BACKGROUND:
Patellofemoral pain (PFP) is defined biomechanically, but is characterised by features that fit poorly within nociceptive pain. Mechanisms associated with central sensitisation may explain why, for some, symptoms appear nociplastic. This study compares psychological and somatosensory characteristics between those with persistent PFP and controls.
METHODS:
150 adults with PFP were compared to 61 controls. All participants completed a survey evaluating participant characteristics, PFP-related constructs and psychological factors: anxiety, depression, pain catastrophizing, kinesiophobia, pain self-efficacy. Participants also attended a session of somatosensory testing, which included knee and elbow thermal and mechanical detection and pain thresholds, conditioned pain modulation (CPM), and temporal summation of pain (TSP). Differences were evaluated using analysis of covariance (sex as covariate). Multivariate backward stepwise linear regression examined how psychological and somatosensory variables relate to PFP (Knee injury & Osteoarthritis Outcome Score-patellofemoral).
RESULTS:
The PFP group had multimodal reduced pain thresholds at the knee and elbow (Standardised Mean Difference (SMD), p: 0.86 to 1.2, <0.001), reduced mechanical detection at the elbow (0.43, 0.01) and higher TSP (0.41, 0.01). CPM was not different. Psychological features demonstrated small effects (0.47-0.59, 0.01-0.04). The PFP group had a 55% (95% CI: 0.47 to 0.62) risk of kinesiophobia and an 11% (0.06 to 0.15) reduced pain self-efficacy risk. Kinesiophobia, knee pressure pain threshold, pain self-efficacy and pain catastrophizing explained 40% of KOOS-PF variance (p = <0.001).
CONCLUSIONS:
Widespread hyperalgesia and evidence of symptom amplification may reflect nociplastic pain. Clinicians should be aware that kinesiophobia and the nociplastic pain may characterise the condition.
SIGNIFICANCE:
(1) Individuals with patellofemoral pain have widespread reduced pain thresholds to pressure and thermal stimuli. (2) Mechanically-induced pain is likely amplified in those with patellofemoral pain. (3) Pain-related fear is highly prevalent and helps explain patellofemoral pain-related disability. WHAT’S ALREADY KNOWN ABOUT THIS TOPIC?: (1) Pressure pain threshold can be lower in individuals with patellofemoral pain. WHAT DOES THIS STUDY ADD?: (1) This is the first study to explore a combined range of psychological and psychophysical tests in patellofemoral pain. (2) This study provides strong evidence of nociplastic pain in patellofemoral pain.
