The T12-L1 spinal motion segment, also called the thoracolumbar junction, connects the thoracic spine – or upper back – to the lumbar spine – or lower back. It consists of the T12 and L1 vertebrae, and the anatomical structures connecting them. This segment provides flexibility to the trunk and low back, supports the upper body, and protects the spinal cord and nerve pathways.
The T12 and L1 vertebrae are connected in the back by a pair of facet joints that allow limited forward, backward, and twisting motions. Articular cartilage enables the facet joints to move smoothly, while muscles, tendons, and ligaments hold the vertebrae together. A strain or tear to any of these tissues can cause back pain and stiffness.
Between the vertebrae is an intervertebral disc that provides flexibility and shock absorption. The disc is made up of a tough outer ring called the annulus fibrosus, which encapsulates a gel-like interior called the nucleus pulposus.
A thin vertebral endplate is situated between the vertebral body and the intervertebral disc. It is made up of two layers. A bony layer which attaches to the vertebral body and a cartilaginous layer which attaches to the intervertebral disc. The endplate facilitates the transport of nutrients to the discs and protects the vertebrae and discs from compressive loads on the spine.
The spinal cord lies within the vertebral foramen, a space formed by the vertebral arch and vertebral body.
The T12 spinal nerve branches out from the spinal cord and exits on each side through the intervertebral foramen. It receives sensory information from the skin on the lower part of the abdomen and flank. The motor component of the T12 spinal nerve sends signals to various muscles in the front and side of the abdomen.
Spinal conditions affecting the T12-L1 motion segment include vertebral fractures, disc herniation, degenerative disc disease, spinal stenosis, and degenerative spondylolisthesis.
The signs and symptoms of these conditions include pain and weakness in the abdomen and flank. If the spinal cord is compressed at the T12 spinal level, it may cause severe pain, neurological deficits in the legs, and loss of bowel and bladder function.
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