LAUSR

STUDY DESIGN Multicenter database review of consecutive adult spinal deformity (ASD) patients. OBJECTIVE The aim of this study was to identify associations between changes in spinopelvic parameters and cervical alignment after thoracolumbar arthrodesis for ASD. SUMMARY OF BACKGROUND DATA Reciprocal cervical changes occur after instrumented thoracic spinal arthrodesis. The timing and relationship of these changes to sagittal alignment and upper instrumented vertebra (UIV) selection are unknown. METHODS In 171 ASD patients treated with thoracolumbar arthrodesis from 2008 to 2012, we assessed changes from baseline to 6-week, 1-year, and 2-year follow-up in C2-C7 sagittal vertical axis (SVA), T1 slope, and C2-C7 lordosis. We used multivariate models to analyze associations between these parameters and UIV selection (T9 or distal vs. proximal to T9) and changes at each time point in thoracic kyphosis (TK), lumbar lordosis (LL), C7-S1 SVA, pelvic incidence, pelvic tilt, and sacral slope. RESULTS Two-year changes in C2-C7 SVA and T1 slope were significantly associated with baseline to 6-week changes in TK and LL and with UIV selection. Baseline to 2-year changes in C2-C7 lordosis were associated with baseline to 6-week changes in C7-S1 SVA (P = 0.004). Most changes in C2-C7 SVA occurred during the first 6 weeks postoperatively (mean 6-week change in C2-C7 SVA: 2.7 cm, 95% confidence interval [CI]: 0.7-4.7 cm; mean 2-year change in SVA: 2.3 cm, 95% CI: -0.1 to 4.6 cm). At 2 years, on average, there was decrease in C2-C7 lordosis, most of which occurred during the first 6 weeks postoperatively (mean 6-week change: -3.2°, 95% CI: -4.8° to -1.2°; mean 2-year change: -1.3°, 95% CI: - 3.2° to 0.5°). CONCLUSION After thoracolumbar arthrodesis, reciprocal changes in cervical alignment are associated with postoperative changes in TK, LL, and C7-S1 SVA and with UIV selection. The largest changes occur during the first 6 weeks and persist during 2-year follow-up. LEVEL OF EVIDENCE 3.