Reference ranges and influencing factors of pressure pain threshold in Chinese patients with knee osteoarthritis.

BACKGROUND

Pressure pain threshold (PPT) is a reliable objective measure of pain sensitization; however, standardized region-specific reference data for Chinese patients with knee osteoarthritis (KOA) remain scarce. This study aimed to establish preliminary PPT reference ranges for end-stage KOA patients and age- and sex-matched healthy controls in Xi'an, Northwest China, and to identify factors influencing PPT.

METHODS

A total of 165 patients with end-stage KOA scheduled for total knee arthroplasty and 146 age- and sex-matched healthy controls were enrolled. PPT at the medial knee and dorsal forearm was assessed using standardized PPT assessment. Demographic characteristics, body mass index (BMI), sociological factors and Central Sensitization Inventory (CSI) scores were collected. Nonparametric analyses, Spearman correlation and hierarchical regression were performed.

RESULTS

KOA patients exhibited significantly lower median PPTs (forearm: 3.79; knee: 4.21 kg·cm-2) compared with controls (forearm: 5.53; knee: 6.57 kg·cm-2; all p < 0.001), with left-shifted and broader 95% reference ranges (KOA: forearm 2.16-6.09; knee 2.07-6.78 kg·cm-2). CSI scores were moderately negatively correlated with forearm PPT (r = -0.567) and weakly correlated with knee PPT (r = -0.389; all p < 0.001). After adjusting for confounders, CSI remained the strongest independent predictor of PPT (forearm: β = -0.403; knee: β = -0.301; all p < 0.001), explaining greater incremental variance (ΔR2 = 0.144 for forearm; ΔR2 = 0.080 for knee) than other factors. In healthy controls, PPT was influenced only by sex, age and BMI (all p < 0.01).

CONCLUSIONS

This study is the first to establish preliminary PPT reference ranges for end-stage KOA patients in Xi'an, Northwest China, suggesting generalized pain hypersensitivity as a predominant phenotype in this cohort. The strong correlation between CSI (subjective) and forearm PPT (objective) provides a preliminary basis for future preoperative stratification and potential perioperative analgesic strategies, with potential clinical translational value.