Defining Clinically Relevant Proximal Junctional Kyphosis.

Area of Science:

• Spine surgery
• Orthopedic research
• Biomechanical engineering

Background:

• Proximal junctional kyphosis (PJK) and failure are common complications after adult spinal deformity reconstruction.
• Current definitions of PJK rely on expert opinion or statistical thresholds, potentially leading to misclassification.
• PJK is better understood as a spectrum of manifestations related to spinal fusion and alignment.

Purpose of the Study:

• To propose a paradigm shift in understanding proximal junctional kyphosis (PJK) as a spectrum of disease.
• To advocate for probabilistic models to predict proximal junctional failure (PJF) in adult spinal deformity.
• To reframe the definition of asymptomatic PJK.

Main Methods:

• Review of existing literature and clinical definitions of PJK.
• Analysis of the limitations of dichotomizing continuous clinical measures.
• Conceptual framework for a spectrum-based approach to PJK and PJF.

Main Results:

• Current definitions of PJK/failure/breakdown are inadequate due to dichotomization of continuous variables.
• A spectrum-based understanding acknowledges PJK as a continuum of manifestations.
• Probabilistic models are needed for personalized medicine in adult spinal deformity.

Conclusions:

• Proximal junctional kyphosis/failure/breakdown should be viewed as a spectrum, not discrete categories.
• The term "asymptomatic proximal junctional kyphosis" is more appropriate than defining arbitrary clinical relevance thresholds.
• A precision medicine approach requires probabilistic models for predicting proximal junctional failure.