A herniated disc occurs when the annulus (an-oo-lus) or outer fibers of the disk is damaged and the soft material inside the disc ruptures out of its normal space. If the annulus tears near the spinal canal, the soft material inside the disc can push into the spinal canal.
A herniated disc in the thoracic spine can be very serious. There is very little extra space around the spinal cord in the thoracic area. So when a herniated disc occurs in the mid back, the pressure on the spinal cord can cause paralysis below the waist. Fortunately, herniated discs are much more common in the lumbar spine, where they are not as serious.
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Herniated discs can occur in children, although it is rare. A true herniated disc is most common in young and middle-aged adults, and generally occurs in the low back. Disc herniations in the thoracic spine mostly affect people between age 40 and 60. In older people, the degenerative changes that occur in the spine with aging make it less likely for them to suffer a true herniated disc.
A disc can rupture suddenly when too much pressure is applied to it all at once. For example, falling from a ladder and landing in a sitting position can cause a great amount of force on the spine. If the force is strong enough either a vertebra can break or a disc can rupture. Bending puts a large amount of stress on the discs between each vertebra. If you bend and try to lift something that is too heavy, the force can cause a disc to rupture.
A disc can also rupture from a small amount of force, usually due to weakening of the annulus from repeated injuries that add up over time. As the annulus becomes weaker, at some point lifting or bending causes too much pressure across the disc. The weakened disc ruptures while doing something that five years earlier would not have caused a problem. This is due to the effects of aging on the spine, which is the most common cause of disc herniation in the thoracic spine.
The material that has ruptured into the spinal canal from the disc can cause pressure on the nerves in the spinal canal. There is also some evidence that the material from inside the disk causes a chemical irritation of the nerve roots. Both the pressure on the nerve root and the chemical irritation can lead to problems with how the nerve root functions. The combination of the two can cause pain, weakness, and numbness in the area of the body to which the nerve supplies sensation (feeling).
The first symptom of a herniated disc is usually pain. The pain is most often felt in the back, directly over the sore disc. If the herniated disc is in the thoracic spine, the pain may also radiate around to the front of the chest. Pressure or irritation on the nerves in the thoracic area can also cause other symptoms. Depending on which nerves are affected, a thoracic disc herniation can include pain that feels like it is coming from the heart, abdomen, or kidneys.
Herniated thoracic discs sometimes press against the spinal cord. When this happens, symptoms may include: