LKnative - Radial nerve block 
Radial nerve (green arrow), triceps muscle (green asterix), humerus (red arrows)
14 – Sonoanatomy of the radial nerve distal to the radial sulcus of the humerus
The radial nerve can be tracked proximally with ultrasound from the lateral epicondyle to the radial humeral sulcus
The radial nerve becomes an anechoic rounded profile just distal to the radial humeral sulcus