Psychosocial factors partially mediate the relationship between mechanical hyperalgesia and self-reported pain

Amplification of sensory signalling within the nervous system along with psychosocial factors contributes to the variation and severity of knee pain. Quantitative sensory testing (QST) is a non-invasive test battery that assesses sensory perception of thermal, pressure, mechanical and vibration stimuli used in the assessment of pain. Psychosocial factors also have an important role in explaining the occurrence of pain. The aim was to determine whether QST measures were associated with self-reported pain, and whether those associations were mediated by psychosocial factors.

Participants with knee pain identified from a population-based cohort completed a tender point count and a reduced QST battery of thermal, mechanical and pressure pain thresholds, temporal summation, mechanical pain sensitivity (MPS), dynamic mechanical allodynia (DMA) and vibration detection threshold performed following the protocol by the German Research Network on Neuropathic Pain. QST assessments were performed at the most painful knee and opposite forearm (if pain-free). Participants were asked to score for their global and knee pain intensities within the past month (range 0-10), and complete questionnaire items investigating anxiety, depression, illness perceptions, pain catastrophising, and physical functioning. QST measures (independent variable) significantly correlated (Spearman's rho) with self-reported pain intensity (dependent variable) were included in structural equation models with psychosocial factors (latent mediators).

Seventy-two participants were recruited with 61 participants (36 women; median age 64 years) with complete data included in subsequent analyses. Tender point count was significantly correlated with global pain intensity. DMA at the knee and MPS at the most painful knee and opposite pain-free forearm were significantly correlated with both global pain and knee pain intensities. Psychosocial factors including pain catastrophising sub-scales (rumination and helplessness) and illness perceptions (consequences and concern) were significant partial mediators of the association with global pain intensity when loaded on to a latent mediator for: tender point count [75% total effect; 95% confidence interval (CI) 22%, 100%]; MPS at the knee (49%; 12%, 86%); and DMA at the knee (63%; 5%, 100%). Latent psychosocial factors were also significant partial mediators of the association between pain intensity at the tested knee with MPS at the knee (30%; 2%, 58%), but not for DMA at the knee.

Measures of mechanical hyperalgesia at the most painful knee and pain-free opposite forearm were associated with increased knee and global pain indicative of altered central processing. Psychosocial factors were significant partial mediators, highlighting the importance of the central integration of emotional processing in pain perception.

Associations between mechanical hyperalgesia at the forearm and knee, psychosocial factors and increased levels of clinical global and knee pain intensity provide evidence of altered central processing as a key mechanism in knee pain, with psychological factors playing a key role in the expression of clinical pain.