where is your lumbar spine and sacrum
The lowest part of the spine is called the lumbar spine. This area usually has 5 vertebrae. However, sometimes people are born with 6 vertebrae in the lumbar region. The base of your spine (called the sacrum) is a group of specialized vertebrae that connects the spine to the pelvis. When one of the bones forms as a vertebra rather than part of the sacrum, it is called a transitional (or sixth) vertebra.
Many nerves of the cauda equina at the inferior end of the spinal cord pass through the sacrum. These nerves enter the sacrum from the vertebral foramen of the lumbar vertebrae through the tunnel-like sacral canal.