Proximal junctional kyphosis and proximal junctional failure in the treatment for adult spinal deformity: Definitions and epidemiology

Proximal junctional failure (PJF) is considered to be one of the most serious complications after correction surgery with a long construct for adult spinal deformity. Proximal junctional kyphosis (PJK) was first defined as an angle between the lower endplate of the uppermost instrumented vertebra (UIV) and the upper endplate of UIV+2 of 10 degrees or greater, and at least 10 degrees greater than the preoperative measurement. Although PJK has been found to cause no significant clinical symptoms, PJF is regarded as a pathology associated with a fracture of UIV or UIV+1, posterior osseoligamentous disruption, or a pullout of instrumentation at the UIV, and may require revision surgery. The incidence of PJK or PJF is influenced by a variety of factors including the pathology of the deformity, surgical procedures and spinal construct, status of osteoporosis, prophylactic procedures, and the follow-up period. Therefore, the reported incidences of PJK vary widely, from 7.7% to 56%, whereas those of PJF vary widely, from 1.4% to 35%.