Defining Clinically Relevant Proximal Junctional Kyphosis

Abstract

Proximal junctional kyphosis and failure are not infrequent complications of adult spinal deformity reconstructions. Efforts to define proximal junctional kyphosis have ranged from expert opinions to statistical analyses of large databases. These approaches fail to recognize that proximal junctional kyphosis/failure/breakdown is likely a spectrum of manifestations secondary to spinal fusions and spinal alignment. The dichotomization (clinically irrelevant vs clinically relevant) of continuous measures will lead to misclassification and misdiagnosis. As adult spinal deformity moves to a precision-medicine-based approach (also known as personalized medicine), work is required to develop probabilistic models to inform patients and surgeons about the likely survivorship of a proximal junctional failure. As such, it is likely better to call proximal junctional segment kyphosis without symptoms "asymptomatic proximal junctional kyphosis" rather than to determine thresholds for "symptomatic" or "clinically relevant."

Keywords: complication; failure; glattes; proximal junctional kyphosis.

Figure

Left: Well-aligned adult with a normal C2-tilt, equal to the odontoid-hip-axis (OD-HA) of approximately 0°. Middle: Adult with ankylosing spondylitis and subsequent thoracic hyperkyphosis leading to an increase in C2-tilt. Right: Adult with ankylosing spondylitis and subsequent lumbar hypolordosis, increase in pelvic tilt, and increase in the C2-pelvic angle.