The chest wall is a major component of the respiratory pump and consists of the rib cage and abdomen. It is inflated by the inspiratory muscles of the rib cage and the diaphragm, and its integrity is key to sustaining ventilation. Disorders affecting the nonmuscular structures of the chest wall (the thoracic spine, ribs, costovertebral joints, abdominal wall, and sternum) may lead to respiratory dysfunction. When the integrity of these nonmuscular components is severely compromised, respiratory failure may ensue. The pathophysiology of disorders affecting these nonmuscular components is generally related to the imposition of excessive elastic loads placed on the respiratory muscles. In some disorders, such as kyphoscoliosis and obesity, the load on the respiratory muscles is chronic and progressive. By contrast, with flail chest, the load on the respiratory muscles is acute. If the respiratory muscles have not adapted or had little time to adapt to loads that increase the work of breathing, respiratory failure may quickly ensue. Other disorders, such as ankylosing spondylitis and pectus excavatum, have a minimal impact on respiratory function. The respiratory muscles are discussed in Chapters 3 and 142.
Kyphoscoliosis (KS) refers to a three-dimensional spinal deformity characterized by excessive curvature of the spine in the lateral plane (scoliosis) and sagittal plane (kyphosis), as well as by vertebral axis rotation.1 Scoliosis, defined as a lateral curvature greater than 10 degrees, is generally associated with kyphosis and spinal axis rotation.2,3 KS is one of the most common spinal abnormalities, with estimates of prevalence in the United States ranging from 1 in 10,000 people for severe deformities to 1 in 1000 people for mild deformities.4 It is classified as idiopathic (no known cause), secondary or paralytic (due to neuromuscular disease), or congenital (associated with vertebral malformation at birth) (Table 83-1).5
TABLE 83-1Causes of Kyphoscoliosis ||Download (.pdf) TABLE 83-1 Causes of Kyphoscoliosis
Paralytic or secondary
Disorders of connective tissue
Vitamin D–resistant rickets
Idiopathic KS usually manifests in late childhood or early adolescence and involves primarily females (ratio of 4:1).2,5 Although largely unknown, the cause of the idiopathic KS likely includes a combination of genetic and environmental factors, which through abnormal bone, muscle growth, or hormonal imbalance lead to increased spine curvature.6 Idiopathic KS is believed to be a multigene condition of autosomal or sex-linked inheritance with variable phenotypic expression.2 Individuals with idiopathic KS may complain of back pain or may have psychological problems.2 When KS is severe, complaints include dyspnea with exertion and constitutional symptoms related to nocturnal hypoventilation. Respiratory failure also may ...