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The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, [1] or as a pair the sitting bones, [2] is a large posterior bony protuberance on the superior ramus of the ischium. It marks the lateral boundary of the pelvic outlet.
The superior ramus is a partial origin for the internal obturator and the external obturator muscles. The inferior ramus serves partially as origin for part of the adductor magnus muscle and the gracilis muscle. The inferior ischial ramus joins the inferior ramus of the pubis anteriorly and is the strongest of the hip (coxal) bones.
Its oblique fibres descend laterally, converging to form a thick, narrow band that widens again below and is attached to the medial margin of the ischial tuberosity. It then spreads along the ischial ramus as the falciform process, whose concave edge blends with the fascial sheath of the internal pudendal vessels and pudendal nerve.
The lesser sciatic foramen is an opening between the pelvis and the back of the thigh. The foramen is formed by the sacrotuberous ligament which runs between the sacrum and the ischial tuberosity and the sacrospinous ligament which runs between the sacrum and the ischial spine.
The internal obturator muscle or obturator internus muscle originates on the medial surface of the obturator membrane, the ischium near the membrane, and the rim of the pubis. It exits the pelvic cavity through the lesser sciatic foramen. The internal obturator is situated partly within the lesser pelvis, and partly at the back of the hip-joint.
The ischial bursa is a synovial bursa located between gluteus maximus muscle and ischial tuberosity. [4] When in a seated position, the ischial bursa is put under the highest amount of pressure, which is most significant against a hard surface. [3] Friction from exercise can lead to inflammation of the ischial bursa, known as bursitis. [1]
The ischial spine is part of the posterior border of the body of the ischium bone of the pelvis. It is a thin and pointed triangular eminence, more or less elongated in different subjects. It is a thin and pointed triangular eminence, more or less elongated in different subjects.
These terms are derived from tuber (Latin: swelling)., [8] as is also protuberance, which occasionally is synonymous with "tuberosity". A ramus (Latin: branch) refers to an extension of bone, [9] such as the ramus of the mandible in the jaw or superior pubic ramus. Ramus may also be used to refer to nerves, such as the ramus communicans.