Femoral canal (canalis femoralis)
This space is pathological and forms exclusively during the development of a femoral hernia, when internal organs protrude beneath the inguinal ligament into the vascular lacuna. The canal lies lateral to the muscular lacuna and is bounded anteriorly and superiorly by the inguinal ligament (lig. inguinale) and the transversalis fascia, posteriorly and medially by the pectineal ligament (lig. pectineale), and anteriorly and inferiorly by the venous lacuna.
The canal has two openings:
- Internal (femoral ring, anulus femoralis): bounded anteriorly by the inguinal ligament, posteriorly by the pectineal ligament, laterally by the femoral vein (v. femoralis), and medially by the falciform margin of the fascia lata.
- External: saphenous opening (hiatus saphenus), which is covered by the cribriform fascia (fascia cribrosa).
The canal contains loose connective tissue, lymphatic vessels, and deep inguinal lymph nodes (including Cloquet's/Rosenmüller's node). In pathology, the hernia sac passes through here.
Adductor canal (canalis adductorius, Hunter's canal)
Located in the middle and lower thirds of the thigh, in the anteromedial region, between the adductor muscles. The canal begins in the upper third of the thigh, where the intermuscular septum overhangs the space, and ends at the adductor hiatus (hiatus tendineus/adductorius) leading into the popliteal fossa.
Walls of the canal:
- Lateral: vastus medialis muscle (m. vastus medialis).
- Medial (roof): vasto-adductor membrane (lamina vastoadductoria).
- Posterior: adductor longus muscle (m. adductor longus) (superiorly) and adductor magnus muscle (m. adductor magnus) (inferiorly).
The canal transmits the femoral artery (a. femoralis), which then continues as the popliteal artery, the femoral vein (v. femoralis), and the saphenous nerve (n. saphenus). Notably, the nerve does not enter the adductor hiatus, but exits the canal through the anterior opening along with the descending genicular artery.
Popliteal fossa (fossa poplitea)
Diamond-shaped and located on the posterior aspect of the knee joint.
Boundaries:
- Superolaterally: tendon of the biceps femoris muscle (m. biceps femoris).
- Superomedially: tendons of the semitendinosus (m. semitendinosus) and semimembranosus (m. semimembranosus) muscles.
- Inferiorly: medial and lateral heads of the gastrocnemius muscle (m. gastrocnemius).
The floor of the fossa is formed by the capsule of the knee joint, the oblique popliteal ligament (lig. popliteum obliquum), and the posterior surface of the femur. The roof is formed by skin and fascia.
The contents are arranged in layers from superficial to deep: closest to the surface is the tibial nerve (n. tibialis), deeper lies the popliteal vein (v. poplitea), and on the very floor is the popliteal artery (a. poplitea). The common fibular nerve (n. fibularis communis) runs more laterally.
Cruropopliteal canal (canalis cruropopliteus)
Extends downwards from the popliteal fossa, situated between the superficial muscles of the leg (triceps surae muscle, m. triceps surae) and its deep layer (tibialis posterior muscle, flexor digitorum longus, and flexor hallucis longus).
In its proximal part, the canal is covered by fascia, and distally it opens via the interosseous aperture near the medial malleolus. It transmits the posterior tibial artery (a. tibialis posterior), accompanying veins, and the tibial nerve (n. tibialis). Compression of structures within this canal can lead to pseudoclaudication syndrome.
Briefly: answers to topical questions
Where is the external ring of the femoral canal located and what is it formed by?
The external ring of the femoral canal is located in the fascia lata 1–2 cm inferior to the medial third of the inguinal ligament. It is represented by the saphenous opening (hiatus saphenus), covered by the cribriform fascia (fascia cribrosa).
The opening is formed by the following structures:
- Falciform margin (margo falciformis) — bounds the opening laterally.
- Superior horn (cornu superius) — the upper part of the falciform margin.
- Inferior horn (cornu inferius) — the lower part of the falciform margin.
What structures form the anterior and posterior walls of the cruropopliteal canal?
The anterior and posterior walls of the cruropopliteal canal are formed by the muscles of the deep and superficial layers of the posterior leg region.
The walls of the canal are formed by the following structures:
- Anterior wall — formed by the tibialis posterior muscle (m. tibialis posterior), and inferiorly by the flexor digitorum longus (m. flexor digitorum longus).
- Posterior wall — formed by the soleus muscle (m. soleus).
What openings does the cruropopliteal canal have?
The cruropopliteal canal has three main openings: one inlet and two outlets.
- Inlet opening — bounded anteriorly by the popliteus muscle (m. popliteus) and posteriorly by the tendinous arch of the soleus muscle (arcus tendineus m. solei).
- Upper outlet opening — bounded laterally by the neck of the fibula (collum fibulae), superiorly by the popliteus muscle (m. popliteus), and inferomedially by the origin of the tibialis posterior muscle (m. tibialis posterior).
- Lower outlet opening — located near the medial margin of the soleus muscle (m. soleus), medial to the Achilles tendon.
What musculoperoneal canals branch off from the cruropopliteal canal?
Sources associate the inferior musculoperoneal canal (canalis musculoperoneus inferior) with the cruropopliteal canal.
- The inferior musculoperoneal canal is formed by the fibula and the flexor hallucis longus muscle (m. flexor hallucis longus).
- Its contents are the fibular artery and veins (a. et vv. fibulares).
- The fibular artery branches off the posterior tibial artery and courses laterally into the inferior musculoperoneal canal.
The superior musculoperoneal canal is also described in literature, but as a canal in the region of the fibular neck containing the common fibular nerve; its direct branching from the cruropopliteal canal is not specified.
Class and exam questions
Where is the internal ring of the femoral canal located and how is it formed?
The internal ring (anulus femoralis) is located in the vascular lacuna. It is bounded anteriorly by the inguinal ligament, posteriorly by the pectineal ligament, medially by the falciform margin of the fascia lata, and laterally by the femoral vein.
What structures pass through the adductor canal?
It transmits the femoral artery, femoral vein, and saphenous nerve (n. saphenus). The artery and vein enter the popliteal fossa, while the nerve exits through the anterior wall of the canal.
How are the elements of the neurovascular bundle arranged in the popliteal fossa?
Proceeding from superficial to deep (and from medial to lateral), the arrangement is as follows: tibial nerve (n. tibialis), popliteal vein (v. poplitea), popliteal artery (a. poplitea).
What else to study on this topic
- Muscles of the dorsum and sole of the foot
- Tendon sheaths and synovial bursae of the foot
- Innervation and blood supply of the foot
- Fasciae of the lower limb and retinacula (retinacula)
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