Carragee, a Stanford associate professor of functional restoration, estimates that up to five percent of the working population in the United States is disabled by low back pain on any given day. Until now, tears in the vertebral discs that cushion the spine have been thought to be the culprit for most of these low back pain complaints. Like spongy coasters sandwiched between each vertebra, the cartilaginous discs protect the bones from banging against each other during running or jumping. But if the hard coating of the disc tears or ruptures, the soft interior can sometimes protrude, pressing on sensitive nerves and causing pain. According to Carragee, acting as the body's shock absorber takes its toll.
Discs become increasingly susceptible to tears or rupture as they age.
The presence of a tear is confirmed by a discography, in which a physician injects a dye into the suspect disc. Dye leaking out of the disc center into the surrounding area sometimes causes pain. Additionally, escaping dye can be confirmed with an X-ray of the lower back. Until now, physicians have thought that the identification of a high intensity zone coupled with discomfort during a discography confirmed that the damaged disc was the source of the patient's back problems, and planned their treatment accordingly. But when the Stanford researchers completed a rigorous comparison of the MRI and discography results of 96 patients with known risk factors for disc degeneration, they found something surprising.