Definition of PJF

PJF was defined as structural failures, such as vertebral fracture at the UIV or UIV+1, failure of UIV fixation, myelopathy, or any need for proximal extension of fusion as described in previous studies.⁴⁾ In making a definition of PJF, a few authors have included PJK, which refers to ligamentous failure and is represented by a proximal junctional angle (PJA) of 10°, 15°, or 20°.^4,13,15,25) However, in our study, PJK with ligamentous failure was excluded from the definition of PJF because it is well-known that benign PJK does not negatively affect clinical outcomes^2,12,13) and rarely necessitates revision surgery.^2,6,7) In our study, three patients underwent revision surgery for progressive PJK, and they were placed in the PJF group. We focused only on PJF accompanied by structural failure because the main interests among surgeons are acute catastrophic PJF rather than later-developing benign PJK.