The pressure on a nerve root in the lower spine (or nerve root compression) may cause back and leg pain. This is because the nerve roots that surround the lumbar part of the spine run to the legs supplying sensation in the lower part of the body. When these nerves are pinched, you may experience pain, weakness and numbness in your legs or toes, although the source of the pain is located in the back.

If the nerve root pinched is situated in the cervical part of the spine, you may experience pain, numbness and weakness in the upper part of your body, such as shoulders and arms.  

This condition is called radiculopathy.

Decompression surgeries aim to relieve pressure from the nerves pinched and alleviate you from the pain.