation at L4 to L5 would cause L5 radiculopathy. Extreme lateral (far lateral) herniations typically affect the exiting nerve root; far lateral herniation at L4 to L5 would cause L4 radiculopathy. A straight leg raise test at an angle lower than 70° suggests radiculopathies. 

Spondylolisthesis

Spondylolisthesis is commonly classified as one of 5 major etiologies: degenerative, isthmic, traumatic, dysplastic, or pathologic. Forward translation of the vertebrae may cause a spinal canal narrowing at the slip's level. In severe L5/S1 slips, the L5 nerve root is most commonly affected by central and lateral recess stenosis, whereas foraminal stenosis results in L4 nerve root compression. The anteroposterior and lateral plain films and lateral flexion-extension plain films are the standard for the initial diagnosis of spondylolisthesis.[18][19]

Spinal Stenosis

Spinal stenosis is a disease resulting from the narrowing of the vertebral spinal canal and the lateral recesses; this often leads to the compression of the structures within the spinal canal, including the spinal cord, nearby nerve tissue, and cerebrospinal fluid. Multiple factors can lead to the narrowing, including herniation of the nucleus pulposus posteriorly, epidural fat deposition, hypertrophy of the posterior longitudinal ligament or the ligamentum flavum, and hypertrophy of the facet joints. Diagnosis is made through imaging with an extended-release x-ray, computerized tomography, and magnetic resonance imaging.[20][21]

Pott Disease

Back pain in tuberculosis can be related to the active disease (secondary to inflammation), bone destruction, and instability. Rest pain is pathognomonic, and rarely, radicular pain can be the main presenting symptom. Constitutional symptoms, including weight or appetite loss, fever, malaise, and fatigue, are less commonly associated with extrapulmonary tuberculosis than pulmonary disease. The initial compression in tuberculosis is secondary to vertebral body collapse, leading to anterior spinal tract involvement (exaggerated deep tendon reflexes and Babinski sign, further progression to upper motor neuron-type motor deficit). Further, the lateral spinal tracts are progressively involved (with loss of crude touch, pain, and temperature), followed by posterior column deficit (eg, sphincter disturbances and complete sensory loss).[22]

Prognosis

Most cases of sciatica resolve in less than 4 to 6 weeks with no long-term complications, even if no medical therapy is sought. In more severe cases or cases where the neurologic deficit is present, the patient may have a more prolonged recovery course. However, recovery is still excellent. Some studies have shown that poor occupational mechanics, psychological depression, and poor socioeconomic situations lead to an increased chance of chronic, recurrent sciatica.[23]

Complications

Sciatica results from pressure on the sciatic nerve. Complications may develop if measures are not taken to relieve the pressure. Potential complications of unresolved sciatic nerve compression include:

• Increased pain over time
• Paresthesias in the affected leg
• Loss of muscular strength in the affected leg
• Loss of bowel or bladder function
• Permanent nerve damage [24]