Response to the commentary by Johnson et al. on ‘Movement-evoked pain is not associated with pain at rest or physical function in knee osteoarthritis’

As the authors of the manuscript entitled ‘Movement-evoked pain is not associated with pain at rest or physical function in knee osteoarthritis’ (Lozano-Meca et al., 2024), recently published in the European Journal of Pain, we have read the recent publication of the commentary by the authors Johnson et al. (2024), and we thank the authors for their wise and accurate comments on our manuscript. We hereby provide some comments and clarifications that will certainly help the potential readers and, in turn, will enhance the scientific conceptualization on movement-evoked pain (MEP, hereinafter). As a matter of fact, Johnson et al. state that ‘the assertion that associations between MEP and PAR have not been studied in KOA is inaccurate; multiple recent studies have examined this relationship in KOA and other musculoskeletal conditions (Fullwood et al., 2021)’. Indeed, in the background section of our manuscript, we highlight the fact that MEP has been studied under different conditions: Fullwood et al. (2021) have reviewed, explored and mapped MEP in an interesting scoping review that focuses on different aspects of the construct, providing a useful framework for the conceptualization and measurement of MEP. In fact, they state that ‘only six studies explicitly tested for statistical differences between pain at rest and MEP’. Those studies focused solely on temporomandibular disorders, neck pain or peripheral neuropathic: solely, Lundblad et al. (2008, 2012), in their research, set the framework of MEP after total knee arthroplasty following different conditions related to osteoarthritis, but not on subjects currently affected of KOA, which tangentially concerns the substratum of our research. Thus, our assumption is sustained and endorsed by the scoping review by Fullwood et al. because potential relationships between pain at rest and MEP are explored, but none of them focuses on subjects under KOA conditions.

In relation to the radiological severity of the subjects analysed and their relationship with MEP, our data related to Kellgren-Lawrence are eminently informative and descriptive due to the low sample size, an issue that prevented us from making more specific analyses by controlling for potentially confounding sociodemographic and/or clinical factors, fact that is already considered and acknowledged within the manuscript as one of the potential limitations of the study. Moreover, we did not focus on causation but solely on association, as stated throughout the manuscript, due to the cross-sectional nature of the study.

In the introduction of our study, we also indicated (when describing MEP) that ‘more recently, it has been defined as pain during walking’, and we provide the reference by Fullwood et al. (2021). We acknowledge the mistake in providing the wrong reference since the aforementioned definition corresponds to the pain linked to an intrinsic form of specific movement extracted from the articles by Lundblad et al. (2008, 2012), who defined the concept as ‘pain during movement’. We apologize for the terminological mistake in this respect.

Finally, Johnson et al. (2024) indicate in their comment that ‘having less pain with movement or movement-evoked hypoalgesia (Butera et al., 2024) is an important consideration which was not discussed’. This is an aspect of paramount importance that, unfortunately, we were not able to include and explore in our research, much to our regret, since the promising framework suggested by Butera on MEP-hypoalgesia was published last February 2024, prior to the publication of our manuscript (December 2023). We will obviously follow the pathway marked by Butera in further research.

We would like to close this letter by thanking Johnson et al. for their comments as well as for their fundamental contribution in conceptually and scientifically building the construct of MEP, the fact that will certainly enhance and improve a deeper understanding of pain and its mechanisms globally, and more specifically as a future cornerstone in the paradigm of pain management. Our gratitude in this respect.