The associations between spinal deformities and pulmonary functions in conservatively treated patients with adolescent idiopathic scoliosis – a systematic review and meta-analysis

Abstract

Introduction: Some studies have shown that teenagers with adolescent idiopathic scoliosis (AIS) display pulmonary impairments although conflicting findings have been reported. Unfortunately, no systematic review or meta-analysis has been conducted to summarize the correlations between various lung function parameters and radiographic phenotypes in these patients, which can help identify AIS patients with pulmonary impairments for timely management. Therefore, the objective of the current metaanalysis was to summarize existing information regarding the associations between various lung function parameters and structural characteristics of patients with AIS. Methods: Candidate publications were identified from eight electronic databases, from inception to November 2016. Two independent reviewers screened the titles, abstracts, and full-text of potential articles based on the eligibility criteria. Another two independent reviewers extracted relevant data and appraised the methodological quality of the included studies. The risks of bias of case-control studies, cross-sectional studies, and longitudinal studies were assessed by the Newcastle-Ottawa Quality Assessment Scale for Case-control Studies, Appraisal Tools for Cross-Sectional Studies, and Quality in Prognostic Study tool, respectively. The associations between various pulmonary parameters and spinal parameters were summarized qualitatively. Meta-analyses were conducted using random-effects models, if appropriate. Results: Of 1,045 identified citations, 18 studies (3,075 participants) met the inclusion criteria. Fourteen included studies (2,766 patients) reported significant low-to-moderate associations between diverse spinal deformity parameters (e.g., axial vertebral rotation) and lung functions (e.g., percent predicted functional vital capacity (%FVC), percent predicted forced expiratory volume in one second (%FEV1), and percent predicted total lung capacity (%TLC) in patients with AIS. Homogenous data from 10 studies were pooled for meta-analyses. The results showed that larger thoracic Cobb angles were related to lower %FVC (r = -0.34; 95%CI: -0.39 to -0.29), lower %FEV1(r = - 0.33; 95%CI: -0.39 to -0.27), smaller %TLC (r = -0.19; 95%CI: -0.25 to -0.13), and smaller percent predicted vital capacity (r = -0.28; 95%CI: -0.34 to -0.22). Conversely, thoracic kyphosis angles were positively associated with %FVC (r = 0.11; 95%CI: 0.07 to 0.15), %FEV1 (r = 0.23; 95%CI: 0.18 to 0.27), and %TLC (r = 0.19; 95%CI: 0.15 to 0.24). Many included studies had suboptimal methodological quality. Notably, many of them did not justify the sample sizes. They also did not report response rates, information about ethics approval, and confounders. Discussion: Severe spinal deformities were found to be related to clinically significant pulmonary impairments in patients with AIS. However, the relations between spinal deformities and pulmonary functions in patients with mild curve remain unclear because static pulmonary function tests may not be sensitive enough to detect subtle pulmonary impairments. To this end, maximal exercise tolerance tests can be prescribed to detect small pulmonary impairments, which are amplified as the demands of pulmonary function are increased by intensive physical work. Additionally, future studies are warranted to consider the influences of other factors (e.g., physical activity levels) in affecting the associations between spinal deformities and lung function, and to determine the possibility of restoring lung functions of these patients by non-surgical and surgical means.