The L5-S1 spinal motion segment is at the bottom of the spine. It serves as the transition between the lumbar and sacral regions, and is also called the lumbosacral joint. This segment consists of the L5 and S1 vertebrae and the anatomical structures connecting them.
A thin segment of bone connects the upper and lower facet joints at the back of the spine. This segment is called the isthmus or pars interarticularis. The isthmus receives a high degree of forces, making it susceptible to stress fractures. A fracture of the isthmus is called spondylolysis. A fractured isthmus may sometimes lead to a forward slippage of the vertebra, known as isthmic spondylolisthesis, which most commonly occurs at the L5-S1spinal segment.
A grading system is used to measure the degree of vertebral slippage in isthmic spondylolisthesis. There are 4 grades ranging from grade 1 to grade 4, and each grade represents a progressively greater degree of forward displacement of the vertebra. Vertebral slippage in isthmic spondylolisthesis rarely exceeds grade 1.
The symptoms are usually mild and occur due to the inflammation or compression of the L5 spinal nerve. L5 nerve root irritation or compression typically causes sciatica or radiating nerve pain in the legs. Mechanical compression of nerves in the spine may cause neurologic claudication, characterized by episodes of low back pain that radiates to both legs, along with sensations of tingling, numbness, weakness, and hamstring spasm.
In some cases, severe compression of the L5 nerve root may cause lumbar radiculopathy – characterized by leg weakness and numbness.
L5-S1 isthmic spondylolisthesis is typically treated with self-care, medication, and physical therapy.
A wait-and-watch approach is used to see if the symptoms resolve with these non-surgical treatments. In rare cases, lumbar spinal fusion surgery may be considered.
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