Identification of intramuscular tissue oedema and changes in muscle contractile properties induced by dry needling

Abstract

INTRODUCTION: Myofascial trigger points are a common cause of clinically observed local muscle pain and tenderness. The improvement associated with the muscle relaxing effect (reduction of muscle stiffness) produced by dry needling (DN) is still not well understood. In this regard, it is believed that the regeneration of tissue destroyed by dry needling through the inflammatory process should do with the return to normality of muscle contractility. A contractility marker (muscle belly displacement, Dm) has been associated with changes in muscle stiffness (increase in Dm = decrease in stiffness and vice versa). The aim of this study was to identify via magnetic resonance imaging (MRI) if the local inflammatory response is immediately induced by DN as well as changes in Dm of asymptomatic patients. METHODS: 18 asymptomatic patients participated in the study. We used an inter-group research design to investigate the regional-signal differences of MRI measurements in the gastrocnemious medialis (GM), before and after 1h DN. The research unit of analysis was the GM. The GM that presented more pain to pressure and reported by visual analogue scale was used for further analysis. The contralateral GM was used as a control group (CG) while the other one was considered the experimental group (EG). MRI Short tau inversion recovery (STIR, signal intensity) was used to identify signal changes due to by local inflammation. Changes in contractile muscle properties were assessed by tensiomyography using the key parameter: Dm (mm). An ANOVA was performed to analyse the influence of DN on the STIR variable and a t-test for dependent samples was performed to compare the pain perception after the DN. RESULTS: The STIR (signal intensity) increased 128.97 % after the DN. The interaction effect showed significant differences (F(1,34) =235, p =0.0001, r =0.93). Bonferronis post hoc tests showed significant differences [mean differences and 95% confidence interval (95% CI) =198 (172 – 224)] signal intensity (F (1,34) =236, p =0.001; r =0.93; d =5.03). The difference between the CG vs. EG in Dm variable was 24.04 % after the DN. In addition, there was a significant effect of the group variable (i.e., CG vs. EG) after controlling the effects with the pre- variable (F(1,33) = 9.95, p =0.003, r =0.48, d =1.10. In relation to pain perception, a significant reduction (t(17) = 12.40, p =0.001, r =0.65, d =1.71) were found. Pearsons correlation did not show correlation between any variable. CONCLUSION: Intramuscular oedema appears immediately after (1h) of the application of DN, therefore indicating an inflammatory process with unexpected reduction in the pain perception. A loss of muscle contractility measured by Dm did not correlate with changes in the STIR. Our results are in line with others found in mice showing signs of an inflammatory response after DN. Our research was limited for the lack of subsequent measurements of MRI to detect when the edema was removed.