Leukocyte-Rich Versus Leukocyte-Poor Platelet-Rich Plasma in the Treatment of Knee Soft Tissue Injuries: A Systematic Review

Background: Platelet-rich plasma (PRP) is increasingly used for knee soft tissue injuries, but variation in leukocyte concentration contributes to uncertainty regarding the clinical relevance of different PRP formulations. Leukocyte-rich PRP (LR-PRP) and leukocyte-poor PRP (LP-PRP) have distinct biological characteristics, yet their comparative clinical benefits remain unclear. Objective: This systematic review aimed to evaluate human evidence comparing LR-PRP and LP-PRP for knee soft tissue injuries and to examine whether differences in leukocyte concentration are associated with clinical or biological outcomes. Methods: The review followed PRISMA 2020 guidelines. PubMed, Scopus, Web of Science, and the Cochrane Library were searched from inception to April 2025. Eligible studies included randomized controlled trials, prospective or comparative cohort studies, and cross-sectional human studies evaluating leukocyte-stratified PRP. Risk of bias was assessed using RoB 2 for randomized trials and the Newcastle-Ottawa Scale for non-randomized studies. Results: Five studies were included in the qualitative synthesis. Most clinical evidence concerned chronic patellar tendinopathy. The strongest head-to-head trial found no significant differences between LR-PRP, LP-PRP, and saline in pain or functional outcomes. LR-PRP showed only a transient early benefit in one trial, while LP-PRP demonstrated no consistent superiority over comparators. Biological profiling identified distinct molecular signatures between formulations. Conclusion: Current evidence does not demonstrate consistent clinical superiority of either LR-PRP or LP-PRP. Implication: Standardized, adequately powered trials are required before leukocyte concentration can guide formulation-specific PRP selection for knee soft tissue injuries.