The sacrum is a large, triangular bone located at the base of the spine. It's formed by the fusion of five vertebrae (S1-S5), a process that typically completes between the ages of 18 and 30. This crucial bone plays a vital role in connecting the spine to the pelvis, providing structural support and stability.
Anatomy and Location
- Shield-shaped bone: The sacrum's shape resembles a shield, fitting snugly between the two hip bones (ilium) to form the posterior wall of the pelvis.
- Base of the spine: It sits directly below the lumbar vertebrae (the lower back bones).
- Pelvic connection: The sacrum articulates with the ilium via the sacroiliac joints, creating a strong and stable connection between the spine and pelvis.
- Fused vertebrae: Five separate vertebrae fuse together during adolescence and young adulthood to create the single sacrum bone.
Function and Importance
The sacrum's key functions include:
- Weight distribution: It transmits the weight of the upper body to the pelvis and legs.
- Pelvic stability: The sacrum is essential for the structural integrity and stability of the pelvis. This is crucial for activities like walking, standing, and bending.
- Motion and balance: The sacroiliac joints allow for a limited range of motion, contributing to overall body movement and balance.
- Protection of spinal cord nerves: The sacrum protects the lower spinal cord and associated nerves.
Sacral Conditions and Injuries
Several conditions can affect the sacrum:
- Sacral fractures: These can result from high-impact injuries, such as falls or car accidents, and are often seen in younger individuals and older adults with osteoporosis.
- Sacral dimples: These are small indentations on the skin overlying the sacrum, often present at birth and generally harmless. However, in rare instances they can be associated with underlying spinal abnormalities.
- Sacral tumors: Chordomas are a type of cancerous tumor that can develop in the sacrum, often near the tailbone.
- Sacral nerve injuries: Damage to the sacral nerves can lead to decreased function in the hips and legs.
Summary
In essence, the sacrum is a vital bone that provides stability and support to the lower back and pelvis. Its unique structure and location are key to human locomotion and overall skeletal health.
