Pulmonary function and thoracic deformities in adolescent idiopathic scoliosis 27 years or longer after spinal fusion with Harrington instrument.

Background: The aim of this study was to conduct an investigation into spinal fusion with Harrington instrument (HI) in patients with adolescent idiopathic scoliosis (AIS) and to survey pulmonary function and thoracic deformity outcomes many years after surgery.

Methods: Subjects comprised 194 patients diagnosed with AIS and treated with spinal fusion using HI between 1968 and 1987. Patients who gave their informed consent were subjected to a complete standing spine X-ray, chest CT, and pulmonary function tests. Eighteen patients were eligible for inclusion. Mean age at the time of follow-up was 49.9 years and the mean duration of follow-up was 35.3 years. CT axial image was used at the apex of the main thoracic curve. Apical vertebral rotation was determined from RA sag measured by the method of Aaro et al. Thoracic cage deformities were measured as follows: Rib hump index (RHi) according to the method of Aaro et al. and posterior hemithoracic symmetry ratio (PHSr) according to the method of Campbell et al.

Results: Pulmonary function tests revealed mean forced vital capacity (FVC) of 2.28 (range: 1.00-3.04) L and mean %FVC of 83.5% (range: 35.6%-117.8%). Restrictive ventilation disorder with %FVC <80% was seen in 5 patients (27.7%). %FVC had strong negative correlations with RA sag (r = -0.798), RHi (r = -0.820, p < 0.001), PHSr (r = -0.705), and proximal thoracic curve (r = -0.721). Main thoracic curve (r = -0.674) and apical vertebral rotation of thoracic curve (r = -0.685) showed moderate negative correlations. Multiple regression analysis revealed RHi was a most significant factor on %FVC.

Conclusions: In AIS patients examined 27 years or longer after surgery, restrictive ventilation defects were observed in 27.7%. Factors aggravating %FVC were large rib humps and large vertebral rotations. Three-dimensional correction of the spine and thoracic cage deformities is vital in order to avoid pulmonary function impairment many years after surgery.