Postoperative Evolution of Sagittal Parameters Over Time Does Not Differ by Upper Instrumented Vertebra.

STUDY DESIGN Retrospective Cohort Study. OBJECTIVE To examine sagittal alignment over time in adult spinal deformity (ASD) and to understand whether these changes vary by choice of upper instrumented vertebra (UIV). SUMMARY OF BACKGROUND DATA Recent ASD literature has focused on specific alignment goals. Less is known about how sagittal parameters evolve over time after surgical correction and whether these changes differ by choice of UIV. METHODS This was a retrospective review of ASD patients from a single institution. Routine 36" sagittal x-rays were obtained preoperatively, prior to hospital discharge, and at 6 months, 1 year, and 2 years and sagittal parameters were measured. Patients with UIV T6 and above were classified as upper thoracic (UT) and T7 and below as lower thoracic (LT). RESULTS A total of 102 patients with mean age 66.0 yrs (±7.7) were included in the analysis (49 UT, 53 LT). All sagittal and coronal alignment parameters demonstrated significant improvement from preoperatively to any postoperative timepoint. While multiple parameters maintained correction over time, others (TK, TPA, and PT) demonstrated significant increase from discharge to 2 years postoperatively, with changes occurring relatively early after surgery, while overall global alignment was maintained. Both UT/LT groups demonstrated significantly greater TK from preoperatively to discharge to 6 months (p   0.05). CONCLUSIONS Our data suggest that while several key parameters are maintained over time out to 2 years postoperatively, TK tends to worsen over time for all patients, while TLK preferentially increases in the LT group. Nevertheless, despite these trends, compensatory changes are seen in PT such that global alignment is relatively maintained.Level of Evidence: 3.