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Taryn Walker B.Kin, MM, 1 Vahagn Karapetyan MD PhD FRCSC,2 Greg McIntosh MSc,3 Christopher S Bailey MD FRCSC,4

1Department of Surgery, Schulich School of Medicine, Western University
2Department of Surgery, Schulich School of Medicine, Western University
3Director of Research Operations, Canadian Spine Outcomes and Research Network
4Department of Surgery, Schulich School of Medicine, Western University

CLINICAL TOOLS

Abstract: Sciatica is a well-recognized complaint, with the hallmark presenting symptom of lancinating pain running down the back of the leg, along the path of the sciatic nerve. While it is typically caused by a herniated lumbar disc within the spinal canal, an understanding of the course of the sciatic nerve and associated regional anatomy is useful in forming a broader differential diagnosis. In rare cases, sciatica, usually bilateral, is associated with a loss of bowel or bladder function, indicating cauda equina syndrome, a medical emergency. Other degenerative conditions of the lumbar spine such as spondylolisthesis and spinal stenosis can occasionally produce sciatica while deep gluteal pain is often used to describe the muscular causes. Malignancy, trauma, vascular causes and ectopic endometrial tissue can cause compression of the lumbosacral plexus within the pelvis and produce similar symptoms. In this review, we highlight the common clinical presentations, physical examination and relevant diagnostic investigations for a broad differential diagnosis of sciatica.
Key Words: Sciatica, leg dominant pain, nerve compression, straight leg raise.

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1. Herniated intervertebral disc accounts for up to 90% of sciatica cases 
2. An understanding of the course of the sciatic nerve and associated regional anatomy can be useful in forming a differential diagnosis; one should consider gluteal region sciatic compression disorders, pelvic pathology involving the lumbosacral plexus, malignancy, infection, trauma and conditions that mimic sciatica.
3. Patients usually have low back pain associated with their leg complaints, but genuine sciatica from a herniated lumbar disc produces leg pain that is the dominant symptom. Back dominant pain, with any direct nerve involvement, can extend into the leg, occasionally all the way to the foot, but unless the leg pain is more intense than the back pain, it is not sciatica. 
4. The physical examination should include checking lower limb reflexes, dermatome and myotome assessment, upper motor neuron tests such as the plantar response and specialized neural tension tests such as the passive straight leg raise (SLR) and slump tests.
5. A positive crossover sign occurs when raising the straight leg on the affected side reproduces not only the typical pain in the affected leg but causes pain to radiate down the seemingly unaffected leg as well. This finding of bilateral sciatica suggests pathology located in the midline, a central disc herniation.
True sciatica from a herniated lumbar disc is when the leg pain is the dominant symptom over back pain. Lancinating, constant, radicular pain down the posterior leg along the path of the sciatic nerve is the hallmark symptom. Activity, prolonged sitting or Valsalva maneuvers such as coughing or bearing down aggravate sciatic pain. A patient may prefer to stand because sitting is intolerable.
Neurogenic Claudication from spinal stenosis is distinctive from herniated lumbar disc sciatica. Unlike classic sciatica, lumbar spinal stenosis neural tension tests are often negative and the neurological assessment may be normal; however, the more classic sciatic presentation, may be present in spinal stenosis if a focal nerve root is also compressed.
To distinguish piriformis syndrome from sciatica, muscle tenderness with deep gluteal palpation and specialized piriformis stretch tests such as the FAIR, Pace and Beatty maneuvers may be helpful.
Greater trochanteric bursitis, meralgia paresthetica, and cluneal nerve entrapment are conditions that can cause pain in a distribution that is similar to the sciatic nerve, but without involving the nerve directly.
Identifying any posterior thigh pain when the leg is elevated above 60 or 70 degrees as sciatica is a common diagnostic error. Unless the leg pain produced is identical to the patient’s chief complaint on history, the test is negative.
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Related Terms: Back Health, sciatica, leg dominant pain, nerve compression, straight leg raise