Abstract: Objective     To accurately localise the nerve entry points (NEPs) of the suboccipital muscles, in order to provide anatomical basis for extramuscular nerve blocks in diseases caused by hypertonia  of the suboccipital muscles.    Methods    Twenty-four adult cadavers were used. The NEPs of the suboccipital muscles (rectus capitis posterior minor muscle, rectus capitis posterior major muscle, obliquus capitis superior muscle and obliquus capitis inferior muscle) were dissected, exposed and labeled with barium sulfate, and then, dissections were sutured back in situ. Spiral CT scan and 3D reconstruction were performed. The curved line connecting the external occipital protuberance and the spinous process of 7th cervical vertebra was designed as the longitudinal reference line (L), and the curved line connecting the mastoid process and the spinous process of 7th cervical vertebra was designed as the horizontal reference line (H). The projection points of NEP on the napex and the opposite side skin were recorded as P point and P' point, respectively. Drawing vertical lines from point P to line H and line L respectively, created intersection points on lines H and L, and they were marked as points PH and PL, respectively. The percentage position of PH and PL on H line and L line respectively and the depth of NEP were determined by Syngo system.   Results   Each of the four suboccipital muscles (rectus capitis posterior minor muscle, rectus capitis posterior major muscle, obliquus capitis superior muscle and obliquus capitis inferior muscle) usually had only one NEP. The PH position of the NEPs were located at 46.29%, 35.85%, 28.88% and 32.29%, respectively on the H line. The PL were located at 27.39%, 39.06%, 35.06% and 40.42%, respectively on the L line. The depth of NEPs on PP' line were at 21.21%, 24.02%, 14.59% and 21.44%, respectively. The above percentage values were all mean values. There was no statistical difference between left and right side and between male and female (P>0.05).    Conclusions The accurate definition of the body surface percentage position and depth of these NEPs is conducive to improve the localization efficiency and efficacy for extramuscular nerve blocks when treating the diseases caused by hypertonia of suboccipital muscle.

Key words:  , Suboccipital muscles,  ,  , Nerve entry points,  ,  ,  , Nerve block,  ,  ,  , Localization