A herniated (slipped) disk occurs when all or part of a disk in the spine is forced through a weakened part of the disk. This may place pressure on nearby nerves.

Causes, incidence, and risk factors
The bones (vertebrae) of the spinal column protect nerves that come out of the brain and travel down your back to form the spinal cord. Nerve roots are large nerves that branch out from the spinal cord and leave your spinal column between each vertebrae.

The spinal bones are separated by disks. These disks cushion the spinal column and put space between your vertebrae. The disks allow movement between the vertebrae, which lets you bend and reach.
• These disks may move out of place (herniate) or break open (rupture) from injury or strain. When this happens, there may be pressure on the spinal nerves. This can lead to pain, numbness, or weakness.
• The lower back (lumbar area) of the spine is the most common area for a slipped disk. The neck (cervical) disks are affected a small percentage of the time. The upper-to-mid-back (thoracic) disks are rarely involved.

Radiculopathy is any disease that affects the spinal nerve roots. A herniated disk is one cause of radiculopathy.

Slipped disks occur more often in middle-aged and older men, usually after strenuous activity. Other risk factors include conditions present at birth (congenital) that affect the size of the lumbar spinal canal.

Low back or neck pain can feel very different. It may feel like a mild tingling, dull ache, or a burning or pulsating pain. In some cases, the pain is severe enough that you are unable to move. You may also have numbness.
The pain most often occurs on one side of the body.
• With a slipped disk in your lower back, you may have sharp pain in one part of the leg, hip, or buttocks and numbness in other parts. You may also feel pain or numbness on the back of the calf or sole of the foot. The same leg may also feel weak.
• With a slipped disk in your neck, you may have pain when moving your neck, deep pain near or over the shoulder blade, or pain that moves to the upper arm, forearm, or (rarely) fingers. You can also have numbness along your shoulder, elbow, forearm, and fingers.
The pain often starts slowly. It may get worse:
• After standing or sitting
• At night
• When sneezing, coughing, or laughing
• When bending backwards or walking more than a few yards

You may also have weakness in certain muscles. Sometimes, you may not notice it until your doctor examines you. In other cases, you will notice that you have a hard time lifting your leg or arm, standing on your toes on one side, squeezing tightly with one of your hands, or other problems.

The pain, numbness, or weakness will often go away or improve a lot over a period of weeks to months.

Signs and tests
A careful physical exam and history is almost always the first step. Depending on where you have symptoms, your doctor will examine your neck, shoulder, arms, and hands, or your lower back, hips, legs, and feet.
Your doctor will check:
• For numbness or loss of feeling
• Your muscle reflexes, which may be slower or missing
• Your muscle strength, which may be weaker
• Your posture, or the way your spine curves
Your doctor may also ask you to:
• Sit, stand, and walk. While you walk, your doctor may ask you to try walking on your toes and then your heels.
• Bend forward, backward, and sideways
• Move your neck forward, backward, and sideways
• Raise your shoulders, elbow, wrist, and hand and check your strength during these tasks

Leg pain that occurs when you sit down on an exam table and lift your leg straight up usually suggests a slipped disk in your lower back.

In another test, you will bend your head forward and to the sides while the health care provider puts slight downward pressure on the top of your head. Increased pain or numbness during this test is usually a sign of pressure on a nerve in your neck.

• EMG may be done to determine the exact nerve root that is involved.
• Myelogram may be done to determine the size and location of disk herniation.
• Nerve conduction velocity test may also be done.
• Spine MRI or spine CT will show that the herniated disk is pressing on the spinal canal.
• Spine x-ray may be done to rule out other causes of back or neck pain. However, it is not possible to diagnose a herniated disk by a spine x-ray alone.

Source: National Institutes of Health (NIH)
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