The Anatomy of Low Back Pain

Understanding the anatomy of the lumbar spine is key to understanding and managing low back pain.

The lumbar spine, commonly called the “low back”, consists of 5 vertebrae, and is located between the thoracic spine (which articulate with ribs) and the sacrum. The vertebrae themselves are given numbers by which they are identified, for example – Lumbar Vertebra 1 = L1, Lumbar Vertebra 2 = L2 and so on.

The normal lordotic curve of the low back is known as a secondary curve, and starts to develop in infancy due to weight bearing caused by learning to sit up and walk.  The low back is especially vulnerable to injury due to its weight bearing task and mobility.

Between each vertebrae throughout the whole spine (except for C1 and C2) is a intervertebral or fibrous disc. The purpose of the disc is to provide cushioning and shock absorption from weight bearing and movement. The intervertebral disc is comprised of the annulous fibrosis and the gel-like centre called the nucleus pulposus – these structures are work together to provide the shock absorption, and are both implicated in disc dysfunction and neurological symptoms.

Facet joints are the articulating surfaces of bone between vertebrae. These synovial joints are known as “plane” joints because their flat surfaces glide over each other. These joints may become inflamed due to injury to the joint or joint capsule itself, or due to compression of the intervertebral discs, forcing them to interact in a “close-packed” position. This close packed position means that the joint surfaces are forced closer together than normal, and will irritate the bone and cartilage during movement as they contact each other and create friction.

During an acute injury, the inflamed tissue in the joints may irritate the nerve roots as they exit the spinal cord via the intervertebral foramina. Eventually, if facet irritation is untreated, bony spurs may develop due to chronic inflammation and cause spinal stenosis – a decrease in the size of the “vertebral foramen” or spinal canal.

In the case of a “bulging” or herniated disc, pressure is exerted on the nerve root as it leaves the spinal cord via the intervertebral foramina. This pinching or pressure on the nerve root will cause sharp, shooting pain, especially when the patient leans forward (flexes) from the hip.  Symptoms will present in the areas that the compromised nerves supply.

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