Abstract: BACKGROUND: Cervical rotatory manipulation is widely used in the treatment of neck-related diseases with a clear curative effect, but it also has some risks in clinical practice. The previous study of our group found that cervical rotatory manipulation can reduce the tensile mechanical properties of the atherosclerotic carotid artery, but it is not clear about the effects of different cervical rotatory manipulations (positioning/non-positioning) and different degrees (mild/moderate/severe) of atherosclerosis on the tensile mechanical properties of the carotid artery. 
OBJECTIVE: To explore the effects of different cervical rotatory manipulations and different degrees of atherosclerosis on the tensile mechanical properties of the internal carotid artery. 
METHODS: The 120 male New Zealand rabbits were randomly divided into eight experimental groups with different degrees of atherosclerosis and different cervical rotatory manipulations: severe atherosclerosis + positioning/non-positioning cervical rotatory manipulation, moderate atherosclerosis + positioning/non-positioning cervical rotatory manipulation, mild atherosclerosis + positioning/non-positioning cervical rotatory manipulation, and normal rabbit + positioning/non-positioning cervical rotatory manipulation, as well as three model control groups: mild/moderate/severe atherosclerosis + non-cervical rotatory manipulation, and the blank control group. Two-factor analysis of variance was used to explore the main effects and interactive effects of different cervical rotatory manipulations and different degrees of atherosclerosis on the tensile mechanical properties of the internal carotid artery. One-way analysis of variance was applied to explore the influence of different cervical rotatory manipulations on the tensile mechanical properties of the internal carotid artery under the same degree of atherosclerosis.  
RESULTS AND CONCLUSION: (1) Both different cervical rotatory manipulations and different degrees of atherosclerosis were the main effect factors affecting the tensile mechanical properties of the internal carotid artery. (2) For both mild and severe atherosclerosis, both positioning and non-positioning cervical rotatory manipulations reduced the maximum stress of the internal carotid artery (P < 0.05) and also increased the physiological elastic modulus of the internal carotid artery (P < 0.05). (3) For moderate atherosclerosis, positioning and non-positioning cervical rotatory manipulations also increased the physiological elastic modulus of the internal carotid artery (P < 0.05). Non-positioning cervical rotatory manipulation reduced the maximum strain of the internal carotid artery (P < 0.05), and its maximum strain was also less than the internal carotid artery of the positioning cervical rotatory manipulations (P < 0.05). (4) For the normal internal carotid artery, in addition to the maximum strain, both positioning and non-positioning cervical rotatory manipulations had no statistically significant effects on other tensile mechanical indicators of the internal carotid artery (P > 0.05). (5) The results suggest that both positioning and non-positioning cervical rotatory manipulations may increase the stiffness of the atherosclerotic internal carotid artery, reducing its elasticity and brittleness. Therefore, both positioning and non-positioning cervical rotatory manipulations may increase the risk of cardiovascular events in mild/moderate/severe atherosclerotic internal carotid artery, and the more severe the atherosclerosis is, the greater the risk of positioning/non-positioning cervical rotatory manipulation treatment, but the risk of positioning cervical rotatory manipulation is not lower than that of non-positioning cervical rotatory manipulation. 

Key words: atherosclerosis, positioning cervical rotatory manipulation, non-positioning cervical rotatory manipulation, tensile mechanical property, factor analysis