This study provides a radiographic assessment of factors associated with failure to achieve adequate post-operative sagittal spino-pelvic alignment following TCTO for ASD. TCTO significantly decreased the mean TK, maximum coronal Cobb angle, SVA and PT. However, 22% of patients had spino-pelvic malalignment following TCTO, a finding known to correlate with poorer clinical outcome [5
]. IDEAL and FAIL patients had similar operative procedures and similar degrees of regional correction, however FAIL patients had greater pre-operative sagittal malalignment. Consequently, these data suggest that additional or alternative correction procedures should be considered when planning TCTO for patients with large spino-pelvic malalignment to reduce the risk of residual post-operative deformity and poor outcomes.
Few reports have addressed the use of TCTO in ASD. The majority of data that does exist on TCTO for ASD includes small case series from a single institution or reports that include thoracic procedures as part of a series of lumbar PSO (LPSO) procedures. O’Shaughnessy et al. [14
] reported on 25 TPSOs performed in 15 ASD patients. Improvements were demonstrated in TK (75.7° to 54.3°, P
< 0.005) and SVA (106.1 to 38.8 mm, P
< 0.005) post-operatively. Mean sagittal correction at the osteotomy site was 16.3°. Correction was greater for more caudal TPSO levels (mean correction 10.7° for T2–T4 TPSO, 14.7° for T5–T8, and 23.9° for T9–T12). The authors noted that TPSOs in lower thoracic segments provide greater sagittal correction, due to the morphology and greater size of these vertebral bodies, and concluded that their current practice is to perform TPVCRs for corrections between T2 and T10 to achieve greater correction.
The present series offers multiple contrasts with that of O’Shaughnessy et al. [14
]. The current study provides a substantially greater number of patients, is a multi-center investigation, and includes both TPSOs and TPVCR procedures. Although the mean number of osteotomies per patient was considerably lower in the present series (1.05) compared with that of O’Shaughnessy et al. (1.67), the degree of sagittal correction for cases with primarily sagittal or multi-planar deformity was comparable, 20.8° versus 16.3°, respectively. The present series does not provide support for the supposition of O’Shaughnessy et al., that TPVCR enables a more robust correction than TPSO, as we identified no significant differences in focal correction at the osteotomy site between the TPVCR and TPSO groups. Compared with patients treated with TPSO, those treated with TPVCR had a non-significant trend toward greater risk of poor post-operative SPA. The direction of this trend is unexpected, and it is possible that unappreciated differences in technique or patient selection may account for this finding. In addition, because the series of O’Shaughnessy et al. does not provide assessment or discussion of pelvic parameters, it is unclear whether residual sagittal malalignment may have been masked by increased pelvic retroversion (elevated PT).
Yang et al. reported a series of 35 adults with ASD treated with PSO (28 LSPO, 7 TPSO) [15
]. They reported significant improvement in focal correction at the osteotomy site, TK, and SVA for patients treated with LPSO. However, they noted only significant improvement in focal correction at the osteotomy site, not TK or SVA, for patients treated with TPSO. They concluded that LPSO offers potential significant improvement of focal, regional, and global spinal alignment, whereas TPSO was only associated with improved alignment at the osteotomy site. These findings contrast with the present series, in which significant improvement in focal, regional, and global alignment were identified following TCTO. This contrast may reflect differences in technique or the relatively small number of patients treated with TPSO in the study by Yang et al. Alternatively, the significant degree of sagittal malalignment in the patient population treated with TPSO by Yang et al. (mean pre-operative SVA = 127 mm) may have been incompletely corrected with a single level TPSO. This latter explanation is consistent with the primary conclusion of the present study; additional or alternative correction procedures should be considered when planning TCTO for patients with substantial spino-pelvic malalignment. Other reports have documented TPSO and TPVCR as treatments for ASD [16
]. However, these cases have typically been included as only a small subset of a larger study of LPSO, and primarily included only distal thoracic (T11 or T12) osteotomies, substantially limiting the ability to provide meaningful comparisons to the present series.
The importance of achieving spinal alignment in ASD surgery has been well established [2
]. Glassman et al. correlated radiographic findings with standardized HRQOL measures in 298 ASD patients, including 172 with and 126 without history of prior spine fusion [2
]. Positive sagittal malalignment proved to be the most reliable predictor of clinical symptoms in both patient groups. The importance of the pelvis in regulating spinal alignment has also been established [9
]. LaFage et al. prospectively correlated spino-pelvic radiographic parameters and HRQOL measures in 125 adults with spinal deformity. The strongest correlations with poor HRQOL measures were SVA, T1 spino-pelvic inclination, and PT [5
Strengths of the present study include the multicenter design and relatively large number of patients. The contribution of cases to the present series from multiple surgeons across the United States strengthens the generalizability of our findings and conclusions. The primary limitations of this study are the retrospective design and the lack of direct correlations with HRQOL measures. Since this study is based on radiographic review, the retrospective design should have limited impact. Correlations between sagittal spinal alignment and HRQOL measures have been reported in multiple prior studies and have been discussed in the present study for context. Efforts are currently underway to provide prospective clinical outcomes assessment following TCTO.