When referring to the spine, the term stiffness is usually used to describe limited mobility, rigidity, or lack of flexibility. Stiffness can occur in any region of the spine but most commonly occurs in the neck or the low back. One of the most common causes of spinal stiffness is prolonged muscle spasm. Spinal segment stiffness can develop secondary to underlying degenerative disease involving the intervertebral disc and/or the spinal facet joints. Pain arising from deep spinal structures including the spinal facet joints may cause reactive muscle guarding (spasm) with resultant spinal segment or regional spinal stiffness. Aging and deconditioning can also cause or contribute to spinal stiffness secondary to a loss of tissue flexibility and development of adhesions (scar tissue).