Study On Imaging And Related Mechanism Of Chronic Myofascial Trigger Points In A Rat Model

Part ⅠAssessment of ultrasound imaging and the effects of ischemia-hypoxia in a rat model of myofascial trigger pointsObjective:(1)To investigate the value of conventional ultrasound and strain ultrasound elastography in the diagnosis of rat model of chronic myofascial trigger points(MTrPs);(2)to confirm whether ischemia-hypoxia conditions mentioned in the integrated hypothesis involve in the formation of active MTrPs and its effect on angiogenesis.Materials and Methods:Twenty-five male Sprague-Dawley rats were randomly divided into two groups:(1)a normal control group(n=10)and(2)a model group(n=15).The active MTrPs model was established as described in the literature through a blunt strike in combination with eccentric exercise.After modelling,each rat was examined by electromyography,conventional ultrasound and strain ultrasound elastography.Then,the muscle tissues from the two groups were cut and sampled for pathological analysis and tissue homogenization.The levels of HIF-1α and VEGF were measured by enzyme-linked immunosorbent assay(ELISA).And the immunohistochemical staining was used to detect microvessel density in two groups.The differences of HIF-1α,VEGF and MVD between the model group and the control group were compared,and the correlations between these indexes and blood flow signal grades of color Doppler flow image(CDFI)were analyzed.Results:In the model group,14 rats were successfully modeled.Via B-mode imaging,a focal hypoechoic region or a hyperechoic region were visualized in all rats of the model group within the right gastrocnemius muscle in an injury area consistent with the location of the palpable nodule identified during physical examination.Higher strain scores were observed in the MTrPs than that of the normal control,presenting with a stiff focal region that was entirely covered in blue or was mostly blue with little green.Compared with the control group,the active MTrPs group exhibited significantly higher HIF-1α and VEGF levels and MVD values.These differences were accompanied by increased blood flow signals.In the active MTrPs group,the blood flow signal grade was positively correlated with the MVD(r=0.707,P=0.005)and independently correlated with the VEGF level(r=0.595,P=0.025),but was not correlated with the expression of HIF-1α(r=0.403,P=0.154).Conclusions:(1)The expression levels of HIF-1α,VEGF and MVD in the MTrPs group were significantly higher than that of normal controls.These datas provided an objective basis for verification of the ischemia-hypoxia involved in the formation of MTrPs mentioned in the integrated hypothesis.(2)In the rat model of MTrPs,gray-scale ultrasound and strain ultrasound elastography can effectively distinguish MTrPs from the surrounding normal muscle tissue.(3)Color Doppler flow image combined with MVD can intuitively verify that the neovasculation and vascular volume compared with the normal control group have increased in the area of MTrPs.Part ⅡMagnetic resonance imaging to assess myofascial trigger points in a rat model and related mechanismObjective:To explore the value of diffusion tensor imaging(DTI)and T2 mapping in the diagnosis of chronic myofascial trigger points(MTrPs)in a rat model and its pathophysiological mechanisms.Materials and Methods:This study enrolled in 14 rats which were established as MTrPs model in the part Ⅰ and 10 rats of normal control.All of the 24 rats from the two groups were examined right gastrocnemius by DTI and T2 mapping to measure the parameters including fractional anisotropy(FA),mean diffusivity(MD),axial diffusivity(AD),radial diffusivity(RD)and T2 values.Their results were compared between MTrPs group and model group.In addition,histopathology analysis was performed in the two groups according to the methods of Part Ⅰ.Enzyme-linked immunosorbent assays(ELISA)was used to detect the differences of interleukin-1β(IL-1β),interleukin-2(IL-2),and substance P(SP)between the two groups and their correlations with T2 value.Results:The active MTrPs of rats displayed significantly increased T2 values and FA(P=0.000)compared with normal controls,whereas MD and RD values were significantly lower(P=0.031,P=0.000,respectively).There was no statistically significant difference in AD between the two groups(P=0.400).These differences were accompanied by elevated levels of IL-1β,IL-2 and SP in the MTrPs group compared to controls(P=0.000).T2 values was positively correlated with elevated IL-1B levels(r=0.543,P<0.05),but was not correlated with IL-2 and SP levels(P>0.05).Pathological sections of the model group showed that round or quasi-round muscle fibers of different sizes were aggregated in cross-section,accompanied by widening of muscle space and infiltration of monocytes.Conclusions:(1)Combined T2 mapping and DTI techniques are sensitive tools to assess the active MTrPs in a rat model.(2)The changes of DTI parameters combined with T2 values and histopathology as well as inflammatory factors indicated that MTrPs was a mildly chronic muscle injury with inflammation caused by excessive contraction of local muscle fibers,accompanied by continuous muscle repair process.Part ⅢClinical application of grey-scale ultrasound and shear wave elastography in the diagnosis of cervicoshoulder myofascial pain syndromeObjective:To investigate the application value of gray-scale ultrasound and shear wave elastography in the diagnosis of cervicoshoulder myofascial pain syndrome(MPS).Materials and Methods:A total of 32 patients with cervicoshoulder MPS who were hospitalized in the rehabilitation department of our hospital from March 2020 to December 2020 were enrolled in this study,as well as 32 cases in the normal control group.All their age ranges were from 25 to 55 years old.The clinician marked the upper trapezius muscle at the site of myofascial trigger points(MTrPs),and then performed gray-scale ultrasound and shear wave elastography,respectively.The sensitivity of gray-scale ultrasound and shear wave elastography to diagnose MTrPs and their corresponding manifestations were observed.The data of shear wave velocity and Young’s modulus in the groups of MTrPs,adjacent MTrPs and normal controls were recorded,and the differences between them were compared.Results:In 32 patients with MPS,the clinician diagnosed 44 MTrPs in bilateral superior trapezius muscles.Among of these MTrPs,14 cases were positive on gray-scale ultrasound,its sensitivity in diagnosis of MTrPs was 31.8%.These displayable lesions were all circular hypoechoic nodules with a size of 0.14±0.023cm2 on two-dimensional ultrasound images.On shear-wave elastography,all areas of MTrPs were shown with a focal hardness region.Young’s modulus value(EI)and shear wave velocity(SWV)of the MTrPs group were 68.39±15.36 kPa and 4.72 ± 0.53 m/s,while those of the adjacent group were 32.36±5.83 kPa and 3.24±0.28 m/s.In normal control group,EI was 21.08±4.10 kPa and SWV was 2.62±0.21 m/s.The MTrPs group was significantly higher than the adjacent group,while both the MTrPs group and the adjacent group were higher than the normal control group with statistical significance(P<0.05).Conclusions:(1)The sensitivity of gray-scale ultrasound in the diagnosis of superior trapezius MTrPs in cervicoshoulder myofascial pain syndrome is low.MTrPs appear as a hypoechoic nodule on gray-scale ultrasound,and their hypoechoic manifestations may be related to inflammatory edema caused by ischemia and hypoxia that induced by excessive contraction of muscle fibers.(2)Shear wave elastography is an objective and effective method to diagnose MTrPs.It can provide the specific hardness to objectively quantify the difference between MTrPs and surrounding muscles.MTrPs is a lesion of local stiffness,and its adjacent area is also harder than normal muscle.