The lumbar spine represents the mid-lower segment of the vertebral column and is composed of five adjacent vertebrae. They are convex anteriorly to form a lumbar lordosis. The lumbar spine facet joints allows limited movements and rotation.
Each lumbar vertebra is formed of: A body which is kidney shaped and is convex anteriorly while flattened posteriorly, pedicles and lamina, transverse processes, articular processes and a spinous process.
The sacrum is the lower most segment of the vertebral column and also forms the posterior wall of the bony pelvis. The sacrum is formed by five fused sacral vertebrae.
The sacrum is formed by fusion of five sacral vertebrae has three surfaces, a base and an apex. The body of the first segment is large and is similar to lumbar vertebra whereas the bodies of the next bones get progressively smaller, are flattened from the back, and curved to shape.
The sacrum articulates with four other bones – iliac bones on either side, L5 above and coccyx below. It is tilted forward and curved with anterior concavity and posterior convexity allowing greater room for pelvic cavity. The curvature of sacrum varies in individuals.