Coronal Imbalance in Adult Spinal Deformity Patients That Develop Proximal Junctional Failure

Introduction: Proximal junctional kyphosis (PJK) is a common complication following correction of adult spinal deformity (ASD) at the transition of fused and mobile motion segments. PJF represents PJK with vertebral fracture, soft-tissue disruption, and/or screw pullout at the upper instrumented vertebra (UIV) accompanied with neurological deficit. Coronal decompensation following long-segment fusion may contribute to the development of proximal junctional pathology. This study reports on the natural history of coronal imbalance in ASD patients that develop PJF after fusion of the thoracolumbar spine to the pelvis.

Methods: A single-institution retrospective review was performed for 1180 ASD patients that underwent posterior instrumented fusion to the pelvis (2009-2021). Patients that developed PJF were grouped by the UIV: upper thoracic (UT, T2-T6, 10 patients), lower thoracic (LT, T8-T11, 35 patients), or lumbar spine (L, L1-L3, 9 patients). Radiographic parameters, including the major scoliotic curve (MSC), coronal and sagittal proximal junctional angle (cPJA/sPJA), and the coronal and sagittal C7 vertical angles (CVA/SVA), were recorded before primary surgery, before revision surgery for failure, and at both 6-week and final follow-up following revision.

Results: From 1180 ASD patients, 54 patients (4.6%) developed PJF (59% female, mean age 65.0 ± 6.8 and BMI 30.3 ± 5.9). Mean follow-up after revision was 3.1 ± 2.7 years. The ΔMSC (UT –17.6 ± 24.7°, LT –11.5 ± 15.97°, L –5.7 ± 7.6°) was calculated as the difference in MSC before revision surgery and before primary surgery. The mean ΔcPJA (UT 0.5 ± 3.6°, LT 0.6 ± 24.7°, L 2.5 ± 8.1°), ΔsPJA (UT: 19.1 ± 11.0°, LT: 14.8° ± 4.0°, L: 16.0° ± 9.0°), ΔCVA (UT: -13.6 ± 35.5 mm, LT –8.1 ± 21.1 mm, L 3.3 ± 29.4 mm), and ΔSVA (UT: -42.8 ± 86.8 mm, LT: 15.9 ± 38.4 mm, L: 48.6 ± 58.5 mm) were also calculated in that manner.

Conclusion : Proximal junctional pathology presents differently clinically and radiographically following PJF after instrumented fusion from the UT, LT, and L spine. In this study, patients with a UIV in the L spine develop more coronal tilt and sagittal imbalance after PJF than patients with an UIV in the UT and LT spine.