Scoliosis is an abnormal curve in the spine to the left or right. It most often occurs during the growth spurt at the age of 9–15 years. The reason for scoliosis is unknown and in most cases, it is mild and will correct itself during growth. However, in some cases it can be severe, causing long-term back problems. Symptoms of scoliosis include a visible curve in the spine, one shoulder raised above the other, or one hip tilted upward. Scoliosis affects an equal number of boys and girls, but in girls it is ten times more likely to need treatment. In more severe cases of scoliosis, a back brace and physical therapy may correct the deformity. In some cases, surgery is required.
Biomechanically, the spine supports the core of the body, and all other body segments are attached to the spine (head, arms/shoulders, pelvis/legs). A curvature in this structural member will limit its ability to carry axial loads. When loads are carried, more stress will be placed upon the ligaments that attach the spinal segments (vertebra) and the muscles that support the spine. This can lead to back pain. Furthermore, the curvature will cause asymmetric loading of the tissue between the vertebra (intervertebral discs), effectively pinching the tissue on the left or right.
There are other problems associated with this spinal deformity. Because the ribs are connected to the spine, this misalignment can decrease the size of the chest cavity. This can apply pressure to the lungs and affect breathing. To understand why this occurs, first consider normal breathing. The muscle used for breathing is the diaphragm, a large sheet-shaped muscle at the bottom of the chest cavity. In its relaxed state, it is curved upward into the chest cavity. When it is contracted, it pulls downward in the center, expanding the size of the chest cavity, like drawing down a piston. This decreases the pressure within the chest cavity, which draws air into the lungs. If the chest cavity is smaller due to scoliosis, less air can be drawn in with each breath. Furthermore, if the chest cavity is already pressurized, it will require more effort to decrease the chest cavity pressure below atmospheric, a requirement for the inward flow of air into the lungs. Both a lower flow volume and greater effort to attain the volume of air will limit the person’s ability to perform strenuous activities that require a higher rate of oxygen consumption.
The decreased chest cavity size also applies pressure to the heart. The cardiovascular system circulates blood throughout the body. Like a refrigeration system, there is a high-pressure and a low-pressure side. Between each beat, the heart fills with blood supplied by major veins on the low-pressure side. External pressure on the heart can reduce the heart’s ability to fill with blood. This can reduce the pump volume and reduce cardiac output, the volume of blood circulating through the body. This can also limit the person’s ability to perform strenuous activities that require a higher rate of oxygen consumption. Limited breathing and heart functioning can combine resulting in an even greater overall impact on a person’s physical capability.
