The lumbar spine (lower back) is a remarkably complex structure. The L4-L5 are the two lowest vertebrae in the lumbar spine, and together with the attached disc, joints, nerves and soft tissues, it provides a variety of functions, including supporting the upper body and allowing motion in multiple directions.
However, with its heavy load and range of flexibility, the L4-L5 segment is also prone to developing pain from injury and/or from degenerative changes, such as:
- The L4 vertebra can slip forward over the L5 vertebra, impinging the nerve root and causing lower back and/or leg pain (sciatica)
- The L4-L5 disc, in between the L4 and L5 vertebrae, can herniate or degenerate, leading to possible leg pain (sciatica) and/or lower back pain
- The two joints called facet joints (or zygapophyseal joints), which connect to the L4 and L5 vertebrae in the back of the spine, can allow abnormal amount of motion and/or develop osteoarthritis
- The back of the L4-L5 segment has a nerve that passes through it, from inside the spinal canal down through the back of each leg (as part of the sciatic nerve). This nerve is called the L4 nerve root. If any in inflammatory proteins from inside the disc herniate and come in contact with this nerve, or if anything presses against it, pain can travel down the nerve (called a radiculopathy, or sciatica).
For more information, see Lumbar Spine Anatomy and Pain
Causes of L4-L5 Pain
Common lower back problems that cause pain in segment L4-L5 include:
- L4-L5 disc herniation: The most common place for a disc to herniate is at L4-L5 or L5-S1 because of the amount of weight these segments carry and due to their range of motion. When the disc herniates, the inner portion leaks out and touches the nearby nerve root, causing pain to radiate in the lower back and/or down the leg.
- L4-L5 degenerative disc disease: If the L4-L5 disc degenerates, the disc between the L4 and L5 vertebrae can become painful and cause lower back pain and/or sciatica.
- L4-L5 spondylolisthesis: Weakness in the bones, joints, and ligaments of the spine can lead to the L4 vertebra slipping forward over the L5 vertebra impinging the nerve root and leading to leg pain and other symptoms.
In addition, several lower back conditions can affect multiple levels of the spine, including L4-L5. Spinal stenosis and osteoarthritis are both common causes of lower back pain and/or leg pain in people over age 60.
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In the vast majority of cases, treatment for any problems that involve the L4-L5 segment will begin with non-operative solutions. Only if the pain is severe, causes disability, and is unresponsive to nonsurgical treatments will surgery be considered.