Analysis of Risk Factors Associated with Proximal Junctional Kyphosis Following Long Instrumented Fusion from L1 to Sacrum: Age Itself Does Not Independently Increase The Risk

This study is a retrospective analysis aimed to understand the incidence and risk factors of proximal junctional kyphosis (PJK) following long instrumented spinal fusion from L1 to the sacrum in patients with mild to moderate sagittal imbalance. It recruited consecutive patient undergone instrumented fusion from L1 to the sacrum for degenerative lumbar disease between June 2006 and November 2019 in a single institution. The patients’ preoperative clinical data, muscle status at T12-L1 on magnetic resonance images, and sagittal spinopelvic parameters were analyzed. Univariate analysis was used to compare clinical and radiographic data between PJK and non-PJK patients. Logistic regression analysis was used to investigate the independent risk factors for PJK. A total of 56 patients were included in the study. The mean age at surgery was 67.3 years and mean follow-up period was 37.3 months. Seven were male and 34 were female. PJK developed in 23 (41.1%) out of 56; of these patients, 20 (87.0%) developed PJK within postoperative 1 year. On univariate analysis between PJK and non-PJK patients, PJK group showed more frequent osteoporosis, lower body mass index, smaller cross-sectional area (CSA) and more fat infiltration (FI) in erector spinae muscle at T12-L1, larger preoperative TLK and PT with statistical significance (plt;0.05). On logistic regression analysis, severe (gt;50%) FI in erector spinae muscle (OR=43.60, CI 4.10-463.06, R2N =0.730, p=0.002) and osteoporosis (OR=20.49, CI 1.58-264.99, R2N =0.730, p=0.021) were statistically significant. Preexisting severe (gt;50%) fat infiltration in erector spinae muscle and osteoporosis were significant independent risk factors associated with PJK following instrumented fusion from L1 to the sacrum, but age was not a risk factor.