There are two basic ways that the spine can cause leg pain. The first is referral pain from structures within the spine itself, such as the disc or the facet joint or the sacroiliac joint. That pain tends to be more dull, deep, vague, achy. The way that we usually think about pain coming from the spine into the leg is more radiating, electric, burning pain. This comes from irritation of a nerve root within the spine. There are a number of variables within the spine that can cause that irritation of the nerve root - herniated discs, spondylolisthesis where the bones slip on each other, facet joint arthropathy with the little joints in the back of the spine can become arthritic. All of which have a common denominator which is that the hole where the nerve exits becomes smaller. As a result of that, there is more of a propensity towards an inflammatory response along that nerve and that can send pain shooting down into the leg, often there is also associated numbness, sometimes there is some weakness.