The Ultrasonographic Findings of Trigger Points of Myofascial Pain Syndrome in a Rabbit Model

ABSTRACT

PURPOSE: Myofascial pain syndrome (MPS) is a common cause of musculoskeletal pain. Myofascial trigger points (MTrPs) have been repeatedly described by numerous authors. However, there have been few studies in which their existence and behavior was supported and their location confirmed. The purpose of this study was to determine whether diagnostic ultrasonography is an objective diagnostic tool which is able to significantly identify or detect the soft tissue changes in the region of clinically identified active MTrPs by using a rabbit experimental model. MATERIALS AND METHODS: Ten MPS model rabbits were used in this study. We made an MPS animal model by causing the rabbits to overuse one leg for 3 weeks by cutting the contralateral L4 spinal nerve root. We compared the ultrasonographic findings of the taut band at pre-OP with those at post-OP during the consecutive three week period. To find the taut bands of the muscle, after skin exposure, the muscles were gently rubbed or pinched with the thumb and index finger on the two opposing surfaces of the muscle across the direction of the fibers. Then, the muscle was held in the same way, but with a 5-8 MHz stick probe being used in place of the thumb. After the palpation of various muscles, we selected the hardest and largest myofascial trigger nodule, in order to observe the ultrasonographic and power Doppler findings of the MPS. The size, shape, echogenecity and vascularity of the MTrPs were observed. RESULTS: The analysis of the results of the ultrasonography revealed that all MTrPs have a hyperechoic area. The mean thickness of the hyperechoic lesion in the biceps was 0.96+/-0.14 cm in the MPS site (at pre-OP?), and 0.49+/-0.12 cm at post-OP 3weeks (p < 0.01). The hyperechoic lesions in all of the studied biceps femoris of the rabbits were observed by high resolution ultrasonography. No definitively decreased vascularity was observed within the hyperechoic area by power Doppler imaging. CONCLUSION: Until now, there has been no objective method for the diagnosis of MPS. However, this study suggests the possibility of using diagnostic ultrasonography as an objective diagnostic tool, by identifying the tissue changes in the region of clinically indicated active MTrPs.