• Mitsuru Yagi, Nobuyuki Fujita, Osahiko Tsuji, Narihito Nagoshi, Takashi Asazuma, Ken Ishii, Masaya Nakamura, Morio Matsumoto, and Kota Watanabe.
• Department of Orthopedic Surgery, Keio University School of Medicine.
• Spine. 2018 Apr 1; 43 (7): 485-491.

Study DesignA 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).ObjectiveTo elucidate the role of bone strength for developing PJF.Summary Of Background DataPJF, 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.MethodsWe 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.ResultsPJF 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).ConclusionLow 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.Level Of Evidence3.

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