Our meta-analysis suggested that PRP injection significantly

improved the functional status, relative to basal evaluations, in patients with knee degenerative pathology, and the beneficial effect was maintained for 1 year after treatment. The major concern regarding our pooled effect sizes is the overestimation of true values because of a lack of control treatments. Only 1 of the included trials used saline as a placebo control, whose effect size was −.29 (95% CI, −.68 to .10) at 2 months and −.48 (95% CI, −.89 to −.07) at 6 months. We believed that the estimated effect of saline injection 5-FU was reliable since it was derived from a double-blind, randomized controlled trial. The result implies a gradual SD-208 functional decline with a significant deterioration identified at 6 months after placebo treatment. In contrast, the PRP group revealed a continual improvement until 12 months. Therefore, the present meta-analysis suggests that the effectiveness of PRP derived from a biological benefit, which could not simply be explained by a placebo effect. The HA effect size pooled in the present meta-analysis indicated that the efficacy reached a highest point at 2 months after injection but declined over time. The change in HA efficacy is comparable to that found in

previous meta-analytic research despite a greater effect size,5 and 39 since we used the patients’ baseline as the reference point and included more small, uncontrolled trials. Current evidence suggests a modest effect of HA in relieving pain in patients with knee OA probably through the mechanism of viscosupplementation and modulation of the early inflammatory response.6 Compared with the HA group, patients treated with PRP demonstrated better effectiveness at 2 time points, and the trend of improvement PIK3C2G was sustained until 12 months (see fig 4). The advantage of PRP over HA remained at 6 months, even when only the results from randomized controlled trials were analyzed. In vitro experiments have

demonstrated the capability of PRP in the temporary modulation of cytokine levels and stimulation of chondral anabolism, which may lead to short-term pain relief and long-term functional improvement, respectively.40 When comparing the temporal changes in clinical outcomes between the 2 regimens, PRP injections provided a more prompt symptomatic relief than HA. Since the main action of HA derives from the restoration of viscoelasticity of synovial fluid, the prolonged efficacy of PRP might imply a regenerating or disease-modifying potential, which has rarely been reported in studies using HA preparations. Several factors mentioned by antecedent research might modify the effect of PRP injections. In terms of the study design, the pooled effect sizes in single-arm and quasi-experimental studies were likely to be higher than that in randomized controlled trials.