Spondylolisthesis is a spinal condition that occurs when one of the vertebrae in the back slides down onto the vertebra below it. If the bone slides too far, it can compress a spinal nerve and cause pain. There are several different categories of spondylolisthesis. Congenital spondylolisthesis is present at birth and is characterized by an abnormal bone formation that makes the vertebrae more prone to sliding. Isthmic spondylolisthesis results from spondylolysis, a condition characterized by small stress fractures in the vertebrae that may weaken the spine and cause slippage. Degenerative spondylolisthesis is the most common of all types of spondylolisthesis. It occurs when the discs that cushion the vertebrae lose fluid with age and are thus less effective at preventing vertebral movement. Other, less-common types of spondylolisthesis include traumatic (i.e., caused by injury), pathological (i.e., the result of disease), and post-surgical. This condition is the most common cause of low back pain in teenagers as it often occurs with growth spurts. Symptoms include low back pain, muscle spasms in the hamstrings, and pain and tingling that radiates down the leg to the feet. Treatment depends on the type and severity of the condition and may range from administration of anti-inflammatory drugs to physical therapy (especially stabilization exercises) to surgery.