ObjectiveTo compare the risk angle and safety angle of needling Yamen (GV 15) between the atlanto-axial dislocation (AAD) patients and healthy subjects.MethodsA total of 177 AAD patients diagnosed and treated at the Center of Upper Cervical Vertebra of Beijing China-Japan Friendship Hospital between January 2010 and January 2018 were included in the AAD group. Another 207 healthy subjects were included in the normal group. There were totally 191 males and 193 females. The MRI scan was performed for the cervical vertebrae to measure the risk angle and safety angle of acupuncture at Yamen (GV 15) on the sagittal image.ResultsIn the AAD group, the risk angle was (13.143.99)degrees and the relative safety angle was (10.313.23)degrees for the perpendicular needling, while the oblique needling risk angle was (9.093.09)degrees for the male; the risk angle was (12.122.74)degrees and the relative safety angle was (10.562.09)degrees for the perpendicular needling, while the oblique needling risk angle was (9.70 +/- 2.95)degrees for the female. In the normal group, the risk angle was (7.89 +/- 1.59)degrees and the relative safety angle was (10.21 +/- 3.55)degrees for the perpendicular needling, while the oblique needling risk angle was (16.07 +/- 1.77)degrees for the male; the risk angle was (6.93 +/- 1.45)degrees and the relative safety angle was (10.70 +/- 2.94)degrees for the perpendicular needling, while the oblique needling risk angle was (14.89 +/- 2.18)degrees 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 significant 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 difference was statistically significant in the normal group (P<0.01). There were no significant differences in the relative safety angle for both the male and the female between the AAD group and the normal group (both P>0.05). For the inner-group comparison, there was no significant difference in the relative safety angle between the male and the female (P>0.05). The oblique needling risk angles for both the males and females were smaller in the AAD group than those in the normal group, and the differences were statistically significant (both P<0.01); the oblique needling risk angle for the male was not significantly different from that for the female in the AAD group (P>0.05); in the normal group, the oblique needling risk angle for the male was larger than that for the female, and the difference was statistically significant (P<0.01).ConclusionUnder the AAD condition, the risk angle and safety angle of acupuncture at Yamen (GV 15) change significantly, perpendicular needling should be better if performed slightly lower than the horizontal direction, and the oblique needling should be safer across the occipital foramen toward the occipital bone.