This article is divided into several pages for easier reading:
- Part 01: Introduction and Defining the Terms.
- Part 02: What is Piriformis Syndrome?
- Part 03: Anatomy of the Gluteal Region.
- Part 04: What can cause Piriformis Syndrome?
- Part 05: Who can be Affected by Piriformis Syndrome?
- Part 06: Prevalence and Risk Factors.
- Part 07: What are the Symptoms?
- Part 08: How is Piriformis Syndrome Diagnosed?
- Part 09: Differential Diagnosis for Piriformis Syndrome.
- Part 10: Treatment.
- Part 11: What is the Prognosis or Outlook?
- Part 12: References and Bibliography.
8.0 How is it Diagnosed?
“…diagnosis is often difficult since there is no gold standard test for this condition.” (Michel et al., 2013, p.372).
Piriformis syndrome should only be diagnosed by a medical professional (i.e. a physiotherapist or medical doctor) who will check for the condition by feeling the pelvic area. If suspected a doctor may refer for physiotherapy. There is currently no consensus on the diagnostic criteria or “gold standard” (Jankovic, Peng & van Zundert, 2013, p.1007), and there remains controversy regarding the proper diagnosis and most effective form of treatment for the condition (Knudsen, Mei-Dan & Brick, 2016; Han et al., 2017). Piriformis syndrome is thought to be an exclusively clinical diagnosis (Han et al., 2017). Its diagnosis is generally accepted only after other causes of pain arising in the buttocks or lower limbs have been eliminated – meaning it is a diagnosis of exclusion.
With this in mind, piriformis syndrome can be diagnosed through one or more of the following methods:
- Physical/clinical examination;
- Medical history;
- Diagnostic tests; and/or
- Anaesthetic injection.
Injection of local anesthetics, steroids, and botulinum toxin into the piriformis muscle can serve both diagnostic and therapeutic purposes (Jankovic, Peng & van Zundert, 2013), and is a widely used method of establishing the diagnosis after initial evaluation (Pace, 1975; Pace & Nagle, 1976; Durrani & Winnie, 1991).
“Necessarily, other pathological conditions of the lumbar, sacral and hip joint areas should be ruled out be examination and x-rays.” (Robinson, 1947, p.355).
8.1 Physical/Clinical Examination
A physical examination should include an examination of the hip and legs to see if movement causes increased low back pain or lower extremity pain (i.e. sciatic pain).
Typically, motion of the hip will recreate the pain. The examination should also be able to identify or rule out other possible causes of the sciatic pain, such as testing for local tenderness and muscle strength.
A number of signs have been described on physical examination:
- Piriformis Line: External palpation of the piriformis line can be used to elicit trigger-point tenderness through a relaxed gluteus maximus muscle. The patient is placed in the Sims position. The piriformis line overlies the superior border of the PM and extends from immediately above the greater trochanter to the cephalic border of the greater sciatic foramen at the sacrum. The line is divided into equal thirds. The fully rendered thumb presses on the point of maximum trigger-point tenderness, which is usually found just lateral to the junction of the middle and last thirds of the line. A positive test is reported to be observed in 59-92% of patients (Durrani & Winnie, 1991; Blaser-Sziede, 2006; Hopayian et al., 2010).
- The Sims position, named after the gynaecologist J. Marion Sims, is usually used for rectal examination, treatments, and enemas. It is performed by having a patient lie on their left side, left hip and lower extremity straight, and right hip and knee bent. It is also called lateral recumbent position.
- Piriformis Sign: This presents as tonic external rotation of the affected lower extremity and is reported to be observed in 38.5% of the patients (Durrani & Winnie, 1991). The medial end of the piriformis muscle should be palpated within the pelvis by rectal or vaginal examination (this test is positive in almost 100% of patients) (Thiele, 1937; TePoorten, 1969; Durrani & Winnie, 1991; Barton, 1991; Travell & Simons, 1992).
- Lasegue’s Sign: This involves pain on the affected side on voluntary adduction, flexion, and internal rotation (Fishman et al., 1998).
- Freiberg’s Sign: This involves pain on passive forced internal rotation of the hip in the supine position, thought to result from passive stretching of the piriformis muscle and pressue on the sciatic nerve at the sacrospinous ligament. This test is positive in 56.2% of the patients (32-63%) (Blaser-Sziede, 2006; Hopayian et al., 2010).
- Pace’s Sign: This consists of pain and weakness on resisted abduction and external rotation of the thigh in a sitting position. It is revealed with the FAIR Test (flexion, adduction, and internal rotation). A positive test is reported to occur in 46.5% of the patients (30-74%) (Blaser-Sziede, 2006; Hopayian et al., 2010).
- Beatty’s Manoeuvre (Beatty Test): This is an active test that involves elevation of the flexed leg on the painful side while the patient lies on the asymptomatic side. Abducting the thigh to raise the knee off the table elicits deep buttock pain in patients with piriformis syndrome but back and leg pain in those with lumbar disk disease (Beatty, 1994; Kirschner et al., 2009).
- Hughes Test: This involves external isometric rotation of the affected lower extremity following maximal internal rotation, may also be positive in piriformis syndrome.
- The seated piriformis stretch test is a passive flexion, adduction with internal rotation test performed as the examiner palpates the deep gluteal region (Martin et al., 2015).
- The active piriformis test is an active abduction and external rotation test while the examiner monitors the piriformis (Martin et al., 2015).
- The combination of the seated piriformis stretch test with the piriformis active test has shown a sensitivity of 91% and specificity of 80% for the endoscopic finding of sciatic nerve entrapment (Martin et al., 2014).
Gluteal atrophy may be present (Robinson, 1947; Pace, 1975; Durrani & Winnie, 1991; Rodrigue, 2001) as well as shortening of the limb on the affected side (TePoorten, 1969; Travell & Simons, 1992; Rodrigue, 2001). Sacroiliac tenderness is reported to be observed in 38.5% of patients (Durrani & Winnie, 1991).
The most consistent findings on physical examination are tenderness on palpation of the greater sciatic notch and pain with maximum flexion, adduction and internal rotation.
8.2 Medical History
A medical history should include an in-depth review of the patient’s symptoms, such as:
- What positions or activities make the symptoms better or worse?
- How long the symptoms have been present?
- If they started gradually or after an injury?
- What treatments have been tried?
It should also include a review of conditions that may be in the patient’s family, for example arthritis.
8.3 Diagnostic Tests and Imaging
X-rays and other spinal imaging studies cannot detect if the sciatic nerve is being irritated at the piriformis muscle. However, diagnostic tests (such as X-rays, magnetic resonance imaging (MRI) and nerve conduction tests) may be conducted to exclude other conditions that may cause symptoms similar to piriformis syndrome. It is important to note that:
- Plain (pelvic) radiographs only assist in the diagnosis of piriformis syndrome in exceptional circumstances (14; 42).
- Electromyograms (EMGs) may reveal abnormalities in the tibial and peroneal divisions of the sciatic nerve.
- Computed tomography (CT), MRI, scintigraphy and ultrasound can help differentiate piriformis syndrome from other possible causes of sciatica and can be used to directly determine the diagnosis of piriformis syndrome by revealing an enlarged piriformis muscle or anatomical variation of the nerves and muscles (Kipervas et al., 1976; Karl et al., 1985; Jankiewicz et al., 1991; Yue, 1998; Rossi et al., 2001; Stewart, 2003; Lee et al., 2004; Smith et al., 2006).
A medical professional may utilise electromyography (EMG) which measures the delay of sciatic nerve conductions as the piriformis muscle is stretched against it by “…comparing posterior tibial and peroneal H reflexes elicited in the anatomic position with H reflexes obtained in flexion, adduction, and internal rotation [normal mean (SD) prolongation: 0.01 (0.62) msec].” (Jankovic, Peng & Zundert, 2013, p.1007). An EMG may be combined with the FAIR test (sometimes known as an electrophysiological FAIR test). A prolongation of 1.86 msec in the FAIR-test is an electrophysiological criterion for diagnosing piriformis syndrome (Fishman & Zybert, 1992; Reichel, 2003).
Magnetic Resonance Neuropathy (MRN) is a technique that was developed specifically to enhance the imaging of nerves. MRN is used to identify and evaluate characteristics of nerve morphology such as:
- Internal fascicular pattern;
- Longitudinal variations in signal intensity and calibre; and
- Connections and relations to other nerves or plexuses.
In 2013, Michel and colleagues (2013) proposed a 12-point clinical scoring system for the diagnosis of piriformis syndrome using 250 intervention patients and 30 control patients. Using their scoring system, Michel and colleagues argued that with a score of 8 or higher, piriformis syndrome was considered probable. Their scoring system had a sensitivity of 96.4% and a specificity of 100% [LINK].
8.4 Anaesthetic Injection
An injection of anaesthetic with or without steroids may help to confirm if the piriformis muscle is the source of the symptoms.
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