Diagnosis and Classification of Proximal Junctional Kyphosis and Proximal Junctional Failure

Pedicle screw instrumentation constructs have become a cornerstone in the treatment of adult spinal deformity and instability. They are known to provide greater rigidity and enhanced ability to correct and maintain spinal alignment. Biomechanical data, however, demonstrate that increased construct stiffness is associated with increased loading within adjacent segments [1– 9]. Increasingly stiff constructs can create vulnerability at the proximal segments and, in some cases, lead to proximal junctional pathologies with various radiographic and clinical manifestations [10–12]. Adjacent segment degeneration (ASD) is a well-documented phenomenon that can occur after thoracolumbar or lumbar spinal fusion [5, 6, 13–24]. Proximal junctional kyphosis (PJK) is a relatively more benign form of junctional pathology, manifesting primarily as a minimally symptomatic radiographic diagnosis [16, 19, 25, 26]. On the other hand, proximal junctional failure (PJF) represents a more severe form of junctional pathology associated with mechanical failure and increased risk of neurologic injury, deformity, pain, and the need for revision surgery [27–30]. PJF has important clinical implications especially for elderly patients with issues of reduced bone density. In this population, increased loads in the setting of decreased bone strength can lead to adjacent segment failure [5, 15, 31, 32]. When proximal junctional failure manifests with clinical symptoms, treatment can be complex, typically requiring osteotomy and extension of instrumentation and fusion. Recently, an increased amount of information describing the incidence, classification, prevention, and treatment of this problem has been developed.