Iliums

Iliums is a nonstandard plural form that is sometimes used in English to refer to more than one ilium, but the preferred anatomical plural is ilia. The ilium is one of the three fused bones that make up each half of the pelvis, along with the ischium and pubis. It forms the upper, wing-like portion of the hip bone.

Anatomy and landmarks. The ilium consists of a central body that participates in forming the acetabulum, the socket of the hip joint, and a broad, flared wing called the ala. The superior border features the iliac crest, which runs from the anterior superior iliac spine to the posterior superior iliac spine. The anterior and posterior superior iliac spines serve as attachment points for ligaments and muscles. The inner surface contains the iliac fossa. The auricular surface articulates with the sacrum at the sacroiliac joint, and the greater sciatic notch lies below the back part of the crest. The ilium also contributes to the greater pelvis and supports abdominal and gluteal muscle attachments.

Development and function. Each ilium develops from primary ossification centers and fuses with the ischium and pubis during childhood to form the hip bone by late adolescence. The ilium supports upper body weight, facilitates upright posture, and provides extensive muscle attachment sites for the gluteal muscles, hip flexors, abductors, and external rotators. It also helps transmit weight from the spine to the lower limbs through the sacroiliac joint.

Clinical relevance. Trauma can injure the ilium or iliac wing, and iliac crest injuries or avulsions are seen in athletes. Pelvic fractures involving the ilium require careful assessment due to proximity to major vessels and organs. In anatomical usage, ilia is the standard plural; iliums is encountered mainly outside specialized medical writing.