302
ANATOMY FOR DIAGNOSTIC IMAGING
Fig. 8.20 Axial section of midcalf.
In the lower leg (Fig. 8.20) the tibia lies anteromedially subcutaneously. The fibula lies laterally and is more centrally placed. The interosseus membrane between these separates anterior and posterior compartments. Anterior to the interosseus membrane lie the extensors (dorsiflexors) of the ankle and toes: tibialis anterior and extensor digitorum longus. Peroneus tertius is also part of this group (it extends the ankle in addition to everting the ankle) and is found below the lower third of the fibula. Posterior to the interosseus membrane lie the flexors (plantar flexors) of the ankle and toes. A deep group includes the tibialis posterior and, in the lower two-thirds, the flexor digitorum and flexor hallucis longus muscles. More superficially lie the soleus and the gastrocnemius muscle with its medial and lateral heads. These latter two muscles unite inferiorly to form the calcaneal (Achilles) tendon. A lateral compartment contains two peroneal muscles: peroneus longus and, in the distal two-thirds, peroneus brevis. These are everters of the ankle. The anterior tibial vessels lie anterior to the interosseus membrane deep to the muscles of this compartment. The posterior tibial and peroneal vessels lie between the deep and the superficial muscles of the posterior compartment. At first close together, these vessels separate as they descend and the peroneal vessels come to lie closer to the fibula in the same muscle plane, while the posterior tibial vessels become closer to the tibia.
THE ARTERIES OF THE LOWER LIMB (Figs 8.21-8.23) The external iliac artery becomes the common femoral artery where it crosses under the inguinal ligament midway between the anterior superior iliac spine and the pubic symphysis. The common femoral artery has three superficial branches at this point, namely: • The superficial circumflex iliac artery; • The superficial inferior epigastric artery; and • The superficial pudendal artery. The profunda femoris artery, its biggest branch, arises 5 cm distal to the inguinal ligament and has six branches as follows: • Medial and lateral circumflex femoral arteries; and • Four perforating arteries. Medial and lateral circumflex femoral arteries These arteries form a ring around the upper femur. The lateral circumflex femoral artery has an ascending branch that anastomoses with a branch of the superior gluteal artery and it also sends a descending branch to the knee. Thus it can provide a route of collateral supply capable of bypassing an obstructed common femoral artery or an obstructed superficial femoral artery.
