The Impact of Anterior Vertebral Body Tethering on Pulmonary Function

Study Design. Retrospective, single-center study. Objective. To examine pulmonary function tests (PFTs) in patients undergoing anterior vertebral body tethering (AVBT). Summary of Background Data. The effect of AVBT on pulmonary status remains unclear. Materials and Methods. The authors examined preoperative and postoperative PFTs following AVBT in a retrospective, single-center cohort of patients. Outcomes were compared using percent predicted values as continuous and categorical variables (using 10% change as significant) and divided into categorical values based on the American Thoracic Society standards. Results. Fifty-eight patients with adolescent idiopathic scoliosis were included, with a mean age of 12.5 +/- 1.4 years and a follow-up of 4.2 +/- 1.1 years. The mean thoracic curve was 47 degrees +/- 9 degrees, which improved to 21 degrees +/- 12 degrees. At baseline, the mean forced expiratory volume in one second (FEV1%) and forced vital capacity (FVC%) values were 79% and 82%, respectively. Four patients had normal FEV1% (>= 100%), 67% had mild restrictive disease (70%-99%) and the rest had worse FEV1%. Mean FEV1 improved from 2.2 to 2.6 L (P<0.05) and FVC improved from 2.5 to 3.0 L (P<0.05); however, % predicted values remained unchanged (FEV1%: 79%-80%; FVC%: 82-80%, P>0.05) with mean postoperative PFTs at 37 +/- 12 months postoperative. The use of miniopen thoracotomy was not associated with worsening PFTs, but extension of the lowest instrumented vertebra below T12 was correlated with decreasing FEV1% in the bivariate analysis (P<0.05). Patients with worse preoperative FVC% (80 +/- 13% vs. 90 +/- 11%, P=0.03) and FEV1% (77 +/- 17% vs. 87 +/- 12%, P=0.06) also had a greater likelihood of declining postoperative FEV1%. Conclusion. Pulmonary function in most patients undergoing AVBT remained stable (76%) or improved (14%); however, a subset may worsen (10%). Further studies are needed to identify the risk factors for this group, but worse preoperative PFTs and extension below T12 may be risk factors for worsening pulmonary function.