Low Bone-Mineral Density Is a Significant Risk for Proximal Junctional Failure after Surgical Correction of Adult Spinal Deformity

Study Design. A propensity-matched comparison of risk factors for proximal junctional failure (PJF), which is a symptomatic proximal junctional kyphosis developing after corrective surgery for adult spinal deformity (ASD). Objective. To elucidate the role of bone strength for developing PJF. Summary of Background Data. PJF, a devastating complication of corrective surgery for ASD, often recurs even after revision surgery. Most studies of risk factors for PJF are retrospective and have a selection bias in surgical strategy, making it difficult to identify modifiable PJF risk factors. Methods. We conducted propensity-matched comparisons of 113 surgically treated ASD patients who were followed for at least 2 years, to elucidate whether low bone-mineral density (BMD) was a true risk factor for PJF in a uniform population from a multicenter database. Patients were grouped as having mildly low to normal BMD (M group; T-score≧-1.5) or significantly low BMD (S group; T-score<-1.5), and were propensity-matched for age, upper and lower instrumented vertebrae, history of spine surgery, and Schwab-Scoliosis Research Society (SRS) ASD classification. PJF was defined as a ≥20° increase from the baseline proximal junction angle with a concomitant deterioration of at least one SRS-Schwab sagittal modifier grade, or any type of proximal junctional kyphosis requiring revision. Results. PJF developed in 22 of 113 patients (19%). There were 48 propensity-matched patients in the M and S groups (24 in each) with similar parameters for age, body mass index, number of vertebrae involved, C7SVA, pelvic incidence -LL, and SRS-Schwab type. In this propensity-matched population, the incidence of PJF was significantly higher in the S group (33% vs. 8%, P<0.01, odds ratio 6.4, 95% CI: 1.2-32.3). Conclusion. Low BMD was a significant risk factor for PJF in this propensity-matched cohort (odds ratio 6.4). Surgeons should consider prophylactic treatments when correcting ASD in patients with low BMD.