OBJECTIVETo determine the effect of tension relaxation by small needle knife on the muscle tension and morphology changes of nerve terminals when sustained pressure was applied to muscular tissue.

METHODSRat gracilis muscles were exposed to pressure in vivo at 70 kPa for 2 hours. Sixty rats were divided into three groups: normal, control and experiment group respectively. In all rats except the six normal ones, the lower legs were considered as the control group, and the right left as experiment group. At day 1, 2 and 3, 9 rats from the two groups were randomly selected and sacrificed in order to determine the muscle tension change. At the same time, muscle histology and morphology changes of nerve terminals were observed.

RESULTSAbnormal tension increased in muscles under compression of 70 kPa. At the 1st and 2nd days, there were no significant differences between the two groups. Compared with control group, the tension was lower in experiment group, and there was statistically significant difference (P < 0.01) between the two groups. Exposure of striated muscle tissue to intensive and prolonged compression may pathologically alter its microstructure. Histological evaluation showed that this stiffening accompanied extensive necrotic damage. The changes could not be found in the nerve terminals.

CONCLUSIONDeep muscle tissue that undergoes prolonged compression may significantly increase its stiffness during acute injury. Tension relaxation applied by small needle knife can effectively reduce the mechanical load which is harmful to the whole tissue.