Have you been told that you have bulging, degenerated discs in your spine? If so, you are not alone. Millions of Americans undergo X-rays, CT scans, and MRI scans of their backs and necks each year and receive the same news. As a result, multiple millions of dollars are spent on medications, physical therapies, surgical procedures, and spinal manipulations in an effort to treat back pain. The people undergoing all this diagnosis and treatment might imagine that other, luckier people have normal spinal discs, but they might be surprised to learn that bulging discs are so common that they may be considered a normal part of aging. Most often, they cause no symptoms or problems, and it pays to be cautious about embarking on courses of investigation and treatment based simply on these “degenerative changes.” But it also pays to know when and why discs do cause trouble.

What and where are spinal discs?

The spine is a column of thick, circular bones—also called vertebral bodies—that in terms of anatomy is divided into three major sections: the cervical (neck) spine, thoracic (mid-back) spine, and lumbar (lower back) spine. The vertebral bodies have flat tops and bottoms, and they sit atop one another, separated by discs that cushion the spine and allow for the compression, rotation, and bending of the entire spinal column. The arches of bone on the back sides of each of the vertebral bodies line up with each other to form a bony tunnel, which surrounds the spinal cord and the nerves that connect it to the body. Pairs of these nerves exit from the sides of this canal below each vertebral body.

Spinal discs are a lot like flattened cream-filled doughnuts, with a soft center called the nucleus pulposus and a tougher perimeter called the annulus. Each annulus is attached to the ligaments that run the length of the spine and hold it together. Every day, gravity squeezes so much water out of each disc that an average adult shrinks by more than one-half inch between morning and night. As a disc loses water and flattens, it may protrude beyond the edges of the vertebral bodies located above and below it. Under these conditions, the ligaments bounding the disc tend to bow outward to accommodate the flattening, and the result is the classic “bulging” discs often seen on back scans. Is such bulging a cause of pain?

When bulging becomes cracking and herniation

Judging by the number of people who have bulging discs and no pain, the answer to this question is, not very often. But discs can cause pain if they are damaged. Cracks can develop in the back part of the annulus, especially in the lower neck and lower back, and are sometimes caused by sudden movement or excessive loading of the neck or back or sometimes with no readily identifiable cause. Risk factors for the development of cracks include age, smoking, and heavy weight lifting. When cracks form in the annulus, nerve fibers send out distress signals which feel like deep back pain that sometimes radiates down the legs. Symptoms usually improve over a period of six to eight weeks, but if the tear is extensive enough, it may open a path for part of the soft nucleus pulposus of the disc to work its way through, becoming a so-called herniated or “slipped” disc.

Location determines  symptoms

Extruded far enough, a herniated disc bulges straight backward into the bony tunnel that houses the spinal cord or off to either side, where it squeezes into the narrow canal that should hold only a spinal nerve root passing out to the body. Depending on the location and the extent of the disc herniation, pain in the back or neck might be accompanied by a set of neurological symptoms including numbness, tingling, and a sense of weakness in an arm or a leg. Symptoms may improve over time with no treatment or with relatively modest treatments, like physical therapy or cortisone injections, as the disc shrinks. But there is potential for the worsening of symptoms, so careful physical evaluation and follow-up are important.

More than 95 percent of disc problems occur in the lumbar spine. Here, as in the neck, discs tend to slip off to the side, compressing single nerves and causing pain to run down a leg or arm or weakness in corresponding muscles. Definite loss of strength in a muscle group controlled by the nerve under pressure most often calls for surgery to decompress the nerve. Sometimes scans indicate that a fragment of disc has broken off and lodged itself under a nerve. Unlike nonfragmented disc herniations, which may gradually shrink and relieve symptoms, symptoms caused by fragmented discs tend to be persistent unless the fragment is removed.

Disc herniation in the upper spine

When discs slip straight back into the central spinal canal, symptoms can range from none to neurological deficits that require immediate decompression surgery. Serious central disc herniations are uncommon in the neck and quite rare in the thoracic spine but in both locations may cause symptoms from the spinal cord itself that include pain, balance problems, weakness in the legs, and an inability to control the bladder.

Disc herniation in the lumbar spine

In the lumbar spine, because the spinal cord does not reach down this far, central disc herniations put pressure on the so-called cauda equine, or “horse’s tail” of nerves that travel down the spinal canal from the spinal cord to their exit points at different lumbar levels. Symptoms here often consist of a confusing array of pain, numbness around the groin and legs in a pattern that traces an area where a saddle would make contact with the body, leg weakness, fecal incontinence, and trouble initiating urination. This combination of symptoms requires immediate surgical decompression.

Surgery or not?

While surgery for severe symptoms is an easy decision and while many disc removals are done with microsurgical techniques and small incisions and are less invasive than in the past, the decision to try to improve back pain alone by operating on a bulging disc is not as easy. To improve the likelihood of good results, studies like disc injections are sometimes done. The dye used helps visualize the disc, and, if the injection reproduces the patient’s pain, confidence that the disc is the source of the back pain increases. Injections can be helpful in determining which of several bulging discs might be the source of pain.

Caution in the decision

Disc removal for pain alone or for pain combined with sensory symptoms that come and go should be approached with caution. First, every attempt should be made to improve the strength of the muscles that support and move the spine, to improve overall posture, and to lose excess weight that the spine is asked to support. Back and neck pain arise from many different structures—muscles, ligaments, tendons, bones, and nerves—and can improve dramatically with improved strength, flexibility, and posture—bulging discs or not.