Several structures in the lumbar spine can cause lower back pain, including the nerve roots that exit the spine, facet joints, intervertebral discs, vertebral bones, and the spinal muscles. Many lumbar spinal conditions are also interrelated. For example, a facet joint instability can lead to disc degeneration, which in turn can compress or irritate the nerve roots.
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The following conditions outline the more common causes of lower back pain with possible leg pain.
A muscle strain typically causes the muscle tissue to get abnormally pulled, overstretched, or torn due to heavy lifting, incorrect lifting, or repetitive use, such as from constant bending. Muscle strains can cause mild to severe pain and also result in associated lower back stiffness.
Muscles may also get deconditioned due to lack of physical activity or from a sedentary lifestyle, causing lower back pain.
Intervertebral discs are spongy pads that act as shock absorbers between each of the lumbar spine's vertebrae. Disc degeneration can create pain in the disc space, resulting in localized back pain.
When a degenerated disc becomes dehydrated and loses its normal height, it causes the area of the disc space to reduce. This reduced space may compress a nearby spinal nerve, causing pain along the path of the nerve. Sciatica is the most common symptom of a pinched lumbar spinal nerve (L4 and/or L5), where shooting pain and/or numbness and weakness is felt in the rear pelvis and down the leg and possibly into the foot.
A disc may herniate gradually as a part of general wear and tear or suddenly due to injury or heavy lifting. During disc herniation, the soft inner contents of the disc (nucleus pulposus) push against its outer covering (annulus fibrosus). The nucleus pulposus may also leak out in severe cases by tearing the fibrous layers of the annulus.
The forward slippage of a vertebra over the one below it is called spondylolisthesis. The slip most commonly occurs in the lower lumbar vertebrae at L4-L5 or L5-S1 due to the high degree of mechanical stress in this region3. If the slipped vertebra compresses the nerve root at these levels, it can result in sciatica.
Facet joint osteoarthritis is the age-related wear and tear that causes the cartilage covering the facets to become worn and frayed. Excess friction can produce bone spurs (abnormal bone growth) and joint inflammation that causes localized back pain and limited range of motion. If a bone spur pinches on a spinal nerve, radicular pain, or sciatica can occur.
Facet joint osteoarthritis is more common in the lower segments of the lumbar spine, with the L4-L5 joint most commonly affected.3
A narrowing of the spinal canal or intervertebral foramen (bony openings for the nerve roots as they exit the spinal canal) is called spinal stenosis. The stenosis can irritate or compress the nerve roots (foraminal stenosis) resulting in sciatica.
If the stenosis compresses the spinal cord (central canal stenosis), neurogenic claudication occurs, resulting in leg pain while walking variable distances. In severe cases, bowel and/or bladder dysfunction, severe leg weakness, and/or numbness may occur.
Less commonly, tumors, cysts, and infections may cause lower back pain. If the spinal cord or the cauda equina (nerves that descend from the spinal cord) is damaged, immediate medical attention is necessary to prevent the progression of signs and symptoms.