Clinics in orthopedic surgery · 2026
Determinants of Thoracic Reciprocal Change and Its Relationship to Proximal Junctional Kyphosis Following Lower Thoracic Fusion for Lumbar Flatback Deformity.
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Shin Tae Soo, Park Jin-Sung, Kang Dong-Ho, Lee Chong-Suh, Park Se-Jun
Аннотация
BACKGROUND: Lumbar flatback deformity (LFD) is characterized by the loss of lumbar lordosis (LL) and global sagittal malalignment, often necessitating thoracolumbar corrective surgery. Lumbar correction induces adaptive changes in unfused thoracic segments, known as thoracic reciprocal change (RC); however, its independent clinical significance remains debatable. This study aims to identify factors associated with thoracic RC after lower thoracic fusion for LFD and to evaluate its independent effect on the development of proximal junctional kyphosis (PJK).
METHODS: This retrospective study included 190 patients who underwent lower thoracic fusion (upper instrumented vertebra at T9 or T10) to the sacrum or pelvis for LFD, with a 2-year follow-up. Sagittal parameters were evaluated preoperatively at 6 weeks postoperatively, and at 2 years. Thoracic RC was defined as the change in thoracic kyphosis (TK) from the preoperative baseline to 6 weeks postoperatively. Thoracic flexibility was assessed using the standing-supine TK difference. Multivariate linear regression was used to identify factors influencing thoracic RC, and multivariate logistic regression was performed to determine independent risk factors for PJK.
RESULTS: Mean TK increased from 5.7° (supine) preoperatively to 26.0° at 6 weeks, resulting in a mean thoracic RC of 20.3°. Thoracic RC was significantly associated with lower preoperative TK, greater thoracic flexibility, greater LL correction, and lower postoperative pelvic incidence (PI) minus LL (PI-LL) mismatch (adjusted R 2 = 0.647). PJK occurred in 47 patients (24.7%). However, the magnitude of thoracic RC did not differ between patients with and without PJK (20.9° vs. 20.0°, p = 0.678). Higher preoperative TK and lower postoperative PI-LL mismatch were independently associated with PJK, whereas thoracic RC was not.
CONCLUSIONS: Thoracic RC after lower thoracic fusion is primarily determined by preoperative thoracic characteristics and the magnitude of lordosis correction. Although associated with an early increase in the postoperative junctional angle, thoracic RC itself does not independently predict the development of PJK. These findings suggest that thoracic RC appears to behave as a compensatory adaptation to sagittal realignment rather than an independent driver of PJK.
METHODS: This retrospective study included 190 patients who underwent lower thoracic fusion (upper instrumented vertebra at T9 or T10) to the sacrum or pelvis for LFD, with a 2-year follow-up. Sagittal parameters were evaluated preoperatively at 6 weeks postoperatively, and at 2 years. Thoracic RC was defined as the change in thoracic kyphosis (TK) from the preoperative baseline to 6 weeks postoperatively. Thoracic flexibility was assessed using the standing-supine TK difference. Multivariate linear regression was used to identify factors influencing thoracic RC, and multivariate logistic regression was performed to determine independent risk factors for PJK.
RESULTS: Mean TK increased from 5.7° (supine) preoperatively to 26.0° at 6 weeks, resulting in a mean thoracic RC of 20.3°. Thoracic RC was significantly associated with lower preoperative TK, greater thoracic flexibility, greater LL correction, and lower postoperative pelvic incidence (PI) minus LL (PI-LL) mismatch (adjusted R 2 = 0.647). PJK occurred in 47 patients (24.7%). However, the magnitude of thoracic RC did not differ between patients with and without PJK (20.9° vs. 20.0°, p = 0.678). Higher preoperative TK and lower postoperative PI-LL mismatch were independently associated with PJK, whereas thoracic RC was not.
CONCLUSIONS: Thoracic RC after lower thoracic fusion is primarily determined by preoperative thoracic characteristics and the magnitude of lordosis correction. Although associated with an early increase in the postoperative junctional angle, thoracic RC itself does not independently predict the development of PJK. These findings suggest that thoracic RC appears to behave as a compensatory adaptation to sagittal realignment rather than an independent driver of PJK.