Ischial tuberosity

The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known informally as the sit bones, or as a pair the sitting bones[1] is a large swelling posteriorly on the superior ramus of the ischium. It marks the lateral boundary of the pelvic outlet.

Ischial tuberosity
Capsule of hip-joint (distended). Posterior aspect. (Ischial tuberosity visible at bottom left.)
The superficial branches of the internal pudendal artery. (Ischial tuberosity visible at center left.)
LatinTuber ischiadicum, tuberositas ischiadica
Anatomical terms of bone

When sitting, the weight is frequently placed upon the ischial tuberosity.[2] The gluteus maximus provides cover in the upright posture, but leaves it free in the seated position.[3] The distance between a cyclist's ischial tuberosities is one of the factors in the choice of a bicycle saddle.


The tuberosity is divided into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, quadrilateral portion.

  • The lower portion is subdivided by a prominent longitudinal ridge, passing from base to apex, into two parts:
  • The upper portion is subdivided into two areas by an oblique ridge, which runs downward and outward:

Additional images

See also


  1. Sills, Franklyn (2004). Craniosacral Biodynamics: The Primal Midline and the Organization of the Body (revised, illustrated ed.). Berkeley, CA: North Atlantic Books. p. 99. ISBN 1-55643-390-5.
  2. Goossens (2005), pp 895–982
  3. Platzer (2004), p 236


This article incorporates text in the public domain from page 235 of the 20th edition of Gray's Anatomy (1918)

  • Goossens R, Teeuw R, Snijders C (2005). "Sensitivity for pressure difference on the ischial tuberosity". Ergonomics. 48 (7): 895–902. doi:10.1080/00140130500123647. PMID 16076744.
  • Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1.
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