| Objective:Daily life activities or sports injury usually cause some chronic pain, which could lead to the pain at joint and spine or the disorders of skeletomuscular system. Most of this chronic pain is muscle pain, and myofascial pain is a common cause of muscle pain. Clinically, chronic myofascial pain syndrome has been characterized by pain, referred pain, autonomic nerve dysfunction and muscle disorders. Myofascial pain could seriously affect people's living and work lead to an increase of the financial burden of society. Now it is believed that myofascial trigger points locate in skeletal muscle or fascia muscularis. In order to study the pathogenesis of the myofascial trigger points, most of current models are simulation models of latent trigger points models which can not represent the whole characters of myofascial trigger points. Therefore, all of these models couldn't explain real changes of trigger points' spontaneous electrical activity (SEA) and histopathological changes. In this study, we will use rats as experimental animals. During experiment, rats were dealt with striking and eccentric exercise to produce the myofascial trigger points in rats. After different longed recovery time, the EMG and histopathological changes at trigger points will be inspected on the nature and pathological character of myofascial trigger points which could infer the possible pathogenesis of myofascial trigger points.Methods:32 male SD rats seven week-old, average weight of 220g-260g, were randomly divided into 4 groups which were A group, B group, C group and D group. There were 8 rats in every group. A group was control group and B group, C group and D groups were experimental groups. A group:During periods of modeling and recovery, all rats in A group weren't given any intervention. Experimental groups:in the first day of every week during modeling period, all rats in experimental groups were stroked at the left vastus medialis, and the next day, all rats were taken to eccentric exercise for 90 min. The modeling period lasted 8 weeks. During recovery periods, without any experimental intervention and normal feeding, all experimental rats were dealt as the control group. The recovery periods of BCD group separately lasted 4,8 and 12 weeks. After recovery period, all groups were detected taut band, contraction knots, local twitch response (LTR) and SEA. Finally, diagnose myofascial trigger points and make muscle biopsy:1.After HE staining, use microscope to record the modules number and observe the shape and size of modules; 2.Using transmission electron microscope (TEM), observe arrangement of myoneme, sarcomere, mitochondria, etc. All the results of experimental groups and control group were compared and analyzed by SPSS17.0 software package.Results:The average number of myofascial trigger points or taut band of A group was 0.13(1/8) and that of B, C, D group was respectively 3.00 (24/8),2.63 (21/8),2.25 (18/8). When acupunctured, all taut band or nodules could be induced LTR. During resting state, the frequency of SEA in a minute of A, B, C, D group was respectively 2.75±2.87,172.57±102.88,151.63±65.37,168.14±64.53. When the control group was compared with every experimental group, P<0.01 which has highly significant difference; while each experimental group was compared, P> 0.05 which didn't have statistical significance. The amplitude of each group's SEA was 26.06±16.67μV,33.08±18.40μV,93.26±163.18μV,78.27±161.68μV. When A, B group and C, D group were compared, there was significant difference, P<0.05, while there was no significant difference between A group and B group and between C group and D group.The cross-section of pathological section showed:A group had regular muscle cell and uniform size, and was not found different sized, round, augmented and deeply stained muscle cell; All experimental groups were found augmented, round and deeply stained contracture nodules, and also found inflammatory cell infiltration and nuclear transfer phenomena (>10%). The Longitudinal section of pathological section showed:the control group showed a tightly and regular arrangement of longitudinal muscle fibers; all experimental groups were appeared disorganized shuttle-shaped muscle fibers which were swollen in central and thin at both ends. The average muscle cell diameter in each group were 22.84±0.48μm,44.73±9.50μm,45.77±8.70μm,47.81±5.84μm. There was a highly significant difference between experimental groups and the control group, P<0.01, while there was no significant difference between experimental groups.The observation of TEM showed:cross-section of the control group showed regularly arranged thin filament and thick filament, a large number of mitochondria which were ovoid and had whole ridge structures; the longitudinal section shows regularly arranged myofibrils with alternating light band and dark band. The cross-section of experimental groups all showed significantly decreased mitochondria which were round and had less ridge structures or abnormal ones; the longitudinal section showed disordered myofibrils which were blurred and whose Z lines had a water-patterns-like changing. The main sarcomere length in each groups were 1.95±0.02μm,1.92±0.08μm,1.53±0.06μm,1.48±0.071μm, there was a highly significant difference between C, D group and A group,p<0.01, while there was no significant difference between A group and B group and between C group and D group,p>0.05.Conclusions:1. All founds of the experiment which conclude taut band or myofascial trigger points, LTR, SEA and pathological changes demonstrate that myofascial trigger points rat model though striking and eccentric exercise is successful. When the recovery period was extended, myofascial trigger points did not disappeared and could prove that myofacial trigger points can exist in the long time, which is in accordance with the characteristics of clinical MTrPs.2.The SEA generated in MTrPs is a kind of abnormal end plate potential with high frequency and low amplitude, which could prove that MTrPs locate near motor end plate.3.The pathological observation of microscopy illustrate that there are abnormally contracted nodules in myofascial trigger points and MTrPs is a kind of abnormal muscle fiber. Inflammatory infiltration suggests that there may be a inflammatory process during the pathogenesis of MTrPs, and the nuclear transfer may point out a muscle repairing process or muscle that is lost of neural control.4.The observation of TEM suggests that muscle with MTrPs has a energy crisis and injury phenomenon; significantly shorten sarcomere can further prove that the muscle fibers near MTrPs are abnormally contracted fiber. |
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