Psychological and pain profiles in persons with patellofemoral pain as the primary symptom

Key points

1. 01Participants with PFP had significantly lower pain thresholds to cold, heat, and pressure at both the knee and elbow, indicating widespread hyperalgesia beyond the local joint.
2. 02Temporal summation of mechanical pain was greater in the PFP group (45% vs 31.4% maximum possible effect), though the between-group effect was small (ES 0.59).
3. 03Conditioned pain modulation did not differ significantly between groups, suggesting descending pain inhibition may be largely intact.
4. 04Kinesiophobia was present in 54.7% of the PFP group (TSK mean 38), and psychological factors predicted 40% of KOOS-PF variance alongside knee pressure pain threshold.
5. 05Psychological features (anxiety, depression, catastrophizing) showed only small between-group effects; their relationship to somatosensory test results was minimal, with only a small correlation between catastrophizing and knee heat pain threshold (rho = -0.29).

How it was conducted

Design

Cross-sectional case-control study

Participants

150 adults with PFP and 61 pain-free controls, aged 18-50, recruited from greater Brisbane region

PFP criteria

Pain behind or around patella aggravated by weight-bearing on a flexed knee, duration at least 6 weeks, worst pain at least 3/10 over past week

Somatosensory tests

Quantitative sensory testing including thermal and mechanical detection thresholds, cold and heat pain thresholds, pressure pain thresholds, temporal summation of pain (TSP), and conditioned pain modulation (CPM) at knee and elbow

Psychological measures

HADS (anxiety and depression), Tampa Scale for Kinesiophobia, Pain Catastrophizing Scale, Pain Self-Efficacy Questionnaire

Primary outcome

Comparison of somatosensory and psychological profiles; multivariate regression using KOOS-patellofemoral subscale as dependent variable

What they found

• Cold pain threshold knee: PFP mean 18.1 (SD 17.7) vs control 5 (SD 1.5), MD -9.5 (99% CI -12.5 to -6.4), ES 1.2, p < .001
• Heat pain threshold knee: PFP mean 42.2 (SD 4.9) vs control 45.7 (SD 3.7), MD 3.4 (99% CI 2.2-4.6), ES 1.1, p < .001
• Pressure pain threshold knee: PFP mean 465 (SD 239) KPa vs control 618.3 (SD 337) KPa, MD -170.7 (99% CI 102.1-239.4), ES 0.96, p < .001
• Cold pain threshold elbow: PFP mean 11.2 (SD 16.1) vs control 5 (SD 1.0), MD -6.2 (99% CI -9.1 to -3.4), ES 0.86, p < .001
• Heat pain threshold elbow: ES 1.02 (99% CI 0.61-1.43), p < .001
• Pressure pain threshold elbow: MD -115.6 (99% CI 64.5-166.7), ES 0.89, p < .001
• TSP: PFP 45% (SD 23.4) vs control 31.4% (SD 21.7) maximum possible effect, MD -13.5 (99% CI -22.5 to -4.4), ES 0.59, p < .001; 69% of PFP vs 49.2% of controls met case threshold (risk difference 0.2)
• CPM: ES 0.40 (99% CI -0.80 to -0.003), not significant (p = .05)
• Anxiety prevalence: 34% in PFP vs 11.5% in controls (risk difference 0.23); depression: 8% vs 1.6% (risk difference 0.06)
• Kinesiophobia: present in 54.7% (82/150) of PFP group; 55% (95% CI 0.47-0.62) risk; PSEQ showed 11% (95% CI 0.06-0.15) reduced pain self-efficacy risk
• Regression model (kinesiophobia TSK beta -0.33, pain self-efficacy PSEQ beta 0.24, knee pressure pain threshold beta 0.19, catastrophizing PCS beta -0.17) explained adjusted R2 = 40% of KOOS-PF variance (p < .001)
• Only significant correlation between psychological factors and QSTs: PCS and knee heat pain threshold (rho = -0.29, p < .01)

Limitations

• Cross-sectional design means causality and direction of observed associations cannot be determined.
• Control group was required to be free of multi-site pain, which differs from the PFP group (92% had other musculoskeletal pains), so some somatosensory differences may reflect widespread pain comorbidity rather than PFP specifically.
• Quantitative sensory testing was not conducted by a blinded assessor, introducing potential observer bias despite use of scripted instructions.
• Recruitment required a minimum pain severity and duration, so findings may not represent the full clinical spectrum of PFP seen in practice.

Why it matters

For patients

People with knee cap pain lasting over a year are more pain-sensitive across their whole body and commonly experience fear of movement, so managing these broader features may be as important as treating the knee itself.

For clinicians

Screening for kinesiophobia and reduced pain self-efficacy is warranted in all patients with PFP, as these psychological factors combined with pressure pain sensitivity account for a substantial proportion of functional disability independent of structural findings.

For readers

This study supports classifying PFP as partly nociplastic in a subgroup of patients, which has implications for choosing management approaches that address central sensitization and pain-related fear alongside biomechanical factors.