The Change Of EMG/MCV After Peripheral Nerve Injury And Its Significance Of Forensic Medicine

IntroductionPeripheral nerve injury generally refers to the nerves of limbs, because majority of peripheral nerves exist in subcutaneous tissues, interosseous groove or muscles, and locate in superficial areas, it is easy for them to be hurt by outside force. Peripheral nerve injury can cause limb motor dysfunction in nerve innervation areas, the major manifestation is the decline of muscle strength, and also other clinical symptoms such as muscle atrophy and sensory dysfunction. In the clinical forensic identification, there are often involved the assessing problems about limb dysfunction after peripheral nerve injury. Due to special psychological effect on the certified people, who often exaggerated or camouflaged the state of diseases, the subjective medical examination results can not be trusted. Therefore, how to objectively assess the extent of peripheral nerve injury and the remaining limb dysfunction is an important issue to be resolved in clinical forensic medicine.Electromyogram (EMG) derives the biological changes after the neuromuscular excitation appeared into signal, and enlarge and record graphic curve, and determine neuromuscular function finally. Motor Conduction velocity (MCV) is used to determinate the conduction velocity of nerve impulses pass through the nerve tissue with a certain distance. With super-stimulation on the proximal and distal points of the neural stem, we can record the compound muscle action potential (Compound Muscle Action Potential, CMAP) on the distal muscles dominated by nerves, that is M-wave. Evoked responses include latency, amplitude, area, nerve conduction velocity and other parameters, and all above parameters can evaluate the motor nerve conduction objectively. In clinical forensic identifications, the muscle strength is an important index of motor function evaluation, while manual muscle test is subjective. Some local scholars have studied the relationship between motor nerve conduction velocity and muscle strength, and then evaluated the extent of muscle strength loss. At present, there are some disputations both at home and abroad on whether gender, weight, and left/right limbs induce significant influences on nerve conduction. Domestic and international studies show that the impact of age on wave amplitude is the greatest, the impact of temperature on the conduction velocity is the most significant,while its impact on wave amplitude is not obvious. In my research EMG / MCV were examined in 60 patients with peripheral nerve injury. Taking health side as the control group, the relation between all abnormal indicators of the change rate at affected side/health side and muscle strength is analyzed in order to seek for objective, stable and the most relevant indicators, and presume the strength levels and provide an objective evidence for clinical forensic identification.Material and MethodsExperimental Subjects: 60 cases of patients with peripheral nerve injury, excluded other history of the nervous system diseases, and their muscle strength inspection can be closely cooperated. Over six months of the course of diseases. Choose affected side as the experimental group and the health side as the compared group.Experimental Methods: Poseidon DNI-200~+-evoked EMG, both stimulating electrode and the reference electrode are Saddle-shaped surface electrode, recording electrode is concentric needle electrodes, ground line is connected between stimulating electrode and the reference electrode. Subjects are in a quiet inspection room, with lying posture, and whole muscles are relax. Room temperature is controlled in the scale of 28℃-35℃. EMG parameter setting: Sensitivity 0.1 mV, Term 5ms, Band-pass frequency 2Hz to 10kHz; MCV parameter setting: Sensitivity 1mV, Term 3ms, Current pulse 0.2ms, Stimulating frequency 2Hz, Band-pass frequency 2Hz to 20kHz.EMG checking method: using concentric needle electrodes penetrate abdominal muscle for recording, and determinating abductor pollicis brevis muscle, little finger muscle, stretch total muscle and the anterior tibial muscle. In a EMG muscle test, observation and analysis: (1) Inserting electrical activity; (2) Spontaneous electrical activity; (3) Motor Unit Potential, MUP; (4) Recruitment and interference electrical activity. Checking methods: using a stimulator with positive and negative electrodes separated by 2cm to 3 cm, and penetrateing concentric needle electrodes into abdominal muscle for recording, putting reference electrodes on muscle tendon, giving super-stimulation on injuried nerve to induce M-wave, observing and recording the latency, wave-amplitude, area and nerve conduction velocity.Standards of determing abnormity: EMG: Measuring the muscles innervated by the impaired nerve, if there have wide the motor unit potential with wide latitude, high wave-amplitud when the fibrillation potential, positive sharp wave, insertion potential extented or slight shrinked; or interference can not be collected during re-contraction , all as abnormal. MCV: stimulating the neural stem, and recording action potential of corresponding abdominal muscle, if the latency prolong, wave-amplitude significantly decrease, waveform clearly separated, conduction velocity slow or no M-wave,all as abnormal.Results1. EMG examination of 60 patients showed that 43 cases have detected fibrillation potentials and positive sharp waves on muscles dominated by injury nerves, the abnormal ratio is 71.7%. Other 17 patients have not detected fibrillation potentials and positive sharp waves.2. MCV examination of 60 patients showed that 10 of MCV (16.7%) have no reaction-wave, muscle strength of muscles innervated by impaired nerves is grade-0. The wave-amplitude, the mean decline rate of areas of 19 nerves are more than 94%, MS of muscles innervated by impaired nerves is grade-I or II. The wave-amplitude, the mean decline rate of areas of 19 nerves are about 51%~67%, MS of muscles innervated by impaired nerves is grade-III-IV. All MCV indexs of 8 nerves are in normal range.3. The comparison of relation between EMG/MCV indicators of affected side/health side and the muscle strength in 60 patients showed: the decreased rate of amplitude have the most significant relation with muscle strength(r=0.971, P<0.001), and the relation between the decrease rate of areas and muscle strength is also significant (r=0.961, P<0.001), both of them have a higher relation than latency and conduction velocity.4. In my experiment, 10 muscles with muscle strength grade-0 have all indicator values are 0. Muscle strength grade I-V have cases 9,10,10,13,8 respectively. In muscle strength grade V and I -V group, IV and I group, III and I group, their MUP voltage decreased rate have significantly different (P <0.05), while other groups have no significant difference. There was no significant difference between the decreased rate of wave-amplitude and areas in I and II group of muscle strength (P>0.05) , while other groups have significant difference. The decreased rates of M-wave amplitude and areas were more than 50% in grade I -IV, while the decreased rate of conduction velocity was maximal in I level of muscle strength, the mean was 51%, and their decreased rate of conduction velocity are 51% 32% 40% and 35% respectively. The decreased rate of conduction velocity and latency of grade II are less than gradeIII.Conclusion1. EMG combined with MCV can identify whether there is peripheral nerve injury or not, ascertain injury nerves and reflect nerve function.2. In EMG / MCV inspection, the decreased rates of MUP peak voltage, amplitude, area, conduction velocity of affected side/health side were significantly related with muscle strength, so did the increased rate of latency. The decreased rate of amplitude had the most significant relation with muscle strength and it's a better Objective indicator for evaluation of muscle strength.3. The muscle strength grade can be approximately presumed by the decreased rates of wave-amplitude, the increased rate of latency, the decreased rates of area and conduction velocity.