There are many causes of low back pain. Doctors are not always able to pinpoint the source of a patient's pain. But they will make every effort to ensure that the patient's symptoms are accurately diagnosed.

The normal process of aging affects spine health sometimes causing degenerative changes to occur in parts of the spine. Major back injury or fracture can make these changes happen faster, adversely affecting the way the spine functions. Daily wear and tear, and certain types of vibration can speed up degeneration in the spine. Strong evidence supports that smoking speeds up degeneration of the spine. In addition, scientists have found links among family members, showing that genetics plays a role in how fast these changes occur.

The intervertebral disc undergoes changes over time. At first, the disc is spongy and firm. Its chemical makeup attracts water into the disc. This gives the disc its ability to absorb shock and protect the spine from heavy and repeated forces. But with time, the disc begins to have less water content, causing it to lose some of its fullness and height. As a result, the vertebral bones begin to press closer together.

As the nucleus in the center of the disc dries out, the disc loses its ability to absorb shock. Forces from gravity and daily activities begin to put extra strain on the disc and other structures of the spine. The annulus around the nucleus weakens and begins to develop small cracks and tears. The body tries to heal the cracks with scar tissue, but it is not as strong as the tissue it replaces.

As the disc degenerates, the space between the vertebral bodies shrinks. This compresses the facet joints along the back of the spinal column. As these joints are forced together, extra pressure builds on the articular cartilage on the surface of the facet joints. This extra pressure can damage the joint or change the way it works. Over time, this may lead to arthritis in the facet joints.

Changes in the annulus, facets, and ligaments cause the spinal segment to become loose and unstable. The extra movement causes even more wear and tear on the spine. As a result, larger and more frequent tears occur in the annulus.

The nucleus may push through the torn annulus and into the spinal canal. This is called a herniation. The disc material that squeezes out can press against nerves and other soft tissues of the spine. The disc also emits enzymes and chemicals that produce inflammation.

Further collapse of the disc causes pressure to build around the nerve roots. Pressure around the nerve roots in the low back can cause pain, numbness, or weakness in the low back, buttocks, and lower limbs and feet. The added tension can also cause small areas of bone tissue to build up into small bumps. These points of bone are called bone spurs. The bone spurs can cause pain by pressing on the soft tissues of the spine. Bone spurs can also put pressure on nerves where they pass through the neural foramen.

A collapsed spinal segment eventually becomes stiff and immobile losing its ability to function. Thickened ligaments and facet joints, scarred and dried disc tissue, and protruding bone spurs prevent normal movement. Typically, a stiff joint doesn't cause as much pain as one that slides around. Therefore, this stage of degeneration may actually lead to pain relief for some people.

Mechanical Pain

Mechanical back pain is caused by wear and tear in parts of the lumbar spine. Mechanical pain usually starts from degenerative changes in the disc. As the disc begins to collapse, the space between the vertebrae narrows. The facet joints may become inflamed and the pain is usually chronic. Inflammation typically gets worse after activity due to strain on the moving parts of the spine. Mechanical pain is usually felt in the back, but it may spread into the buttocks, hips, and thighs, rarely traveling past the knee.

Compressive Pain

Compressive pain occurs when a nerve exiting the lumbar spine is squeezed or pinched. This can happen when a disc herniates, or when a nerve gets pinched where it leaves the spine. Compressive symptoms concern doctor's more than mechanical pain.

The nerve pressure causes symptoms in the areas where the nerve travels, rather than in the low back. This happens because pressure on the spinal nerve affects structures away from the spine. As a result, a person's back may not hurt, yet they feel pain, numbness, or weakness in their leg or foot. This indicates there's a problem with the body's electrical wiring.