Objectives: To explore the changes of elbow flexor muscle strength after musculocutaneous nerve injury and its correlation with needle electromyography (nEMG) parameters.
Methods: Thirty cases of elbow flexor weakness caused by unilateral brachial plexus injury (involving musculocutaneous nerve) were collected. The elbow flexor muscle strength was evaluated by manual muscle test (MMT) based on Lovett Scale. All subjects were divided into Group A (grade 1 and grade 2, 16 cases) and Group B (grade 3 and grade 4, 14 cases) according to their elbow flexor muscle strength of injured side. The biceps brachii of the injured side and the healthy side were examined by nEMG. The latency and amplitude of the compound muscle action potential (CMAP) were recorded. The type of recruitment response, the mean number of turns and the mean amplitude of recruitment potential were recorded when the subjects performed maximal voluntary contraction. The quantitative elbow flexor muscle strength was measured by portable microFET 2 Manual Muscle Tester. The percentage of residual elbow flexor muscle strength (the ratio of quantitative muscle strength of the injured side to the healthy side) was calculated. The differences of nEMG parameters, quantitative muscle strength and residual elbow flexor muscle strength between the two groups and between the injured side and the healthy side were compared. The correlation between elbow flexor manual muscle strength classification, quantitative muscle strength and nEMG parameters was analyzed.
Results: After musculocutaneous nerve injury, the percentage of residual elbow flexor muscle strength in Group B was 23.43% and that in Group A was 4.13%. Elbow flexor manual muscle strength classification was significantly correlated with the type of recruitment response, and the correlation coefficient was 0.886 (P<0.05). The quantitative elbow flexor muscle strength was correlated with the latency and amplitude of CMAP, the mean number of turns and the mean amplitude of recruitment potential, and the correlation coefficients were -0.528, 0.588, 0.465 and 0.426 (P<0.05), respectively.
Conclusions: The percentage of residual elbow flexor muscle strength can be used as the basis of muscle strength classification, and the comprehensive application of nEMG parameters can be used to infer quantitative elbow flexor muscle strength.
目的: 研究肌皮神经损伤者的屈肘肌力变化及其与针极肌电图指标的相关性。方法: 收集单侧臂丛神经损伤（累及肌皮神经）致屈肘肌力降低案例30例，根据Lovett肌力分级标准进行徒手肌力评定，并将30例受试者分为A组（伤侧徒手肌力1级和2级，16例）和B组（伤侧徒手肌力3级和4级，14例）。对所有受试者的伤侧和健侧肱二头肌行针极肌电图检测。记录肱二头肌复合肌肉动作电位（compound muscle action potential，CMAP）的潜伏期和波幅。受试者进行最大随意收缩时，记录募集反应类型以及募集电位的平均转折数和平均波幅，并采用microFET 2便携式肌力测试仪检测屈肘定量肌力。计算残存屈肘肌力百分比（伤侧与健侧定量肌力的比值）。比较各针极肌电图指标、定量肌力、残存屈肘肌力百分比在两组之间和组内伤侧与健侧之间的差异。分别分析屈肘徒手肌力分级、定量肌力与针极肌电图指标的相关性。结果: 肌皮神经损伤后B组的伤侧残存屈肘肌力百分比为23.43%，A组的伤侧残存屈肘肌力百分比为4.13%。伤侧徒手肌力分级与募集反应类型相关，相关系数为0.886（P<0.05）。伤侧定量肌力与CMAP潜伏期、波幅以及募集电位的平均转折数和平均波幅均相关，相关系数分别为-0.528、0.588、0.465、0.426（P<0.05）。结论: 残存屈肘肌力百分比可作为肌力分级的依据，针极肌电图指标的综合分析可用于推断屈肘定量肌力。.
Keywords: biceps brachii; compound muscle action potential; forensic medicine; maximal voluntary contraction; muscle strength; musculocutaneous nerve injury; needle electromyography; recruitment potential.