In this study we analyzed pulmonary function after a minimal invasive anterior approach for spinal correction and fusion of adolescent idiopathic thoracic scoliosis. The results demonstrate a significant improvement of FEV1, FEV1% and TLC after a minimal invasive thoracotomy at a minimum of two years of follow-up. Our results are comparable to those of other studies that showed an improvement of absolute PFT results between 12% and 15% after thoracoscopic procedures [3, 19].
In immature patients the absolute values of pulmonary function increase by growth. Normalizing pulmonary function values for age, height and sex corrects largely for the increase in lung volumes because of growth. These corrected values are called percentage predicted values. The percentage predicted values are most appropriate to compare preoperative and postoperative values for a given approach . The improvement of % predicted FEV1 (86,7% preoperative versus 96% postoperative) therefore is not the effect of age but a true improvement.
The anterior approach to the thoracic spine by standard thoracotomy has been reported to have long-term detrimental effects on pulmonary function. Graham et al.  showed that pulmonary function test values after anterior spinal fusion via rib resection thoracotomy returned to within 94% to 96% of baseline by the 2-year follow-up visit, but were still statistically less than the preoperative values (P ≤0.05). Sudo et al.  showed that the average percent-predicted forced vital capacity and forced expiratory volume in 1 second were significantly decreased during long-term follow-up (12–18 years, average 15,2 years) measurements (73% and 69%; P = 0.0004 and 0.0016, respectively).
The thoracoscopic approach to the spine has been suggested to be less invasive and thereby could have a less detrimental effect on pulmonary function. There are few studies that compare the effect of surgical approach to the thoracic spine on pulmonary function. Lenke et al. compared open versus endoscopic anterior fusion combined with posterior fusion and found no significant difference in pulmonary function after 2 years of follow-up. Lonner et al. showed in a study comparing thoracotomy, thoracoscopy and a thoracoabdominal approach better pulmonary function test results after thoracoscopy compared with thoracotomy.
The size of the thoracotomy appears to be of influence on postoperative pulmonary function. This has been shown in a study by Namboothiri et al.. They compared two groups with adolescent idiopathic thoracic scoliosis who underwent two-stage surgery using an anterior release and posterior fusion and instrumentation. One group had a standard large thoracotomy in which the thoracotomy size was 15–20 cm and another group had a minimal open thoracotomy in which the thoracotomy size was 5–7.5 cm. Both groups showed a decline in FEV1 and FVC values at 2 weeks and 3 months after the thoracotomy, but this decline was smaller in the small thoracotomy group. In our study the length of the skin incision was 7 cm. The rib dissection subperiostally was 10–12 cm length and we used 2 extra portals of 2 cm length each. This makes our incision length 14–16 cm, but the size of the thoracotomy that is of influence on pulmonary function is 10–12 cm. This is between a large thoracotomy size and mini open. Our patients demonstrated a significant improvement of FEV1, FEV1% and TLC. We performed anterior instrumentation and fusion together with an anterior release, which requires single lung ventilation. Single lung ventilation can cause high airway pressures and ventilation-perfusion mismatches which can lead to life threatening complications such as air throughout the chest, mediastinum, abdomen, and subcutaneous tissues . However, we did not have such life threatening complications in our series of patients.
Newton et al.  showed that preoperative pulmonary function test values were the strongest predictors of 2-year pulmonary function after surgery. They also showed that, two years after anterior thoracic scoliosis correction, the thoracoscopic group was superior with regard to both absolute pulmonary function test volumes and percentage predicted values as compared with the open thoracotomy group that included a thoracoplasty.
The results of our study demonstrate improved pulmonary function test results after minimal invasive thoracotomy.
We used fluoroscopy to insert all the screws. One could state that our technique leads to more fluoroscopy use but this is comparable to the use of fluoroscopy with the screw placement in posterior instrumentation.