Objective: To compare the risk angle and safety angle of n eedli ng Ya me n (GV 15) betwee n the atla nto-axial dislocati on (AAD) patients and healthy subjects. Methods: A total of 177 AAD patients diagnosed and treated at the Center of Upper Cervical Vertebra of Beijing Chin a-Japa n Frie ndship Hospital betwee n January 2010 and January 2018 were in eluded in the AAD group. Ano ther 207 healthy subjects were included in the normal group. There were totally 191 males and 193 females. The MRI sean was performed for the cervical vertebrae to measure the risk angle and safety angle of acup un cture at Ya me n (GV 15) on the sagittal image. Results: In the AAD group, the risk angle was (13.14±3.99)° and the relative safety angle was (10.31±3.23)° for the perpendicular needling, while the oblique needling risk angle was (9.09±3.09)° for the male;the risk angle was (12.12±2.74)° and the relative safety angle was (10.56±2.09)° for the perpendicular needling, while the oblique needling risk angle was (9.70±2.95)° for the female. In the normal group, the risk angle was (7.89±1.59)° and the relative safety angle was (10.21±3.55)° for the perpendicular needling, while the oblique needling risk angle was (16.07±1.77)° for the male;the risk angle was (6.93±1.45)° and the relative safety angle was (10.70±2.94)° for the perpendicular needling, while the oblique needling risk angle was (14.89±2.18)° for the female. The perpendicular needling risk angles for the males and females in the AAD group were larger than those in the normal group, and the differences were statistically significant (both P<0.01);for the inner-group comparison, there was no sigrHficant difference in the perpendicular needling risk angle between the male and the female in the AAD group (P>0.05);however, the perpendicular needling risk angle for the male was larger than the female, and the differenee was statistically significant in the normal group (P<0.01). There were no sign讦icant differences in the relative safety angle for bo
