The common term for the bony prominences felt beneath the buttocks when sitting is the “sit bone,” but the precise anatomical name is the ischial tuberosity. These paired structures are thickened, lower parts of the pelvis that support the body. The ischial tuberosities function as the main weight-bearing points for the torso while in a seated position. Understanding this bony landmark is important for understanding movement, posture, and common sources of lower-body discomfort.
The Proper Anatomical Name
The ischial tuberosity is a specific feature of the ischium, one of the three bones—along with the ilium and pubis—that fuse to form the larger hip bone, or pelvic girdle. It is a large, rough, and rounded prominence situated on the posteroinferior aspect of the ischium. This structure is the most robust part of the ischium, designed to withstand the forces of body weight.
The term “tuberosity” refers to a large, rounded projection on a bone, typically serving as a site for muscle and ligament attachment. Since humans have two hip bones, these structures are referred to in the plural as the ischial tuberosities. These bony points are easily palpable and form the foundation upon which the trunk rests when a person is seated.
Function in Posture and Movement
The primary function of the ischial tuberosity is to act as the direct contact point for weight transfer from the upper body to the seat surface. When a person sits, the large gluteus maximus muscle moves out of the way, allowing the tuberosity to bear the load. This weight-bearing role is fundamental for stable sitting posture, aligning the body over a firm base.
The ischial tuberosity is also a major origin point for several powerful muscles and ligaments that drive lower-body movement. The entire hamstring muscle group originates directly from this bony prominence. Also attaching here is a portion of the adductor magnus muscle and the sacrotuberous ligament, which helps stabilize the pelvis.
The attachment of the hamstrings is significant because these muscles are responsible for extending the hip and flexing the knee. The ischial tuberosity acts as a mechanical anchor, allowing for powerful movements like running, jumping, and straightening the torso. Its rough surface provides a secure connection for these large tendons and ligaments.
Common Causes of Pain
Because the ischial tuberosity is subjected to pressure and tension, it is susceptible to several common causes of localized pain. One frequent source of discomfort is ischial bursitis, often nicknamed “weaver’s bottom,” which involves the inflammation of the bursa located over the tuberosity. This bursa is a fluid-filled sac that acts as a cushion between the bone and the overlying muscles and tendons.
Prolonged sitting, especially on hard surfaces, can compress this bursa, causing irritation and pain. Another common issue is hamstring tendonitis, which is the inflammation of the hamstring tendon at its origin point. This pain often results from repetitive stress or overuse from activities like running or cycling.
Pain can also arise from direct injury, such as a contusion from a fall, or an avulsion fracture where a forceful muscle contraction pulls a small piece of bone away. If pain is persistent, severe, or accompanied by numbness or weakness, a medical evaluation is recommended to differentiate between conditions like bursitis, tendonitis, and referred pain from the lower back.