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The lumbar region of the spine, more commonly known as the lower back, consists of five vertebrae labeled L1 through L5. The lumbar region is situated between the thoracic, or chest, region of the spine, and the sacrum.
The lumbar spine typically has a slight inward curve known as lordosis.
The lower back region contains large muscles that support the back and allow for movement in the trunk of the body. These muscles can spasm or become strained, which is a common cause of lower back pain.
The five vertebrae of the lumbar spine are connected in the back by facet joints, which allow for forward and backward extension, as well as twisting movements. The two lowest segments in the lumbar spine, L5-S1 and L4-L5, carry the most weight and have the most movement, making the area prone to injury.
In between vertebrae are spinal discs, which cushion the joints of the spine and provide support. Discs in the lumbar region of the spine are most likely to herniate or degenerate, which can cause pain in the lower back, or radiating pain to the legs and feet.
The spinal cord travels from the base of the skull to the joint at T12-L1, where the thoracic spine meets the lumbar spine. At this segment, nerve roots branch out from the spinal cord, forming the cauda equina.
Some lower back conditions may compress these nerve roots, resulting in pain that radiates to the lower extremities, known as radiculopathy.