Structure and boundaries
Essentially, the obturator canal is an osteofibrous tunnel. Its superior wall is formed by the groove on the inferior surface of the pubic bone. Inferiorly, the canal is bounded by the obturator membrane and muscle fibers attaching along its edges.
The canal has two openings:
- Internal (pelvic) opening — faces inward, opening directly into the prevesical cellular space of the lesser pelvis.
- External opening — is located at the upper margin of the external obturator muscle (m. obturatorius externus). Externally, this opening is reliably covered by the pectineus muscle (m. pectineus), which is why surgeons must transect this specific muscle during surgical access.
Topography and landmarks
Bony and soft-tissue landmarks are used to accurately determine the location of the canal. The projection of the canal onto the skin is located 1.2–1.5 cm inferior to the inguinal ligament (lig. inguinale) and 2.0–2.5 cm lateral to the pubic tubercle (tuberculum pubicum).
Important superficial structures that must be taken into account are located in this topographical region:
- Superior groups of lymph nodes (nodi inguinales superficiales superomediales et superolaterales).
- Inferior group of inguinal nodes (nodi inguinales superficiales inferiores).
- Saphenous hiatus (hiatus saphenus).
- Great saphenous vein (v. saphena magna), draining into the deep venous system in the area of the saphenous hiatus.
Contents: vessels and nerve
A neurovascular bundle passes through the canal, including the obturator artery, vein, and nerve.
Blood supply and anastomoses: The obturator artery (a. obturatoria) forms important collateral circulation pathways. It actively anastomoses with the medial circumflex femoral artery (a. circumflexa femoris medialis) and the inferior gluteal artery (a. glutea inferior).
Innervation: The obturator nerve (n. obturatorius) divides into anterior and posterior branches. They are responsible for innervating the adductor muscles of the thigh, the gracilis muscle (m. gracilis), and provide sensory innervation to the skin on the medial aspect of the thigh.
Clinical significance: referred pain phenomenon
The trunk of the obturator nerve passes through the pelvic cavity in close anatomical proximity to the uterus and ovaries. This close relationship causes an important clinical symptom — the referred knee pain phenomenon.
The essence of the phenomenon is that the patient complains of severe pain in the knee joint area, yet objective examination reveals no pathology of the joint itself. The pathogenesis of this condition is associated with irritation of the n. obturatorius trunk within the lesser pelvis. The primary cause of this irritation is inflammatory processes of the uterus or its appendages (e.g., adnexcitis). Inflammation spreads to the nerve, and the brain interprets the pain impulse as originating from the nerve's innervation zone — in this case, the medial surface of the thigh and the knee area.
Briefly: answers to topical questions
Which muscles does the obturator nerve innervate?
The obturator nerve innervates the adductor muscles of the thigh, the gracilis muscle, and the external obturator muscle, as well as the skin of the medial aspect of the thigh.
- Pectineus muscle (m. pectineus) — thigh adduction
- Adductor longus muscle (m. adductor longus) — thigh adduction
- Adductor brevis muscle (m. adductor brevis) — thigh adduction
- Adductor magnus muscle (m. adductor magnus) — thigh adduction
- Gracilis muscle (m. gracilis) — thigh adduction
- Obturator externus muscle (m. obturatorius externus) — thigh adduction and external rotation
With which arteries does the obturator artery form anastomoses?
The obturator artery anastomoses with the medial circumflex femoral artery, the inferior gluteal artery, and the pubic branch of the inferior epigastric artery in the corona mortis region.
- Medial circumflex femoral artery (a. circumflexa femoris medialis) — collateral blood supply to the hip joint
- Inferior gluteal artery (a. glutea inferior) — anastomosis shown on the pelvic collateral diagram
- Pubic branch of inferior epigastric artery (r. pubicus a. epigastricae inferioris) — forms the dangerous anastomosis corona mortis
What is the "crown of death" (corona mortis) and how is it topographically related to the obturator canal?
Corona mortis is an anatomical vascular variation consisting of an anastomotic connection between the obturator artery and the external iliac artery or its branch, the inferior epigastric artery. It is located close to the pubic bone, near the pubic symphysis.
- Prevalence — in 25–35% of patients.
- Clinical significance — high risk of massive hemorrhage during pelvic fractures and surgical approaches in the inguinal canal region.
Class and exam questions
Where is the internal opening of the obturator canal located?
The internal (pelvic) opening faces the prevesical cellular space of the lesser pelvis.
Which muscle must be transected to access the external opening?
The external opening is covered by the pectineus muscle (m. pectineus), which must be transected during surgical access.
Why does adnexitis cause knee pain?
The obturator nerve passes through the lesser pelvis close to the uterus and ovaries. When they are inflamed, the nerve trunk is irritated, causing referred pain in its innervation zone (including the knee joint).
With which arteries does the obturator artery anastomose?
It forms anastomoses with the medial circumflex femoral artery and the inferior gluteal artery.
What else to study on this topic
- Anastomoses of the obturator artery
- Branches of the obturator nerve and their innervation zones
- Prevesical cellular space of the lesser pelvis
- Topography of superficial inguinal lymph nodes
- Surgical approaches in the medial thigh region
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