Based on this large retrospective review from a multicenter prospectively collected database, earlier reports that suggested inferiority of posterior approaches for TK correction as compared with anterior approaches should be called into question.[29,33,34] Although the shift from anterior to posterior approaches in AIS was initially associated with less TK restoration, it improved with time. This initial decrease in TK restoration with PSF as compared with ASF conforms with early concerns reported in the literature.[20,29] Our data are a reflection of the emerging collective realization of the importance of the sagittal plane. The earlier primarily posterior pedicle screw group was associated with slightly less TK restoration as compared with the earlier era of predominantly anterior approaches. However, this has improved with the contemporary approach, restoring patients to a similar degree to that found in the predominantly anterior era. This continuous improvement process deserves special mention. By auditing our results, comparing best practices and education of surgeons, and measuring outcomes after practice changes, we have made significant progress in restoration of TK in AIS by posterior means, which is admittedly difficult to do. Kyphosis restoration techniques are not easily articulated or taught. The use of newer techniques such as segmental uniplanar screws,[43,44] ultra-high strength 5.5-mm stainless steel or cobalt chrome rods, larger diameter rods, aggressive rod contouring,[47–49] periapical Ponte-type posterior column opening osteotomies,[50–55] segmental direct vertebral derotation,[36,43,56,57] and simultaneous translation technique on two rods[58–60] likely contributed to the improvement in sagittal plane restoration and is supported in the current literature.[36–38] In the present study, there was a large shift in adoption of these techniques, and the contemporary PSF group was instrumented with larger rods that were typically stainless steel or cobalt chrome, and routinely had posterior column osteotomies with direct vertebral rotation maneuvers.
Strengths of this study include its prospective inclusion of a large number of patients over a 20-year period from multiple centers and surgeons and a minimum of 2 years of follow-up. This certainly enhances this study's applicability to other surgeons who treat AIS. Additionally, correction of 3D TK was performed to more accurately assess patients' sagittal alignment. Weaknesses of the study include its retrospective design with regard to the descriptors pertaining to exact correction techniques used aside from approach. However, it should be noted that all data used within this study were prospectively collected.
Future efforts in this area may involve analysis using direct calculation of 3D parameters, which may now be obtained from biplanar slot scanning radiographic imaging methods. These measurements may yield more insight into the magnitude of deformity in the sagittal plane and the efficacy of surgical correction.[61–63] Furthermore, sagittal plane correction may eventually be judged based on patient-specific goals obtained from spinopelvic parameters rather than utilizing thresholds such as 10 or 20°.[64–67] Ideally, a purely prospective cohort study with detailed descriptors of fusion techniques and longer-term follow-up would help to answer whether the utilization of newer techniques has improved thoracic kyphosis restoration in patients with structural main thoracic adolescent idiopathic scoliosis, and this is underway. In summary, this study supports the adoption of contemporary posterior techniques in the correction of thoracic kyphosis in AIS utilizing pedicle screw fixation and 3D correction strategies.
Grants were received from DePuy Synthes Spine, Inc. and EOS Imaging, Inc. to the Setting Scoliosis Straight Foundation in support of this Harms Study Group research.
Relevant financial activities outside the submitted work: board membership, consultancy, grants, stocks, royalties, payment for lecture, expert testimony, travel/accommodations/meeting expense.
Spine. 2020;45(23):1625-1633. © 2020 Lippincott Williams & Wilkins