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 swelling
posteriorly
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
on the
superior ramus of the
. It marks the lateral boundary of the
pelvic outlet
The lower circumference of the lesser pelvis is very irregular; the space enclosed by it is named the inferior aperture or pelvic outlet. It is an important component of pelvimetry.
Boundaries
It has the following boundaries:
* anteriorly: the pub ...
.
When
sitting
Sitting is a List of human positions, 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, in ...
, the weight is frequently placed upon the ischial tuberosity. The
gluteus maximus
The gluteus maximus is the main extensor muscle of the hip. It is the largest and outermost of the three gluteal muscles and makes up a large part of the shape and appearance of each side of the hips. It is the single largest muscle in the huma ...
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, when on a two-wheeled bicycle, called bicycling or biking, is the use of cycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", or "bikers". Apart from two ...
's ischial tuberosities is one of the factors in the choice of a
bicycle saddle
A bicycle saddle, often called a bicycle seat, is one of five contact points on an upright bicycle, the others being the two pedals and the two handles on the handlebars. (A bicycle seat in the specific sense also supports the back.)
The bic ...
.
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 Adductor may refer to:
* One of the anatomical terms of motion
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminolo ...
** 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
The semimembranosus muscle () is the most medial of the three hamstring muscles in the thigh. It is so named because it has a flat tendon of origin. It lies posteromedially in the thigh, deep to the semitendinosus muscle. It extends the hip j ...
arises
** From the lower and inner, the long head of the
biceps femoris
The biceps femoris () is a muscle of the thigh located to the posterior, or back. As its name implies, it has two parts, one of which (the long head) forms part of the hamstrings muscle group.
Structure
It has two heads of origin:
*the ''long ...
and the
semitendinosus
The semitendinosus () is a long superficial muscle in the back of the thigh. It is so named because it has a very long tendon of insertion. It lies posteromedially in the thigh, superficial to the semimembranosus.
Structure
The semitendinosus, r ...
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, 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 sometimes c ...
File:Slide3ADA.JPG, Anterior view of the pelvis with the ischial tuberosity labelled in the lower part of the image
See also
*
Ischial bursitis
Ischial bursitis (also known as weaver's bottom) is inflammation of the synovial bursa located between gluteus maximus muscle and ischial tuberosity.
Signs and symptoms
Ischial bursitis causes pain down the posterior aspect of the upper th ...
*
Sitting disability
A sitting disability is a condition in which a person has difficulties sitting or is unable to do so at all; usually due to pain. This can affect people who face little or no chronic problems with standing, as well as those who do, such as mobil ...
Notes
References
*
*
External links
* - "The Female Perineum: Bones"
* - "Major Joints of the Lower Extremity: Hip bone (lateral view)"
* (, , )
{{Authority control
Bones of the pelvis
Ischium