This is a very common cause of lower back disorders. Facet joints occur in pairs at the back of each vertebra and they prevent excessive motion of the spine. When these joints are exposed to excessive trauma - from sports, work, normal aging, etc. - they can become inflamed and motion may be restricted at a particular level of your spine. This may cause low back pain or even pain which is felt in the back of the thigh. Low back muscles will spasm which may further complicate the situation.