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  • Dr. Brian Abelson DC

Sciatica Unraveled: Non-Disc Causes & Diagnosis (Part 2)

In Part 1, we explored the role of disc herniation in causing sciatica, specifically focusing on disc protrusions, extrusions, and sequestrations. We also examined how conservative therapy is often the first line of treatment for most disc herniations, as long as no red flags are present.

In this continuation of the sciatica series, we will delve into three key topics related to sciatic nerve entrapment:

  • Non-discogenic causes of sciatica - sciatic nerve tethering.

  • Direct compression of the sciatic nerve.

  • Diagnosis of sciatica.



There are numerous types of non-discogenic syndromes that cause sciatic-like pain. Some of these are caused by restrictions in sciatic nerve motion (which can then lead to nerve entrapment) while other types involve direct sciatic nerve compression.

An example of non-discogenic sciatic nerve pain, which involves reduced sciatic nerve mobility, is "Deep Gluteal Syndrome" (DGS).

Deep Gluteal Syndrome (DGS) is a condition characterized by the compression or irritation of nerves and blood vessels in the deep gluteal (buttock) region, leading to a variety of symptoms such as pain, numbness, tingling, and weakness in the buttocks and legs.

Various factors can cause DGS, including:

  • Piriformis syndrome: Tightness or inflammation of the piriformis muscle, which extends from the lower spine to the hip joint, compresses nearby nerves and blood vessels.

  • Sciatic nerve compression: The sciatic nerve, running from the lower back through the buttocks and legs, may be compressed or irritated by adjacent muscles, bones, or tissues.

  • Vascular compression: Compression of blood vessels in the deep gluteal region can lead to decreased blood flow and oxygenation in the affected tissues.

  • Trauma or injury: Damage to the deep gluteal region tissues resulting from a fall, car accident, or other traumatic events can cause DGS symptoms.

DGS presents as deep pain or abnormal sensations in the hip, buttocks, and posterior thigh. This pain often stems from fibrous collagen bands that restrict nerve movement or gliding at various locations along the sciatic nerve.

Under normal conditions, the sciatic nerve stretches and glides through its surrounding tissue in sync with knee and hip joint movements (1). This process allows the sciatic nerve to accommodate compressive forces generated during regular motion.

In DGS, fibrous bands hinder sciatic nerve mobility, resulting in sciatic neuropathy (ischemic neuropathy). These fibrous bands are typically located lateral or medial to the sciatic nerve (2).



Image: In this image, you can see the sciatic nerve in a cross section (left image), as well as a sagittal section(right image). Amazingly, at it widest point, the sciatic nerve is as wide as your thumb!

Research has identified three types of fibrous bands often involved in the entrapment of the sciatic nerve (3):

  1. Purely fibrous bands.

  2. Fibrovascular bands.

  3. Pure vascular bands.

Evidence regarding the effects of these fibrous bands comes from studies employing endoscopy. Endoscopy involves examining the interior of the body using a lighted, flexible instrument called an endoscope. Researchers have frequently observed fibrous bands in patients experiencing sciatic nerve entrapment (4).

The entrapment of the sciatic nerve, due to the presence of fibrous bands, can occur at various locations, including:

Sciatic nerve entrapment can occur at various anatomical locations due to the presence of fibrous bands, including:

  1. The greater sciatic notch and ischial tuberosity (5).

  2. The ischial tunnel region at the quadratus femoris muscle (5).

  3. The proximal insertion of the hamstrings and, more distally, at locations along the hamstrings, which may correspond to previous injury sites (7).

  4. The piriformis muscle and the obturator internus-gemelli complex (6).

DGS Symptoms

Symptoms of Deep Gluteal Syndrome (DGS), whether or not fibrous bands are involved, can differ based on the root cause. Possible symptoms may include:

  • Intense pain in the buttocks

  • Sensations of numbness or tingling in the buttocks or legs

  • Leg weakness

  • Limited range of motion in the hip joint

  • Pain that intensifies when sitting or engaging in specific activities

  • Discomfort or pain in the groin area



Examples of direct compression of the sciatic nerve include Piriformis Muscle Entrapment, Gemelli-Obturator Internus Muscle Entrapment, Quadratus Femoris Muscle-Ischiofemoral Entrapment, and Hamstring Muscle Related Entrapments. These conditions can occur either in conjunction with, or independently of, sciatic nerve entrapment caused by fibrous bands.

Piriformis Syndrome (PS)

Piriformis Syndrome, characterized by low back and buttock pain, is often used interchangeably with Deep Gluteal Syndrome (DGS). However, entrapment of the sciatic nerve caused by Piriformis Syndrome is not always associated with the presence of fibrous bands related to DGS (8).

Several biomechanical and genetic factors may contribute to Piriformis Syndrome. For instance, women are six times more likely to be diagnosed with this condition than men, which has been attributed to a wider quadriceps-femoris muscle angle in the os coxae in women (9).

Variations in the anatomy of the piriformis muscle can result in the sciatic nerve passing under, over, or even through the middle of the muscle. Although it is speculated that these anatomical differences might make some patients more susceptible to Piriformis Syndrome, current research does not support this hypothesis.

Studies have indicated that an anatomical (direct compression) cause of Piriformis Syndrome accounts for only about 15% of cases (10). Most cases are due to environmental factors, such as micro-trauma, direct trauma, post-surgical complications, and biomechanical compensation (11, 12).

Interestingly, the sciatic sheath, which surrounds the sciatic nerve, is a continuation of the piriformis fascia. It has been hypothesized that increased tension in the piriformis fascia could produce symptoms resembling sciatic nerve compression (17).

Please Note: It is important to consider that Piriformis Syndrome is often an overused diagnosis. If an individual experiences back and hip pain that extends to the foot, disc involvement should be considered first, rather than the piriformis muscle.


Gemelli-Obturator Internus Entrapment

The gemelli and obturator internus muscles are part of the lateral rotator group of the hip. This group consists of six small muscles responsible for laterally rotating the femur within the hip joint.

In this entrapment syndrome, the sciatic nerve is compressed between the piriformis muscle and the superior gemelli/obturator internus (13).

Both the obturator internus and the gemelli are enveloped by the obturator fascia, which is a continuation of the iliac fascia (17).

As we discuss fascial connections, it is essential to emphasize a crucial point: the anatomist's scalpel is what separates these six lateral rotator muscles. In reality, these muscles work together as a functional unit, and their fascial connections play a critical role in their integrated function.

As a student in the dissection lab, I quickly realized that all of the deep lateral hip rotator muscles were closely connected by fascia.

The notion that you can treat any of these muscles individually or that they operate independently is simply preposterous!

All lateral rotators (the "magnificent six" - deep six rotators) can influence one another's function through their fascial connections.

My candid opinion: Anyone asserting otherwise should head back to the dissection lab for a refresher!

Photo Stecco, Carla; Stecco, Carla. Functional Atlas of the Human Fascial System E-Book (Page 313). Elsevier Health Sciences.


Quadratus Femoris - Ischiofemoral Entrapment

Quadratus femoris-ischiofemoral entrapment is a condition in which the quadratus femoris muscle, extending from the ischial tuberosity (sit bones) to the upper part of the femur (thigh bone), compresses or irritates the nearby sciatic nerve.

This impingement syndrome results from a narrowing of the space between the femur and the ischial tuberosity (14). With this syndrome, sitting can be challenging, as can walking with an elongated stride (15).

The exact etiology of quadratus femoris-ischiofemoral entrapment remains unclear, but it is believed to be associated with abnormal hip joint mechanics, muscle imbalances, or alterations in the morphology of the femur or pelvis. Symptoms of quadratus femoris-ischiofemoral entrapment may include:

  • Pain in the hip, groin, or thigh

  • Numbness or tingling in the hip or thigh

  • Weakness in the hip or thigh

  • Decreased range of motion in the hip joint

  • Pain that intensifies with sitting or specific activities


Hamstring Related Entrapment's

Hamstring injuries can significantly impact sciatic nerve function. During the acute stage of a hamstring injury, swelling (edema) in the area can lead to sciatic nerve irritation.

In cases of chronic hamstring dysfunction, inflammation may be the underlying cause of entrapment.

Chronic inflammatory states can result in scar tissue formation (between muscles, tendons, and fascia - fibrosis), which, in turn, can lead to sciatic nerve entrapment during hip motion (16).

Hamstring-related sciatic nerve entrapment can be caused by various factors, including:

  • Overuse or repetitive strain: Activities involving repeated or prolonged use of the hamstring muscles, such as running, cycling, or jumping, can cause muscle tightness and inflammation.

  • Trauma or injury: A fall, car accident, or other traumatic event can damage the hamstring muscles and lead to symptoms of hamstring-related sciatic nerve entrapment.

  • Anatomical abnormalities: Some individuals may have a naturally narrow or constricted sciatic nerve tunnel or variations in the nerve's course, increasing the risk of compression.

Symptoms of hamstring-related sciatic nerve entrapment may include:

  • Deep buttock pain

  • Numbness or tingling in the buttocks or legs

  • Weakness in the legs

  • Pain that worsens with sitting or specific activities

  • Reduced range of motion in the hip joint

  • Groin pain or discomfort

Please Note: Sciatic nerve tethering or direct compression of the sciatic nerve may still involve the intervertebral disc. Additionally, it is crucial to note that anatomical compression (such as Piriformis Syndrome) accounts for only about 15% of cases (10).



All patients exhibiting sciatica-like symptoms should undergo a comprehensive assessment, including history, observation, and standard orthopedic and neurological testing.

A primary objective of this examination process is to ensure that we are dealing with a mechanical case of sciatica and not an underlying pathological condition.


Orthopedic assessment of the lumbar region is an important aspect of diagnosing and treating musculoskeletal conditions that affect the lower back. The lumbar region is particularly susceptible to injury due to its location and the amount of weight and pressure it bears. The assessment involves a thorough evaluation of the spine, muscles, and nerves in the lower back, and helps to identify any underlying problems that may be contributing to pain, stiffness, or limited range of motion.

The assessment typically begins with inspection and observation, followed by a range of motion test to assess flexibility and mobility of the spine. Palpation is used to identify any areas of tenderness or swelling, and special tests such as the Straight Leg Test, Bragard Test, Neural Tension tests, and Well Leg Raise Test are used to assess nerve function and rule out specific conditions such as disc herniation or radiculopathy. Other tests such as the FABER Test, Thomas Test, and Trendelenburg Test assess hip and leg function, while the Homans Test helps to rule out deep vein thrombosis. A thorough orthopedic assessment of the lumbar region can help to accurately diagnose and effectively treat a wide range of musculoskeletal conditions that affect the lower back.

Orthopedic Assessment Video

Low Back Examination

To observe a demonstration of the standard orthopedic tests conducted during a clinical examination of the low back, click on the video located to the right. The video showcases various tests that are commonly used to diagnose musculoskeletal conditions that affect the lower back.



Performing a thorough neurological examination is crucial in diagnosing musculoskeletal conditions. This examination should include evaluating various components, such as dermatomal patterns, deep tendon reflexes, myotomes, plain radiographs, and the Babinski sign.

Dermatomal patterns are useful in identifying changes in sensation. However, it is important to note that dermatomal charts may not precisely pinpoint the level of nerve root lesion due to individual variability and overlapping between dermatomes. Moreover, there is no consensus among dermatome charts.

Deep tendon reflexes provide information about the integrity of both the peripheral and central nervous systems. Decreased tendon reflexes typically indicate peripheral nervous system problems, while increased reflexes indicate central nervous system problems. The reflex grading system ranges from 0 (absent) to 4 (clonus), and is tested at the patellar (L3-L4), medial hamstring (L5-S1), lateral hamstring (S1-S2), posterior tibial (L4-L5), and Achilles (S1-S2) reflex points.

Myotomes are groups of muscles innervated by the motor fibres of a single nerve root, and are evaluated to determine the degree of motor function. Plain radiographs are recommended for patients who are 50 years or older, and those with pain, a history of serious trauma, cancer, fractures, metabolic bone disease, infections, or inflammatory arthropathies. Motor grading is evaluated on a scale of 0 (no visible or palpable contraction) to 5 (full range of motion against gravity and full resistance), and is assessed at the knee extension (L3), ankle dorsiflexion (L4), great toe extension (L5), ankle plantar flexion, ankle eversion, hip extension (S1), and knee flexion (S2) points.

Finally, the Babinski sign is indicative of an upper motor neuron lesion (UMNL). Overall, a thorough neurological examination can provide valuable insights into the diagnosis and treatment of musculoskeletal conditions.

Lower Limb Neuro Examination video

The Lower Limb Neurological Examination is an essential component of the overall neurological examination process, and is performed to evaluate the sensory and motor neurons that supply the lower limbs. This examination aids in identifying any dysfunction in the nervous system, and serves as a valuable screening and investigative tool.

Peripheral Vascular Examination - Video

Conducting a peripheral vascular examination is a vital means of identifying any signs of vascular-related pathology, and can help prevent cardiovascular and cerebrovascular complications. This examination is a valuable tool for ruling out any possible issues. The video presented here demonstrates some of the most commonly used procedures in daily clinical practice.


Orthopaedic Physical Assessment – David J. Magee

Dutton's Orthopaedic: Examination, Evaluation and Intervention, Fifth Edition



Imaging plays a crucial role in the diagnosis of sciatica and identifying the underlying cause of nerve root compression. Several imaging modalities are utilized to evaluate patients with sciatica, including X-ray, magnetic resonance imaging (MRI), ultrasound, and other imaging procedures.


X-ray imaging is often used to rule out other possible conditions, such as a fracture or tumor. However, X-rays have limited utility in diagnosing sciatica because they cannot visualize the soft tissues or nerves.


MRI is considered the gold standard for evaluating patients with sciatica, providing detailed images of the spinal cord, nerve roots, and surrounding soft tissues. It is highly sensitive and can identify herniated discs, spinal stenosis, and other abnormalities that may be compressing the nerve roots.


Ultrasound imaging can be used to visualize the sciatic nerve and its surrounding structures, providing real-time images of nerve compression and potential entrapment sites. It is often used for diagnosing piriformis syndrome and other causes of sciatica.

Other imaging procedures that may be used to diagnose sciatica include computed tomography (CT) scans and myelography. CT scans provide detailed images of the bones and soft tissues, while myelography uses contrast dye to highlight the spinal cord and nerve roots, making them more visible on X-ray or CT images.



In conclusion, there are various non-discogenic syndromes that can cause sciatic-type pain. Some of these syndromes involve restricting sciatic nerve motion or direct compression of the sciatic nerve, while others involve fibrous bands that can decrease sciatic nerve mobility and cause sciatic neuropathy. Direct compression only accounts for about 15% of cases, while other syndromes are more prevalent.

It is essential to perform a complete physical examination that includes a comprehensive history to accurately diagnose sciatica. When a patient presents with back and leg pain, and the leg pain is worse than the back pain, it is crucial to consider disc-related issues until proven otherwise. If a patient's leg pain becomes low back pain, disc-related issues are likely the cause. The diagnostic process is ongoing, and a working diagnosis may change over time. Therefore, examining, re-examining, and re-examining again is crucial.

In the next part of this series, "Sciatica - Treatment - Logic & Recommendations," we will discuss conservative treatment options for sciatica, including spinal manipulation/mobilization and myofascial release procedures.

Sciatica Part 1 – What Are You Dealing With

Sciatica Part 2 – Causes & Diagnosis

Sciatica Part 3 – Treatment - Logic & Recommendations

Sciatica Part 4 – Exercise & Activities of Daily Living



Dr. Abelson is committed to running an evidence-based practice (EBP) that incorporates the most up-to-date research evidence available. He combines his clinical expertise with the specific values and needs of each patient to deliver personalized care that is both effective and patient-centered.

As the developer of Motion Specific Release (MSR) Treatment Systems, Dr. Abelson operates a clinical practice in Calgary, Alberta, under the name Kinetic Health. He has authored ten publications to date and continues to offer online courses, in addition to his live programs, to healthcare professionals seeking to expand their knowledge and skills in treating patients with musculoskeletal conditions. By staying current with the latest research and offering innovative treatment options, Dr. Abelson is dedicated to helping his patients achieve optimal health and wellness.


References Part 2:

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  2. Martin HD, Kivlan BR, Palmer IJ, Martin RL. Diagnostic accuracy of clinical tests for sciatic nerve entrapment in the gluteal region. Knee Surg Sports Traumatol Arthrosc. 2014;22(4):882–8.

  3. Hernando MF, Cerezal L, Pérez-Carro L, Abascal F, Canga A. Deep gluteal syndrome: anatomy, imaging, and management of sciatic nerve entrapments in the subgluteal space. Skeletal Radiol. 2015;44(7):919–34.

  4. Martin HD, Shears SA, Johnson JC, Smathers AM, Palmer IJ. The endoscopic treatment of sciatic nerve entrapment/deep gluteal syndrome. Arthroscopy. 2011;27(2):172–81. [PubMed]

  5. 12. Spinner RJ, Tiel RL. Sciatic nerve compression and piriformis syndrome. In: Midha R, Zager EL, editors. Surgery of Peripheral Nerves : A Case-Based Approach. New York: Thieme; 2008. pp. 186–191.

  6. Adams JA. The pyriformis syndrome -- report of four cases and review of the literature. S Afr J Surg. 1980;18:13–18.

  7. Lohrer H, Nauck T, Konerding MA. Nerve entrapment after hamstring injury. Clin J Sport Med. 2012 Sep;22(5):443-5.

  8. Luis Perez Carro, Moises Fernandez Hernando, Luis Cerezal, Ivan Saenz Navarro, Ana Alfonso Fernandez, and Alexander Ortiz Castillo1 Deep gluteal space problems: piriformis syndrome, ischiofemoral impingement and sciatic nerve release Muscles Ligaments Tendons J. 2016 Jul-Sep; 6(3): 384–396.

  9. Klein MJ. Piriformis syndrome. eMedicine Specialities: Physical Medicine and Rehabilitation: Lower limb Musculoskeletal conditions 2010 fckLR

  10. Lori A, Boyajian-O’ Neill, et al. Diagnosis and management of piriformis syndrome:an osteopathic approach. J Am Osteopath Assoc Nov 2008;108(11):657-664

  11. Tonley JC, Yun SM, et al. Treatment of an individual with piriformis syndrome focusing on hip muscle strengthening and movement reeducation: a case report. J Orthop Sports Phys Ther 2010;40(2):103-111.

  12. Lori A, Boyajian-O’ Neill, et al. Diagnosis and management of piriformis syndrome:an osteopathic approach. J Am Osteopath Assoc Nov 2008;108(11):657-664.

  13. Filler AG, Gilmer-Hill H. Piriformis syndrome, obturator internus syndrome, pudendal nerve entrapment, and other pelvic entrapments. In: Winn HR, editor. Youmans neurological surgery. 6th ed. Philadelphia: Saunders; 2009. pp. 2447–55.

  14. Taneja AK, Bredella MA, Torriani M. Ischiofemoral impingement. Magn Reson Imaging Clin N Am. 2013;21(1):65–73.

  15. Torriani M, Souto SC, Thomas BJ, Ouellette H, Bredella MA. Ischiofemoral impingement syndrome: an entity with hip pain and abnormalities of the quadratus femoris muscle. AJR Am J Roentgenol. 2009;193(1):186–90.

  16. Bucknor MD, Steinbach LS, Saloner D, Chin CT. Magnetic resonance neurography evaluation of chronic extraspinal sciatica after remote proximal hamstring injury: a preliminary retrospective analy-sis. J Neurosurg. 2014;121(2):408–14. [PubMed]

  17. Stecco, Carla; Stecco, Carla. Functional Atlas of the Human Fascial System. Elsevier Health Sciences.

  18. Dr. Shawn Thistle - RRS Education - Chiropractic Care for Disc Patients April 28th 2019

#Sciatica #NonDiscogenicSciatic #PiriformisSyndrome #ObturatorInternusEntrapment #Quadratusfemoris

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