Anatomical landmarks for ankle block

Abstract

We aimed to describe anatomical landmarks to accurately locate the five nerves that are infiltrated to accomplish anaesthesia of the foot in an ankle block. Twenty-four formaldehyde-fixed cadaveric ankles were studied. Photographs of cross sections of the frozen legs, cut at a horizontal plane across the most prominent points of the medial and lateral malleoli, were analysed. The curvilinear distance from the most prominent point of the closest malleolus to each of the five cutaneous nerves and their depth from the skin surface were measured. Sural, tibial, deep peroneal, saphenous and medial dorsal cutaneous nerves were located 5.2 ± 1.3, 9.2 ± 2.4, 7.4 ± 1.9, 2.8 ± 1.1, 2.1 ± 0.6 mm deep to the skin surface. The curvilinear distances from the medial malleolus to the tibial, deep peroneal and saphenous nerves were 32.5 ± 8.9, 62.8 ± 11.1 and 24.4 ± 7.9 mm, respectively. The curvilinear distances from the lateral malleolus to the sural and medial dorsal cutaneous branches of superficial peroneal nerves were 27.9 ± 6.3 and 52.7 ± 7.3 mm, respectively. The deep peroneal nerve was found between the tendons of the extensor hallucis longus and the extensor digitorum longus in the majority of specimens, while the medial dorsal cutaneous nerve was almost exclusively found on the extensor digitorum longus tendon. The sural and tibial nerves were located around halfway between the most prominent point of the relevant malleolus and the posterior border of the Achilles tendon. In conclusion, this study describes easily identifiable, palpable bony and soft tissue landmarks that could be used to locate the nerves around the ankle.

Keywords: Anatomy; Lower extremity; Regional anaesthesia.

Fig. 1

Anatomical landmarks for ankle block. A Medial and lateral views of the foot and leg. B, the horizontal line drawn across the most prominent point of the medial malleolus (MM) and the most prominent point of the lateral malleolus (LM), which is parallel to the knee joint line; A, Achilles tendon. B Cross section of the ankle at a horizontal plane across the most prominent point of the medial malleolus and the most prominent point of the lateral malleolus, which is parallel to the knee joint line. 1, Achilles tendon; 2, tibial nerve; 3, posterior tibial veins; 4, flexor hallucis longus; 5, posterior tibial artery; 6, flexor digitorum longus; 7, tibialis posterior; 8, medial malleolus; 9, talus; 10, great saphenous vein; 11, saphenous nerve; 12, tibialis anterior; 13, extensor hallucis longus; 14, anterior tibial vein; 15, anterior tibial artery; 16, deep peroneal nerve; 17, medial dorsal cutaneous nerve; 18, extensor digitorum longus; 19, lateral malleolus; 20, peroneus longus and brevis; 21, small saphenous vein; 22, sural nerve. C Cross section of the ankle across the plane described in methods, showing the measurements taken for the tibial nerve. MM, the most prominent point of the medial malleolus; T1, the curvilinear distance from the MM to the point where the perpendicular line drawn from the middle of the tibial nerve meets the skin surface; T2, the direct distance from the MM to the posterior border of the Achilles tendon; T3, the direct distance from the MM to the point where the perpendicular line drawn from the middle of the tibial nerve meets the T2 line; dT, the perpendicular distance from the tibial nerve to the skin surface; A, Achilles tendon. D As in C, measurements to the sural nerve. LM, the most prominent point of the lateral malleolus; SR1, the curvilinear distance from the LM to the point where the perpendicular line drawn from the middle of the sural nerve meets the skin surface; SR2, the direct distance between the LM and the posterior border of the Achilles tendon; SR3, the direct distance from the LM to the point where the perpendicular line drawn from the middle of the sural nerve meets the SR2 line; dSR, the perpendicular distance from the sural nerve to the skin surface; SR, sural nerve; A, Achilles tendon. E As in C, measurements to the saphenous nerve and medial dorsal cutaneous nerve. MM, most prominent point of the medial malleolus; LM, most prominent point of the lateral malleolus; S, the curvilinear distance from the MM to the point where the perpendicular line drawn from the middle of the saphenous nerve meets the skin surface; dS, perpendicular distance from the saphenous nerve to the skin surface; SP, curvilinear distance from the LM to the point where the perpendicular line drawn from the middle of the medial dorsal cutaneous nerve meets the skin surface; dSP, the perpendicular distance from the medial dorsal cutaneous nerve to the skin surface; 1, saphenous nerve; 2, great saphenous vein.; 3, medial dorsal cutaneous nerve; 4, extensor digitorum longus tendon. F As in C, measurements to the deep peroneal nerve. MM, the most prominent point of the medial malleolus; DP, the curvilinear distance measured from MM to the point where the perpendicular line drawn from the middle of the nerve meets the skin surface; dDP, the perpendicular distance from the deep peroneal nerve to the skin surface; 1, deep peroneal nerve; 2, anterior tibial artery and vein; 3, extensor hallucis longus tendon; 4, extensor digitorum longus tendon