ísquio

The ischium, or os ischii, is one of the three bones that make up the hip bone (os coxae) in humans. It forms the lower, posterior portion of the pelvis and contributes to the acetabulum, the socket for the thigh bone, along with the ilium and pubis. The ischium helps support the body’s weight when sitting and provides attachment points for muscles and ligaments.

Anatomically, the ischium consists of a body and a ramus. The body forms the posterior part of the acetabulum and features the ischial spine, which marks the boundary between the greater and lesser sciatic notches. The ischial tuberosity, a prominent rounded projection on the inferior part of the bone, serves as the main weight-bearing area when seated and is a key attachment site for the hamstring muscles. The ramus extends anteriorly and merges with the inferior ramus of the pubis to form the ischiopubic ramus.

Articulations and landmarks: the ischium articulates with the ilium and pubis at the acetabulum, and with the pubis via the ischiopubic ramus. The greater and lesser sciatic notches, separated by the ischial spine, are transformed into foramina by the sacrospinous and sacrotuberous ligaments.

Function and attachments: the ischial tuberosity provides attachment for the hamstrings (semitendinosus, semimembranosus, and the long head of the biceps femoris) and for the sacrotuberous ligament. Its structure supports weight bearing in a seated position and serves as a leverage point for surrounding muscles.

Development and clinical notes: the ischium develops from cartilage and fuses with the ilium and pubis during adolescence. Fractures or avulsion injuries involving the ischial tuberosity or ramus can occur with trauma or high-load sports.