Summary: Patients who undergo posterior spinal instrumentation and fusion (PSIF) for adolescent idiopathic scoliosis (AIS) commonly loose lumbar lordosis (LL) which is associated with a concomitant increase in pelvic tilt (PT).
Introduction: Spino‐pelvic relationship highly influences sagittal balance. This study investigates the effect of decreased LL after PSIF on the change in PT. Furthermore, this study examines the patient‐specific relationship between LL and pelvic incidence (PI), testing the hypothesis that lumbar spinal fusion resulting in “mismatched LL” is associated with increased PT.
Methods: Query of a prospective multicenter database identified 155 AIS patients at least 2 years after PSIF with lowest instrumented vertebra between L2‐L5. LL (T12‐S1), LL within fusion (LLIF), LL below fusion (LLBF), sagittal balance (SB), PT, and PI at preop and 2 years postop were measured. Change in PT was compared between patients with “appropriate” or “inappropriate” LL as defined by the relationship between LL and PI. Appropriate LL was defined by both the relationship commonly used in clinical practice (LL = PI+10), and a research driven model from the literature (LL = 0.56PI + 33.43). Health related quality of life measures (HRQOL) were also examined.
Results: 38% of patients had loss of LL 2 years after PSIF. Patients with loss of LL had a significantly higher rate of increased PT than patients without loss of LL (73% vs. 40%, p<0.0001). In multiple regression, change in LL, LLIF and change in SB all had significant predictive effect on PT (p<0.001, R2=0.21). Using either the clinical practice definition or the research driven model, patients with LL < 2SD (12°) from predicted were more likely to have increased PT (p=0.046 and p=0.027, respectively). There were no significant associations between changes in LL or PT and HRQOL.
Conclusion: Iatrogenic loss of LL commonly occurs in lumbar fusion for AIS. This loss of LL is strongly associated with a reciprocal increase in PT. As such, spinal fusion can have unintended effects on sagittal alignment which may have unknown consequences in the future.
Significance: Correlation between HRQOL and adequate LL (defined as LL proportional to a patient‐specific PI) has been established in the adult population. The possible implications of poor sagittal balance after PSIF for AIS warrants continued attention and investigation.