Optimal Dosage of Platelet-Rich Plasma Injections in Patients With Osteoarthritis of the Knee: A Scoping Review.

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Knee osteoarthritis (KOA) is a healthcare burden affecting over 595 million people worldwide. Recently, intra-articular platelet-rich plasma (PRP) injections from the patient's blood have shown promise in slowing KOA progression due to platelets' regenerative properties. This study aimed to evaluate the optimal dosing and schedule for PRP therapy in managing mild to moderate KOA. A systematic search was conducted across Embase, Ovid Medline, Web of Science, Cochrane Central, and CINAHL using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to identify articles published from August 2015 to March 2024. Keywords included "platelet rich plasma," "knee osteoarthritis," and "administration schedule." Inclusion criteria were studies on human patients utilizing PRP as monotherapy in experimental trials, while review articles, editorials, case reports, and meta-analyses were excluded. Three reviewers independently extracted and described patient interventions and outcomes, focusing on Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Visual Analog Scale (VAS), and imaging changes. Thirty-nine publications with PRP monotherapy protocols were found, with fourteen meeting the inclusion criteria. Twelve studies were randomized clinical trials, and two were longitudinal cohort studies, totaling 1704 patients with a mean follow-up of 7.51 ± 4.82 months. The most common PRP protocol was 4.357 ± 1.419 mL infusions, with three doses every four weeks and a single dose being frequent. Platelet values varied, with seven including a mean platelet count, three reporting that the platelet concentration in each dose had to be at least 150,000/μL, and four did not include platelet concentration. There was notable variation in PRP acquisition protocols, blood volume, and centrifugation processes across studies. Therapeutic benefits were represented by WOMAC and VAS scores rather than imaging changes. PRP injections appear to be safe and effective for symptomatic relief of knee pain associated with mild to moderate osteoarthritis (OA). The average infusion volume was 4 mL, administered at three doses four weeks apart. Given that platelet-derived growth factors promote the proliferation of chondrocytes and mesenchymal stem cells, leading to the stimulation of articular cartilage remodeling, further studies are warranted to assess the optimal platelet count necessary for the long-term effects of PRP in knee cartilage healing and sustained symptomatic improvement.