Maximal Respiratory Muscle Strength and Vital Capacity in Children With Early Onset Scoliosis

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Study Design.Descriptive cross-sectional study.Objective.To measure respiratory muscle function in children with early onset scoliosis (EOS), determine the frequency of respiratory muscle weakness, and correlate these measures with vital capacity, body mass index, and Cobb angle.Summary of Background Data.Progressive restrictive respiratory disease is common among children with moderate to severe EOS. Reduced respiratory muscle strength is associated with the loss of lung function in adolescents and adults with scoliosis. We hypothesized that reduced inspiratory and expiratory respiratory muscle strength also occur in children with EOS and correlate with reduced vital capacity, poor nutritional status, and severity of the spine deformity.Methods.We measured maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP), forced vital capacity (FVC), body mass index IBMI), and Cobb angle in 49 children with EOS but with no diagnosis of underlying muscle weakness. We measured these indices in 12 children serially over 18 months to see if abnormal respiratory muscle function was sustained.Results.FVC averaged 51% (SD 21) of predicted norms with 26 subjects having an FVC <50% predicted. The mean MIP was 57% (SD 25) and the mean MEP was 53% (SD 23) of predicted norms. Thirteen (27%) of the group had MIP values >2SD below the age and sex-based norms. BMI ranged between 1% and 99% of age-based norms. Cobb angle averaged 59° (SD27). MIP% and MEP% significantly correlated with FVC% (r =0.37, P = 0.01 and r = 0.52, P < 0.001 respectively)) but not with BMI or Cobb angle. Reduced MIP% and MEP% were sustained over 7 to 41 months.Conclusion.Respiratory muscle weakness is common and persistent in children with EOS and correlates with reductions in vital capacity. Mechanisms for abnormal respiratory function are unclear but must be determined to develop surgical treatment strategies that preserve respiratory muscle function in children with EOS throughout childhood.Level of Evidence: 2

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