Abstract and Introduction
Study Design: A multicenter, prospectively collected database of 20 years of operatively treated adolescent idiopathic scoliosis (AIS) was utilized to retrospectively examine pre- and postoperative thoracic kyphosis at 2-year follow-up.
Objective: To determine if the adoption of advanced three-dimensional correction techniques has led to improved thoracic kyphosis correction in AIS.
Summary of Background Data: Over the past 20 years, there has been an evolution of operative treatment for AIS, with more emphasis on sagittal and axial planes. Thoracic hypokyphosis was well treated with an anterior approach, but this was not addressed sufficiently in early posterior approaches. We hypothesized that patients with preoperative thoracic hypokyphosis prior to 2000 would have superior thoracic kyphosis restoration, but the learning curve with pedicle screws would reflect initially inferior restoration and eventual improvement.
Methods: From 1995 to 2015, 1063 patients with preoperative thoracic hypokyphosis (<10°) were identified. A validated formula for assessing three-dimensional sagittal alignment using two-dimensional kyphosis and thoracic Cobb angle was applied. Patients were divided into 1995–2000 (Period 1, primarily anterior), 2001–2009 (Period 2, early thoracic pedicle screws), and 2010–2015 (Period 3, modern posterior) cohorts. Two-way repeated measures analysis of variance and post-hoc Bonferroni corrections were utilized with P < 0.05 considered significant.
Results: Significant differences were demonstrated. Period 1 had excellent restoration of thoracic kyphosis, which worsened in Period 2 and improved to near Period 1 levels during Period 3. Period 3 had superior thoracic kyphosis restoration compared with Period 2.
Conclusion: Although the shift from anterior to posterior approaches in AIS was initially associated with worse thoracic kyphosis restoration, this improved with time. The proportion of patients restored to >20° kyphosis with a contemporary posterior approach has steadily improved to that of the era when anterior approaches were more common.
Level of Evidence: 3
Considerable variability exists in surgical approach, implant choice, configuration, and reduction methods for the correction of thoracic adolescent idiopathic scoliosis (AIS) and the treatment approach has certainly undergone tremendous evolution in the last 20 years. Although it appears that AIS patients have similar mortality rates compared with the normal population, severe thoracic deformity may lead to functional pulmonary impairment.[1–14] Also, surgical correction of this deformity has been shown to improve thoracic volume, pulmonary function, and lumbar lordosis.[15–20] In addition to coronal plane deviation and axial plane rotation, an essential lesion in thoracic scoliosis is loss of kyphosis, or development of lordosis at the apex, due to anterior spinal overgrowth.[21–28] In the quest for true three-dimensional (3D) correction, some surgeons are focused on the assessment, restoration, and best method for evaluation of innovative techniques to restore kyphosis.
Traditionally, anterior spinal fusion (ASF) was performed in the interest of sparing distal fusion levels and allowed for historically greater correction and derotation as compared with posterior spinal fusion (PSF) with hook or hybrid constructs. However, posterior procedures are more versatile and familiar to scoliosis surgeons and became overwhelmingly more common with the adoption of pedicle screw constructs. Several reports demonstrate superior correction of severe sagittal and coronal deformities with the use of all-pedicle screw constructs compared with hybrid and hook constructs, suggesting anterior spinal release may be avoided for almost all spinal deformities.[30–32] Axial and coronal deformity has been reliably corrected using a posterior approach with all-screw constructs; however, this can result in postoperative loss of thoracic kyphosis (TK) and subsequently, lumbar lordosis (LL). Newton et al recommend a posterior column lengthening and/or an anterior column shortening to achieve restoration of normal TK and maximal LL after observing a decrease in TK and concordant loss of LL with the posterior approach for AIS.
Although earlier reports suggested inferiority for TK correction with posterior approaches as compared with the anterior method, new techniques have made posterior-only procedures increasingly favorable.[29,33–35] Excellent correction of thoracic hypokyphosis at 2-year follow-up with the use of segmental uniplanar pedicle screws, high-yield strength rods, aggressive differential rod contouring, periapical Ponte osteotomies, and segmental direct vertebral body manipulation has been demonstrated.[36,37] Additionally, the simultaneous translation technique on two rods has demonstrated superior efficacy to cantilever reduction in the correction of thoracic hypokyphosis.
With these considerations, we sought to compare the trends in surgical management of AIS patients with thoracic hypokyphosis (3D TK <10°) by approach and their associated corrections from 1995 to 2015. We hypothesized that operatively treated AIS patients with preoperative 3D thoracic hypokyphosis (<10°) prior to 2000 would have superior TK restoration (i.e., predominately isolated ASF, Figure 1A–D), but the learning curve with pedicle screws would reflect, at first, an inferior restoration of TK (i.e., early PSF, Figure 2A–D) but eventual improvement with the ensuing adoption of posterior column osteotomies, differential rod contouring, and 3D correction strategies (i.e., contemporary PSF, Figure 3A–D).
A representative case from Period 1 (1995–2000), demonstrating preoperative posteroanterior (A) and lateral (B) views and 2-year postoperative posteroanterior (C) and lateral (D) views of the spine with instrumented anterior spinal fusion.
A representative case from Period 2 (2001–2009), demonstrating preoperative posteroanterior (A) and lateral (B) views and 2-year postoperative posteroanterior (C) and lateral (D) views of the spine with instrumented posterior spinal fusion utilizing a hybrid construct of hooks, sublaminar wires, and pedicle screws.
A representative case from Period 3 (2010–2015), demonstrating preoperative posteroanterior (A) and lateral (B) views and 2-year postoperative posteroanterior (C) and lateral (D) views of the spine with instrumented posterior spinal fusion utilizing a selective segmental pedicle screw construct.
Spine. 2020;45(23):1625-1633. © 2020 Lippincott Williams & Wilkins