ORIGINAL ARTICLE

Prevalence of Piriformis Syndrome in Chronic Low Back Pain Patients. A Clinical Diagnosis with Modified FAIR Test Chee Kean Chen, MD, MMed*; Abd J. Nizar, MD, MMed† *Department of Anesthesiology and Intensive Care, Sarawak General Hospital, Kuching, Sarawak; †Department of Anesthesiology and Intensive Care, University Science of Malaysia, Kubang Kerian, Kelantan, Malaysia

n

Abstract

Purpose: Piriformis syndrome is a collection of symptoms and signs of pain from piriformis muscle and is characterized by pain in buttock with variable involvement of sciatic nerve. This syndrome is often overlooked in clinical practice because its presentation has similarities with other spine pathologies. A major problem with the clinical diagnosis of piriformis syndrome is the lack of consistent objective findings and an absence of single test that is specific for piriformis syndrome. Therefore, a precise and reliable clinical method of diagnosing piriformis syndrome should be developed by clinicians. Methods: This is a prospective observational study involving 93 consecutive patients who attended the Pain Management Unit for chronic low back pain. The diagnosis of piriformis syndrome was made using the modified Flexion Adduction Internal Rotation (FAIR) test, which is a combination of Lase`-

Address correspondence and reprint requests to: Chee Kean Chen, MD, MMed, Department of Anaesthesiology and Intensive Care, Sarawak General Hospital, Jalan Hospital, 93586 Kuching, Sarawak, Malaysia. E-mail: [email protected]. Disclosure: This study was done with no financial support or sponsorship. There is no conflict of interest related to this study. Submitted: March 17, 2012; Revision accepted: May 23, 2012 DOI. 10.1111/j.1533-2500.2012.00585.x

 2012 The Authors Pain Practice  2012 World Institute of Pain, 1530-7085/12/$15.00 Pain Practice, Volume ••, Issue •, 2012 ••–••

gue sign and FAIR test. Prevalence of piriformis syndrome based on this technique was compared with the previous data using other techniques. Chi square (v2) analysis was performed to detect the relationship between piriformis syndrome and the potential risk factors. Results: On the basics of our diagnostic criteria, the prevalence of piriformis syndrome was 17.2% among low back pain patients. All the patients diagnosed with piriformis syndrome responded well with piriformis muscle injections. No significant associations were detected between piriformis syndrome and spine disorders. Conclusions: Piriformis syndrome is a painful condition that is often overlooked in the differential diagnosis of chronic buttock or low back pain. The modified FAIR test together with piriformis muscle injection is potentially a reliable method for the clinical diagnosis of piriformis syndrome. n Key Words: lower back pain, myofacial pain syndromes, sciatica

INTRODUCTION Piriformis syndrome is defined as collection of symptoms and signs of pain arises from piriformis muscle, with or without sciatic nerve entrapment.1 It has been documented as a contributory cause for sciatica,

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buttock, and low back pain.2,3 This syndrome presents as pain and localized tenderness around the gluteal region at the area of piriformis muscle and is usually described as a deep, aching type of pain with or without signs and symptoms of sciatica.4,5 Piriformis syndrome usually manifests as myofascial pain syndrome, where either pain originates from the muscle itself, as nerve entrapment syndrome, or both.6 This syndrome occurs most frequently among populations in their fourth and fifth decade of life and affects individuals regardless of type of occupations and level of activity. The reported prevalence of piriformis syndrome among chronic low back pain patients varies widely, between 5% and 36%.7–9 Piriformis syndrome is often underscored in the differential diagnosis of chronic hip, buttock, and low back pain as it is frequently unrecognized or is misdiagnosed in clinical settings.2,10 Controversies exist as to whether the current clinical diagnosis reflects the true figure on the prevalence of piriformis syndrome, as it is frequently confused with various low back pain disorders.4 Piriformis syndrome can have similar presentations as other somatic pain disorders, such as intervertebral disc pathology, lumbo-sacral radiculopathy (sciatica), sacro-iliac disorders, and trochanteric pathology.2,4,11 In extreme cases, misdiagnosis of piriformis syndrome-related back pain with ‘‘sciatica’’ as prolapsed intervetebral disc may lead to unnecessary surgery.10 Delay in the recognition and hence treatment for piriformis syndrome may progress to pathologic conditions of the sciatic nerve and chronic dysfunction of musculoskeletal system because of compensatory changes, resulting in pain, paresthesia, hyperesthesia, and muscle weakness.4,12 The main concern with the diagnosis of piriformis syndrome is the lack of consistent objective findings, which leads in many cases to unnecessary imaging studies and to time loss in searching for etiology of buttock or low back pain. Of the many diagnostic techniques, the Flexion Adduction Internal Rotation (FAIR) technique had shown high specificity and sensitivity when used in combination with functional electromyography examination.13,14 Tenderness at the gluteal region around the piriformis muscle (Lase`gue sign) has been noted to be the most consistent clinical finding in piriformis syndrome.2 We evaluated the prevalence of piriformis syndrome among patients with chronic buttock and low back pain using a combination of FAIR and Lase`gue sign (modified FAIR test), together with piriformis muscle injection.

METHODS After obtaining approval by the Ethics Committee of University Science Malaysia, 93 consecutive patients who attended the Pain Management Unit at Hospital University Science Malaysia, Kelantan, in 2010 for chronic buttock and low back pain (ie, lasting more than 6 months) were enrolled in this prospective observational study. All patients who presented with buttock and low back pain with or without sciatica regardless underlying pathology were included in the study. Low back pain is defined as back pain arising from the area between the subcostal margin and gluteal region. Sciatica is defined as symptoms of pain, numbness, electric current, or needle prick sensation in the distribution of sciatic nerve as a result of sciatic nerve irritation, for example, injury to or compression on the nerve. Demographic data of the patients, chronicity of back and buttock pain and primary diagnosis were collected and examined. Piriformis syndrome was diagnosed among chronic buttock and low back pain patients by using the modified FAIR test. The FAIR test was performed on the patient in supine position, with the affected hip flexed at 60 and the knee flexed at 90. With the hip being stabilized, a single examiner will internally rotate and adduct the hip by applying downward pressure onto the knee (Figure 1). Modified FAIR test was carried out by applying digital pressure over the piriformis

Figure 1. Flexion Adduction Internal Rotation test.

Diagnosis of Piriformis Syndrome with Modified FAIR • 3

Figure 3. Piriformis myogram. Figure 2. Modified Flexion Adduction Internal Rotation test.

muscle during the FAIR test maneuver (Figure 2). This technique is therefore a combination of FAIR test and Lase`gue sign. Modified FAIR test is considered positive if there is localized tenderness over the piriformis muscle during deep pressure application with reproduction of sciatic symptoms. Patients with positive modified FAIR test were then further confirmed with piriformis muscle injection. Piriformis muscle injection was done in an aseptic technique under real-time fluoroscopic guidance. The area of maximum tenderness was viewed under fluoroscopy to provide a guide to the point of needle insertion. After performing piriformis myogram with 0.5 mL of contrast, which showed a band of contrast across the location of piriformis muscle from sacrum to greater trochanter of femur (Figure 3), an injectate of 1.5 mL of lignocaine 2.0% and 0.5 mL triamcinolone acetonide 20 mg was injected. Reduction in visual analogue score (VAS) of > 50% after the injection was considered as fulfillment of diagnostic criteria for piriformis syndrome. The patients with positive modified FAIR test were then tabulated according to socio-demographic data, associated spine disease or medical disorders and the various variables of piriformis syndrome presentation. Data collected were then analyzed using the SPSS software version 16.0 (SPSS Inc., Chicago, IL, USA). Chi square (v2) analysis was performed to detect the association between the clinical diagnosis of piriformis and the potential risk factors.

Table 1. Demographic Characteristics of Respondent

Gender Male Female Age group (years) < 30 31 to 40 41 to 50 51 to 60 > 60 Body mass index Underweight (< 18.5) Normal (18.5 to 24.9) Overweight (25.0 to 29.9) Obese (> 30.0) Duration of back pain < 1 year 1 year 2 years 3 years > 3 years

Sample Population N = 93 n (%)

Patients with PS N = 16 n (%)

36 (38.7) 57 (61.3)

6 (37.5) 10 (62.5)

11 15 28 14 25

(11.8) (16.1) (30.1) (15.1) (24.9)

2 2 5 4 3

(12.5) (12.5) (31.2) (25.0) (18.8)

1 37 30 25

(1.1) (39.7) (32.3) (26.9)

0 6 5 5

(0.0) (37.4) (31.3) (31.3)

16 18 19 19 21

(17.2) (19.4) (20.4) (20.4) (22.6)

4 2 2 4 4

(25.0) (12.5) (12.5) (25.0) (25.0)

PS, piriformis syndrome.

RESULTS Ninety-three patients with chronic low back and buttock pain caused by various etiologies were enrolled into this study. Sixteen patients (17.2%) were diagnosed to have piriformis syndrome with modified FAIR test, and all 16 patients (100%) had > 50% reduction in VAS after piriformis injection. Majority of the patients (82.8%) with piriformis syndrome presented with sciatica. Women constituted 62.5% of the total number of

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Table 2. Characteristics of Piriformis Syndrome Among Chronic Low Back Pain Patients Character of Piriformis Syndrome

Frequency (n)

Type of respondent With piriformis syndrome Without piriformis syndrome Piriformis syndrome with sciatica Yes No Visual analogue score (0 to 100 mm) < 40 40 to 60 > 60 Oswestry Disability Index Mild (0 to 20) Moderate (21 to 40) Severe (41 to 60) Response to piriformis muscle injection Yes No

16 77

Table 3. Recognized Various Spine Pathologies and Associated with Secondary Piriformis Syndrome

Percentage

17.2 82.8

13 3

81.3 18.7

0 4 12

0 25.0 75.0

1 7 8

6.2 43.8 50.0

16 0

100.0 0

patients with piriformis syndrome. Age, gender, BMI, and duration of pain had no significant associations with the development of piriformis syndrome (Table 1). Baseline pain score (VAS) was found to be moderate (VAS 40 to 60 mm) in 25% of the piriformis syndrome patients, and the remaining 75% of them reported severe pain (VAS > 60 mm). Baseline Oswestry Disability Index (ODI) among patients with piriformis syndrome was found to be moderate in 43.8% of patients (ODI 20 to 40), and severe disability was recorded in 50% of them (ODI > 40) (Table 2). A large proportion of patients who presented with sacroiliac joint syndrome, facet joint arthropathy, spinal stenosis, and prolapsed intervertebral disc were diagnosed to have piriformis syndrome based on the modified FAIR test. However, all the spine conditions mentioned were found to have no statically significant association with the clinical diagnosis of piriformis syndrome (Table 3).

DISCUSSION Piriformis syndrome is a collection of symptoms and signs of pain from piriformis muscle and is characterized by pain in buttock with variable involvement of sciatic nerve. The reported prevalence of piriformis syndrome varies widely, between 6% and 36%, depending on the diagnostic criteria used and the characteristics of the sample population.1,7–9 In 1976, Pace and Nagle8 reported that 6% of 750 patients who were admitted through the hospital for ‘‘problem back service,’’ had piriformis syndrome, diagnosed using Freiberg test and Pace test. In a study of 93 patients with sciatica by Benson and Schutzer,9 15% were

Spine Diseases/Medical Disorders Lumbar facet joint syndrome Spinal stenosis Sacroiliac joint disorder Prolapsed intervertebral disc Failed back surgery syndrome

Sample Population N = 93 (%) 28 24 15 16 15

(30.1) (25.8) (16.1) (17.2) (16.1)

Subset Patient with PS* n = 16 (%)

P

6 (17.6) 6 (20.0) 6 (28.6) 5 (23.8) 1 (6.3)

0.932 0.622 0.117 0.362 0.202

PS, Piriformis syndrome. *The total number of subset patient with piriformis syndrome was more than 16 as some patients presented with more than one spine pathology.

diagnosed to have piriformis syndrome with FAIR test and palpation of the greater sciatic notch. By using painful rectal examination and in the absence of other findings, 6% of patients with sciatica were diagnosed to have piriformis syndrome by Hallin.4 To date, there are no set criteria for the clinical diagnosis of piriformis syndrome. This is because even until recently, there is no controlled trial assessing the reliability of clinical features and determining the efficacy of treatments for piriformis syndrome.1 The main problem with the clinical diagnosis of piriformis syndrome is lack of consistent objective findings. Over the years, various different maneuvers, as summarized in Table 4, were introduced to diagnose piriformis syndrome. However, no single test or sign is reliable and consistent in all cases.5,19 The major clinical findings in piriformis syndrome include tenderness over buttock area (Lase`gue sign), extending from the sacrum to the greater trochanter and piriformis tenderness on rectal or pelvic examination. Durrani & Winnie reported that the clinical diagnosis of piriformis syndrome can be enhanced by the reproduction of sciatica in 92% of the piriformis syndrome patients upon deep digital palpation on the gluteal region at onethird of the distance from the greater trochanter.2 This is because the etiology of piriformis syndrome can be partly due to myofascial pain syndrome of the piriformis muscle or secondary to various spine and pelvic diseases.6,15 A case series by Barton in 1991 showed that piriformis symptoms can be aggravated by prolonged flexion, adduction, and internal rotation (FAIR) of the hip in the absence of low back or hip findings.15 Fishman et al. demonstrated objective electromyography (EMG) findings in patients with piriformis syndrome. A delay in H reflex on EMG in the FAIR position in patients with piriformis syndrome was discovered by them, as to compare with asymptomatic controls. Thus, a delay in H reflex at 3 standard devia-

Diagnosis of Piriformis Syndrome with Modified FAIR • 5

Table 4. The Various Diagnostic Techniques in Clinical Diagnosis of Piriformis Syndrome Diagnostic Test/Sign Pace sign Flexion Adduction Internal Rotation test Beatty test Solheim’s sign Freiberg sign Lase`gue sign

Description Pain and weakness are experienced on resisted abduction and external rotation of the thigh.8 Pain is felt when the hip is flexed to an angle of 60 and the knee is flexed to an angle of 60 to 90, at the same time the hip is adducted and internally rotated.15 Pain and recreation of sciatic symptoms when the patient lies on the unaffected side, lifting and holding the superior knee approximately 4 inches off the examination table.23 Pain with adduction of the flexed thigh, which stretches the piriformis muscle against the sciatic nerve.24 Pain is experienced during passive internal rotation of the hip.25 Localized pain when pressure is applied over the piriformis muscle and its tendon, especially when the hip is flexed at an angle of 90 and the knee is extended.26

tions, FAIR test had sensitivity and specificity of 0.881 and 0.832, respectively.13 In this study, we evaluated the prevalence of piriformis syndrome via a combination of the two most reliable clinical diagnoses of piriformis syndrome: Lase`gue sign and FAIR test (modified FAIR test). Clinical tests for piriformis syndrome are aimed at assessing the tension of the sciatic nerve and the irritability of the piriformis muscle. The rationale of combining both tests was that an inflamed and irritable piriformis muscle would be more sensitive to external pressure in stretched condition. Thus, the combination of both tests was expected to increase the efficacy of diagnosis of piriformis syndrome. Patients who were diagnosed to have piriformis syndrome with modified FAIR test was subjected to piriformis muscle injection. All 16 patients had > 50% pain relief, and the sciatica experienced was disappeared after the piriformis muscle injection (11 patients had complete pain relief and the remaining 5 patients had > 50% reduction in VAS). When these patients were reexamined with modified FAIR test, all of them did not experience similar pain intensity as prior to injection (modified FAIR test was found to be negative in 10 patients while 6 others claimed that tenderness was still present but VAS was 50% lower compare to that prior to injection). All 16 patients with piriformis syndrome had a mean follow-up of 13 months, range from 9 to 17 months. Two patients required only single piriformis injection (during diagnostic block) for pain relief lasting for twelve months. Ten patients required 2 injections while the remaining 4 required 3 injections. All the subsequent piriformis injections were done under fluoroscopic guidance. The duration of pain relief after piriformis muscle injection varied among patients, depending on the primary pathology and the chronicity of pain. There was no complication related to piriformis injection noted in the course of this study. With the advancement of technology, contemporary electro-diagnostic, and imaging techniques has been intro-

duced into clinical practice and has shown to increase the efficacy in diagnosing piriformis syndrome.13–16 However, the selection criteria in these studies and the validity of these techniques have been vigorously disputed.17,18 In this study, the authors used piriformis muscle injection to confirm the diagnosis of piriformis syndrome as this technique served both diagnostic and therapeutic purposes, and it is also widely accepted.19,20 The prevalence of piriformis syndrome among chronic low back pain patients was 17.2% in this study using modified FAIR test. This figure was consistent with previous prevalence rates for piriformis syndrome. Comparing with the study with sample population of similar characteristics, the prevalence in this study was higher than those in a study by Cummings in 1991. In Cumming’s series of 123 patients who visited his clinic for lumbo-gluteal pain with or without radicular pain, 12 patients (10%) were diagnosed to have piriformis syndrome. However, the author did not specify which diagnostic test was used to make the diagnosis of piriformis syndrome. Dry needling technique or acupuncture was used to confirm the diagnosis, while piriformis muscle injection with local anesthetic was used in this study.1 The higher prevalence of piriformis syndrome from this study indirectly implies that piriformis syndrome has been under-diagnosed, and this delay in diagnosis and treatment for chronic back pain patients have led to unnecessary suffering.9 Although piriformis syndrome may only involves piriformis muscle itself, this entity frequently occurs as part of a cluster of soft tissue injuries, for example, facet joint, sacroiliac joint, or intervertebral disc, as a result of rotation or flexion of the torso and hip.2 In our pain unit, facet joint pain was diagnosed by medial branch of dorsal rami block; sacroiliac joint pain was diagnosed by diagnostic sacroiliac joint injection; spinal stenosis and prolapsed intervertebral disc are diagnosed by magnetic resonance imaging; failed back surgery syndrome was diagnosed clinically by history and phys-

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ical examination. This study failed to demonstrate any significant associations between the clinical diagnosis of piriformis syndrome and spine pathology. Previously, sacroiliac joint disorder has been considered a common component of piriformis syndrome.21 However, there is still controversy whether a relationship between piriformis and sacroiliac disorder exists.22 As this was a non-controlled study, sensitivity and specificity of modified FAIR test in diagnosis of piriformis syndrome are unable to be determined in this study. The findings of this study merit further investigation on the sensitivity and specificity of modified FAIR test. There were several limitations related to the study design. First, the confirmation of piriformis syndrome by piriformis injection may not be conclusive as there is some degree of pain relief when injecting local anesthetic into a tender area of muscle. We did not perform rectal or vaginal examinations, which may provide important information in making the diagnosis. The small sample size in this study could also be a limiting factor, as a bigger sample population may have shown significant association between piriformis syndrome and spine pathology. Piriformis syndrome should always be included in the differential diagnosis of chronic buttock or low back pain as it is not an uncommon disorder. Modified FAIR test together with piriformis muscle injection can be a reliable technique for clinical diagnosis of piriformis syndrome.

ACKNOWLEDGEMENTS The authors thank Dr. Esther Lim Hui Cheng for her helpful comments on the manuscript.

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