P83. Preoperative Hounsfield units at the planned upper instrumented vertebrae (UIV) may predict proximal junctional kyphosis (PJK) in adult spinal deformity

BACKGROUND CONTEXT Proximal Junctional Kyphosis (PJK) following surgery of ASD is common and poor bone quality is noted to be one of the risk factors. Bone Densitometry (DEXA) of the spine does not accurately assess bone quality, especially in those who have severe degenerative conditions, deformity or prior fusions. HUs on standard CT can be used as an alternative in evaluating localized bone quality and correlation between local HU and the incidence of PJK are not clear. PURPOSE The study aimed to investigate the association between the local bone marrow density represented in Hounsfield Units (HU) of vertebral body of the planned UIV and UIV+1 on preoperative CT scan and the correlation with PJK in patients after surgery for ASD. STUDY DESIGN/SETTING Retrospective case control study. PATIENT SAMPLE Sixty-three patients were included from a single institution database from 2013-18. Inclusion criteria are patients: age≥18 years, diagnosis of spinal deformity, preoperative CT scan present, and a minimum of 1-year follow-up. OUTCOME MEASURES Mean HU of UIV and UIV+1, incidence of PJK, and change of PJK angle. METHODS Patient demographic and radiographic parameters were recorded. Local vertebral HU of UIV and UIV+1 was measured on preoperative CT scan. Patients were separated into three groups, no PJK, non-bony PJK, and bony PJK groups, which were distinguished by cause of PJK. The risk factors between the three groups and the correlation of mean HU and progression of PJK angle were also analyzed. RESULTS The incidence of PJK was 36.5%(n=23) and there were two revisions for PJK (3.2%). There was no difference between groups in the preop, postop, and corrections of the spinopelvic and sagittal radiographic parameters. The ANOVA showed that the mean HU was significantly different within the three groups (p=0.025). The posthoc analysis for the three groups showed the mean HU in the bony PJK group (HU:109.0) was significantly lower compared to the no PJK group (HU:168.7, p=0.038). The mean HU in the non-bony PJK group (HU:141.7) showed no difference compared to the other two groups. Multivariate analysis demonstrated a significant negative correlation between mean HU and PJK angle (r=0.475, p CONCLUSIONS Our study demonstrates a significant negative correlation between mean HU of UIV and UIV+1 and the progression of postoperative PJK angle. In ASD patients, the mean HU less than 120HU was an independent factor of bony PJK. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.