Future directions in painful knee osteoarthritis: harnessing complexity in a heterogeneous population

Abstract

This perspective article proposes a conceptual model for the pain experience for individuals diagnosed with knee osteoarthritis (OA). Pain in knee OA is likely a heterogeneous, multifactorial phenomenon that involves not only the OA disease process but also elements specific to patient psychology and pain neurophysiology. The relevant contributions to the pain experience for any individual patient remain difficult, if not impossible, to definitively determine, and the rationale for many clinical treatment decisions arises primarily from a mechanistic understanding of OA pathophysiology. The Osteoarthritis Research Society International (OARSI) recently identified "phenotyping" of OA pain as a research priority to "better target pain therapies to individual patients." This perspective article proposes that contributions from 3 domains--knee pathology, psychological distress, and pain neurophysiology--should be considered equally important in future efforts to understand pain phenotypes in knee OA. Ultimately, characterization of pain phenotypes may aid in the understanding of the pain experience and the development of interventions specific to pain for individual patients.

Figures

Figure 1.

The pain experience in knee osteoarthritis (OA) is a “black box.” Pain appears to be influenced by certain factors—we have provided some examples in this diagram—but the precise contributions to an individual patient's pain experience remain unknown.

Figure 2.

A conceptual model for pain in knee osteoarthritis, emphasizing important contributions from each of the following domains: (1) knee osteoarthritis pathology, (2) psychological distress, and (3) neurophysiological changes in the processing of pain. Variables from these domains (examples provided) are proposed to interact to result in an individual clinical pain experience.

Figure 3.

Patients may present with similar pain reports but with different pain phenotypes. Patient 1 demonstrates moderate levels of joint involvement with high levels of psychological distress. Patient 2 demonstrates moderate levels of joint involvement with low levels of psychological distress. These 2 patients would likely warrant different treatment approaches.

Figure 4.

Pain phenotype could influence patients' prognosis. Patient 1 demonstrates moderate levels of joint involvement, in combination with moderate psychological distress and moderate signs of altered pain neurophysiology. Patient 2 demonstrates moderate levels of joint involvement with low levels of psychological distress and minimal changes to pain neurophysiology. In this depiction, involvement of multiple variables across domains has a cumulative effect, leading to poor prognosis.

Figure 5.

The clinical report of pain may be modified by variables in each domain. Patient 1 demonstrates how the presence of central sensitization might serve to augment the pain resulting from apparently low levels of joint involvement. Patient 2 demonstrates the capacity for the nervous system to modulate pain, diminishing the pain experience in cases of severe joint involvement.