The obturator foramen is a large, bilaterally paired opening and a significant anatomical landmark of the hip bone. It serves as a conduit for various essential elements that connect the pelvic region to the lower limbs.
Location
The obturator foramen is precisely located on the anterior and inferior aspects of the bony pelvis. It is situated below and slightly in front of the acetabulum, which is the hip socket where the thigh bone articulates. This opening is found on each side of the pelvis, forming a prominent aperture within the hip bone itself. The foramen lies anterior to the ischial tuberosity, the bony prominence commonly known as the “sitting bone,” and inferior to the pubic symphysis, the cartilaginous joint connecting the left and right pubic bones. Its distinct location allows for critical anatomical connections between the pelvic cavity and the thigh.
The Bones That Define It
The obturator foramen is not a simple hole but a carefully constructed opening formed by specific parts of the hip bone. It is primarily enclosed by two of the three bones that fuse to create the hip bone: the ischium and the pubis. These bones contribute distinct sections to define the foramen’s margins.
The inferior and posterior aspects of the foramen are formed by the ramus of the ischium and the inferior pubic ramus, which together create the ischiopubic ramus. The superior margin of the foramen is defined by the superior pubic ramus and a portion of the ischium’s body. Along the superior margin, specifically on the inferior surface of the superior pubic ramus, there is a small indentation called the obturator groove. This groove is important because it is not fully covered by the membrane that otherwise spans the foramen, thus forming a small passageway for structures.
What Passes Through
While the obturator foramen is a large opening, it is mostly covered by a fibrous sheet called the obturator membrane. This membrane provides attachment points for muscles and helps to complete the pelvic floor. A small, uncovered section of the foramen remains in its superolateral aspect, forming a distinct channel known as the obturator canal.
This canal serves as a conduit for several structures passing between the pelvis and the medial compartment of the thigh. The elements traversing this canal include the obturator nerve, obturator artery, and obturator vein. The obturator nerve is responsible for both motor and sensory functions, providing sensation to the skin of the inner thigh and innervating the adductor muscles that bring the legs together. The obturator artery supplies blood to the adductor muscles of the thigh. The obturator vein drains blood from the hip joint and pelvic muscles, leading to the internal iliac vein.
Clinical Insights
The obturator foramen can be involved in medical conditions. One uncommon condition is an obturator hernia, which occurs when abdominal contents, such as a loop of intestine, protrude through the obturator canal. This type of hernia is rare, accounting for less than 0.04% of all hernias, and is more frequently observed in older, underweight women. Symptoms can include abdominal pain, nausea, vomiting, and pain radiating to the inner thigh, often making diagnosis challenging.
The obturator nerve is also susceptible to compression or injury. This can lead to a condition known as obturator neuropathy or entrapment, characterized by pain in the groin and inner thigh, numbness, and weakness in the adduction (bringing together) of the leg. Nerve issues can arise from trauma, surgery, or tight muscles.