Studies Of Electromyographical Action Potentials And Histopathology Of Myofascial Trigger Points In Rats

Objective:General body pain, most around joints and the spine, is often caused by injuries during daily life activities and sports, which leads to the function disability of joint. This pain has been identified as a result from a histopathology in skeletal muscles. Therefore, the pain is considered as a myofacial pain syndrome, associated with skeletal muscles in which myofascial trigger points activated by many different factors, especially by different kinds of injuries from different life activities.Clinically, pain can be relieved and normal function can be restored through the inactivation of the myofascial trigger points and can be recovered by insistent treatment. But the pathogenesis of myofascial trigger point pain has been unclear. Spontaneous electrical activity (SEA) was found in animal models of myofascial pain trigger points from the research of Yao and Huang; It was found from the studis of Han etc. that the intermittent spontaneous EMG and histopathological changes of muscle fibers showed that it was a gaint and round muscle fiber in the center of the figure. In the experiment of Hubbard and Berkoff, the SEA found around the trigger points showed a resistant low-voltage accompanying a sporadic high-voltage sharp wave. Kruse etc. observed the abnormal action potential in the zone of trigger points. All the evidences stated above confirmed indirectly that abnormal electrical signals were found in trigger points, but characteristics of electrophysiology are not complete and concrete. Although methodological information was provided by animal model of myofascial trigger point from the studies of Yao, Huang and Han, the characteristics of electrophysiology of trigger point were not observed in detail and histological perform was not very clear neither, so it was not to say that the trigger point found by them were the activated ones. Therefore, the aim of this study is to rebuild the animal model of myofascial trigger points to observe the SEA in trigger points and confirm the success of the animal model and whether changes come from motor endplate according to the factor of injuries. And histopathological changes were further observed to confirm the changes of trigger point muscle fibers. Methods:16 male SD rats with average weight of 220g-250g were randomly divided into group A and B. Group A was normal control group, and group B was experimental group. The proximal part of vastus medialis muscle was marked in group B. After group B was combated, the next day, it would do eccentric exercise. The period was 8 weeks. When 8 weeks was gone, group B was kept like the normal group for 4 weeks.At the end of the experiment, results were tested:spasmodic muscle fiber, number of trigger points, twitch response and histopathologic changes. The number and size of nodules will be recorded. All results above were compared with the control group, and all data was analyzed by SPSS16.0 software.Results:The average number of trigger points was 2 in group B (16/8). The trigger points were not be found in group A. Amplitude and time-limit in resting-state:fibrillation potentialⅠwas found in the experimental group, its amplitude compared with that of end-plate potential in control group when insert into the muscle, P<0.01. Mean had a highly significant difference. Time-limit of fibrillation potentialⅠin experimental group was compared with that of end-plate potentials in the control group, P> 0.05. Mean had no statistical significance. Amplitude of fibrillation potentialⅡin experimental group was compared with end-plate potential in control group,0.010.05. Mean had no statistical significance.Amplitude and time-limit of action potential in vastus medialis muscle: Amplitude of experimental group was compared with control group, P<0.01. Mean had highly significant difference. Time-limit of experimental group was compared with control group, P<0.01. Mean had highly significant difference.Biopsy:Contractural round nodules were not found in control group, but were found in experimental group. Average diameter of muscle fiber in control group was 27.84±6.61um; The average diameter of muscle fiber in experimental group was 41.84±6.82um and was compared with the control group, P<0.01. Mean had highly significant difference. And all slices of 40 piece of horizontal and vertical slice were found nodules. And the average number of nodules was 6 (240/40). Circular and spindle-shaped muscle fibers were both gathered.Conclusion:1 Spontaneous potentials of Myofascial trigger points were led by abnormal endplate (fibrillation potentials and positive phase potential), and short spikes of trigger points showed that muscle-derived skeletal muscle was injury.2 Round nodules and spindle-shaped muscle fiber found in trigger points of skeletal muscle were considered that muscle fiber had feature of skeletal muscle-derived injury.3 Characteristic of spontaneous end-plate potential and pathological changes demonstrated that model of trigger points according to the eccentric exercise combining combat was successful.