Protocol Heterogeneity in Platelet-Rich Plasma Treatment for Knee Osteoarthritis: A Scoping Review of Preparation, Delivery, and Outcomes

Platelet-rich plasma (PRP) is a commonly used intra-articular therapy for knee osteoarthritis (OA), yet substantial heterogeneity in PRP preparation and delivery limits comparability across trials and complicates clinical translation. We conducted a scoping review in accordance with PRISMA and PRISMA-ScR guidance. MEDLINE and Embase were searched from inception to 15 November 2025 for English-language randomized controlled trials comparing PRP with non-regenerative comparators (e.g., hyaluronic acid, corticosteroids, radiofrequency ablation, or saline placebo) in adults with knee OA. Data were charted on study characteristics, OA severity, injection guidance, centrifugation protocols, injected PRP volume and platelet concentration, dosing regimens, follow-up, adverse events, and overall conclusions (superior/non-inferior/inferior). Twenty-one studies (2012–2025) were included, spanning multiple regions and enrolling 21–288 participants per study with follow-up from 12 weeks to 60 months. PRP protocols varied widely, including single- versus double-spin centrifugation, spin rates and durations, injected volumes (approximately 1.4–8 mL), and platelet enrichment (approximately 1.15x to 9.85x baseline when reported). The most common regimen was three injections, typically weekly. Across studies, major adverse events were not reported, and post-injection pain or transient synovitis/effusion were the most frequent events. PRP for knee OA is generally safe and frequently demonstrates comparable or improved outcomes versus standard injectables, but marked protocol heterogeneity persists. Standardized reporting and consensus parameters for PRP preparation and administration are needed to improve reproducibility and guide evidence-based practice.