Figure 2.

Diagrams illustrating the developed and tested injection technique for each nerve. (a) Superficial branches of radial nerve (RSbr nn.). A 25 G × 5/8 inch needle is inserted subcutaneously (SC) from a point at the center of the limb at the level of the antebrachiocarpal joint. The needle is advanced approximately 10 mm SC at a 10–20° angle to the long axis of the limb with the bevel facing up. Once the tip of the needle is 3–5 mm from the confluence point of the accessory cephalic and cephalic veins, the injection is made (0.07 ml/kg). (b) Dorsal branch of ulnar nerve (UDbr n.). A point is located lateral to and at the same level as the accessory carpal bone (ACb), positioned between the ACb and the styloid process of the ulna (SpU). A 25 G × 5/8 inch needle is inserted SC distal to proximal so the tip lies at the midpoint of the groove formed between ACb and the SpU, and then the injection is made (0.04 ml/kg). (c) Median nerve (M n.) and superficial branch of palmar branch of ulnar nerve (UPbrS n.): a 25 G × 5/8 inch needle is inserted SC at the distal border of the carpal pad and approximately 5 mm lateral to it, perpendicular to the long axis of the metacarpus, with the bevel facing up. The needle is inserted SC until the point is located two-thirds of the distance from the lateral aspect of the limb to the medial aspect. Two-thirds of the injectate volume is deposited at this point and the remaining volume is injected while the needle is withdrawn (0.08 ml/kg total). Gentle massage is applied to the injected volume under the skin for 5 s. Deep branch of palmar branch of ulnar nerve (UPbrDp n.): a 25 G × 5/8 inch needle is inserted almost perpendicular to the ACb in a mediolateral direction such that the needle contacts the medial palmar aspect of the midpoint of the ACb with the bevel facing up. The needle is then redirected dorsally and advanced on the medial side of the ACb 2–3 mm until it penetrates the flexor retinaculum. At this point the injection is performed (0.01 ml/kg of injectate). Red dots indicate the site of needle insertion. The blue arrows represent the direction of needle insertion to reach the desired injection site