Ischial tuberosity

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.

Ischial tuberosity
Capsule of hip-joint (distended). Posterior aspect. (Ischial tuberosity visible at bottom left.)
Details
Identifiers
Latin	tuber ischiadicum, tuberositas ischiadica
TA98	A02.5.01.204
TA2	1342
FMA	17010
Anatomical terms of bone [edit on Wikidata]

When sitting, the weight is frequently placed upon the ischial tuberosity.^[3] The gluteus maximus provides cover in the upright posture, but leaves it free in the seated position.^[4] The distance between a cyclist's ischial tuberosities is one of the factors in the choice of a bicycle saddle.

Divisions

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 outer gives attachment to the adductor magnus
  • The inner to the sacrotuberous ligament
• The upper portion is subdivided into two areas by an oblique ridge, which runs downward and outward:
  • From the upper and outer area the semimembranosus arises
  • From the lower and inner, the long head of the biceps femoris and the semitendinosus

Additional images

• 
  Muscles of the gluteal and posterior femoral regions, with ischial tuberosity highlighted in red
• 
  Right hip bone. External surface.
• 
  Right hip bone. Internal surface.
• 
  Plan of ossification of the hip bone
• 
  Diameters of inferior aperture of lesser pelvis (female)
• 
  Right hip-joint from the front
• 
  The obturator externus
• 
  Anterior view of the pelvis with the ischial tuberosity labelled in the lower part of the image

See also

• Ischial bursitis
• Sitting disability