Your spine has 33 vertebral bones. In the middle and on the sides of these bones are openings that allow nerves to enter and exit. These nerves travel out to your legs, arms, and other parts of your body. The spaces where the nerves enter and exit are called foramina (singular foramen). Each foramen is formed by the facet joint (the space between two discs). Sometimes, the foramen can become too narrow and start to compress the nerves entering and exiting. This can cause symptoms such as numbness, pain, or weakness. This is called foraminal stenosis.
Depending on where foraminal stenosis occurs in your back, it can affect other parts of your body as well. For instance, if a foramen in your neck starts to compress a nerve, you might feel painful symptoms in your upper extremities such as your arms, shoulders, and hands. If the foramen is compressing a nerve in your lower back, though, you’ll feel symptoms in your lower extremities, such as your legs, buttocks, and feet.