Background:Intra-articular injections of autologous platelet-rich plasma (PRP) have been shown to reduce joint pain in many patients with mild to moderate knee osteoarthritis (OA) (PRP responders). However, for unclear reasons, 20% to 30% of patients experience little to no improvement in symptoms (PRP nonresponders). Understanding the mechanisms underlying PRP's action is crucial to address this limitation. In vitro and animal studies suggest that the benefits of PRP in knee OA are partly attributable to exosomes secreted by platelets and other cells. Purpose/Hypothesis:This study aimed to (1) determine the effects of intra-articular PRP injections in patients with symptomatic knee OA on pain and physical function, and (2) evaluate whether PRP exosome concentration and size were associated with therapeutic efficacy. Responsiveness to PRP therapy in patients with knee OA may be related to exosome concentration and size. Study Design:Case-control study; Level of evidence, 3. Methods:A total of 60 patients seeking nonsurgical treatment of symptomatic mild to moderate knee OA-Kellgren-Lawrence (KL) grades 1 to 3-were prospectively enrolled in the study. Baseline descriptive and health data were collected, including patient-reported pain and functional outcomes at baseline, 6 weeks, and 12 weeks after injection. PRP responders were defined as patients with ≥20% reduction in the Numerical Rating Scale (NRS) of joint pain at 12 weeks after treatment. Exosome size and concentration and platelet concentration were measured in each sample. Logistic regression was used to explore relationships between responder status and patient factors-age, body mass index (BMI), sex, and KL grade. The mean exosome size and concentration were also compared between responders and nonresponders using an independent t-test. Results:Of the 58 patients included in the analyses, 43 (73%) reported a 20% reduction in NRS scores. The mean exosome size among a subset of patients who reported unacceptable pain symptoms before treatment (n = 43) was 80.8 ± 2.7 nm for responders and 78.0 ± 1.5 nm for nonresponders, a statistically significant difference (P = .005). There was no significant difference between responders and nonresponders in terms of platelet or exosome concentration. Age, BMI, sex, and KL grade were not significantly associated with the odds of PRP treatment response (all P > .05). Conclusion:PRP-derived exosome size appears to be associated with improvements in pain at 12 weeks after injection.
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