Assessment of the Change in Alignment of Fixed Segment After Adult Spinal Deformity Surgery.

STUDY DESIGN

Retrospective study.

OBJECTIVE

To determine the prevalence of loss in fixed segment alignment after surgical correction of adult spinal deformity (ASD) and identify associated risk factors.

SUMMARY OF BACKGROUND DATA

Altered fixed segment alignment influences global spinal alignment; however, associated risk factors have not been determined.

METHODS

Data of 63 patients with ASD (55 females; mean age, 68.0 yrs), who underwent corrective fusion from the lower thoracic spine to the pelvis and completed the 2-year follow up, were retrospectively analyzed. Change in alignment early postoperatively and at 2 years postoperatively was evaluated using the fixed segmental angle (FSA) and fixed vertebral angle (FVA). The predictive value of the following parameters was evaluated: age, sex, body mass index (BMI), high grade osteotomy, rod material, screw loosening, spinopelvic parameters [T1 pelvic angle (TPA), sagittal vertical axis (SVA), pelvic tilt (PT), lumbar lordosis (LL), thoracic kyphosis (TK), and proximal junctional kyphosis (PJA), and Oswestry Disability Index (ODI) scores].

RESULTS

Change of 2.4° in FSA and -3.1° in FVA were identified 2 years postoperatively, with higher intrarater and interrater reliability for FSA. Based on minimal detectable change in FSA, patients were classified into two groups: (+) loss (ΔFSA >3°) and (-) loss (ΔFSA ≤3°). Correction loss occurred in 17 patients; these patients had a greater BMI, higher rate of high-grade osteotomies, commercially pure titanium (CP) rods implanted, screw loosening, higher preoperative and postoperative TPA, and higher TPA, SVA, and PT after 2 years, than patients without correction loss.

CONCLUSION

The loss of sagittal fixed segment alignment was relatively high at 27%. Greater BMI, high-grade osteotomies, CP rod use, and sagittal malalignment were associated with correction loss after ASD surgery.

LEVEL OF EVIDENCE