Efficacy of multiple autologous apheresis platelet-rich plasma injections for treating knee osteoarthritis and its influencing factors: a retrospective cohort study

Background The lack of standardized Platelet-Rich Plasma (PRP) protocols for Knee Osteoarthritis (KOA), combined with significant patient variability, leads to inconsistent PRP effectiveness across studies. This study aims to assess the influence of PRP injection frequencies on KOA treatment and explore the role of patient characteristics and PRP properties in the treatment's effectiveness. Methods A retrospective cohort study was conducted with KOA patients who received three PRP injections (4-week intervals) at a hospital in Chongqing. The Wilcoxon signed-rank test was used to analyze differences in self-reported recovery rates across different treatment time points, with Bonferroni correction applied for significance level adjustment (alpha). The Mann-Whitney U test, Kruskal-Wallis H test, Spearman correlation analysis, and restricted cubic spline models were used to assess the associations between sex, baseline Kellgren-Lawrence grade, age, PRP red blood cell (RBC) concentration, PRP white blood cell (WBC) concentration, PRP platelet concentration, the multiple of PRP platelet concentration relative to the baseline autologous level (Enrichment-PLT), and self-reported recovery rates. Results The study included 28 KOA patients. Significant improvement in self-reported recovery rate was observed 4 weeks after the first treatment (median: 30.0%, P < 0.008) and after the second treatment (median: 45.0%, P < 0.008). However, no significant change was noted 4 weeks after the third treatment (median: 55.0%, P = 0.058), and recovery rates at 8, 12, and 24 weeks post-third treatment showed no significant differences compared to 4 weeks (all P > 0.008). Additionally, no correlations were found between sex, baseline Kellgren-Lawrence grade, age, PRP RBC concentration, PRP WBC concentration, PRP platelet concentration, or Enrichment-PLT and self-reported recovery rates. Conclusion At least two PRP injections are recommended, with effects lasting for at least 24 weeks. Factors such as sex, age, baseline Kellgren-Lawrence grade, and PRP properties (prepared by apheresis) do not significantly affect treatment outcomes.