Anatomy

Spinal discs are made with two types of tissue, the annulus fibrosis and nucleus pulposus. The annulus (outer part of the disc) is a tough, gristle-like tissue that forms layers or rings. The nucleus (the soft center of the disc) has a more pulpy, fluid-like consistency. The annulus and nucleus are shown below:

Each disc is between two bony vertebral bodies which together form a "bone disc column" (see "Spine Basics"). Behind this column lies a "nerve column" where your nerves are located. Bony structures such as the facet joints protect this "nerve column" much like your skull protects your brain (see Figure 2).

As seen in Figure 2 above, the two "columns" are beside each other. The "bone-disc column" is in front. It allows the nerve roots to exit freely from the "nerve column." Problems and pain associated with discs can occur when the disc wears out or leaves its column to enter the nerve column. In such cases, the disc can put pressure on the nerve root and cause inflammation.

Function

The intervertebral disc has several very important functions. It acts as a cushion or shock absorber. The intervertebral disc accepts and distributes the forces that travel through the spine-like those forces created when you are walking or sitting. Lifting puts even greater force on the lumbar discs. The least force of all occurs when you lie down (which explains why we suggest short term bed rest for some spine problems).

What's more, the intervertebral disc acts as a stabilizer. It helps to hold the vertebrae together and controls normal motion. The intervertebral disc also acts as a spacer. It pushes the bony vertebrae apart to provide the correct relationships for the facet joints and the ligaments, and forms the foramen (openings) that the nerves use to exit the spinal column.

Disc Degeneration

A degenerated disc is a disc that has lost its thickness or height as shown in Figure 3. The disc's ability to function as a shock absorber, stabilizer, and spacer lessens as the disc wears out (degenerates).

Ligaments, muscles, facet joints, and nerve roots are strained when a disc wears out. Pain is often the result. Although discs degenerate normally with age, injury can accelerate the process.

The main symptom of disc degeneration is pain. Other things happen to your spine as the disc degenerates-the facet joints wear out and bone spurs may form. Back pain might be due to disc instability. The operation designed to stabilize this condition is called a "fusion."

Disc Herniation

Bulging of the nucleus through weakened or torn annular rings can cause direct pressure on or inflammation of a nerve root. Figure 4 shows the progression of a disc herniation.

Figure 5 shows the disc herniation pressing on the nerve root. Lumbar nerve roots join to form a large nerve called the "sciatic nerve." The sciatic nerve supplies sensation and muscle function to the legs.

Surgery

The objective of surgery is to remove the ruptured piece of disc and leave the rest of the disc intact. Removing the ruptured piece of disc will relieve pressure on the nerve root and decrease your leg pain. This surgery will narrow the space between the vertebrae slightly and cause extra pressure on the facet joints.

Due to this, it is not uncommon to have some back pain after surgery. This spinal change is the primary reason for strengthening the muscles around the spine to reduce stresses on the facet joints or ligaments

Facet Joint

Each disc/vertebra level has two facet joints that help link the vertebra to its mate. These joints are covered with a smooth cartilage surface (like in knee joints, etc.).

"Facet Joint Syndrome" is the wearing out and other changes to this cartilage that may cause back pain (see "Facet Joint Syndrome" for more information).

Bone Spurs/Calcium Buildup

We often hear the term "bone spurs" referred to as "calcium buildup". Vertebrae may form bone spurs (in response to the disc's degeneration) to help stabilize (reduce movement) in the spine. This explains why we get stiffer as we get older.

These spurs can pinch a nerve and cause aching leg pain

Thickened Ligaments

Ligaments run along the vertebrae the entire length of the spine.

They help support the spine and add some strength to the discs.

Ligaments may thicken with aging and press on nerves.

Rehabilitation and Maintenance

It is important that normal stability and function around an injured disc is restored and maintained. This rehabilitation and maintenance can be achieved with specific strengthening exercises for the back.