Darmbein

Darmbein, known in Latin as os ilii, is the largest part of the hip bone (os coxae). It forms the superior portion of the pelvis and contributes to the acetabulum, the socket that articulates with the femoral head. The ilium also participates in the sacroiliac joint with the sacrum.

Anatomy and features: The ilium consists of a body and a broad ala (wing). The iliac crest runs along the superior border; the anterior superior iliac spine (ASIS) and anterior inferior iliac spine (AIIS) lie on the anterior margin, while the posterior superior iliac spine (PSIS) and posterior inferior iliac spine (PIIS) lie on the posterior margin. The inner surface forms the iliac fossa; the outer surface shows the gluteal lines. The auricular surface on the posterior portion articulates with the sacrum, and the greater sciatic notch lies near the posterior border. Together with the pubis and ischium, the ilium contributes to forming the acetabulum, the hip socket.

Function and clinical relevance: The ilium provides broad attachment sites for the gluteal muscles on the outer surface and for abdominal and back muscles on the inner surface. It helps transmit body weight from the spine to the lower limbs and defines the boundaries of the true and false pelvis.

Development and naming: The ilium ossifies from multiple centers and fuses by late adolescence. The term Darmbein reflects the German name for this bone; in English-language texts it is called the ilium (os ilii).