Apical Control Technique with Traditional Growing Rods Improves Outcomes in Congenital Early-Onset Scoliosis

This is the authors' abstract. We don't add key points for this paper.

Commentary The study by Wang et al. is destined to become a premier reference with regard to the treatment of congenital early-onset scoliosis and, by extension, most types of early-onset scoliosis because of the demonstrated efficacy of the apical control technique (ACT). The study shows improved radiographic and pulmonary function outcomes at maturity when ACT is added to the traditional dual growing rod (TDGR) technique (ACT-TDGR), compared with TDGR without apical control, in patients with congenital early-onset scoliosis. Why add apical control to traditional distraction-based growing instrumentation? In a landmark article, Dubousset et al.1 described "spinal penetration," in which a progressive scoliotic apex translates and rotates into the convex hemithorax, reducing endothoracic volume and initiating a volume-depletion deformity that can evolve to thoracic insufficiency syndrome (TIS). Many believe that this progressive pathoanatomy is responsible for the disabling respiratory sequelae of TIS. TDGR, with only end-vertebral anchors, has limited biomechanical ability to correct or prevent apical penetration solely by distraction; serial lengthenings are relatively helpless to unwind an uninstrumented apex that has been free to develop the crankshaft phenomenon during vertebral growth in the presence of a fixed distraction length2,3. This study by Wang et al. confirms the value of controlling an apex made up of anomalous vertebrae with growth potential. In addition to obtaining better coronal plane correction at the index surgical procedure, due to short-segment apical vertebral resection and fixation added to a growth-sparing technique, the ACT group had better penetration and rotational parameters at maturity, fewer instrumentation-related complications, and a reduced need for both formal final fusion and osteotomies performed at that final surgical procedure. Furthermore, the improved initial correction and additional fixation were not detrimental to eventual thoracic spine length. An even more compelling outcome, and the take-home message, involves the pulmonary function test results at maturity and the correlation with curve magnitude, T1-12 spinal length, and apical vertebral translation. It is a rare data set that confirms increasingly better pulmonary function test results with the confluence of 3 critical measures—smaller curves, less apical penetration (apical vertebral translation), and thoracic lengths of ≥18 cm or even ≥22 cm4. The percentage of normal predicted pulmonary function test values in this study may be artificially elevated and not directly comparable with other studies due to the use of patient height—rather than arm span—as the standardizing calibration for patients with scoliosis. Nevertheless, the greater absolute volumes and the upward trend in the percentage of predicted volumes with greater T1-12 length confirm that the 3-dimensional corrections with ACT, when combined with sufficient thoracic length (76% of patients achieved ≥18 cm, not easily obtained in congenital cases4), provide encouraging pulmonary outcomes (≥70%), which exceeded the pulmonary function tests of the TDGR group that had the same coronal curve magnitude. Considering the relentless deterioration of lower pulmonary function test values <60% over time reported by Bouton et al.5, the outcomes in the patients in the study by Wang et al. likely had better than the usual values, near 55%, typically reported for patients with traditional growing rods. This is compelling evidence that the ACT method is indeed capable of positively improving outcomes, as measured by pulmonary function tests, in early-onset scoliosis rather than simply stabilizing respiratory status at the preoperative level or preventing it from progressing to frank disability.