Ischial tuberosity Definition
It is a large bony projection at the junction of the lower end of the body of the left and right ischium, the lower back part of the hip bone, and its ramus. It is also known by several other names like:
- Tuber ischiadicum
- Tuberosity of the ischium
- Sitting bone
- Sitz bone
Ischial tuberosity Location
Specifically, it is situated near the lateral boundary of the pelvic outlet, the space enclosing the lower circumference of the lesser pelvis.
Ischial tuberosity Anatomy
The gluteus maximus, which is the broad, thick, outermost muscle of the buttocks, involved in the rotation and extension of the thigh, covers the bony growth when standing. However, the superficial muscle shifts behind it when an individual sits. The swollen structure mainly comprises of the following:
Lower portion: It is rough and triangular in shape. A longitudinal ridge that passes from base to apex further divides it into two parts.
Upper portion: This represents an upper, smooth, quadrilateral region, which is subdivided into two sections, by an oblique ridge, running downward and outward.
Ischial tuberosity Function
The location of the bony swelling enables it to bear the weight of the body in a seated position. It is a potential site of attachment for several muscles and ligaments such as:
- Adductor magnus: It is a large triangular muscle, situated on the medial side of the thigh that adducts the leg at the hip. It is also responsible for the lateral and internal rotation of the upper leg.
- Sacrotuberous ligament: It is situated at the lower and back part of the pelvis. Its function is to anchor the sacrum to the hip bones to prevent tilting.
- Semimembranos muscle: It is the most medial of the three hamstring muscles in the back of the thigh. It helps to extend the hip joint and bend the knee joint.
- Biceps femoris: It is a muscle of the posterior thigh that extends the hind limb when propelling, rearing or kicking.
- Semitendinosus: The muscle is located in the back of the thigh. Its function is similar to semimembranos muscle.
Ischial tuberosity Pain
Ischial bursitis is a common condition affecting a wide range of athletes, in which the fluid-filled bursa lying over the bony growth undergoes severe inflammation and causes pain. An avulsion fracture of the sitting bone occurs when the ligaments holding the hamstrings to the hips tears, and breaks off a piece of the hip bone in the process. Overuse of the tuberosity of the ischium can damage the hamstring muscles, resulting in tendonitis. In some cases, repetitive activities can cause inflammation of the apophysis of the bony swelling that leads to apophysitis. Various treatment methods are available to alleviate the acute pain syndrome, including surgery, cortisone injections, non-steroidal drugs, and rehabilitative exercises to help restore strength as well as stability.