Metatarsal and Transthecal Blocks

The metatarsal block is an easy technique for providing good pain relief after surgical procedures on the toes.^[260] The child is placed in the supine position, and the head of the relevant metatarsal is palpated. The technique consists of inserting a standard intramuscular needle into the dorsum of the foot in close contact with the medial border of the base of the metatarsal up to the sole, until the distal extremity of the needle is felt and seen as it pushes the skin of the sole. A volume of 1 to 3 mL of 0.25% to 0.5% plain bupivacaine or 0.2% to 0.5% ropivacaine is then injected while the needle is slowly withdrawn. The same procedure is repeated along the lateral border of the same metatarsal to provide full anesthesia of the relevant toe.

A still simpler technique can be used instead. The synovial sheath of the flexor tendon of each toe is surrounded by a fibrous sheath, within which run all the nerves supplying the toe. The intrathecal technique consists of filling this closed fascial sheath with a local anesthetic in order to contact and block the nerves supplying the toe with a single-injection technique. The child is placed in the supine position. The anesthesiologist locates by palpation the head of the relevant metatarsal on the sole of the foot and inserts an intradermic needle perpendicular to the skin, in the center of the skin projection of this metatarsal head, until bone contact is made. To prevent any subperiosteal injection, the needle is slightly withdrawn before injecting 1 to 3 mL of local anesthetic until resistance to injection is felt. Within 2 minutes, full anesthesia of the relevant toe is obtained in virtually all

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These two techniques have many advantages over the classic ring block because they are safer (i.e., no terminal artery nearby and virtually no complications), simpler, and less painful in conscious patients, even though injection is not pain free. However, the technique should be avoided in cases of infection to avoid bacterial contamination of the synovial sheath.