Topographical study of the trapezius muscle, greater occipital nerve, and occipital artery for facilitating blockade of the greater occipital nerve

The aim of this study was to clarify the topographical relationships between the greater occipital nerve and the trapezius muscle and between the greater occipital nerve and the occipital artery in the occiput in order to increase the success rate of greater occipital nerve blockade. Fifty-six halved heads of 28 cadavers were used in this study. The piercing points and the courses of the greater occipital nerve and occipital artery were analyzed by dividing a line connecting between the external occipital protuberance and mastoid process into three equal parts. A circle with a radius of 2 cm drawn at the medial trisection point of this line was divided into four equal sectors. The greater occipital nerve simply passed the lateral border of the trapezius muscle and then pierced the fascia connecting the cranial attachment of the trapezius muscle with the sternocleidomastoid muscle in 62.5% of the specimens, whereas it pierced the muscle itself in the other 37.5%. The greater occipital nerve and occipital artery pierced the fascia within the 2-cm-radius circle in 85.7% and 98.2% of the specimens, respectively. The piercing points of the greater occipital nerve and occipital artery were observed most frequently in the inferomedial (42.9%) and inferolateral (37.5%) sectors of the circle, respectively. The greater occipital nerve and occipital artery pierced the same sector of the circle and accompanied each other in 51.8% of the specimens. These results are expected to improve the understanding of the topographical relationships between the greater occipital nerve and trapezius muscle and between the greater occipital nerve and occipital artery in the occiput, and thus provide helpful information for the management of occipital neuralgia.