Body Mass Index as an Indicator of Pulmonary Dysfunction in Patients With Adolescent Idiopathic Scoliosis

Abstract

Prospective clinical study. To investigate the factors correlated with pulmonary function in adolescent idiopathic scoliosis (AIS) patients, and to determine the influence of body mass index (BMI) on the pulmonary function. Impaired pulmonary function has been reported in patients with AIS. The factors reported to affect pulmonary function included the curve magnitude, location of the apex vertebrae, decrease in thoracic kyphosis, and the number of vertebrae involved. A low BMI has been well confirmed in AIS patients. However, the relationship between BMI and pulmonary function has never been investigated. One hundred twenty female patients with a single thoracic curve were enrolled in this study. Pulmonary function test and radiographic examination were performed. Several radiographic parameters, including the curve magnitude, the curve type, location of the apical vertebra, the number of vertebrae involved, and the degree of thoracic kyphosis, were recorded. BMI was calculated according to the measurements of standing height and body weight. Patients were divided into 2 groups according to BMI, (group A >17.5 kg/cm and group B ≤17.5 kg/cm), and the pulmonary function was compared between the 2 groups with students t test. Partial correlation analysis and stepwise multiple regression analysis were used to assess the association between BMI and the results of the pulmonary function test. The receiver operating characteristics curve was created to identify the best dividing point for diagnostic variables. The average percentage of predicted vital capacity, forced vital capacity, and forced expiratory volume in 1 second was significantly decreased in patients with a lower BMI. A positive correlation was found between BMI and pulmonary function (r=0.41, P<0.001). The stepwise regression analysis showed that low BMI was significantly associated with pulmonary function impairment (R=0.206, P<0.001). According to the receiver operating characteristics curve, patients with a BMI <17.7 kg/cm are prone to have abnormal pulmonary function. BMI was found to be an important indicator for pulmonary function in AIS patients. The decreased BMI could explain approximately one-fifth of the variation in pulmonary impairment in AIS patients, which might shed some light on the rehabilitation of preoperative pulmonary function.