Sciatica is a debilitating condition in which the patient experiences pain and/or paresthesias in the distribution of the sciatic nerve or an associated lumbosacral nerve root. Often, a common mistake is referring to any low back pain or radicular leg pain as sciatica. Sciatica is specific to the pain that is a direct result of sciatic nerve or sciatic nerve root pathology. The sciatic nerve is made up of the L4 through S2 nerve roots which coalesce at the pelvis to form the sciatic nerve. At up to 2 cm in diameter, the sciatic nerve is easily the largest nerve in the body. Sciatica pain often is worsened with flexion of the lumbar spine, twisting, bending, or coughing. The sciatic nerve provides direct motor function to the hamstrings, lower extremity adductors, and indirect motor function to the calf muscles, anterior lower leg muscles, and some intrinsic foot muscles. Also, indirectly through its terminal branches, the sciatic nerve provides sensation to the posterior and lateral lower leg as well as the plantar foot. It is an important distinction to know that most cases of sciatica result from an inflammatory condition leading to an irritation of the sciatic nerve. Conversely, direct compression of the nerve leads to more severe motor dysfunction which is often not seen, and if present, would warrant a more meticulous and expeditious workup.
Any condition that may structurally impact or compress the sciatic nerve may cause sciatica symptoms. The most common cause of sciatica is a herniated or bulging lumbar intervertebral disc. In the elderly population, 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 spasm and/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.
Sciatica has some unique epidemiologic characteristics:
The sciatic nerve is made up of the L4 through S2 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 exiting the pelvis the nerve courses inferior and anterior to the piriformis and posterior to gemellus superior, gemellus inferior, obturator internus, and quadratus femoris. Next, the sciatic nerve enters posterior thigh and courses through biceps femoris. Finally, the sciatic nerve 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.
Patients with sciatica usually experience pain in the lumbar spine, and almost invariably the pain will be unilateral. A common characteristic is that pain may be radicular to the ipsilateral affected extremity. Often, patients may describe pain or a burning sensation deep in the buttocks, and frequently they will describe paresthesia that accompanies the pain. Less commonly there is associated ipsilateral leg weakness. These patients may describe the affected leg 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. The straight-leg test is performed by having the patient lay 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 degrees of hip flexion and experienced primarily in the back is likely due to a lumbar disc herniation. Pain and parenthesis that are felt in the leg are likely due to lateralizing compression of a peripheral nerve. While not absolute, musculoskeletal causes of the pain will usually reproduce pain above 70 degrees of flexion and below 30 degrees of flexion.
Sciatica is a clinical diagnosis, and therefore, a thorough history and physical examination are necessary for a complete evaluation and diagnosis. Imaging is initially of little value. If warranted, plain films of the lumbosacral spine may evaluate for fracture or spondylolisthesis. Noncontrast CT scan may be performed to 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, MRI is the imaging modality of choice. In cases where the neurologic deficit is the present or mass effect is suspected, immediate MRI is the standard of care in establishing the cause of the pain and ruling out pressing surgical pathology.
A thorough differential list is important in considering a diagnosis of sciatica and should include.
Piriformis syndrome is a specific condition of special mention as it 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 to the piriformis muscle can cause "sciatica symptoms." Often overuse injuries, particularly in runners or other endurance athletes, cause inflammation of the piriformis muscle and the ensuing symptoms mimic sciatica. Therefore, these patients tend to have increased pain from the application of 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 stretches, as well as hamstring stretches, are helpful to release this muscle tension and to treat this painful condition. In addition, rest from the activity causing the pain is helpful.
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 course of recovery. 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.
In general, sciatica can be managed conservatively. If the spinal mass effect is diagnosed, for example, an epidural abscess or epidural hematoma, an immediate consultation with a spinal surgeon should be obtained.
Clinicians should always look for and inquire about red flags when evaluating sciatica or in patients who present with any low back pain. Simple sciatica is a benign disease and presence of red flags would prompt much more consideration of the differential diagnosis to ensure a more serious underlying medical or surgical cause of the back pain is not present. A history of IV drug abuse is a risk for epidural abscess and seeding of bacteria anywhere in the body (endocarditis, cerebral abscess, among others). Additionally, those whom have HIV, diabetes, or are immunocompromised have a much higher risk of all infections, and epidural abscess must be considered. Any history of bowel or bladder incontinence, urinary retention, or lower extremity weakness suggest acute neurologic deficit and should prompt more aggressive workup. Anticoagulant use is a risk for all sources of bleeding including epidural abscess. A history of trauma, malignancy, or tuberculosis may suggest fracture, metastasis, and more serious causes of the back pain should be ruled out before a simple diagnosis of sciatica is used. And lastly, fevers, night sweats, chills would not be typical symptoms seen in simple sciatica and thus should prompt further consideration in the workup.
The key to sciatica is patient education. There are many causes of sciatica and the disorder is best managed with a team of healthcare professionals that includes an orthopedic surgeon, physical therapist, neurologist, rehabilitation nurse, and a pain specialist. Unless there is an acute compression of the spinal nerves, the majority of cases of sciatica are best managed conservatively. Patients should be encouraged by the clinician and nurse to lose weight, stop smoking and enroll in a physical therapy program. Bed rest should be limited. The pharmacist should caution the patient against the use of prescription-strength medications to avoid dependence and other adverse effects and if narcotics are used, they should assist the team in making sure the course is very short and not refilled. Surgery should only be undertaken when conservative methods have failed but the patient must be educated on the risks of surgery and the potential complications. Finally, even after surgery participation in regular exercise is essential. (Level V)
The outcomes of patients with sciatica are difficult to analyze. Every surgical study measures different parameters as good-outcome and hence the data are either misinterpreted or hyped. In general, patients with chronic pain (more than 6 months) have a poorer outcome following surgery than patients with acute pain (less than 6 months). Some studies report a cure rate of more than 75% but then there are other studies that report cure rates of less than 50%. There are several newer orthopedic procedures to manage sciatica and all report success rates of 70% and above in the short term. Irrespective of the short-term result, the majority of patients with sciatica tend to have residual or recurrent pain in the long term. Many continue to be dependent on pain medications, are disabled and have a poor quality of life. (Level V)
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