isquion

The isquion, or isquión in some languages, refers to the posterior and inferior portion of the hip bone (os coxae). It forms part of the acetabulum with the ilium and pubis and contributes to the boundary of the pelvic cavity and the obturator foramen. The isquion consists of a body, which forms the postero-inferior part of the acetabulum, and a ramus that unites with the inferior ramus of the pubis to form the ischiopubic ramus.

Prominent features include the ischial tuberosity, a thick, rough projection that bears weight when sitting; the ischial spine, which separates the greater and lesser sciatic notches; and the greater and lesser sciatic notches that provide passage for nerves and vessels. The inferior portion features the ischiopubic ramus that articulates with the pubis.

Development: the ilium, ischium, and pubis fuse in the acetabulum during adolescence to form a single os coxae.

Function: serves as a site of muscle origin for the hamstring muscles (semitendinosus, semimembranosus, long head of biceps femoris) and as a weight-bearing region when seated; attachment points for ligaments like the sacrotuberous.

Clinical notes: fractures or avulsion injuries of the ischial tuberosity can occur in athletes, often with sudden acceleration or sprinting; fractures of the acetabulum are more complex.