Proximal and Distal Junctional Kyphosis and Failure

Junctional kyphosis is an important and common complication of long fusions for deformity in the adult and the child, both above and below the fused levels. The proximal and distal extents of long posterior fusions in adults with spinal deformity are considered “at risk” for failure owing to increased loads and motion at the last instrumented vertebra and the unfused adjacent segment. Postoperative failures at the proximal and distal zones can manifest at any time postoperatively as an increase in kyphosis, and thus are defined under the umbrella terms “proximal junctional kyphosis” (PJK) and “distal junctional kyphosis” (DJK). There are variations in the definition of PJK. The definition proposed by Glattes and colleagues is most commonly used and is as follows: a postoperative proximal junctional Cobb angle of 10 degrees or more between the lower end plate of the upper-instrumented vertebra (UIV) and the upper end plate of two supraadjacent vertebrae (UIV+2) when compared with the preoperative state. This same definition is also commonly applied to distal junctional pathology. The purpose of this chapter is to discuss the mechanisms of PJK and DJK and surgical strategies that may be useful to avoid junctional complications above and below long fusions for spinal deformity.

Common causes of PJK and DJK include adjacent segment disc degeneration, pseudarthrosis, vertebral body fracture, vertebral body subluxation/dislocation, and/or instrumentation pullout. Failures that occur acutely (<6 months postoperatively) are termed “junctional failures.” The mechanism for junctional failures is most often caused by one of the following three etiologies: (1) vertebral fracture of the last instrumented vertebra or a fracture at one level adjacent to the last instrumented vertebra, (2) failure of fixation at the last instrumented vertebra, or (3) osteoligamentous disruption. In an attempt to capture the different characteristics of PJK, Yagi et al. proposed a three-domain classification system consisting of “type of failure” (1: disc/ligamentous; 2: osseous; 3: implant/osseous interface), “grade” of increase in the proximal junctional angle (PJA; A:10–19 degrees; B: 20–29 degrees; C: >30 degrees), and “spondylolisthesis” above the UIV (proximal functional failure [PJF]-N: no; PJF-S: yes) ( Table 60.1 ). Understanding the risk factors for junctional failure, and the characteristic failure mechanisms in the upper thoracic, thoracolumbar, and lumbar spine, is important to develop surgical strategies for prevention and avoidance of PJK and DJK.