Orientation of the Upper-most Instrumented Segment Influences Proximal Junctional Disease Following Adult Spinal Deformity Surgery

Study Design. Retrospective review of a prospective database. Objective. The aim of this study was to define the role of sagittal orientation of the construct at the upper instrumented levels in the development of proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) patients. Summary of Background Data. PJK following ASD surgery remains challenging. The final alignment of the upper instrumented vertebral segments has been proposed as a risk factor for PJK, but has not been fully investigated. Methods. ASD patients with 2-year follow-up and long posterior fusion to the pelvis were analyzed. Radiographic measurements included pelvic incidence (PI), lumbar lordosis (LL), pelvic tilt (PT), sagittal vertical axis, and two upper-most instrumented vertebra (UIV) parameters: UIV slope (UIV vs. horizontal) and inclination of the proximal-end of the construct. UIV parameters were secondarily evaluated with regard to the compensatory impact of post-PJK increased PT (PREF). A comparison between PJK and non-PJK patients was performed, according to the UIV location (upper thoracic [UT] or thoracolumbar). Results. A total of 252 patients (mean age, 61.5 years, 83% females) were included. PJK incidence was 56% at 2-years. PJK patients had a greater change in LL and thoracic kyphosis than non-PJK patients. In the UT group, there was no difference in UIV slope for PJK versus non-PJK. However, PJK patients had a smaller inclination of the upper instrumented segments versus vertical (P< 0.001) and the PREF (P = 0.005). Similarly, in the LT group, PJK patients had a posterior inclination versus the vertical (P< 0.001) and the PREF (P = 0.041). Conclusion. Analysis revealed that a more posterior construct inclination was present in patients who developed PJK. These results support previous hypotheses suggesting that PJK may develop in response to excessive spinal realignment. Proper rod contouring, especially at the proximal end, may reduce the risk of PJK.