Background/Purpose

Cortically mediated changes in body perception have been linked to a variety of chronic pain conditions, including knee osteoarthritis (OA).  However, associations between body perception and pain neurophysiology have yet to be examined, and the role of body perception in the etiology or mechanisms of chronic pain remains largely unknown. Therefore, the purpose of this study was to assess measures of cortical body representation in a population of people with knee OA, to determine the relationship with physiological measures of pain sensitivity and systemic pain modulation.

Methods

Forty-six people with knee OA (68% female, average age = 65.0 ± 8.5 years) were assessed in this cross-sectional study.  Measures of body perception included an assessment of motor imagery performance (via a right-left lower extremity recognition task), an assessment of tactile acuity (two-point discrimination threshold) at the knee joint, and an assessment of knee size perception.  To assess perception of knee size, a single photograph for each participant, capturing both of the participant’s lower extremities. This photograph was then digitally manipulated to make either the right or left knee appear larger or smaller than reality. An array of images containing several of these manipulations (ranging from 85% to 115% of the original size) was  displayed to the participant, who was instructed to select the most accurate representation. The relative size of the more painful knee was selected for analysis.  Pain sensitivity was assessed by measuring pressure pain threshold (PPT) at the medial knee joint. Conditioned pain modulation (CPM), via a cold pressor paradigm, was performed at the forearm to assess endogenous analgesic pathways. Bivariate Pearson correlation coefficients were then determined between measures of cortical body representation and measures of pain neurophysiology.

Results

Although motor imagery performance and tactile acuity appeared weakly related to each other (r=-0.24, p=0.08), no significant associations were found between either of these measures and any measure of pain neurophysiology.  Perception of knee size was not related to PPT but was significantly associated with CPM, such that participants with higher capacity for descending analgesia tended to overestimate the size of the more painful knee (r=0.56, p=<0.0001).

Conclusion

For the first time, this study provides evidence linking a specific measure of pain neurophysiology to body perception.  Descending analgesia may affect a person’s overall perception of the knee joint, with potential functional sequelae deserving of further study. Alternatively, abnormalities in knee perception may contribute to diminished capacity for endongenous pain inhibition, thereby exacerbating pain. Regardless of the direction of the relationship, a relatively simple assessment of knee size perception could allow clinicians to identify people with deficits in systemic pain modulation who may require  alternative treatment approaches.

---

« Back to 2014 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/systemic-pain-modulation-is-related-to-body-perception-in-people-with-knee-osteoarthritis/