The L5-S1 spinal motion segment is at the bottom of the spine. This motion segment serves as the transition between the lumbar and sacral regions, and is also called the lumbosacral joint. Between the L5 and S1 vertebrae is a wedge-shaped 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. The L5-S1 disc experiences some degree of degenerative changes due to wear and tear and aging. As it degenerates, it becomes flatter, stiffer, and less capable of absorbing stresses. When these changes cause painful symptoms, it is diagnosed as lumbar degenerative disc disease.
Typical symptoms include lower back pain or sciatica pain that radiates into the thigh, leg, and foot. One way L5-S1 degenerative disc disease causes pain is through inflammation of the L5 spinal nerve. When the outer part of a disc breaks down, the inner portion of the disc can leak out or herniated and release inflammatory proteins that irritate the L5 nerve.
Another cause of pain is when the degenerated L5-S1 disc does not absorb stresses, leading to instability and abnormal movement in the motion segment. In response to the L5-S1 segment instability, the back muscles may spasm, causing back pain and stiffness. In some cases, the disc space height may collapse enough to compress the L5 nerve root, leading to lumbar radiculopathy- characterized by leg weakness and numbness.
The symptoms of L5-S1 degenerative disc disease often resolve gradually over a long period of time as inflammatory proteins decrease and the disc eventually collapses into a more stable position.
