Back Problems: Vertebrae and Low Back Pain

The back, more than any other structure of the human body, requires a combination of flexibility, conditioning, and biomechanical efficiency to maintain its stability and integrity for a lifetime of performance.

The spinal column is a stack of individual bones, known as vertebrae, separated by spongy pads, known as intervertebral discs, commonly referred to as discs. The vertebrae provides the framework to which the large muscles of the back attach, house and protect the long canal of nerves, known as the spinal cord, that transport sensory and motor messages between the body and brain. The spine is not a perfectly straight column, but rather an S-shaped curve. There is an inward curve up by the neck, the cervical region of the spine, an outward curve in the upper back, the thoracic region, and another inward curve in the low back, the lumbar region. When these normal curves are maintained the position is referred to as a neutral spine and the stress placed on the spinal column can be appropriately dispersed.

The lumbar spine, or lower back, bears a great deal of stress both from the frequent impact of the lower extremities and from the twisting and maneuvering of the upper extremities; as a result, it’s extremely prone to injury. Back pain afflicts 85% of all Americans at some point in their lifetime and is one of the main causes for time off or missed work and a trip to the doctor.

Once injured, the lower back can cause a protracted episode of chronic pain. With the network of nerves running though the spinal canal an injury or tissue damage can cause pain that radiates to far away areas of the body, shooting down past the buttocks, thigh and even into the foot. 90% of all mechanical back pain goes away on its own with the assistance of conservative treatment like light stretching, over-the-counter pain medication, topical analgesics and adequate rest from the offensive activities.

Vertebrae are the bones that make up the spine. There are seven in the cervical region, each bone is labeled C1 through C7, which are involved in the movement of the neck. These are the smallest bones of the spine because they have the least amount of weight to bear, but they are also the most prone to severe traumatic injury. The central 12 vertebrae, labelled T1 through T12, make up the thoracic region of the spine. They’re not involved in movement to the extent that the upper and lower regions of the spine are, but they serve the function along with the ribs, of creating a cavity, the thoracic cavity, to support and protect the heart and lungs. The next five vertebrae, labelled L1 through L5, are the thickest, but also the most prone to stress injuries because they bear the brunt of weight from above and force from below. The sacrum is a series of five fused vertebrae that sit just below the lumbar spine. The space between the lowest lumbar vertebrae and the sacral vertebrae is the most mobile part of the lower spine and the most susceptible to injury. Below the sacrum is the coccyx, or tailbone, which is the very base of the spine. Each vertebrae has a solid portion called the body toward the front of the body and the ring of the bone that extends toward the rear of the body. It’s this ring of bone that houses the spinal cord in a cavity called the spinal canal.

The areas where vertebrae come in contact with each other are known as facet joints. These joints are just like other major joints of the body, they have articular cartilage, ligaments and a joint capsule. Each intervertebral disc is made of fibrocartilage, and each sits between the vertebrae. These discs make up about 25% of the length of the spinal column. The discs act as shock absorbers and allow the spine to flex and extend. The structure of each disc can be compared to a jelly donut, there is a center of semifluid material, the nucleus pulposus, that is surrounded by a strong ring of fibrocartilage, the annulus fibrosus. When bending forward, the front of the jelly donut, the disc, is compressed, and the nucleus pulposus, the jelly, is pushed backward. When bending backward the process is reversed.

Longitudinal ligaments are strong ligaments that stabilize the bones of the spine, preventing excessive bending and rotation. The primary trunk muscles for bending backward, or extending, at the waist are known as the erector spinae group. This layered series of muscles includes the iliocostalis, longissimus and spinalis muscles. The rectus abdominis is the primary trunk muscle for flexing, or bending forward, at the waist. The internal oblique and external oblique muscles of the abdomen, when working simultaneously, aid the rectus abdominis in flexing the trunk. When they act individually, they rotate or bend the trunk to the side. The incidence of back problems increases sharply with age, but a little knowledge can go a long way toward avoiding and addressing such injuries.

Recall that the intervertebral discs are filled with a gel-like material called the nucleus pulposus. When bending forward or backward, one side of the vertebrae compress against each other, squeezing the discs and pushing the nucleus pulposus in each disc toward the opposite side. As long as the fibrous capsule enveloping the fluid remains intact, the system functions adequately. But an acute injury, such as twisting the spine or suddenly compressing it under heavy weight, can damage the fibrous ring, the annulus fibrosus, that contains the nucleus. This also occurs with wear and tear or overuse. Aging also decreases the fluid content of the discs. n all cases the result is known as a herniated disc