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The Lumbar spine

The lumbar spine consists of 5 separate vertebral bones, which are named, from above downwards, the first, second, third, fourth and fifth lumbar vertebrae.

If you are interested in understanding the structure of a typical lumbar vertebra it will help to have an actual lumbar bone to handle. This will help to visualize the 3D structure of the bone.

A typical lumbar vertebra

A typical lumbar vertebra is a very irregular bone with many projections so it looks rather complex to start with. The front part of the bone is a solid block called the vertebral body, which carries the main weight of the body. The body is rectangular and box-shaped, with flat upper and lower surfaces and somewhat concave sides. Viewing from above the body appears kidney-shaped.

The pedicles (”little feet”) stick out from the back of the vertebral bodies. They are solid pillars which tend towards the upper edge of the vertebra - a way of figuring out which way up it is in life. The pedicles are the start of the neural arch, the arch of bone which projects from the vertebral body and protects the spinal cord and other nerves.

From the pedicles come the laminae (singular lamina, meaning leaf or plate), which are flatter sheets of bone that face towards the midline and meet there. From this junction projects a further projection of bone, the spinous process, the end of which can be seen in many (thinner) persons as the knobbles along the spine in the midline.

Each lumbar vertebra has four projections from its rear surface which bear the small spinal joints or facet joints. There are two upper articular processes and two lower. The upper processes of one vertebra reach upwards to join up with the lower articular processes of the vertebra above to make up the facet joints.

The other main notable features of a vertebra are the spaces which are formed by its structure. The neural arch and the back of the vertebral body surround a space called the vertebral canal, which carries the spinal (nerve) cord and other important structures.

Looking from the side two notches can be seen on a lumbar vertebra, a smaller one on the top surface and a larger one below. The smaller notch below connects with the larger lower one of the vertebra above to make up the intervertebral foramen. This is a very important space as through this hole exit the nerve roots, the nerves which supply the legs. It may be a nerve root which is involved in sciatica.

 


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