How is the pelvic girdle attached to the vertebral column?

The pelvic girdle is attached to the vertebral column through the sacroiliac joint, a weight-bearing synovial joint located at the base of the spine.123

This connection occurs where the sacrum—the triangular bone formed by fused vertebrae at the base of the vertebral column—articulates with the ilium, the uppermost bone of the pelvis. The joint is stabilized by several key structures:143

• Cartilage: Thin plates of cartilage cover the contiguous surfaces of the sacrum and ilium, with additional masses of fibrocartilage helping to join the bones.23
• Ligaments: Strong fibrous attachments, including the anterior and posterior sacroiliac ligaments and interosseous ligaments, bind the girdle to the vertebral column.23
• Synovial Fluid: A small cavity within the joint contains synovial fluid, which cushions the area against pressure.23

Due to these robust attachments and the irregular surfaces of the bones, the sacroiliac joint allows for very little movement, providing the stability necessary to support the weight of the upper body.23