Ismail Ebrahimi Takamjani - Department of Physiotherapy, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran
Kamran Ezzati - Neuroscience Research Center, Poorsina Hospital, Faculty of medicine, Guilan University of Medical Sciences, Rasht, Iran
Saemeh KHANI - Department of Physiotherapy, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran
Javad Sarrafzadeh - Department of Physiotherapy, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran
Abbas Tabatabaiee - Department of Physiotherapy, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran

Background: Lumbar multifidus muscle provides stability to the spine. The present study aimed to evaluate the reliability of ultrasound findings in patients with lumbar multifidus myofascial pain syndrome (MPS).Methods: A total of ۲۴ cases (۷ females, ۱۷ males, mean age: ۴۰.۱۳± ۵.۶۹, BMI: ۲۶.۴۸±۴.۹۶) with multifidus MPS were assessed. The variables were muscle thickness in rest and contraction, thickness changes, and cross-sectional area (CSA) in rest and contraction. Two examiners performed the test and retest sessions.Results: The active trigger points of lumbar multifidus on the right and left side of the cases were ۴۵.۸ % and ۵۴.۲%, respectively. The intraclass correlation coefficient (ICC) values for muscle thickness and thickness changes showed moderate to very high reliability for both within and between intra-examiner measurements. (ICC, ۱st examiner: ۰.۷۸-۰.۹۶; ICC, ۲nd examiner: ۰.۸۶-۰.۹۵). In addition, the ICC values of within and between-session intra-examiner for CSA were high. (ICC, ۱st examiner: ۰.۸۳-۰.۸۸; ICC, ۲nd examiner: ۰.۸۴-۰.۸۹). The ICC and standard error of measurement (SEM) of inter-examiner reliability ranged between ۰.۷۵ to ۰.۹۳ and ۰.۱۹ to ۰.۸۸ for multifidus muscle thickness and thickness changes. The ICC and SEM of inter-examiner reliability ranged between ۰.۷۸ to ۰.۸۸ and ۰.۳۳ to ۰.۹۰ for CSA of the multifidus muscle. Conclusion: The within and between-session reliability of multifidus thickness, thickness changes, and CSA was moderate to very high in patients with lumbar MPS when taken by two examiners. Furthermore, the inter-examiner reliability of these sonographic findings was high. Level of evidence: III

Low back pain, Myofascial pain syndrome, Multifidus thickness, Ultrasound, Trigger points