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. This occurrence is not dangerous and does not appear to have any serious side effects.
The lumbar spine is shaped like a backward "C", just like the cervical spine. This shape is called a lordotic curve. If you think of the entire spine as having an "S"-like shape, the lumbar region would be the bottom of the "S". The vertebrae in the lumbar spine are the largest of the entire spine. The lumbar spinal canal is also larger than in the cervical or thoracic segments of the spine. The size of the lumbar spine allows for more space for nerves to move about.
When people experience pain in their spine it often occurs in the lumbar region. This is because the lumbar spine is connected to your pelvis, which is where most weight bearing and body movement takes place. Typically this is where people tend to place too much pressure, such as when lifting up a heavy box, twisting to move a heavy load, or carrying a heavy object. These activities can cause repetitive injuries that can lead to damage to the parts of the lumbar spine.