Same impact momentum causes different degrees of spinal cord injury

The weight-drop impact is widely used in making animal model of spinal cord injury(SCI).But there has not yet been an appropriate unit for the quantification of the impact.In this study,we compared the degrees of the spinal cord injury caused by weight-drop impact with the same momentum but different combinations of drop weight and drop height,in order to test whether‘‘momentum’’is capable of being the unit for the quantification of weightdrop impact.Thirty adult rats were randomly allocated to three groups and were injured with 5 g–10 cm(group A),10 g–2.5 cm(group B)and 15 g–1.11 cm(group C)impacts with the same momentum to the spinal cord,respectively.Open-field locomotor function was evaluated using the Basso–Beattie–Bresnahan(BBB)locomotor rating scale.The percentage of spared tissue area(STA)at the epicenter,and 500,1000 and 1500 lm from the epicenter was calculated using serial sections stained by hematoxylin and eosin.As a result,the behavioral recovery(BBB scores)and the STA percentage were similar in group B and group C.However,the BBB score in group A was significantly lower than that in groups B and C at the same time point post injury.The STA percentage was significantly less and the lesion/cavity length was significantlygreater in group A than in groups B and C.These suggested that the 5 g–10 cm weight-drop impact,compared with the other two impacts with different weights and heights,caused a greater damage of the spinal cord when the momentum was the same.So,these impacts with the same momentum but different weights and drop heights cause different degrees of spinal cord injury.Momentum alone is inadequate to be the unit for the qualification of weightdrop impact and to be used to predict the extent of injury.