There are two main types of low back pain, mechanical type pain and compressive type pain.

The result of inflammation caused by irritation or injury to the disc, the facet joints, the ligaments or the muscles of the back is mechanical type back pain. Disc degeneration is a common cause of mechanical pain. Although mechanical type pain usual starts near the lower spine it may spread to include the buttock and thigh areas. Mechanical type pain will rarely spread below the knee.

Compressive type pain is the pain from nerve roots that leave the spine being irritated or pinched. A herniated or bulging disc is a common cause of compressive type pain. The sciatic nerve joins with the nerves that exit the lower lumbar section of the spine. This sciatic nerve controls the muscles of the lower leg and also provides sensations. The normal function of the sciatic nerve can be impeded by pressure on the nerve roots of the lumbar spine. Numbness in the area supplied by the nerve is one of the earliest signs that there is pressure being applied on the nerve root. There is pain in the same area, usually extending below the knee to the foot. It is not unusual for the back itself to be painless. Finally, the muscles that the nerve controls may become weak and the reflexes disappear.

Spinal stenosis can also cause compressive type pain. In some people, degeneration of the spine can result in a narrowing of the spinal canal where the spinal nerves are located. This causes all of the nerves within the spinal canal to become inflamed and fail to function properly. Numbness can involve both of the lower extremities. The numbness may become worse with activities such as walking. Pain can involve both of the lower extremities. The pain becomes worse with activities such as walking and gets better after short periods of rest. Weakness of the muscles of both legs may also occur and again this may get worse when activity increases.

Bulging discs are fairly common in both young adults and older people. They are not cause for panic. Abnormalities, such as bulging or protruding discs, are seen at high rates on MRIs in patients both with and without back pain. Some discs most likely begin to bulge as a part of both the aging process and the degeneration process of the intervertebral disc. A bulging disc is not necessarily a sign that anything serious is happening to your spine.

A bulging disc is known as a "contained" spinal disorder because the nucleus pulposus remains encased in the annulus fibrosis. At this stage, a bulging disc is not necessarily a serious problem. In fact, bulging discs are common among much of the population and many people do not experience symptoms. A bulging disc becomes problematic when it presses up against the nerves of the spinal column, causing numbness and/or pain.

The precise nature of symptoms from a bulging disc will depend on where in the spine the disc is located. Some patients may experience symptoms of pain and discomfort in the legs and feet, others in the arms and in other regions of the body. The diagnosis for bulging discs is usually made after a complete medical history has been taken and MRIs, CT scans, and/or X-rays have confirmed the presence of bulging.