Changes in Diaphragm Intrusion and Thoracic Dimensions After Posterior Spinal Fusion in Patients With Neuromuscular Scoliosis

Background: Cerebral palsy (CP) can cause scoliosis with large thoracolumbar or lumbar curves. Such curves may impair pulmonary function by causing the abdomen and diaphragm to encroach on the thorax. Our purpose was to investigate changes in diaphragm position and other thoracic radiographic measurements at 2 years after posterior spinal fusion (PSF). Methods: Retrospective review of data from 56 pediatric patients (Gross Motor Function Classification System >3) who underwent PSF for CP-related (neuromuscular) scoliosis at one US academic hospital from 2010 to 2018. In this study, we used radiographs taken preoperatively and 2 years after PSF to measure lung volume, diaphragm intrusion index (DII), diaphragm vertebral level (DVL), space available for the lung (SAL), and T1-S1 height. Results: Lung volume had increased by a mean 902 cm3 (range, -735 to 2697 cm3) at 2-year follow-up. DII improved from a mean (and SD) of 61%+/- 12% to 71%+/- 11% on the left side and 58%+/- 14% to 68%+/- 11% on the right (P<0.001). DVL increased caudally by a mean 1.2 vertebral levels bilaterally, with a mean postoperative position between T8 and T9. Lung space became more symmetrical as the SAL increased from 0.76 to 0.91 (P<0.001). T1-S1 height increased by a mean 7.5 +/- 4.3 cm. Conclusions: These findings suggest a new way to understand changes in thoracic volume and redistribution of thoracic and lumbar balance when correcting the collapsing spinal deformity in CP. A more caudal postoperative diaphragm position with less diaphragm intrusion into the thorax may reflect an improved length-tension configuration, which could in turn produce greater diaphragmatic strength and endurance. Level of Evidence:Level III