pelvus

The pelvus, in anatomical terms, refers to the bony ring at the base of the spine that forms the pelvis. It supports the upper body, transmits weight to the lower limbs, and encloses pelvic organs such as the bladder, reproductive organs, and part of the digestive tract. The pelvus consists of the paired hip bones (os coxae), the sacrum, and the coccyx, which together create a closed ring.

Each os coxae is formed by three fused bones: the ilium, ischium, and pubis. The two hip bones join anteriorly at the pubic symphysis and articulate posteriorly with the sacrum at the sacroiliac joints. The pelvus is divided by an imaginary line called the pelvic brim into the greater (false) pelvis and the lesser (true) pelvis. The pelvic inlet marks the boundary between them, while the pelvic outlet lies at the inferior end of the true pelvis. The true pelvis contains the pelvic viscera, whereas the false pelvis largely corresponds to the lower abdomen.

Joints and ligaments stabilize the pelvus. The sacroiliac joints connect the sacrum to the ilia; the pubic symphysis joins the two pubic bones anteriorly; the lumbosacral joint links the lumbar spine to the pelvis. Supporting ligaments reinforce these joints, and the pelvic floor muscles, including the levator ani and coccygeus, form a muscular diaphragm that supports pelvic organs.

Nerves, arteries, and veins supply and innervate the pelvus. Primary blood supply comes from branches of the internal iliac artery, with venous drainage to the internal iliac veins. The lumbosacral plexus provides motor and sensory innervation, complemented by pelvic splanchnic nerves; the pudendal nerve supplies perineal structures.

Clinical relevance includes pelvic fractures, obstetric considerations in the female pelvis, pelvic organ prolapse, and various imaging and surgical planning scenarios. Developmentally, the pelvus arises from fused components of the ilium, ischium, and pubis that form the acetabulum and the pelvic ring, continuing to mature through adolescence.