ristiluuhua

Ristiluuhua, also known as the sacrum, is a large, triangular bone located at the base of the spine. It is formed by the fusion of five sacral vertebrae. The sacrum articulates with the last lumbar vertebra at its superior end and with the coccyx, or tailbone, at its inferior end. On either side, it articulates with the ilium bones of the pelvis, forming the sacroiliac joints, which are crucial for weight transfer from the torso to the legs.

The sacrum plays a vital role in supporting the body's weight and transmitting forces during locomotion. Its broad, posterior surface provides attachment points for various muscles, including those of the back and gluteal region. The anterior surface is concave and forms part of the pelvic cavity. Within the sacrum are the sacral foramina, openings through which the sacral nerves exit the spinal canal. These nerves innervate the pelvic organs and the muscles of the legs and feet.

Deformities or injuries to the sacrum can lead to pain and functional impairments, affecting posture, gait, and the ability to perform daily activities. Conditions like sacral spina bifida, a birth defect where the spinal cord doesn't close completely, involve the sacrum. Fractures of the sacrum, though less common than other spinal fractures, can occur due to high-impact trauma and may require surgical intervention. The sacrum's unique anatomical position and its integral role in the axial skeleton make it a critical component of the human body's structure and function.