Pulmonary Function in Adolescent Idiopathic Scoliosis

• a - Harms Study Group

Introduction: Many studies have addressed pulmonary function in adolescent idiopathic scoliosis (AIS), examining the natural history and effects of treatment. Most of these studies are based on moderate sized cohorts and have concluded that the effect of scoliosis on pulmonary function is clinically negligible until curve severity reaches greater than 100°. The goal of this study was to examine the relationship between radiographic deformity and pulmonary function in a large cohort of patients (n=515) with AIS.

Methods: Data was collected from patients in a multicenter AIS database. Patients without prior scoliosis surgery were included in the study cohort if they had posteroanterior and lateral radiographs and concomitant pulmonary function tests including forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and/or total lung capacity (TLC). Data analysis was conducted using regression analyses with ± = 0.02.

Results: The study cohort included 515 AIS patients (426 females and 89 males) who were an average of 14.5±2.3 years old. 65% of patients had Lenke 1 curve patterns. Across all curve types, the average thoracic curve magnitude was 51±14°, while the average lumbar curve was 36±13°. The maximum coronal curve ranged from 33° to 110°. Average thoracic kyphosis (T5 to T12) was 24±14° with a range from -10° to 64°. The average FVC for the entire cohort was 2.96 ± 0.77 L, or 87 ± 17 % predicted FVC (range: 22 to 140% predicted). As the thoracic curve increased, FVC decreased with a coefficient of multiple determination (R2) of 0.08 (p <0 .001). In addition, a reduction in thoracic kyphosis also correlated with decrease FVC (R2="0.04," p < 0.001). Similar patterns were found for FEV1 and TLC (82±17% 89±16% predicted, respectively). Using the American Thoracic Society criteria pulmonary impairment, patients grouped into two categories: normal function to mild impairment (>65% predicted pulmonary function) or moderate to severe impairment (d”65% predicted pulmonary function). As shown in Figure 1, the percentage of patients with moderate to severe impairment increased with thoracic curve magnitude; of the 110 patients who had thoracic curves >60°, 30% had moderate to severe pulmonary impairment. Significant sagittal deformities were also associated with pulmonary impairment. 29% of patients with hypokyphosis (<10 ° T5 to T12 kyphosis) and 80% patients with excessive kyphosis (>60° T5 to T12 kyphosis) also had moderate to severe pulmonary impairment.

Conclusion: These results indicate that pulmonary function is affected by spinal deformity in AIS patients. The degree of pulmonary impairment appears to be clinically significant at much lower thoracic curve values than the current literature suggests. Sagittal plane deformities also contribute to pulmonary impairment. There is a possibility that biplanar deformities contribute synergistically to impairment and the association between spinal deformity and pulmonary function warrants further research.

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