OBJECTIVE: Myofascial pain syndrome (MPS) is a major musculoskeletal problem and a leading cause of disability worldwide. Extracorporeal shockwave therapy (ESWT) and trigger point injection (TPI) have shown positive results for MPS but no previous study has investigated the combined effects of radial shockwave and trigger point injection of lidocaine for upper trapezius myofascial pain syndrome. METHOD: For this purpose, forty-five participants were randomly divided into shockwave (n = 15), shockwave with ultrasound-guided trigger point injection (combined; n = 15), and control (standard care; n = 15) groups. Participants were assessed at baseline, one week and four weeks by using the visual analog scale, neck disability index, electromyography, infrared thermography, and sonoelastography. RESULTS: Compared with control group, both shockwave and combined groups showed a statistically significant reduction in pain (P<0.01), functional disability (P<0.01), skin temperature (P<0.01), and elastic stiffness, with greater reduction in the combined group (P<0.01) than shockwave group (P<0.05) at four weeks. However, no significant difference was found in electrical activity between the groups (P>0.05). The combined group also showed significant differences in pain (P<0.05) and elastic stiffness (P<0.01) compared with shockwave group at four weeks. CONCLUSION: Our study revealed that extracorporeal radial shockwave therapy combined with trigger point injection of lidocaine was more effective for decreasing pain and elastic stiffness in upper trapezius myofascial pain syndrome at four weeks.