Regional Anaesthesia of the Foot Achieved from Two Cutaneous Points of Injection: An Anatomical Study
Abstract
Purpose of the study: Regional anaesthesia for the lower extremity distal to the ankle joint, knows as anaesthetic ankle block or foot block, involves a series of injections of local anaesthetic to block the peripheral nerves that supply innervation to the foot. Since the tibial nerve block is not always effective, the aim of this study was to design a modified technique of anaesthetic application.
Material: The study was carried out on 30 human cadavers provided by the Institute of Anatomy, 1st Faculty of Medicine, Charles University in Prague, and included data on a total of 60 lower extremities. Methods: Information about position of the tibial nerve (or its branches, i.e., the medial plantar and lateral plantar nerves) and the sural nerve was obtained using a set of special measurement devices designed for this purpose.
The following distances were measured; the length of a basic line, i.e., distance between the posterior margin of the medial maleollus and the medial edge of the Achilles tendon (at the level of the upper part of the heel bone); the distance between the medial edge of the Achilles tendon and the tibial nerve; and the distance between the tibial nerve (its deep location) in the neurovascular plexus and the basic line. The location of the sural nerve behind the lateral maleollus was found by measuring the nerve distance from the posterior margin of the lateral maleollus and measuring the distance between this margin and the lateral edge of th Achilles tendon.
Results: The distance between the posterior margin of the medial maleollus (medial edge of the sulcus for the posterior tibial muscle tenton) and the medial edge of the Achilles tendon (at the level of the upper part of the heel bone) was 46.3 mm +- 5.2 mm. The depth of tibial nerve location, i.e. distance from the basic line to the neurovascular plexus, was 11.6 mm +- 1.3 mm.
The distance between the posterior margin of the lateral maleollus and the lateral edge of the Achilles tendon (at the level of the upper part of the heel bone) was 37.1 mm +- 4.3 mm. The sural nerve was located at a distance of approximately 18.3 mm +- 1.9 mm from the posterior edge of the lateral maleollus.
Discussion: The study was concluded by proposing a modified technique of local anaesthetic ankle block using two points of anaesthetic injection. The first point is located immediately in front of the medial edge of the Achilles tendon and above the upper edge of the calcaneus.
The anaesthetic applied will block the tibial and sural nerves, with the sural nerve being blocked by the anaesthetic delivered with a needle advanced through the soft tissues ventral to the Achilles tendon. The second area of application is located at 2 cm above the ventral fold of the ankle joint on the lateral edge of the anterior tibial muscle tendon and provides subcutaneous infiltration anaesthesia for the superficial and deep peroneal nerves and the saphenous nerve.
Conclusions: The results of this anatomical study provided a basis for a modified technique of regional anaesthesia of the foot. Its major clinical attributes involve reduced necessity to manipulate with the patient, and sensory and motor blockage of all nerves supplying innervation to the foot from only two points of injection.