Obturator Foramen Definition
The obturator foramen is covered by a thin fibrous membrane called obturator membrane, which covers the inner and outer surfaces of the internal and external obturator muscles.
Its superior edge, which is missing from the membrane, forms the ‘obturator canal’ that allows the obturator nerves, arteries and veins to leave the pelvis and enter the medial compartment of the thigh.
The foramen itself is bound by thin, uneven edges, to which a strong membrane is attached, and has a deep groove (the obturator groove) which runs through the pelvis medially and downwards.
This groove converts the canal into a band, which is a particular part of this membrane attached to two tubercles:
- the posterior obturator tubercle at the medial edge of the ischium, before the acetabular notch
- the anterior obturator tubercle between the obturator crest and the superior ramus of the pubis
The obturator foramina reflect the general gender differences between male and female pelvis and are oval in men and broad and triangular in women.
Unilateral pelvic hypoplasia caused by differences in the size of the obturator foramen is rare. Still, it has been reported in individuals whose pelvis has a double obturator foramen (one above and one below the hip bone).