Authors: Thefanis Tsiligiannis and Theodoros B Grivas
Idiopathic scoliosis, a common disorder of lateral displacement and rotation of vertebral bodies during periods of rapid somatic growth, has many effects on respiratory function. Scoliosis results in a restrictive lung disease with a multifactorial decrease in lung volumes, displaces the intrathoracic organs, impedes on the movement of ribs and affects the mechanics of the respiratory muscles. Scoliosis decreases the chest wall as well as the lung compliance and results in increased work of breathing at rest, during exercise and sleep. Pulmonary hypertension and respiratory failure may develop in severe disease. In this review the epidemiological and anatomical aspects of idiopathic scoliosis are noted, the pathophysiology and effects of idiopathic scoliosis on respiratory function are described, the pulmonary function testing including lung volumes, respiratory flow rates and airway resistance, chest wall movements, regional ventilation and perfusion, blood gases, response to exercise and sleep studies are presented. Preoperative pulmonary function testing required, as well as the effects of various surgical approaches on respiratory function are also discussed.
Idiopathic scoliosis has direct effects on many aspects of the respiratory function and, although there have been reviews on the subject, the purpose of this review is a detailed discussion on how scoliosis is affecting different aspects of breathing and especially how it is reflected in the results of the various tests of respiratory function.
Scoliosis is the most common 3-dimensional deformation abnormality of the spine with direct effects on the thoracic cage, with a reported prevalence in the general population varying significantly from 0.3% to 15.3%. It is the result of a pathologic process which leads to lateral curvature of the spine. It can be congenital, due to vertebral or rib malformation, secondary to a variety of systemic or neuromuscular disorders, or idiopathic. Idiopathic scoliosis accounts for approximately 85% of cases and it is defined as a structural scoliosis for which no specific cause can be established. Based on population studies it is considered a single-gene disease with variable penetrance and heterogeneity. Idiopathic scoliosis is further categorized as infantile, juvenile and adolescent, according to the age at which the spinal deformity is first noticed. Its diagnosis can be made after exclusion of a primary etiology such as vertebral anomaly, neuromuscular disorder, Marfan syndrome or other disorder. Another classification is based on the quantification of the severity of the scoliosis by the use of radiographic measurements of the angle of the curvature in the spine (Cobb angle), as well as the level of the apex of the spinal curvature (cervical, high thoracic, thoracolumbar, lumbar), and the number of curves (single or double). These characteristics are used for comparison, prognosis and development of treatment guidelines.
The effects of scoliosis in the anatomy of the chest are quite complex. It was reported that the plot of segmental thoracic ratios by age groups, a method of assessment of the morphology of rib cage in anteroposterior radiographs, is one way of expressing the proportional changes of thoracic viscera, mainly the heart and lungs and principally the lungs during growth. The relative narrowing of the girls’ lower thorax between childhood and puberty is consistent with the proportionate change in the girl’s lung in the later stages of growth reported by Simon et al. The narrowing of the girls’ lower thorax between childhood and puberty is also documented assessing the segmental rib-vertebra angles (RVAs) in Segmental patterns of chest radiographs in children.
The upper chest in Infantile Idiopathic Scoliosis (IIS) is funnel – shaped. It was reported that the narrow rib – cage at T1–4 in children with IIS compared with the controls is very highly significant. The funnel – shaped upper thoracic cage of IIS is like that of each of: a) a normal human foetus, b) asphyxiating thoracic dysplasia (Jeune’s disease) and c) a normal adult rabbit. The rib cage in Adolescent Idiopathic Scoliosis (AIS) patients was also documented to be narrower than in the non scoliotic counterparts. Consequently if the chest cannot develop normally during growth, there is insufficient space available for pulmonary alveolar growth, with resultant extrinsic restrictive lung disease. Scoliosis can affect pulmonary function in many ways. At an early stage it is usually painless and asymptomatic. Most investigators who have studied the impairment of pulmonary function in scoliosis generally agree that (1) a Cobb angle greater than 90 degrees greatly predisposes to cardiorespiratory failure, (2) lung function abnormalities are detectable when a Cobb angle is greater than 50 to 60 degrees, (3) lung function abnormalities are mainly of the restrictive type and (4) the duration of scoliosis correlates with the patients degree of disability. Its natural history is associated with curve progression, cardiopulmonary impairment, back pain, cosmetic deformity and neurologic compromise. A great variety on the degree of these manifestations exists, depending on age of onset, genetic background and curve pattern.
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