High Prevalence of Pain Sensitization in Knee Osteoarthritis: A Meta-Analysis with Meta-Regression

OBJECTIVE: The aim of this meta-analysis was to study the evidence on pain sensitization in knee osteoarthritis (OA), providing a quantitative synthesis of its prevalence and impact. Factors associated with pain sensitization were also investigated. METHODS: Meta-analysis; PubMed (MEDLINE), Cochrane Central Register (CENTRAL), and Web of Science were searched on February 2021. Level I to level IV studies evaluating the presence of pain sensitization in patients with symptomatic knee OA, documented through a validated method (questionnaires or quantitative sensory testing), were included. The primary outcome was the prevalence of pain sensitization. Factors influencing the prevalence were also evaluated, as well as differences in terms of pain thresholds between knee OA patients and healthy controls. RESULTS: Fifty-three articles including 7,117 patients were included. The meta-analysis of proportion documented a prevalence of pain sensitization of 20% (95% confidence interval [CI] = 16%-26%) with a significant heterogeneity of results (I(2) = 89%, P < 0.001). The diagnostic tool used was the main factor influencing the documented prevalence of pain sensitization (P = 0.01). Knee OA patients presented higher pain sensitivity compared with healthy controls, both in terms of local pressure pain threshold (standardized mean difference [SMD] = −1.00, 95% CI = −1.67 to −0.32, P = 0.007) and distant pressure pain threshold (SMD = −0.54, 95% CI = −0.76 to −0.31, P < 0.001). CONCLUSIONS: Knee OA pain presents features that are consistent with a significant degree of pain sensitization. There is a high heterogeneity in the reported results, mainly based on the diagnostic tool used. The identification of the best methods to detect pain sensitization is warranted to correctly evaluate and manage symptoms of patients affected by knee OA. REGISTRATION: PROSPERO CRD42019123347.