The Diagnostic Accuracy of Gluteal Trigger Points to Differentiate Radicular From Nonradicular Low Back Pain.

The Clinical Journal of Pain Publish Ahead of Print DOI:10.1097/AJP.0000000000000311

The diagnostic accuracy of gluteal trigger points to differentiate radicular from nonradicular low back pain Farhad Adelmanesh, MD1, Ali Jalali, MD2, Armin Shirvani, MD3, Kambiz Pakmanesh, MD4, Marina Pourafkari, MD5, Gholam Reza Raissi, MD4, Yoram Shir, MD1 1

The Alan Edwards Pain Management Unit, McGill University Health Centre, Montreal,

Canada 2

Department of Anesthesiology, Tehran University of Medical Sciences, Tehran, Iran

3

Faculty for Medical Education, Shahid Beheshti University of Medical Sciences, Tehran,

Iran 4

Department of Physical Medicine and Rehabilitation, Iran University of Medical Sciences,

Tehran, Iran 5

Department of Radiology, Shahid Beheshti University of Medical Sciences, Tehran, Iran

*Corresponding author: Farhad Adelmanesh The Alan Edwards Pain Management Unit McGill University Health Centre Montreal General Hospital 1650 Cedar Ave., Room A5-140 Montreal QC, Canada Postal code: H3G1A4 Tel: (+1) 514-934-8558 Fax: (+1) 514-934-8096 Email: [email protected] Funding and conflict of interest disclosures: The Louise and Alan Edwards Foundation, Montreal, Canada, provided Dr. Adelmanesh with a clinical research grant. The authors declare no conflict of interest.

Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of the article is prohibited.

Abstract Objectives: Low back pain (LBP) is highly prevalent and costly to the society. Previous studies have shown an association between radicular LBP and trigger points in the superiorlateral quadrant of the gluteal area (GTrP). The objective of current study was to evaluate the diagnostic value of GTrP to predict nerve root involvement among patients with LBP. Methods: In a prospective, diagnostic accuracy study 325 consecutive patients with LBP were recruited. At first step, patients were evaluated for the presence or absence of the GTrP. A different investigator, blinded to the GTrP findings, then performed history-taking and physical examination. Subsequently all patients underwent a lumbar spine MRI and, when indicated, electrodiagnostic tests. Based on the clinical and ancillary tests findings, a multidisciplinary panel of experts (the ‘reference standard’), blinded to the GTrP evaluation, allocated patients to radicular vs. non-radicular LBP groups. The agreement between the GTrP findings, as a diagnostic test and the reference standard allocation was evaluated in a 2 by 2 contingency table. Results: The specificity of the GTrP test was 91.4% and its sensitivity was 74.1%. The area under the ROCcurve was 0.827 (0.781-0.874). Positive likelihood ratio was 8.62 and negative likelihood ratio was 0.28. Positive and negative predictive values were 91.9% and 72.7%, respectively. Discussions: As a clinical finding, trigger points in superior-lateral quadrant of gluteal area are highly specific indicators for radicular LBP. Incorporating these trigger points evaluation in routine physical examination of patients with LBP could decrease the need for more costly, time consuming and invasive diagnostic tests. Key Words: sensitivity; specificity; low back pain; trigger point; radiculopathy.


Introduction The one month prevalence of low back pain (LBP) is 37%1 and almost 80% of the general population will develop LBP at least once in their life-time.2 Chronic LBP is the main factor limiting regular activity in young adults under the age of 45 years.3 The cost of LBP has been steadily rising during the last decades, partially due to the social and legal acceptance of LBP as a cause for disability. The estimated direct cost of LBP at the United States alone is more than 100 billion dollars annually, whereas the indirect cost may be five to six times higher. 4 Nevertheless, LBP is a symptom rather than a disease, caused by multiple etiologies, alone or in combination.5 Differentiating the cause of LBP could be a significant challenge for practitioners trying to identify the anatomical and pathological sources of LBP. Diagnosis is the first essential step in planning patients’ management. Based on a joint clinical practice guideline published by the American College of Physicians and the American Pain Society, following a systemic history taking and physical examination clinicians should place patients with LBP in one of three broad categories: nonspecific or mechanical LBP, radicular LBP caused by nerve root irritation or other specific causes of LBP such as cancer.6 Differentiating radicular from non-radicular LBP is important since they differ in the extent and type of the clinical evaluation, management plan and the need for diagnostic tests (e.g., MRI and EMG).6 Patients with radicular LBP need more frequent clinical re-evaluation, may need different rehabilitation programs and specialists’ referral. 6 In addition, the clinician may select dissimilar pharmacological therapy and diagnostic or therapeutic interventions (e.g., radiofrequency denervation or surgery).6,7 For example, a patient with radicular LBP may benefit from trans-foraminal steroid injection whereas a patient with non-radicular LBP may be offered a spinal manipulative treatment or medial branch block for facet joint-induced pain. Furthermore, surgery has yielded better results in patients with radicular LBP compared to patients with axial LBP.7,8


Although the rate of interventional and surgical procedures for LBP has been rising steadily, their indication and effectiveness are still debatable.7 Not surprisingly, the utilization of more sophisticated techniques, in hope to better identify the etiology of LBP, contributes significantly to the rise in its cost. Radicular pain, caused by nerve root irritation, is one of the most commonly identified LBP etiologies. Magnetic resonance imaging (MRI) is currently the most advocated ancillary test in trying to differentiate radicular from non-radicular LBP. However, this test has high false positive and negative results.9,10 Other commonly used diagnostic tests, such as diagnostic injections, are also poorly correlated with clinical findings.7 Clinical evaluation is an essential first step in disease diagnosis. Ideally, the pursuing workup should agree with clinical findings in order to validate the diagnosis. The accuracy of a diagnostic test, used to classify a patient as having disease or being disease-free, is valuable when making treatment decisions. Accordingly, diagnostic accuracy studies evaluate the agreement between the proposed test and the reference standard to identify the target condition.11 The myofascial pain syndrome (MPS) and its hallmark trigger points with its key element “energy crisis” was first described by Travell, and Simon.12 Based on this theory an initiating event, can result in a cascade with increased acetylcholine release and calcium concentration resulting in increased energy demand while muscle circulation has deteriorated and metabolites accumulated. Trigger points are therefore caused by sensitization or irritation of a part in muscle pain pathway which can be either peripheral or central.13 MPS can be attributed to poor posture, minor muscle injuries, psychological stress, referred pain from viscera or joints, neuropathies and neuromusculoskeletal etiologies such as disk lesion.13 Active trigger points (TrPs) are defined as hyperirritable foci in the muscle and could designate segmental sensitization.14 TrPs could develop as a result of exposure to mechanical


or chemical irritants, causing tissue damage and creating irritable foci that can generate continuous impulses.15,16,17 As a result of these foci, segmental sensitization might occur in peripheral nerves and the spinal cord. The hyperactivity induced by irritated nerves may lead to muscle spasm, tightness and the appearance of active trigger points in myotomes corresponding to the involved segments in the spine.14,18,19 Since lumbosacral disc herniation can irritate nerve roots, one may assume that nerve root irritation may cause both radicular LBP and TrPs formation. Indeed, segmental sensitization mediated by nerve root irritation is associated with the presence of trigger points14,18,19 and TrPs in the superior-lateral quadrant of the gluteal area (GTrP) are frequently identified in patients with lumbosacral radiculopathy.20 Based on the presumption that when a finding is prevalent in a medical condition, the finding (i.e., GTrP) could be used as a diagnostic test to distinguish the condition in question, the aim of the current study was to evaluate whether the existence of GTrP could help to differentiate radicular from non-radicular LBP. Materials and Methods This prospective, diagnostic accuracy study of patients with LBP was conducted in accordance with the STARD guidelines for reporting diagnostic accuracy studies11 from May 2012 to January 2013. The study was approved by the institutional review board of the Hospital, in accordance with the World Medical Association Declaration of Helsinki. The research was organized at the Pain Clinic of the physical medicine and rehabilitation department of a general referral hospital. A written informed consent was signed and collected from all patients before joining the study. Study synopsis


In consecutively referred patients with LBP presence or absence of the GTrP was evaluated by a trained examiner at first stage of the physical examination, whom was not otherwise involved in the following steps of the patients’ evaluations. Subsequently, patients were evaluated by history, physical examination and MRI scanning. Based on the diagnosis most consistent with patients’ clinical and MRI findings a multidisciplinary panel of experts, considered as the ‘reference standard’, allocated patients to one of the two groups, with or without radicular LBP. Electrodiagnostic studies were used when the clinical evaluation and MRI findings were discordant, borderline or ambiguous. The panel of experts was blinded to GTrP evaluation findings. The diagnostic accuracy of GTrP to differentiate radicular from non-radicular LBP pain was evaluated by comparing the agreement between the presence or absence of the GTrP with the reference standard allocations in a 2 by 2 contingency table. A. screening: Patients were evaluated and recruited in a tertiary pain clinic in Physical Medicine and Rehabilitation department. The patients were referred from different departments of the hospital, including the emergency department, and entered the study within two days of referral. Included in the study were consecutively referred patients over 18 years old with any type of LBP, defined as pain between the thoraco-lumbar and lumbosacral junctions for any duration. Patients with history of lumbar spine surgery, rheumatologic diseases, fibromyalgia syndrome and peripheral neuropathy were excluded from the study (Figure 1). Excluded patients received out of the study therapy at the clinic as clinically indicated. B. GTrP evaluation: Eligible patients were guided to the evaluation room and were asked to lie down in prone position on the examination table. The presence or absence of the GTrP was determined at the first step of the clinical evaluation by a trained physician with seven years of experience in evaluating patients with LBP. To avoid Pygmalion Effect (researcher’s beliefs affecting outcome) the physician testing for GTrP entered the examining room once


the patient was already lying in prone position on the examination table. By employing this method the evaluator remained unbiased, being blinded to signs such as subjects’ posture, gait and facial expression. The GTrPs were evaluated using a flat palpation technique where taut bands and trigger points were compressed between the thumb or the index finger against the underlying tissue or bone.21 The points were considered GTrP when the combination of taut band, tenderness and pain recognition were present. Local twitch response, referred pain and jump sign that could also accompany trigger points were evaluated but their existence was not essential for the diagnosis.22,23 When found, the same investigator quantified pain pressure threshold of the GTrP by using a digital pressure algometer (Pain Test®, Wagner; USA). This was done by placing the algometer’s probe (1 cm2 surface area) perpendicular to the GTrP and increasing the pressure at a rate of 1kg/cm2/second until pain was elicited. C. Clinical evaluations: A second clinician (with 12 years of experience) who was blinded to the GTrP test findings, then recorded patients’ medical history, and performed a standardized physical examination. The clinical evaluation included specific diagnostic tests for LBP, excluding superior-lateral quadrant of the gluteal area (Appendix). Radicular LBP was considered in patients presenting with one or more of the following findings: a history of LBP radiating to the posterior or lateral thigh, leg and foot, dermatomal sensory changes, changes in deep tendon reflexes of the lower limb and weakness of the lower limb. Nonradicular LBP was defined as pain limited to the back with no radiation below the knee. D.MRI scanning: After the clinical evaluation, lumbar spine MRI scanning was done in all patients within two days of the clinical evaluation. Images were interpreted by an experienced neuro-radiologist and a physiatrist who were blinded to the findings of the previous steps. E. Patients’ categorization: By integrating the results of the medical history, physical examination and MRI, a multidisciplinary panel of experts considered as the ‘reference standard’, who were blinded to the results of the GTrP test assigned the patients as having


radicular or non-radicular LBP. MRI results that were discordant with patients’ clinical findings were considered false positive and were ignored. Based on the American Pain Society guidelines7,24, when the concordance between the clinical and MRI findings were borderline or ambiguous (i.e., suspicious somatic referred pain, peripheral neuropathy, etc.), the panel of experts recommended electrodiagnostic studies that were done at the same or following day. These patients were then re-evaluated and categorized to the appropriate groups, radicular vs. non-radicular LBP. The electrodiagnostic studies were done by a physiatrist with 15 years of expertise, who was blinded to the GTrP test findings. The electrodiagnostic study comprised at least one lower-limb motor nerve and one sensory nerve conduction evaluation, and needle electromyography.25 A standard 6 points method, including paraspinal muscles evaluation was used for needle electromyography tests. Patients with signs of acute or chronic/active nerve root involvement detected in at least two muscles were considered to have lumbosacral radiculopathy and were included in the radicular LBP group.25,26 Conversely, when no active nerve root involvement was detected by electrodiagnostic studies patients were considered as having non-radicular LBP. Patients with signs of peripheral neuropathy were excluded from the study. Statistical analysis Sample size was calculated by using Buderer’s formula27 and was based on the authors previous study that found the prevalence of GTrP in patients with nerve root irritation was about 75%20 and on the results of a pilot study performed by the authors showing that 48% of LBP patients referred to the clinic where the current study was done presented with GTrP (unpublished data). The sample size was therefore calculated assuming 75% sensitivity and 50% prevalence for consecutively referred patients with LBP in the following equation: N

Z 2( Sen 1 Sen ) L 2 Prevalence

1.96 2 0.75 (0.25) 0.07 2(0.5)

294


Where L=accuracy (should be at least 1/10 of the sensitivity) and Z=confidence interval for two standard deviations. Estimating a 10% patients’ drop-out and missed data, 325 patients were deemed to be sufficient for this study. Recorded were patients’ demographic information (age and gender), pain duration and the presence or absence of the GTrP. The one sample Kolmogorov-Smirnov was acquired to determine normal distribution for numeric variables such as age, pain duration and algometry scores. Mode and median were reported instead of mean and standard deviation for numeric variables not following normal distribution. The chi square test was used to compare female and male frequency in both radicular and non-radicular LBP groups. Measures of statistical uncertainty were reported with 95% confidence intervals. Sensitivity, specificity, positive and negative likelihood ratios (LR) and positive and negative predictive values were calculated by utilizing a 2 by 2 contingency table.27 Presence or absence of the GTrP was considered as positive or negative GTrP test, respectively. True positive was defined as patients with positive GTrP test that had radicular LBP. True negative was defined as patients with negative GTrP test without radicular LBP. False positive was defined as patients with positive GTrP test that did not have radicular LBP and false negative was defined as patients with negative GTrP test with radicular LBP. A ROC curve was plotted by using true positive rate against false positive rate for the GTrP test.28 IBM SPSS Statistics v.18 was used for statistical assistance. Results Out of 413 screened patients, 325 patients finished the study and their results were included in the final analysis. Seventy six candidates were excluded on initial screening and 12 patients dropped out after signing the consent and their results were not included in the final analysis (Figure 1). One hundred and forty patients (43%) were found to have non-radicular


and 185 patients (57%) had radicular LBP (Table 1). Of the patients with non-radicular LBP, 79 were females and 61 were males with a mean age of 41.35±13.96 years. Their pain started between 1 week and 14 months before visited at the clinic (mode=4 month; median= 7 months). The majority (109/140; 77.8%) had mechanical LBP and the others were mainly diagnosed to have sacroiliac joint or facet joint mediated pain. Of the 185 patients with radicular pain 98 were females and 87 were males with mean age of 43.48±13.08 years. Pain duration was between 1week and 34 months (mode=6 months; median=15 months). There was no significant difference in male and female distribution between radicular and nonradicular LBP groups (P>0.5) and chi = 0.384. The GTrP test was positive in 12 patients with non-radicular LBP (8.5%) and in 137 patients (74.1%) with radicular pain. The average GTrP pain threshold, when found, for the non-radicular group was 4.66±1.28kg/cm2 and for the radicular LBP group was 4.83±1.07kg/cm2 (P=0.6). The specificity of the GTrP test in the radicular LBP group was 91.4% (CI 95%: 86.8-96%) and the sensitivity was 74.1% (CI 95%: 67.7-80.3%).The area under the ROC curve was 0.827 (0.781-0.874; Figure2).The positive LR was 8.62 and the negative LR was 0.28. The positive and negative predicting values were 91.9% (CI 95%: 87.6-96.3%) and 72.7% (CI 95%: 66.1-79.3%), respectively. Discussion To our knowledge this is the first study evaluating the diagnostic usefulness of GTrP to detect nerve root involvement among patients with LBP. The results show that more than 90% of the patients with GTrPs were diagnosed to have radicular LBP. The specificity of the GTrP test (91.4%), and its high positive LR and positive predictive value (8.62 and 91.9%, respectively) indicate that GTrP test could accurately predict radicular pain in the majority of patients referred with LBP. These values are higher compared to other currently used tests to diagnose radiculopathy, including MRI scanning, physical tests such as straight leg raising


(SLR) test and diagnostic injections (see below). When combining the GTrP test with other clinical diagnostic examinations this rapid and easily performed test may help diagnosing radiculopathy in LBP patients. The test may, therefore, decrease the need for more sophisticated ancillary tests and procedures and might lower the costs of treating these patients. In contrast to its high specificity, the sensitivity of the GTrP test was 74.1%, indicating that as a diagnostic test, the absence of GTrPs is not as useful as their presence. Still, the sensitivity of the GTrP test in consecutively referred patients was higher compared to other clinical tests currently used to differentiate radicular from non-radicular LBP. For example the pooled sensitivity of the SLR test in consecutively referred patients was 0.5229 and 0.3330, compared to74.1% for the GTrP test in the present study. When a diagnostic test is positive the measure that shows how confident a practitioner can be that the condition in question truly exists is called “Diagnostic Confidence”.31 The diagnostic confidence of positive GTrP test in the current study (i.e., positive predictive value) was almost 92%; indicating that clinicians can be 92% confident that GTrP test truly designates radicular LBP. One should not forget, however, that diagnostic confidence is the product of pretest odds and LR that create the post-test odds. Inevitably, prevalence, sensitivity and specificity of a test can have substantial impact on the diagnostic confidence that might be higher or lower at different clinical settings. Since it is the first time that GTrP test is used as a diagnostic test we cannot compare the results of the current study to other clinical settings. However, the effect of these variables on diagnostic confidence has been evaluated and published for other diagnostic tests in patients with LBP. For example, lumbar medial branch blocks are commonly performed as a diagnostic test for facet joint-induced pain. Assuming sensitivity of 100% and specificity of 88% for this procedure, and a prevalence of 5% for


facet joint induced-pain, the diagnostic confidence is 30%. However, if the prevalence is considered to be 15% the diagnostic confidence will increase to 60%.32 Among the existing clinical and ancillary tests used to differentiate radicular from nonradicular LBP, lumbar spine MRI is considered as the reference standard for diagnosing herniated lumbosacral disc and/or spinal canal stenosis. Depending on the age of the asymptomatic adults, MRI has 25-70% false positive and15-35% false negative rates.9,10 The findings of the current study, showing less than 9% false positive results, suggest that the GTrP evaluation might be superior to MRI for diagnosing radiculopathy in patients with LBP. Similarly, the SLR (Lasegue) test has its limitations in diagnosing radiculopathy, with highly variable sensitivity and specificity.33 In studies comparing the SLR test to surgical findings as the reference standard the pooled sensitivity was 0.91 (0.78–0.97) and specificity was 0.32 (0.17–0.52).33 However, in a non-surgical scenario, when patients were consecutively selected regardless of their surgical needs, the sensitivity was 0.5229 and 0.3330 and the specificity was 0.8929 and 0.87.30 Thus, positive GTrP test might have a better diagnostic accuracy than SLR test. Finally, diagnostic injections have been recommended as the reference standard to identify the pain etiology in some patients with LBP.34 However, these procedures are not adequately specific, with high false positive rates for a single block, ranging from 25% to 41%.35,36,37 The high false positive results of the diagnostic injections could be related to their capacity to desensitize other potential sources of pain, such as muscles and ligaments when performing a medial branch block38 or when spillage of the anesthetic injectate to intervertebral foramen and/or epidural space happens following injection to the facet joints.39,40 Indeed, no correlation was found between radiologic findings and the responses to diagnostic blocks.41,42,43 It could be argued that in the current study some patients diagnosed with radicular pain had other, non-radicular sources of pain, such as the sacro-iliac or the facet joints.8 Although


possible, the likelihood of such misdiagnosis is low since concurrent sources of pain in patients with LBP are uncommon.44,45 In addition, in the current study LBP patients were assigned to radicular vs. non-radicular groups by employing a combination of standardized and meticulous clinical evaluation, ancillary tests, and opinion of the multidisciplinary panel of experts. Finally, tender points typifying other common LBP etiologies have distinctive anatomical locations, dissimilar to GTrP. In the current study GTrPs were located at the superior-lateral part of the gluteal area. In contrast, tender points associated with sacroiliac joint disease are typically located inferior-medially to the posterior superior iliac spine,46,47 tender points accompanying facet joints pain are usually located over the involved joints48 and those associated with piriformis syndrome are located over the sciatic notch.8 Nevertheless, it is still premature to consider the GTrP test as pathognomonic for patients with radicular LBP. Other studies should be done directly comparing the existence of GTrP to additional specific reference standard tests to rule out other possible diagnoses. In summary, the findings of the present study indicate that the existence of GTrP is a highly specific indicator of radiculopathy in patients with LBP. Although suggestive, the lack of GTrP is not sensitive enough to rule out nerve root involvement. Using the GTrP test as an indicator for radiculopathy may decrease the need for more costly, time consuming and invasive diagnostic tests such as imaging and diagnostic injections. Although future studies should directly compare the GTrP test to other validated tests, the authors recommend its routine use when evaluating patients with LBP. References 1. Papageorgiou AC, Croft PR, Ferry S, et al. Estimating the prevalence of low back pain in the general population. Evidence from the South Manchester Back Pain Survey. Spine 1995;20:1889-94


2. Zhang YG, Guo TM, Guo X, et al. Clinical diagnosis for discogenic lower back pain. Int J BiolSci 2009;5:647-658 3. Karas R, McIntosh G, Hall H, et al. The relationship between nonorganic signs and centralization of symptoms in the prediction of return to work for patients with lower back pain. PhysTher 1997;77:354-360 4. Dagenais S, Tricco AC, Haldeman S. Synthesis of recommendations for the assessment and management of low back pain from recent clinical practice guidelines. The Spine Journal 2010;10: 514-529 5. Zhang Y, Sun Z, Liu J, et al. Advances in susceptibility genetics of intervertebral degenerative disc disease. Int J BiolSci 2008;4:283-290 6. Chou R, Qaseem A, Snow V, et al; Clinical Efficacy Assessment Subcommittee of the American College of Physicians; American College of Physicians; American Pain Society Low Back Pain Guidelines Panel. Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Ann Intern Med. 2007; Oct 2;147(7):478-91 7. Chou R, Loeser JD, Owens DK, et al. American Pain Society Low Back Pain Guideline Panel. Interventional therapies, surgery, and interdisciplinary rehabilitation for low back pain: an evidence-based clinical practice guideline from the American Pain Society.Spine 2009;34(10):1066-77 8. Barr KP, Harrast MA. Low back pain, Physical Medicine and Rehabilitation, 4th edition.Edited by Braddom RL. Philadelphia, PA, Elsevier, 2011, pp 880-904 9. Boden SD, Davis DO, Dina TS, et al. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg Am 1990;72(3):403-8


10. Jackson RP, Cain JE Jr, Jacobs RR, et al. The neuroradiographic diagnosis of lumbar herniated nucleus pulposus: II. A comparison of computed tomography (CT), myelography, CT-myelography, and magnetic resonance imaging. Spine 1989;14(12):1362-7 11. Bossuyt PM, Reitsma JB, Bruns DE, et al. The STARD statement for reporting studies of diagnostic accuracy: explanation and elaboration. Clinical Chemistry.2003;49(1):7–18 12. Travell JG, Simons DG. Myofascial pain and dysfunction, vol 1 and 2. Baltimore: Williams & Wilkins, 1992 13. Hong C-Z. Muscle pain syndromes. In: Braddom RL, Chan L, Harrast MA editors. Physical Medicine and Rehabilitation. Philadelphia: Saunders, 2011. p 974 14. Gunn CC. Radiculopathic pain: Diagnosis, treatment of segmental irritation or sensitization. J Musculoskeletal Pain 1997;5(4):119-134 15. Hoheisel U, Mense S, Simons 0, et al. Appearance of new receptive fields in rat dorsal horn neurons following noxious stimulation of skeletal muscle: a model for referral of muscle pain? NeurosciLett1993;153:9-12 16. Shah JP, Danoff JV, Desai MJ, et al. Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points. Arch Phys Med Rehabil 2008;89(1):16-23 17. Shah JP, Phillips TM, Danoff JV, et al.An in vivo microanalytical technique for measuring the local biochemical milieu of human skeletal muscle. J Appl Physiol 2005;99: 1977-1984 18. Fischer AA. New developments in diagnosis of myofascial pain and fibromyalgia. Phys Med Rehabil Clin North Am 1997;8:1-27 19. Chu J. Dry needling (intramuscular stimulation) in myofascial pain related to lumbosacral radiculopathy. Eur J Phys Med Rehabil1995;5(4):106-121


20. In Press: Adelmanesh F, Jalali A, Jazayeri SM, et al. Is There an Association Between Lumbosacral Radiculopathy and Painful Gluteal Trigger Points? A Cross-sectional Study. Am J Phys Med Rehabil 2015;March 12, doi:10.1097/PHM.0000000000000261 21. Dommerholt J, Shah JP: Myofascial Pain Syndrome, Bonica’s Management of Pain, 4th edition. Edited by Fishman SM, Ballantyne JC, Rathmell JP, Philadelphia, PA, Lippincott Williams and Wilkins; 2010, pp 462 22. Mense S, Simons DG. Muscle pain. Understanding its nature, diagnosis, and treatment. Philadelphia, Lippincott Williams & Wilkins, 2001 pp 225 23. Robinson JP, Arent-Nielsen L. Muscle pain syndromes. Physical medicine and rehabilitation, 3rd edition. Edited by Braddom RL. Philadelphia, PA, Elsevier, 2007, pp 1003 24. Fisher M. Electrophysiology of radiculopathies. Clin Neurophysiol, 2002;113(3):317-335 25. Dillingham TR, Lauder TD, Andary M,et al. Identifying lumbosacral radiculopathies: an optimal electromyographic screen. Am J Phys Med Rehabil, 2000;79(6):496-503 26. Tong HC, Haig AJ, Yamakawa KS, et al. Specificity of needle electromyography for lumbar radiculopathy and plexopathy in 55- to 79-year-old asymptomatic subjects. Am J Phys Med Rehabil, 2006;85(11):908-12 27. Buderer NM. Statistical methodology: I Incorporating the prevalence of disease into the sample size calculation for sensitivity and specificity. Acad Emerg Med, 1996;3:895–900 28. Fawcett T. An introduction to ROC analysis. Pattern Recognit Lett, 2006;27:861-74 29. Majlesi J, Togay H, Unalan H, et al. The sensitivity and specificity of the Slump test and the Leg Raising tests in patients with lumbar disc herniation. J Clin Rheumatol, 2008;14(2):87-91 30. Kosteljanets M, Bang F, Schmidth-Olsen S. The clinical significance of straight-leg raising (Lasegue’s sign) in the diagnosis of prolapsed lumbar disc. Interobserver variation and correlation with surgical finding. Spine 1988;13(4):393-395


31. Sackett DL, Haynes RB, Guyatt GH, et al. Clinical Epidemiology: A Basic Science for Clinical Medicine, 2nd ed. Boston, Little, Brown & Co., 1991;119-139 32. Curatolo M, Bogduk N: Diagnostic And Therapeutic Nerve Blocks, Bonica’s Management of Pain, 4th edition. Edited by Fishman SM, Ballantyne JC, Rathmell JP, Philadelphia, PA, Lippincott Williams and Wilkins; 2010, pp 1412-18 33. Vroomen PC, de Krom MC, Knottnerus JA. Diagnostic value of history and physical examination in patients suspected of sciatica due to disc herniation: a systemic review. J Neurol, 1999;246(10):899-906 34. Sehgal N, Dunbar EE, Shah RV,et al. Systematic Review Of Diagnostic Utility Of Facet (Zygapophysial) Joint Injections In Chronic Spinal Pain: An Update. Pain Physician, 2007;10:213-228 35. Schwarzer AC, Aprill CN, Derby R, et al. The false-positive rate of uncontrolled diagnostic blocks of the lumbar zygapophysial joints. Pain, 1994;58: 195-200 36. Manchikanti L, Pampati V, Fellows B, et al. Prevalence of lumbar facet joint pain in chronic low back pain. Pain Physician, 1999;2:59-64 37. Manchikanti L, Pampati V, Fellows B, et al. The diagnostic validity and therapeutic value of lumbar facet joint nerve blocks with or without adjuvant agents. Curr Rev Pain, 2000; 4:337-344 38. Hirsch C, Ingelmark B, Miller M. The anatomical basis for low back pain. Acta Orthop Scand, 1963;33:1-17 39. Yamashita I, Cavanaugh M, Ozaktay AC, et al. Effect of substance P on mechanosensitive units of tissue around and in the facet joint. J OrthopRes, 1993;11:205–14 40. Destouet JM, Gilul LA, MurpheyWA, et al. Lumbar facet joint injection: indication, technique, clinical correlation, and preliminary results. Radiology, 1982;145:321–5


41. Lawrence JS, Bremner JM, Bier F. Osteo-arthrosis. Prevalence in the population and relationship between symptoms and x-ray changes. Ann Rheum Dis, 1966;25:1-24 42. Magora A, Schwartz A. Relation between the low back pain syndrome and x-ray findings. Scand J Rehabil Med, 1978;8:115-12 43. Schwarzer AC, Wang SC, O'Driscoll D, et al. The ability of computed tomography to identify a painful zygapophysial joint in patients with chronic low back pain.Spine, 1995;20:907-912 44. Schwarzer AC, Aprill CN, Bogduk N. The sacroiliac joint in chronic low back pain. Spine, 1995;20:31-37 45. Schwarzer AC, Aprill CN, Derby R, et al.The prevalence and clinical features of internal disc disruption in patients with chronic low back pain. Spine, 1995; 20:1878-1883 46. MaigneJY, AivaliklisA,PfeferF. Results of sacroiliac joint double block and value of sacroiliac provocation tests in 54 patients with low back pain. Spine,1996;21:1889–92 47. Forst SL, Wheeler MT, Fortin JD, et al. The Sacroiliac Joint: Anatomy, Physiology and Clinical Significance. Pain Physician, 2006;9:61-68 48. Helbig T, Lee CK.The lumbar facet syndrome.Spine, 1988;13(1):61-4 49. Frontera RW, Silver JK, Rizzo TD Jr.Essentials of physical medicine and rehabilitation, 2nd edition. Philadelphia, PA, Elsevier; 2008, pp 229-230 50. Buckup K. Clinical tests for musculoskeletal system. New York, Thieme, 2004, pp 27 51. Laslett M, Young SB, Aprill CN, et al. Diagnosing painful sacroiliac joints: A validity study of a McKenzie evaluation and sacroiliac joint provocation tests. Aust J Physiother, 2003;49:89–97 52. Fishman LM, Anderson C, Rosner B. BOTOX and physical therapy in the treatment of piriformis syndrome. Am J Phys Med Rehabil, 2002;81:936 –942


53. Kirschner JS, Foye PM, Cole JL. Piriformis syndrome, diagnosis and treatment. Muscle and Nerve, 2009;40:10-18

Figure legends Figure 1. Study flow chart Appendix. Physical examination of the low back Table 1. Contingency table: agreement between the results of GTrP test and the reference standard Figure 2. Receiver Operating Characteristic (ROC) curve of the GTrP test Table 1. Contingency table: agreement between the results of GTrP test and the reference standard Radicular

Non-radicular

Total

LBP

LBP

GTrP positive

137

12

149

GTrP negative

48

128

176

Total

185

140

325

GTrP: gluteal trigger point, LBP: low back pain


Figure 1 Click here to download Figure: Figure 1_01.tif


Figure 2 Click here to download Figure: Figure 2_01.tif


Effects of compression at myofascial trigger points in patients with acute low back pain: A randomized controlled trial.

Trigger points and acupuncture points for pain: correlations and implications.

Comparison of Transforaminal and Parasagittal Epidural Steroid Injections in Patients With Radicular Low Back Pain.

Epidemiology, etiology, diagnostic evaluation, and treatment of low back pain.

Diagnostic uncertainty and recall bias in chronic low back pain.

Is There an Association Between Lumbosacral Radiculopathy and Painful Gluteal Trigger Points?: A Cross-sectional Study.

Chronic pain syndromes and their treatment. II. Trigger points.

Trigger points in 48 dogs with myofascial pain syndromes.

Somatosensory nociceptive characteristics differentiate subgroups in people with chronic low back pain: a cluster analysis.

A Novel Nitronyl Nitroxide with Salicylic Acid Framework Attenuates Pain Hypersensitivity and Ectopic Neuronal Discharges in Radicular Low Back Pain.

Low-back pain.

Low back pain.

Postpartum low-back pain.

Medical approach to low back pain.

Low back pain due to extramedullary hemopoiesis.

Low back pain tied to spinal endometriosis.

Intravenous lidocaine for the emergency department treatment of acute radicular low back pain, a randomized controlled trial.

The accuracy of pain drawing in identifying psychological distress in low back pain-systematic review and meta-analysis of diagnostic studies.

Epidemiology of low back pain.

Lumbar disc screening using back pain questionnaires: oswestry low back pain score, aberdeen low back pain scale, and acute low back pain screening questionnaire.

Accuracy of physical therapists' prognosis of low back pain from the clinical examination: a prospective cohort study.

Trajectories of low back pain.

Predicting disability time using formal low back pain measurement: the Low Back Pain Simulation Scale.

Tensiomyography, sonoelastography, and mechanosensitivity differences between active, latent, and control low back myofascial trigger points: A cross-sectional study.