The hip bone (also pelvic bone, coxal bone, innominate bone latin: os coxae) is a bony structure composed of the ilium, ischium and pubis, which forms around age 20. The left and right hip bones join at the pubic symphysis.
Several structures on each side form between the three bones composing the hip bone, such as the acetabulum and obturator foramen.
The acetabulum is a deep cavity in the hip bone, where the head of the thigh bone (femur) fits forming the hip joint. The ischium forms the lower and side borders of the acetabulum, the forms the upper boundary, while the rest formed by the pubis, near the midline.
The acetabulum features the following landmarks:
- lunate surface,
- acetabular fossa,
- acetabular notch,
- iliopubic eminence.
The lunate surface of the acetabulum is the curved articular surface surrounding the acetabular fossa, which articulates with the head of the femur.
The acetabular fossa is a circular non-articular depression located at the center of the acetabulum of the hip bone, which is occupied by the ligament of the head of the femur. Downwards the acetabular fossa is continuous with the acetabular notch.
The acetabular notch is a deep notch in the acetabulum of the hip bone, which is continuous with the acetabular fossa below it. The edges of the notch serve for attachment of the ligament of the head of the femur. The acetabular notch is transformed into a foramen by the transverse acetabular ligament, and through this foramen nerves and blood vessels enter the hip joint.
The iliopubic eminence (or iliopectineal eminence) is a flat prominence at the proximal part of the pubis marking the point of union between the ilium and pubis bones. The iliopubic eminence is the medial boundary of the groove, over which the iliacus and psoas major muscles pass.
The obturator foramen is a large opening on each side of the pelvic skeleton in the hip bone formed by the ischium and pubic bones. The obturator artery, vein, and nerve pass out of the pelvis through the obturator foramen.