The obturator foramen is the largest foramen in the skeleton, formed by the ischium posteriorly and the pubis anteriorly and superiorly. It is almost entirely covered by the obturator membrane, which leaves only a small superolateral gap, the obturator canal, through which the obturator nerve, artery, and vein pass from the pelvis into the medial thigh. The obturator internus muscle lines the inner surface of the foramen and membrane.
| Articulations |
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|---|---|
| Landmarks |
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| Ossification | Enclosed by the pubis and ischium, whose primary centres appear at about the fourth to fifth fetal month; the ischiopubic ramus closing its inferior border fuses at about 7-8 years. |
The obturator foramen and the obturator canal are relevant in obturator hernia, a rare hernia occurring predominantly in elderly thin women where abdominal contents herniate through the obturator canal and compress the obturator nerve, producing the Howship-Romberg sign (medial thigh pain reproduced by hip extension, adduction, and internal rotation). The obturator canal is accessed in obturator nerve block for hip adductor surgery. Acetabular fractures involving the anterior column may disrupt the superior pubic ramus adjacent to the obturator foramen.
Small bowel herniation through the obturator canal compresses the obturator nerve, producing the pathognomonic Howship-Romberg sign of medial thigh pain worsened by hip extension and adduction; CT confirms a soft tissue mass at the medial obturator foramen and emergency surgery prevents bowel strangulation.
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