The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large
posterior bony protuberance on the
superior ramus of the
. It marks the lateral boundary of the
pelvic outlet.
When
sitting
Sitting is a basic action and resting position in which the body weight is supported primarily by the bony ischial tuberosities with the buttocks in contact with the ground or a horizontal surface such as a chair seat, instead of by the low ...
, 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.
[Platzer (2004), p 236] The distance between a
cyclist
Cycling, also known as bicycling or biking, is the activity of riding a bicycle or other types of pedal-driven human-powered vehicles such as balance bikes, unicycles, tricycles, and quadricycles. Cycling is practised around the world fo ...
's ischial tuberosities is one of the factors in the choice of a
bicycle saddle
A bicycle saddle, sometimes called a bicycle seat, is one of five contact points on an upright bicycle, the others being the two Bicycle pedal, pedals and the two handles on the Bicycle handlebar, handlebars. (A bicycle seat in the specific sense ...
.
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 adductor magnus is a large triangular muscle, situated on the medial side of the thigh.
It consists of two parts. The portion which arises from the ischiopubic ramus (a small part of the inferior ramus of the pubis, and the inferior ramu ...
** The inner to the
sacrotuberous ligament
The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends.
Structure
It runs from the sacrum (the lowe ...
* 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
File:Tuberosity of the ischium.PNG, Muscles of the gluteal and posterior femoral regions, with ischial tuberosity highlighted in red
File:Gray235.png, Right hip bone. External surface.
File:Gray236.png, Right hip bone. Internal surface.
File:Gray237.png, Plan of ossification of the hip bone
File:Gray239.png, Diameters of inferior aperture of lesser pelvis (female)
File:Gray339.png, Right hip-joint from the front
File:Gray436.png, The obturator externus
The external obturator muscle or obturator externus muscle (; OE) is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis.
It is sometimes considered part of the medial compartment of thigh, and sometime ...
File:Slide3ADA.JPG, Anterior view of the pelvis with the ischial tuberosity labelled in the lower part of the image
See also
*
Ischial bursitis
*
Sitting disability
Notes
References
*
*
External links
* (, , )
{{Authority control
Bones of the pelvis
Ischium