• Dr. Brian Abelson DC

Sciatica Part 2 – Causes & Diagnosis

Updated: Nov 2

In Part 1, we discussed how Sciatica can be caused by disc herniation. Specifically due to disc protrusions, disc extrusions, and disc sequestration. We also reviewed how most disc herniations can first be treated with conservative therapy (as long as no red flags are present).

Moving forward in this blog we will be covering three key topics that involve entrapment of the of sciatic nerve:

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

  • Direct compression of the sciatic nerve.

  • Diagnosis of Sciatica.

In Part 2 of the Sciatica series, I will answer one of the most common questions I get from patients.

"How do you know that nerves can become tethered by layers of tissue (collagen)? And what evidence do you have to support this theory?"

These are great questions - not only will I answer them, but I will also provide research references to support these perspectives.



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 that involves decreased sciatic nerve mobility is “Deep Gluteal Syndrome” (DGS).

DGS is characterized by deep pain or abnormal sensations in the hip, buttocks, and posterior thigh. The pain experienced in DGS occurs due to fibrous bands of collagen that restrict nerve movement or gliding at various locations along the sciatic nerve.

Normally the sciatic nerve stretches and glides through its surrounding tissue in conjunction with knee and hip joint movement (1). This is how the sciatic nerve accommodates for compressive forces that are created during normal motion.

With DGS, fibrous bands decrease sciatic nerve mobility, causing sciatic neuropathy (ischemic neuropathy). These fibrous bands are usually found 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 demonstrated that there are three types of fibrous bands that are often involved in entrapment of the sciatic nerve (3).

  • Purely fibrous bands.

  • Fibrovascular bands.

  • Pure vascular bands.

Evidence about the effects of these fibrous bands comes from research using endoscopy. (Endoscopy refers to performing an examination of the inside of the body by using a lighted, flexible instrument known as an endoscope.) Using endoscopy, researchers have commonly found fibrous bands in patients suffering from sciatic nerve entrapment (4).

Entrapment of the sciatic nerve, due to the presence of fibrous bands, can occur in multiple locations, including:



Examples of direct compression of the sciatic nerve would be Piriformis Muscle Entrapment, Gemelli-Obturator Internus Muscle Entrapment, Quadratus Femoris Muscle- Ischiofemoral Entrapment, and Hamstring Muscle Related Entrapments. Each of these conditions can occur in combination with, or without, entrapment of the sciatic nerve by fibrous bands.

Piriformis Syndrome (PS)

Piriformis Syndrome causes low back, and buttock pain. Piriformis Syndrome (PS) and Deep Gluteal Syndrome (DGS) are often used as synonyms. But in reality, entrapment of the sciatic nerve caused by PS is not always related to the presence of fibrous bands that causes DGS (8).

There are several bio-mechanical and genetic factors that could lead to PS. For example, women are 6x more likely to be diagnosed with Piriformis Syndrome than men. Research has shown that this is due to the fact that women have a wider quadriceps-femoris muscle angle in the os coxae (9).

By considering variances in the anatomy of the piriformis muscle, we will see that in some cases, the sciatic nerve passes under, over, and even through the middle of the piriformis muscle. Though it has been postulated that these anatomical differences could make some patients more susceptible to PS, research does not currently confirm this hypothesis.

Research has shown that an anatomical (direct compression) cause of Piriformis Syndrome only accounts for about 15% of cases (10). Research also shows that most cases are due to environmental factors such as micro trauma, direct trauma, post-surgical complications, and bio-mechanical compensation (11, 12).

What is interesting to note is that the sciatic sheath (that surrounds the sciatic nerve) is a continuation of the piriformis fascia. It has been hypothesized that increased tension in piriformis fascia could cause symptoms that replicate sciatic nerve compression. (17)

Note: In my opinion, Piriformis Syndrome is often an overused diagnosis. If you have back and hip pain, and the pain goes right down to the foot, you should first think of disc involvement, not the piriformis muscle.


Gemelli-Obturator Internus Entrapment

The gemelli and obturator internus muscles form part of the lateral rotator group of the hip. This group is composed of six small muscles which laterally rotate the femur within the hip joint.

With this entrapment syndrome, the sciatic nerve is compressed between the piriformis muscle and superior gemelli/obturator internus (13). The obturator internus and the gemelli are both surrounded by the obturator fascia, which is a continuation of the iliac fascia (17).

While we are on the topic of fascial connections, there is an important point that I believe should be emphasized. It is the anatomist scalpel that separates these six lateral rotator muscles.

As a student in the dissection lab, it was obvious to me that all of the deep lateral hip rotator muscles are strongly connected (by fascia).

The idea that you can treat any one of these muscles separately or that they somehow function independently is just NOT TRUE!

All lateral rotators (mobile wad of six - deep six rotators) can affect each other’s function through their fascial connections.

My Opinion: Anyone who tells you differently must return to the dissection lab!

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


Quadratus Femoris - Ischiofemoral Entrapment

This impingement syndrome is caused by a narrowing of the space between the femur and the ischial tuberosity (14). With this syndrome, sitting will often be difficult, as will walking with a lengthening stride (15).

This entrapment syndrome can be due to an acute injury or be caused by a chronic condition that develops over a long time.

In the case of a chronic condition, fibrotic tissue in this area can entrap the sciatic nerve.


Hamstring Related Entrapment's

Hamstring injuries can greatly affect sciatic nerve function. During the acute stage of a hamstring injury, the swelling (edema) in this area commonly results in sciatic nerve irritation.

In cases of chronic hamstring dysfunction, inflammation may be at the root of the entrapment.

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

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



All patients showing Sciatica-like symptoms should be run through a comprehensive assessment that includes history, observation, and standard orthopedic and neurological testing.

One of the major objectives of this examination process is to make sure that we are actually dealing with a mechanical case of Sciatica and not some underlying pathological condition. The following tests represent some of the standard procedures that we use in our clinical practice to evaluate sciatica cases.

Note: Probably the weakest area for most practitioners is their history taking!


Active and Passive Range of Motion

Flexion of Lumbar Spine: Normal 45 to 60 degrees. Flexion (including cervical flexion) places traction on the lumbosacral nerve roots and sciatic nerve.

Extension of Lumbar Spine: Normal 20 to 35 degrees.

Lateral Flexion of Lumbar Spine: Normal 15 to 20 degrees.

Rotation of Lumbar Spine: Normal 3 to 18 degrees. Note: internal rotation of the hip stretches the piriformis muscle which can increase sciatic nerve tension.


Special Tests (Click the name of the test to go to the appropriate test video)

Straight Leg Raise Test - SLR

With the patient supine, to be positive, SLR should produce ipsilateral leg pain between 10° and 60°. SLR that produces pain in the opposite leg carries a high probability of disk herniation.

  • SLR1 – IVD and nerve root.

  • SLR 2 – Sciatic and tibial nerve.

  • SLR 3 – Sural nerve.

  • SLR 4 – Common peroneal nerve.

Well Leg Raise Test Large IVD protrusion.

Bechterew's Test - Like a SLR but seated

Slump Test.

  • ST 1 – Spinal cord, nerve roots, single leg extension while sitting.

  • ST2 – Obturator nerve – sitting, hip abduction.

  • ST3 – Femoral nerve, side lying.

  • ST4 – Spinal cord, nerve roots, bilateral leg extension while sitting.

Braggard’s Test – Disc herniation, tumor, meningitis.

Nachlas Test – L2, L3 nerve roots (posterior), femoral nerve (anterior), tight quadriceps.

Brudzinski-Kernig Test – Meningeal irritation, nerve root involvement, dural irritation.

Valsalva Maneuver – Increased intrathecal pressure. The Dejerine triad (coughing, straining while holding the breath, and sneezing) increases intrathecal and intradiskal pressure.

Bowstring Test – Pressure or tension on the sciatic nerve.

Homan's Sign - Possible deep vein thrombosis

Note: A lumbar disc herniation can be painless and often evolves slowly. A disc herniation can also mimic SI joint dysfunction, hip problems, and mechanical low back pain (18). Never rely on just one orthopaedic test, doing a combination of tests will always give you better results.

Low Back Examination - Effective Orthopaedic Testing

This video covers some of the common causes of low back pain (including sciatica) and how to diagnose them using orthopaedic examination procedures. (Note: This video is available for the public on November 7/2022)


Orthopaedic Physical Assessment – David J. Magee https://amzn.to/3zgu0za

Dutton's Orthopaedic: Examination, Evaluation and Intervention, Fifth Edition https://amzn.to/3st1AOv



It is extremely important to perform a thorough neurological examination. This examination should include:

Dermatomal Patterns – Dermatome maps are clinically useful in determining a change in sensation. That being said, dermatomal charts may NOT show you an exact level of nerve root lesion. We must take into consideration that there is great deal of individual variability and overlap between dermatomes. Even the dermatome charts do not have consensus.

Deep Tendon Reflexes - Changes in deep tendon reflexes caused by disc herniation. Deep tendon reflexes provides information about the integrity of both the peripheral and central nervous systems. Typically, decreased tendon reflexes indicate that there is a problem with the peripheral nervous system, while increased reflexes indicate a problem with the central nervous system.

  • Patellar (L3-L4).

  • Medial hamstring (L5-S1).

  • Lateral hamstring (S1-S2).

  • Posterior tibial (L4-L5).

  • Achilles (S1-S2).

Reflex Grading (18):

0 - Absent

1 - Reduced

2 - Normal

3 - Exaggerated

4 - Clonus

Myotomes - A group of muscles innervated by the motor fibres of a single nerve root is known as a myotome.

  • Plain radiographs are indicated for patients 50 years and older. Also patients who are experiencing pain, have a history of serious trauma, or other conditions such as: cancer, fractures, metabolic bone disease, infections, or inflammatory arthropathies.

  • Knee extension (L3).

  • Ankle dorsiflexion (L4).

  • Great toe extension (L5).

  • Ankle plantar flexion, ankle eversion, hip extension (S1).

  • Knee flexion (S2).

Motor Grading (18):

0 - No visible or palpable contraction. (None)

1 - Visible or palpable contraction, no movement. (Trace)

2 - Full range of motion with gravity eliminated. (Poor)

3 - Full range of motion against gravity. (Fair)

4 - Full range of motion against gravity and moderate resistance. (Good)

5 - Full range of motion against gravity, full resistance. (Normal)

Babinski Sign – Upper motor neuron lesion (UMNL).

Lower Limb Neuro Examination

The lower limb neurological examination is part of the overall neurological examination process and is used to assess the motor and sensory neurons which supply the lower limbs. This assessment helps to detect any impairment of the nervous system. It is used both as a screening and an investigative tool. (Note: This video is available for the general public on November 11/2022)

Peripheral Vascular Examination - Key Points

A peripheral vascular examination is a valuable tool used for ruling out signs of vascular-related pathology. The detection and subsequent treatment of PVD can potentially mitigate cardiovascular and cerebrovascular complications. In this video we go over some of the common procedures we perform in daily clinical practice. This video is available for the public on November 14/2022.


Orthopaedic Physical Assessment – David J. Magee https://amzn.to/3zgu0za

Dutton's Orthopaedic: Examination, Evaluation and Intervention, Fifth Edition https://amzn.to/3st1AOv



Plain radiographs are indicated for patients 50 years and older. Also patients who are experiencing pain while resting, have a history of serious trauma, or other conditions such as: cancer, fractures, metabolic bone disease, infections, or inflammatory arthropathies.

Caution: Mechanical pain varies in intensity with position or activities. Continuous pain at rest should generate suspicion of infection or cancer. Just as in cases of progressive neurological deficits, continuous pain at rest requires the appropriate imaging.



There are numerous types of NON-discogenic syndromes that cause sciatic-type pain. Some of these involve restricting sciatic nerve motion which can lead to entrapment, others involve direct compression of the sciatic nerve. In certain types of Sciatica, fibrous bands can decrease sciatic nerve mobility and cause sciatic neuropathy.

Examples of direct compression of the sciatic nerve would be Piriformis Muscle Entrapment, Gemelli-Obturator Internus Muscle Entrapment, Quadratus Femoris Muscle- Ischiofemoral Entrapment, and Hamstring Muscle Related Entrapments. Each of these conditions can occur with or without entrapment of the sciatic nerve by fibrous bands. Direct compression only accounts for about 15% of cases.

Key Points (18):

  • Always do a complete physical examination that includes a comprehensive history.

  • When a patient presents with back and leg pain, and the leg pain is worse than the back pain think disc until proven otherwise. Disc issues should always be in your list of differentials.

  • If a patients leg pain becomes low back pain you are probably dealing with a disc issue.

  • Diagnosis is an ongoing process, we are always dealing with a working diagnosis that may change. Examine -> Re-Examine -> Re-Examine again!

In part three of “Sciatica – Treatment - Logic & Recommendations” we will discuss conservative treatment of Sciatica including the use of 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 believes in running an Evidence Based Practice (EBP). EBP's strive to adhere to the best research evidence available, while combining their clinical expertise with the specific values of each patient.

Dr. Abelson is the developer of Motion Specific Release (MSR) Treatment Systems. His clinical practice in is located in Calgary, Alberta (Kinetic Health). He has recently authored his 10th publication.


Make Your Appointment Today!

Make an appointment with our incredible team at Kinetic Health in NW Calgary, Alberta. Call Kinetic Health at 403-241-3772 to make an appointment today, or just click the MSR logo to right. We look forward to seeing you!


References Part 2:

  1. Lewis AM, Layzer R, Engstrom JW, Barbaro NM, Chin CT. Magnetic resonance neurography in extraspinal sciatica. Arch Neurol. 2006;63(10):1469–72.

  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 http://emedicine.medscape.com/article/308798-overview

  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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