Thoracic Insufficiency Syndrome

Thoracic insufficiency syndrome, a newly characterized disease, is defined as the inability of the thorax to support normal respiration or lung growth. The thorax, which includes the spine, the rib cage, and the sternum, is the engine of respiration. It must have adequate volume for the underlying lungs to grow and it must be able to change that volume for breathing (respiration) to occur.

Thoracic insufficiency syndrome plays a part in the development of a child in two distinct ways. The first is the inability to support normal respiration. A thorax in early stages of deformity from scoliosis or from fused or absent ribs may have a minor degree of inhibition of respiration and the patient may appear normal. As the deformity worsens, the respiration can become more labored with increase respiratory rate and the inability to keep up with playmates in play activities. When thoracic volume is severely decreased and the diaphragm is the sole source of respiratory effort, then children may need aides such as nasal oxygen, BiPap ( pressure mask delivering oxygen), or even ventilator support to maintain life sustaining oxygen levels in their blood. The second component of thoracic insufficiency syndrome is the inability of the thorax to support lung growth. Early in life, a small thorax may be adequate for an infant, but if the child grows without the thorax enlarging with normal growth sufficiently to accommodate adult size lungs, then by the time the patient becomes a teenager, the thorax that was adequate during early childhood is very inadequate for adult oxygenation needs.

In thoracic insufficiency syndrome, the three-dimensional deformity of the thorax can limit its important role as a respiratory engine. Diseases can affect the spine and rib cage in many different ways, but the common problems are deficiencies in thoracic volume, symmetry, and function.

Most of the work of breathing is accomplished by the work of the diaphragm muscle, which is the thin muscle at the base of the thorax underneath the lungs. When the diaphragm contracts, the volume of the thorax increases with the air brought into the lungs. When the diaphragm muscles relax, air is forced out of the lungs. Another important contribution to the act of breathing is the outward expansion of the chest wall itself from the many small muscles between the ribs. For the thorax to have optimal efficiency as a respiratory pump, it must have ideal volume for age, the ribs need to have a symmetrical shape in order for them to move properly, and the diaphragm muscle must be properly anchored at the base of the chest. In congenital scoliosis, there can be missing or fused ribs. When there is an absence of ribs of the chest wall, the underlying lung collapses inward with breathing without effectively expanding. In fused ribs and congenital scoliosis, the concave side of the curve usually contains a lung constricted by the fused ribs. Additional loss of thoracic volume may be seen in scoliosis when the curve rotates the spine into the chest on the convexity of the curve, often protruding deeper into the chest in a deformity called lordosis (sway back), flattening the chest with loss of thoracic volume. In this instance, the ribs cannot move well enough to contribute to respiration, and breathing becomes totally dependent on the diaphragm muscle. Increasing deformity of the thorax results in greater volume loss and may lead to respiratory problems to a point that a child may require oxygen or even ventilator support.