Sacrum

A triangular bone located at the base of the spine, forming the posterior aspect of the pelvis.

The sacrum is a large, wedge-shaped bone made up of five fused vertebrae, known as sacral vertebrae, which are numbered S1 to S5. It connects the spine to the pelvis and is an essential component of the vertebral column. It helps to support the upper body while standing and moves the forces of weight efficiently to the lower limbs.

Terminologia Anatomica

sacrum

System

Skeletal system

Function

The sacrum plays a crucial role in maintaining an upright posture, supporting and stabilizing the spine and pelvis during movement. It also provides attachment points for various muscles and ligaments, which contribute to the mobility of the lower back and pelvic region. In addition, the sacrum houses the sacral canal, which contains spinal nerves that help facilitate communication between the brain and the lower body. The overall structure of the sacrum contributes to the formation of the pelvic cavity, aiding in the protection of the reproductive organs, bladder, and rectum, while also providing a stable foundation for the pelvis during activities such as walking, running, and lifting.

Location

Situated at the base of the lumbar spine, the sacrum is located between the last lumbar vertebra (L5) above and the coccyx (tailbone) below. It is positioned centrally within the pelvis, forming the back part of the pelvic girdle. The sacroiliac joints, where the sacrum meets the ilium of the pelvis, further anchor the sacrum in place, facilitating its role in weight transfer from the upper body to the lower limbs. Its structure forms a bridge between the spine and the pelvis, positioning it as a vital connector for the skeletal system.

Did You Know?

The sacrum was referred to as the 'sacred bone' in ancient times due to its association with the vertebral column and its importance in human anatomy.
The shape of the sacrum varies among individuals and can be adapted for bipedal locomotion versus quadrupedal movement.
In some animals, the sacrum includes more than five fused vertebrae, reflecting variations in locomotion and body structure.