This article is divided into several pages for easier reading:

2.0     What is Piriformis Syndrome?

There are many contrasting definitions of piriformis syndrome as highlighted below:

“The term, pyriformis syndrome, is applied to that type of sciatica which is due to an abnormal condition of the pyriformis muscle, and which is usually traumatic in origin.” (Robinson, 1947, p.355).

“…the compression of the sciatic nerve within the infrapiriform foramen.” (Kouvalchouk, Bonnet, de Mondenardho, 1996, p.647).

“PS may be defined as a neuromuscular disorder that is presumed to occur when the sciatic nerve is compressed or involved at the level of the piriformis muscle.” (Miller, White & Ross, 2012, p.577).

“Piriformis syndrome is a rare entrapment neuropathy, and there is usually some confusion about its diagnosis.” (Zeren, 2015, p.987).

“…the compression or the irritation of the sciatic nerve by the adjacent piriformis muscle in the buttock leading to symptoms that include buttock pain, leg pain, and altered neurology in the sciatic nerve distribution.” (Knudsen, Mei-Dan & Brick, 2016).

“Piriformis Muscle Syndrome (PMS) is a neuromuscular disorder caused by the sciatic nerve becoming compressed in the infrapiriformis (sub-pyramidal) canal and occasioning sciatic-type pain, tingling, and numbness in the buttocks along the sciatic nerve pathway down to the lower thigh and into the leg.” (Michel et al., 2013, p.372).

The common theme among definitions is the entrapment or compression of the sciatic nerve.

2.1     Types of Piriformis Syndrome

There are “two types of piriformis syndrome” (Boyajian-O’Neill et al., 2008, p.658; Miller, White & Ross, 2012):

  1. Primary piriformis syndrome has an anatomic cause, such as a split piriformis muscle, split sciatic nerve, or an anomalous sciatic nerve path.
  2. Secondary piriformis syndrome occurs as a result of a precipitating cause, including macro-trauma, micro-trauma, ischemic mass effect, and local ischemia.

Among patients with piriformis syndrome, fewer than 15% of cases have primary causes (Boyajian-O’Neill et al., 2008).

In the fourth edition of his book, ‘Focal Peripheral Neuropathies’, John Stewart (2010) describes four distinct clinical subtypes of piriformis syndrome:

  1. Proximal sciatic neuropathies;
  2. Neurogenic piriformis syndrome;
  3. Posttraumatic piriformis syndrome; and
  4. Non-specific piriformis syndrome.

Stewart also suggested five components of diagnostic criteria:

  1. Signs and symptoms;
  2. Electro-diagnostic findings;
  3. Imaging;
  4. Findings at surgery; and
  5. Response to surgical decompression.

Miller and colleagues (2012, p.577) state that “To date, no clinical studies have confirmed the usefulness of this classification and in particular, whether patients diagnosed by these criteria respond in a predictable way to treatment.”

2.2     Other Terms for Piriformis Syndrome

Piriformis syndrome is known by a variety of terms, as highlighted below:

  • “Pyriformis syndrome” (Robinson, 1947, p.355);
  • Piriformis syndrome (PS or PiM (Gulledge, 2014));
  • Piriformis muscle syndrome (PMS);
  • Deep gluteal syndrome (Jankovic, Peng & van Zundert, 2013; Martin et al., 2015);
  • Pelvic outlet syndrome (Hopayian, 1999); and
  • Infrapiriform Foramen Syndrome (Reichel & Gaerisch, 1988). As it is analogous to other entrapment neuropathies, such as carpal tunnel syndrome.
  • Wallet sciatica or fat wallet syndrome (named due to direct pressure from sitting with a wallet in the back pocket).

According to Martin et al. (2015, p.99) “…the term ‘deep gluteal syndrome’ instead of ‘piriformis syndrome’ is now preferred to describe the presence of pain in the buttock…”

For the purposes of this article the term piriformis syndrome is used throughout to avoid confusion.

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