Elastic resistance to puncture of the sciatic nerve (cadaver specimen). CT scan of the thigh at the level of the trochanter minor (a). You can see the sciatic nerve between the adductor muscles (Adductor Magnus muscle) and hamstrings (Long hear of biceps muscle and semitendinosus). In figures (b), (c), and (d), we can see the elastic resistance to puncture the nerve. This effect is important to prevent the puncture of the fascicles or group of fascicles (see Chap. 15)

Sciatic nerve intraneural injection (cadaver study). (a) Proximal spread. (b) View of the needle inside the nerve. (c) Distal intraneural spread. (a) The subepineurial contrast in the middle of the nerve is surrounded by a thin halo. (c) Air can be seen inside the nerve, with an increase of the area of the nerve

(a–c) Sciatic nerve intraneural injection after popliteal block. View the separation of fascicles of the sciatic nerve, with concentric layers of contrast on the right side (a). The section area of the block side (a) is greater than the area of the contralateral side (c) (white arrows)

Sciatic nerve intraneural injection after popliteal block. Coronal view in consecutive sections that show the separation of fascicles of the sciatic nerve (black arrows), with contrast between the fascicles. White arrows are marking the level of injection and showing proximal and distal spread between the fascicles