what is ischial tuberosity
(Redirected from Tuberosity of the ischium). The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known informally as the sitz bone, or as a pair the sitting bones) is a large swelling posteriorly on the superior ramus of the ischium.It marks the lateral boundary of the pelvic outlet.hen sitting, the weight is frequently placed upon the ischial tuberosity. The gluteus maximus provides cover in the upright posture, but leaves it free in the seated position.