[Truncal anesthesia of the foot at the level of the ankle: an additional reference mark for the approach to the posterior tibial nerve]

Abstract

Nerve trunk blocks at the ankle could be a most interesting technique of regional anaesthesia. Unfortunately the posterior tibial nerve is difficult to locate with the usual recommended anatomical landmarks (the tibialis posterior artery). The use of the flexor hallucis longus tendon as an additional landmark has been tested in 71 patients scheduled for surgery on the foot (emergency trauma surgery, amputations, ingrowing toe-nails, removal of bedsores, verrucas). Seventy per cent were males. Their age ranged from 3 to 92 years (average 62 years), with 26% being less than 50 years old, and 43% more than 70. A block of the subcutaneous nerves, at the level of the ankle, (medial and lateral sural cutaneous, superficial peroneal, saphenous, medial calcaneal nerves) was followed by a block of the posterior tibial and deep peroneal nerves (sub-aponeurotic nerves). The total number of nerves blocked depended on the use of an ankle tourniquet, and the area involved by surgery. For each nerve blocked, 3 to 6 ml of a mixture containing equal parts of 2% lignocaine and 0.5% bupivacaine were used. The maximum doses injected were 4 mg.kg-1 lidocaine and 1 mg.kg-1 bupivacaine. Anaesthesia was obtained in 10 +/- 3 min, lasting from 180 to 240 min. There were 88.7% excellent results (n = 63), with 7% fair (n = 5) and 4.2% bad (n = 3) results. Failure concerned 5 cases of tibial nerve block, often due to landmark difficulties (great toe previously amputated, significant ankle oedema, lack of operator experience) and, in 3 cases, forgetting to block a nerve involved.(ABSTRACT TRUNCATED AT 250 WORDS)