Adjacent Segment Disease after Long Spinal Fusion Ending at L5 for Adult Spinal Deformity: A Retrospective Cohort Study

Study Design: This is a retrospective cohort study using data from the adult spinal deformity (ASD) database of a single institution.Purpose: To investigate the incidence of proximal junctional failure and distal junctional failure (DJF) after ASD surgery with a lower instrumented vertebra (LIV) at L5. Overview of Literature: Spinopelvic fixation from the lower thoracic vertebra to the pelvis is the current gold standard treatment for ASD.However, the LIV at L5 is acceptable in some cases.Methods: Fifty-six patients who underwent corrective surgery for ASD with LIV at L5 were included.The upper instrumented vertebra (UIV) was T7 in one patient, T9 in 14, T10 in three, T11 in four, T12 in eight, L1 in 10, and L2 in 16.Regarding clinical parameters, age, sex, curve types of Scoliosis Research Society-Schwab classification, number of levels fused, follow-up period, hip bone mallow density, revision surgery rate, and radiographic measurements were compared between the T (UIV: T7 -10) and TL (UIV: T11 -L2) groups.Results: The revision surgery rate was 19.6% overall.In the T and TL groups, it was 27.8%, and 15.8%, respectively (p = 0.305).The rate of DJF in the T group (33.3%) was significantly higher than in the TL group (5.3%).The rate of proximal junctional kyphosis in the T group (55.6%) was higher than in the TL group (28.9%), with no significant difference.The mean global alignment, sagittal vertical axis, and C7 plumb line-central sacral vertical line were not different between both groups.Conclusions: ASD surgery with LIV set at L5 and UIV set at the thoracic vertebrae (T7 -T10) has a risk of adjacent segment disease.