الملخص
BACKGROUND: Superior trunk of brachial plexus nerve is the part where brachial plexus nerve injury occurred easily during the process of delivery.OBJECTIVE: To perform elongation test, stress relaxation and creeping test on superior trunk of brachial plexus nerve of fresh fetal corpses, and to analyze the mechanical characters of elongation and mechanical characters of visco-elasticity.DESIGN: A randomized and controlled experiment, multiple variable analysis.SETTING: Department of Radiology, China-Japan Union Hospital, Jilin University, Department of Engineering Mechanics, Nanling Campus, Jilin niversity.MATERIALS: The specimens were 30 dead and fresh fetuses aged 6.5 to 8 months, including 16 male and 14 female.METHODS: ①After efrosting at ordinary temperature, superior trunk of brachial plexus nerve was taken out, and 100 samples were cut out along the length wise of specimen. 32 samples were used in elongation test, 32 in stress relaxation test and 32 in creeping test and 4 in pre-test. ②Elongation test, stress relaxation test and creeping test were separate and each test was subdivided into 4 groups: male fetus group of 6.5 to 7 months ,male fetus group of over 8 months, female fetus group of 6.5 to 7 months and female etus group of over 8 months, with 8 samples in each group. ③Superior trunk of brachial plexus nerve was performed one-way elongation test ,and destroy load , intensity limit, maximum strain were obtained; Superior trunk of brachial plexus nerve as performed stress relaxation test and creeping test, and data and curve of stress relaxation test and creeping test were obtained. Experimental data were given normalized treatment and normalized stress relaxation function and normalized creeping function and curve were derived. The experimental data were performed regression analysis with one-dimensional linear regression analysis, then regression coefficient was obtained and experimental curve was fitted.MAIN OUTCOME MEASURES: Mechanical characters of elongation and mechanical characters of visco-elasticity of superior trunk of brachial plexus nerve.RESULTS: ①Destroy load, intensity limit and maximum strain of superior trunk of brachial plexus nerve were all less in fetus group of 6.5 to 7 months than in the fetus group of over 8 months (P ＜ 0.05). There was no significant difference of mechanical characters of elongation among brachial plexus nerves between male and female (P ＞ 0.05). ② 7 200 s creeping quantity was larger in female fetus group of over 8 months than in the male fetus group of over 8 months [(10.2±1.1)%, (7.2±1.08)% ,P ＜ 0.05].7 200 s creeping quantity was basically close in female fetus group of 6.5 to 7 months group to male fetus group of 6.5 to 7 months [(16.7± 1.6)%,(15.1±1.2)%,P ＞ 0.05]. ③ 7 200 s stress relaxation quantity was basically similar in male fetus group of over 8 months to female fetus group of over 8 months (P ＞ 0.05). 7 200 s stress relaxation quantity was larger in male fetus group of 6.5 to 7 months than in female fetus group of 6.5 to 7 months (P ＜ 0.05).CONCLUSION: In the process of delivery, at the same external force, only fewer fetuses with poor ability to resist external force present brachial plexus nerve injury. The individual difference of mechanical characters of elongation of superior trunk of brachial plexus nerve might be caused by heredity, dystrophy and other factors. In addition, at the same strain, the creeping quantity is larger in the female group of small month than in the female group of large month, which might be due to that the development of brachial plexus nerve is not mature in the fetus of small months as that in the fetus of large months.