FACTORS DETERMINING PULMONARY-FUNCTION IN ADOLESCENT IDIOPATHIC THORACIC SCOLIOSIS

Adolescent idiopathic thoracic scoliosis may lead to severe pulmonary impairment and early death, but the responsible factors are poorly und erstood; pulmonary function is only weakly related to the angle of sco liosis. We performed a cross-sectional study using multivariate analys is to identify the individual and additive influence of different feat ures of spinal deformity and nonstructural factors on pulmonary impair ment. Pulmonary function was assessed by measuring lung volumes and di ffusing capacity, with a priori selection of vital capacity (expressed as percentage of predicted, % VC) as the primary index of pulmonary i mpairment. Radiologic and physiologic measurements were made independe ntly in 66 subjects who had not previously had spinal surgery. Angle o f scoliosis (p = 0.01) was one of four features of spinal deformity as sociated with reduced % VC; greater number of vertebrae involved (p = 0.007), cephadal location of the curve (p = 0.04), and loss of the nor mal thoracic kyphosis (p = 0.002) made an equal and additive contribut ion to pulmonary impairment. Spinal deformity led to reductions in VC, primarily by reducing TLC. Spinal column rotation, respiratory muscle strength, and duration of the curvature were not related to pulmonary function (p > 0.05). We conclude that features of the spinal deformit y are the major determinants of pulmonary impairment in idiopathic tho racic scoliosis but that the relationship between deformity and impair ment is complex. The severity of pulmonary impairment cannot be inferr ed to a clinically useful extent from the angle of scoliosis alone.