The impact of vertebral fractures on pulmonary function tests in patients with interstitial lung disease. A cross-sectional study

Background: Data on the impact of vertebral deformities on lung function in interstitial lung diseases (ILDs) are limited. This study aimed to evaluate the association between vertebral deformities, quantified by the spinal deformity index (SDI), and pulmonary function parameters, independently of ILD pattern and thoracic morphometric indices. Methods: This cross-sectional study included adult patients diagnosed with ILD who underwent high-resolution computed tomography (HRCT) and pulmonary function tests (PFTs). PFTs included absolute and percent predicted values of forced vital capacity (ppFVC), absolute and percent predicted total lung capacity (ppTLC), forced expiratory volume in one second (FEV₁), and percent predicted diffusing capacity of carbon monoxide (ppDLCO). The SDI was calculated from T4 to T12 on sagittal HRCT reconstructions. Results: A total of 200 patients were analyzed: 76 with idiopathic pulmonary fibrosis (IPF), 65 with systemic sclerosis–associated ILD (SSc-ILD), 31 with idiopathic inflammatory myopathy–associated ILD, and 28 with other ILDs. At least one mild thoracic vertebral fracture was detected in 46 subjects (23%). Each one-point increase in SDI was associated with a 2.9% reduction in ppFVC (p < 0.01), a 2.7% reduction in ppTLC (p < 0.01). Absolute FVC and TLC declined by 95.6 mL (p < 0.05) and 199.5 mL (p < 0.05) per SDI point, respectively, with consistent results after multiple imputation. Conclusions: Vertebral deformities quantified by SDI are independently associated with reduced lung volumes in ILD patients, beyond fibrotic pattern and thoracic morphometry. These findings reveal a novel bone–lung interaction and support the inclusion of vertebral assessment in the comprehensive evaluation of ILD.