Anatomy of Kyphosis
Because kyphosis (also known as abnormal kyphosis) causes an abnormal curving of the spine, to fully understand it, you should understand how a normal spine curves and looks. Take a look at the image below: It shows the different regions of the spine and which way they curve.
A quick rundown of spinal anatomy:
- Cervical Spine: This is your neck, which begins at the base of your skull. It contains 7 small bones (vertebrae), which doctors label C1 to C7 (the "C" means cervical). The numbers 1 to 7 indicate the level of the vertebrae. C1 is closest to the skull, while C7 is closest to the chest. The cervical spine has a lordotic curve, which means that it should curve outward. Kyphosis rarely affects the cervical spine, but it is possible.
- Thoracic Spine: Your mid-back has 12 vertebrae that are labeled T1 to T12 (the "T" means thoracic). Vertebrae in your thoracic spine connect to your ribs, making this part of your spine relatively stiff and stable. Your thoracic spine doesn't move as much as the other regions of your spine, like the cervical spine.
The thoracic spine is supposed to have a kyphotic curve; it should curve inward. However, it can start to curve too much, either because of poor posture or because of structural defects. That's hyperkyphosis, commonly shortened to simply kyphosis.
- Lumbar Spine: In your low back, you have 5 vertebrae that are labeled L1 to L5 (the "L" means lumbar). Some people have 6 lumbar vertebrae. These vertebrae are your largest and strongest vertebrae, responsible for carrying a lot of your body's weight. The lumbar vertebrae are also your last "true" vertebrae; down from this region, your vertebrae are fused. In fact, L5 may even be fused with part of your sacrum.
The lumbar spine has a lordotic curve (outward curve). Kyphosis can affect the lumbar spine, especially in a region called the thoracolumbar region—the area where the thoracic and lumbar regions come together.
- Sacrum/Coccyx: The sacrum has 5 vertebrae that usually fuse by adulthood to form one bone; the coccyx—most commonly known as your tail bone—has 4 (but sometimes 5) fused vertebrae. The sacrum and coccyx are also part of your pelvis, and they should have a kyphotic curve (inward).
From behind, the normal spine appears straight. The spinal curves described above are visible when you view the spine from the side. These inward and outward curves help our back carry our weight and are also important for flexibility.
We're born with a kyphotic spine—a spine that curves outward. This is called the primary curve. As we grow, we develop secondary curves: As infants, we develop a lordotic curve in the cervical spine to hold our heads up, and as toddlers, we develop a lordotic curve in the lumbar spine to walk.
As you can tell just from the descriptions of curves, the spine is a complex thing—and we haven't even gotten to the various components of the spine. It's made up of many parts: vertebrae (bones), discs, ligaments, cartilage, tendons, blood vessels, nerves, the spinal cord, and muscles.
The vertebrae stack one on top of each other and are supposed to be rectangular. (One form of kyphosis, Scheuermann's kyphosis (or disease) causes the vertebrae to become triangular or wedge shaped—more on that in the Causes of Kyphosis article.) The vertebrae line up to form a protective tunnel (the spinal canal) to house the spinal cord and spinal nerves. These nerves run down the center of the vertebrae and exit to various parts of the body, such as the legs and arms.
In between the vertebrae, you have intervertebral discs. They act like pads or shock absorbers for your movements, and they also are part of that protective spinal canal. Every disc is made up of a tire-like outer band called the annulus fibrosus and gel-like inner substance called the nucleus pulposus.
Your back also has muscles, cartilage, ligaments, tendons, and blood vessels. Muscles are strands of tissues that act as the source of power for movement. Cartilage is a hard but slippery substance that makes it easier for your joints to move. Ligaments are the strong, flexible bands of fibrous tissue that attach the bones to the intervertebral discs, and tendons connect muscles to bones and discs. Blood vessels provide nourishment. These parts all work together to help you move about, and they also help stabilize your spine.