Pain phenotypes in knee osteoarthritis
Osteoarthritis of the knee (OA) is the most common form of arthritis and effects large numbers of elders, limiting their function and causing significant levels of pain. Historically seen as a disease of ‘wear and tear’, the modern diagnostic criteria for OA is a combination of clinical features, examination and radiological findings.
However, these broad criteria encompass a heterogeneous range of presentations and may overlook several clinically relevant variables which can affect patient management and outcome. Examples of this include poor correlation between radiological findings and symptom severity, as well as the reported inconsistent efficacy of several interventions within the literature. It has previously been hypothesized that several sub categories exist within OA, each with their own unique pain presentations, or pain phenotypes.
This hypothesis was explored recently by applying a latent class analysis to multiple pain-related variables of 3,500 participants who took part in the Osteoarthritis Initiative study. The resulting classes were compared on the following demographic and clinical factors: age, sex, pain severity, disability, walking speed, and use of arthritis-related health care. From the authors' analysis, 4 separate categories emerged:
Class 1: high levels of co-morbidity
Class 2: higher knee joint sensitivity
Class 3: greater psychological distress
Class 4: mild OA - lesser radiographic OA, little psychological involvement, greater strength, and less pain sensitivity
The results of this analysis support the emerging narrative that OA is a multifactorial disease with a complex interplay of physical, environmental and psychological factors contributing to symptomatic manifestation. Further to this, should the concept of pain phenotypes be validated by ongoing research, it may have a profound effect on the future physiotherapy research/ practice in OA, as interventions and clinical trials could be tailored to specific phenotypes.
> From: Kittelson et al., Arthritis Care Res 68 (2017) 612-620. All rights reserved to American College of Rheumatology. Click here for the online summary.