Posterior leg region

Superficial structures and skin innervation

An extensive network of venous and neural pathways lies beneath the skin of the posterior leg region. The key venous vessel is the small saphenous vein (v. saphena parva). It originates in the subcutaneous tissue, courses around the lateral malleolus, and runs upward and medially. In the lower third of the leg, it gives off numerous perforating veins (vv. perforantes) connecting it to the deep venous system. Ascending into the middle third, the vein pierces the fascia, runs within the fascial cleft (Pirogov's canal), passes subfascially between the heads of the gastrocnemius muscle, and empties into the popliteal vein (v. poplitea). Along its path, the vein is accompanied by the medial sural cutaneous nerve (n. cutaneus surae medialis).

Skin innervation has a distinct zonal distribution:

• Lateral surface is supplied by the lateral sural cutaneous nerve (n. cutaneus surae lateralis), a branch of the common fibular nerve.
• Distal region and skin of the lateral malleolus are innervated by the sural nerve (n. suralis), which is formed by the union of the medial and lateral sural cutaneous nerves.
• Posteromedial surface receives branches from the saphenous nerve (n. saphenus), which is a branch of the femoral nerve.
• Remaining skin areas are supplied by small branches of the tibial and fibular nerves.

Fascia and muscle layers

The crural fascia (fascia cruris) forms an isolated posterior fascial compartment (compartimentum cruris posterius) on the posterior surface. Medially, the fascia attaches to the tibia (tibia), and laterally, it sends a septum to the fibula (fibula), reliably separating the posterior compartment from the lateral one. Within the compartment, the deep fascial layer divides the muscles into two layers: superficial and deep.

The superficial layer includes the gastrocnemius, soleus, and plantaris muscles. The narrow tendon of the plantaris muscle (m. plantaris) runs directly beneath the gastrocnemius muscle. The tendons of these three muscles merge to form the strong calcaneal (Achilles) tendon (tendo calcanei), which attaches to the calcaneal tuberosity (tuber calcanei).

Deep layer consists of flexor muscles. Their topography from the medial to the lateral margin is as follows:

1. Flexor digitorum longus (m. flexor digitorum longus).
2. Tibialis posterior (m. tibialis posterior) — occupies a central position.
3. Flexor hallucis longus (m. flexor hallucis longus). It is important to note that despite its lateral position within the compartment, the tendon of this muscle courses medially toward the great toe, passing through the medial retromalleolar region.

Topography of anatomical canals

The most important fascial space in this region is the cruropopliteal canal (canalis cruropopliteus). Vessels and nerves enter it through the superior inlet. From this canal, the anterior tibial artery (a. tibialis anterior) branches off into the anterior fascial compartment. It enters there via the upper outlet of the canal, which is bounded by three structures:

• Laterally: neck of the fibula (collum fibulae);
• Superiorly: popliteus muscle (m. popliteus);
• Medially and inferiorly: origin of the tibialis posterior muscle.

Another significant pathway is the inferior musculofibular canal (canalis musculofibularis). Vessels from the main deep bundle pass into it. The walls of this narrow canal are formed by: the tibialis posterior anteriorly, the fibula laterally, and the flexor hallucis longus posteriorly.

Deep neurovascular bundle of the leg

The main neurovascular bundle runs in the deep fascial compartment of the leg. It includes the posterior tibial artery (a. tibialis posterior), which is a direct and larger continuation of the popliteal artery, and the tibial nerve (n. tibialis). The nerve is located strictly lateral to the arterial trunk.

At the border of the upper and middle thirds of the leg, a large branch arises from the posterior tibial artery and courses obliquely downward and laterally into the musculofibular canal.

The topography of the main bundle changes along its course. In the upper third, it lies directly on the posterior surface of m. tibialis posterior. However, in the lower third, due to the anterior displacement of the belly and tendon of the tibialis posterior muscle, the bundle shifts and rests upon the flexor digitorum longus. The bundle emerges from beneath the soleus muscle at the border of the middle and lower thirds of the leg.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Specific topographic features of Pirogov's canal
• Anastomoses between the great and small saphenous vein systems
• Cross-over of deep flexor tendons in the lower third of the leg
• Topography of the branches of the posterior tibial artery
• Perforating veins (perforators) and their clinical significance

Other topics in the "Lower Limb" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.