Background and Objective: Proximal junctional kyphosis (PJK) is a common complication of long spinal fusion. The relationship between body mass index (BMI) and PJK is controversial. This study aimed to evaluate the relationship between patient BMI and PJK prevalence in patients undergoing long spinal fusion.
Methods: This retrospective study included 76 patients who underwent long spinal fusion (≥5 levels or pelvic fixation) for degenerative canal stenosis with a minimum 24-month follow-up. PJK was defined as ≥10° increase in Cobb angle between the UIV inferior endplate and the UIV+2 superior endplate.
Results: PJK occurred in 26 patients (34.2%) at early follow-up (≤6 months) and in 18 patients (23.7%) at late follow-up (>6 months). Mean BMI was significantly higher in the early PJK group (29.6 vs. 23.4 kg/m², P < 0.001). BMI was an independent predictor of early PJK (OR = 1.32, 95% CI: 1.18-1.48, P < 0.001). Overweight patients (BMI>25) had a 69.6% early PJK rate vs. 20.5% in normal-weight patients. Surgically treated early PJK patients had higher mean BMI (30.8 vs. 28.4 kg/m², P = 0.023).
Conclusion: Higher BMI is significantly associated with early PJK following long spinal fusion, particularly in the first 6 months postoperatively.