Correlation of preoperative deformity magnitude and pulmonary function tests in adolescent idiopathic scoliosis

Study Design. Clinical study correlating preoperative pulmonary function tests (PFTs) to radiographic measures of thoracic deformity severity in adolescent idiopathic scoliosis (AIS) patients. Objective. To determine (1) the incidence of clinically relevant (<65% predicted value) pulmonary impairment in AIS patients; (2) if patients with more severe deformity have greater impairment of PFTs than those with lesser deformity; (3) the effect, if any, of juvenile onset deformity (onset < age 10) on preoperative PFTs. Summary of Background Data. Patients with late-onset (adolescent) spinal deformity are generally believed to have no respiratory morbidity except in severe curves exceeding 100°. Methods. A large multicenter database of surgically treated AIS patients with Lenke 1 to Lenke 4 curves was queried to report preoperative PFTs and correlate them with radiographic measures of coronal, sagittal, and axial plane deformities. Results. Nineteen percent of 858 patients had <65% predicted forced expiratory volume in 1 second (FEV₁ ) and forced vital capacity (FVC) before surgery, and had larger main thoracic (MT) curves and greater axial rotation than those with predicted PFT values >65%. Patients with MT curves >70°, and especially >80°; proximal thoracic (PT) curves which were >30° or structural; or T5-T12 kyphosis <10° had significantly(P ≤ 0.001) lower FEV₁ or FVC compared to those with less deformity. Axial plane deformity did not correlate with PFT impairment. Juvenile-onset patients had greater PFT impairment than AIS patients, along with slightly larger MT curves. Patients who were braced before surgery had worse PFTs than those had no treatment before surgery. Conclusion. Preoperative PFTs are clinically impaired in 19% of AIS patients, and correlate significantly with the MT and sagittal plane deformity severity, and with PT curve severity to a lesser degree. PFTs do not correlate with degree of axial deformity. From a purely pulmonary standpoint, attention directed to coronal and sagittal plane deformity correction appears warranted, to address the specific deformities which are associated with PFT impairment.