Greengrass RA, Narouze S, Bendtsen T, et al. Cervical plexus and greater occipital nerve blocks: controversies and technique update. Regional Anesthesia & Pain Medicine 2019;44:623-6.

In this article the last two references (number 18 and 19) are missing:

Greher M, Moriggl B, Curatolo M, et al . Sonographic visualization and ultrasound-guided blockade of the greater occipital nerve: a comparison of two selective techniques confirmed by anatomical dissection. Br J Anaesth. 2010; 104:637–42. This reference was inadvertently omitted as reference number 18 from the reference list, and it was mistakenly exchanged with reference number 13 in support of the description of the ultrasound-guided greater occipital nerve block technique on page 626.

Narouze S. Occipital neuralgia diagnosis and treatment: the role of ultrasound. Headache. 2016; 56:801–7. This reference is missing as reference number 19, and it is incorrectly exchanged with reference number 14 in support of the recommendation of Doppler ultrasound for identification of blood vessels prior to needle insertion on page 626.

doi:10.1136/rapm-2018–100261