You may be familiar with groin or abdominal hernias, which occur when a loop of bowel pushes through the abdominal wall. The word "hernia" does come from the Latin word hīra, meaning "gut." But doctors use the term more generally to refer to the abnormal protrusion of any body structure through an opening. An intervertebral disc hernia—or disc herniation, as it's generally called—occurs when the outer portion of a disc in the spine ruptures. The pulpy contents of the disc spill through the new opening, perhaps irritating spinal nerves or compressing the spinal cord itself. Sometimes disc herniation is called a "slipped disc," "prolapsed disc," or "ruptured disc." To a doctor there may be subtle differences among the terms, but for our purposes they essentially all mean the same thing.
What is disc herniation?
Your spine is a sturdy structure made up of vertebral bones alternating with fibrous discs. These discs act as shock absorbers to protect the vertebrae (spinal bones) and keep them from rubbing together. Without the discs to give our bodies strength and flexibility, there would be no stickball or skiing or spinning, and the downward dog at yoga class would be out of the question.
Each intervertebral disc is made up of a soft, pliant core, called the nucleus pulposus, surrounded by a tough, fibrous outer ring, called the anulus fibrosus. Herniation occurs when the perimeter of a disc breaks down, allowing its gelatinous contents to fill any crack, tear, or outpouching (Figure 1). The ruptured disc may crowd the spinal canal, pressing on nerves that exit the canal at that level. The result is persistent pain in the back, neck, shoulders, arm, or leg.
How common is disc herniation?
Disc herniation is usually diagnosed in patients between ages 30 and 50.1 Men are twice as likely as women to have a herniated disc.
When researchers want to measure the incidence of disc herniation, they must first define what they mean by the term. For example, will a bulging disc be counted as a herniation? If so, how large of an outpouching is considered to be a bulge? When different research groups use different definitions, their studies yield conflicting data from which few conclusions can be drawn. As a result, the true incidence of disc herniation is unknown. Estimates vary from 20% to 83% of the population in the United States.2 The bottom line is this: Disc herniation is extremely common but is of concern only when it produces symptoms.
What causes disc herniation?
The word “disc” calls to mind a hockey puck or a frisbee. But durable as an intervertebral disc may be, it’s still a body tissue. That means it’s vulnerable to injury, disease, and the forces of aging. A single, excessive strain or traumatic injury can cause a disc to herniate. Autoimmune conditions, such as lupus and rheumatoid arthritis, are associated with degenerative disc disease (DDD), which compromises the strength and anatomic structure of the discs, often leading to disc herniation.
Disease, aging and injury are often overlapping factors in disc herniation. For example, shoveling snow is easy when you’re young. But as you age and perhaps develop DDD, you could herniate a disc while performing exactly the same task. So the aging process and DDD can contribute to a seemingly straightforward back injury.
Changing disc composition
Researchers now believe that the development of degenerative disc disease, which often precedes disc herniation, is 75% genetic. 3 This degenerative process, then, is largely out of your control. As you age, each disc gets a bit flatter, like the sole of a worn-out sneaker. The nucleus loses water content, and collagen fibers in the outer ring weaken. As its composition changes, the disc becomes less able to absorb shock as you move. That’s why your back sometimes hurts after you perform simple tasks like planting bulbs or power-washing the deck—tasks that used to be a cinch.
Less support from surrounding structures
It’s not just the discs that deteriorate over time. Surrounding ligaments that help keep the discs in place become less able to constrain joint motion. Even the vertebrae deteriorate with age. Each vertebra is capped with an endplate composed of bone and cartilage. This strong, porous interface serves as a transition point between the disc and the vertebra.
Each endplate is thicker at the edges than in the center, like the lens in a pair of prescription eyeglasses. This configuration helps distribute the load of your body weight to adjacent vertebrae, taking some of the pressure off the disc. The endplate thins out over time, becoming calcified and brittle. It also becomes less efficient at buffering mechanical forces as you lift, twist, bend, and so on. 4 With less protection from the endplate, more of the load falls on the aging disc. It deteriorates further, and the anulus (outer ring) may ultimately rupture.
What are the symptoms disc herniation?
Any disc can herniate, but those in the cervical spine (neck) and lumbar spine (lower back) are the most likely to do so. The thoracic spine (the middle portion) is more stationary than the neck and lower-back areas, so discs there are more stable and provoke fewer symptoms if they do herniate.
A herniated disc causes pain by compressing either a nerve or the spinal cord itself. Nerve pain in general is called neuropathy. When the disc compresses a nerve, the pain is called radiculopathy. When the disc compresses the spinal cord, the pain is called myelopathy. Radiculopathy and myelopathy, then, are types of neuropathy.
In many people, disc herniation produces no symptoms. In 85% of those who do have symptoms, the pain resolves within 12 weeks with no treatment. The remaining 15% of patients, though, face chronic neuropathy.1
The location of the pain depends on what’s being compressed. Nerve compression usually affects only one side of the body. If you’re right-handed and the pain is on that side, you may find yourself using your left hand to open doors, hold a scrub brush, use a mouse, and so on (and vice versa for left-handed people).
Spinal cord compression, on the other hand, usually affects both sides of the body, and the pain is more diffuse, or spread out. If the pain is only on one side, it’s the side opposite the compression.2 For instance, if the cord were being squished on the left, you’d feel pain on your right side. Be sure to report all of your symptoms to your doctor to help him or her pinpoint the vertebral level at which your pain originates.
Compression of cervical spinal nerves (cervical radiculopathy)
The disc that lies between the sixth and seventh cervical vertebrae (C6-C7) is the most susceptible to a painful herniation.1 Compression of nerves at this level or elsewhere in the cervical spine produces pain in the neck, shoulder blade, arm, or hand. You might feel a knot or muscle spasm in your upper back. You might even have tingling or numbness in certain fingers.
Compression at this level can also reduce your range of motion and cause muscle weakness, sensory abnormalities, decreased grip strength, or loss of fine motor skills. You may drop things more often or have trouble picking up and holding eating utensils or other small objects, such as a hairbrush or toothbrush.
Compression of lumbar spinal nerves (lumbar radiculopathy)
Compression of nerves in the lumbar spine causes pain, tingling, or numbness in the lower back, buttocks, leg, or foot. You may also have muscle spasms in your lower back. Pain that extends from the buttocks, down the leg, and sometimes into the foot is known as sciatic pain. Sciatic pain, or sciatica, is common among people with lumbar disc herniation. The pain may be constant or intermittent. You may have trouble sitting or standing for long periods of time, and your reflexes may be sluggish on the affected side.
Compression of spinal cord (cervical or lumbar myelopathy)
Compression of the spinal cord at any level can cause myelopathy (pain), muscle weakness and sensory deficits. Compression at the lumbar level can cause difficulty walking, muscle weakness, and cramping. Report any bowel or bladder dysfunction to your doctor right away, since it may indicate that you have a dangerous condition called cauda equina syndrome.
How is disc herniation diagnosed?
Your doctor will ask about your general medical history, including your medications and any past surgeries. He or she will ask you to characterize your pain—for instance, is it sharp, stabbing, or aching? Does it feel like an electric shock? The physician will want to know when the pain began, what (if anything) brought it on, whether it’s constant or intermittent, and which activities (such as walking) make it worse or better. The doctor will perform a thorough physical examination to assess your strength, sensation (for example, with a pinprick test), reflexes, and gait (walking ability).
Your doctor may send you for x-rays to exclude other conditions associated with back pain, such as fractures. X-rays can also reveal bone spurs, a narrowed spinal canal, and other findings associated with disc herniation.
If your pain persists after at least 6 weeks of conservative treatment (see “How is disc herniation treated?”), your physician will probably also order a magnetic resonance imaging (MRI) scan of the spine. An MRI can confirm the diagnosis of disc herniation, reveal its precise location, and show any associated inflammation, swelling, or changes in the vertebral endplates or bone marrow.
A sophisticated magnetic resonance scan called diffusion tensor imaging (DTI) can reveal nerve root compression at a microscopic level, supplying granular information that’s helpful in surgical planning.2
A CT scan of the spine is known as CT myelography. It visualizes the bony structure of the spine in minute detail and can reveal degenerative processes like osteoporosis as well as disease conditions, such as an infection or spinal tumor.
How is disc herniation treated?
Your physician will probably allow 6 to 12 weeks to elapse before pursuing any treatment or diagnostic testing, since most back pain resolves on its own (see “What are the symptoms disc herniation?”). Treatment of disc herniation begins with physical therapy and nonopioid medications, progressing to prescription pain medication and surgical intervention, as needed.
A physical therapist can perform an in-depth assessment to design a treatment plan for you. It might include massage, traction, application of heat or ice, ultrasound, or electrical muscle stimulation using a transcutaneous electrical nerve stimulation (TENS) unit. The therapist can show you range-of-motion, strengthening, and conditioning exercises that may improve spinal function and ease pain.
For pain relief, your doctor can recommend over-the-counter pain relievers or prescribe effective nonopioid medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), anticonvulsants, or antidepressants. Anticonvulsants aren’t prescribed to pain patients for convulsions, though—medications such as gabapentin (Neurontin) block nerve pain signals in patients with disc herniation. Likewise, certain antidepressants are useful for pain management even in patients without depression. Opioid (narcotic) pain relievers may be prescribed if necessary, depending on your diagnosis and medical history.
Using x-ray guidance, your doctor can inject anesthetic medications or corticosteroids into the space surrounding the spinal cord (the epidural space). This intervention can block transmission of pain signals for as long as 3 months.
In traditional open surgery and in less sophisticated minimally invasive procedures, the surgeon must make an incision large enough to see the operative field. After cutting through layers of muscle and tissue down to the spine, the surgeon uses a device called a retractor to pull apart the muscle, creating a window through which he or she can operate.
Cutting through and retracting the muscle this way can damage not only the muscle tissue, but also nearby tendons, ligaments, nerves, and blood vessels. The term invasive or minimally invasive is appropriate because the surgeon must launch a sort of methodical attack on the body in order to reach the offending disc. Let’s take a closer look, and see how keyhole surgery eliminates these problems.
Traditional open surgery is an invasive procedure. The word invasive comes from the Latin prefix in–, meaning “into,” + the root word vadere, meaning “to go.” The term describes any procedure in which the skin is cut or punctured by an instrument. Even drawing your blood for lab tests is technically considered invasive.
But invasive surgery carries special risks. The surgeon may have to cut through layers of muscle and other tissue to reach the disc or discs to be removed and replaced, and/or the vertebrae to be fused. As a result, you spend more time under anesthesia (with its attendant risks), lose more blood, and have a greater risk of infection. Your recovery will take longer than with a minimally invasive procedure, and the process of wound healing may be more complicated. You’ll also have a larger surgical scar, too—an issue of concern to some.
Of course, traditional surgery also offers the promise of healing and pain relief. Many people with chronic pain are willing to assume some risk and endure a period of recovery in order to achieve the expected benefit of the procedure. For some patients, particularly those injured in accidents, a traditional procedure is the best or only viable approach. Your neurologist or orthopedic surgeon will discuss your options with you.
Minimally invasive surgery
Fortunately, most disc herniations can be corrected with minimally invasive surgery (MIS) or, more specifically, minimally invasive spine surgery (MISS). A minimally invasive surgical approach reduces operative time, blood loss, risk of infection, and recovery time, and yields a better cosmetic result. Nevertheless, most minimally invasive surgical procedures still require cutting through the soft tissues — muscles, ligaments, tendons, and blood vessels — to reach the herniated disc. There’s less trauma to these tissues than in traditional open surgery, but there’s still enough damage to require a short hospital stay and several weeks of recovery time.
Pioneering surgeons have found a clever solution to the problem of tissue trauma. It’s not as minimally invasive as a blood draw at the lab, but close. They’ve incorporated fluoroscopy—real-time x-ray guidance—to eliminate the need for direct visualization of the surgical field.
Like an experienced pilot relying on his instrument panel to navigate through storm clouds, the surgeon uses fluoroscopic images on a screen in the operating room to guide the way as he tunnels through the muscle with an instrument called a tube retractor. This nifty tool moves aside or parts the tissue, rather than slicing through it, in order to reach the spine.
Once this tunnel has reached the spinal anatomy in question, it’s left in place. The surgeon can then slip instruments in and out of it to cut, shape, and remove disc material as necessary. He can even insert graft material or fixation devices (such as screws) through the tunnel.
There aren’t many pilots who could get you through a thunderstorm without taking a nosedive. Likewise, only a few surgeons have the qualifications, advanced training, and experience to perform keyhole surgery. A growing number of patients are taking the time to find one who does.