OBJECTIVE To compare the clinical effectiveness of the triple intra-articular injection of platelet-rich plasma (PRP) with respect to the single injection in patients with mild osteoarthritis of the knee. METHODS A total of 35 patients with a clinical and radiographic diagnosis of osteoarthritis grade I and II were analyzed. They were randomized into two groups: single application (18 patients) and
triple application (17 patients). Both groups were evaluated using the Visual Analogue Scale (VAS), the Western Ontario and McMaster Universities (WOMAC) index, and the Health Survey 12v2 (SF-12) at baseline and at 6, 12, 24, 36 and 48 weeks post-treatment. RESULTS Both treatments significantly decreased the level of pain (VAS) (single, from 7.3+/-2.1 to 4.6+/-2.7 and triple, from 6.6+/-2.4 to 0.9+/-1.4; p lt 0.05) and the total WOMAC (single, from 44.2+/-19.7 to 26.7+/-24.9 and triple, from 41.4+/-15.5 to 7.2+/-7.3; p lt 0.05) at the end of the study. The triple application showed better improvement in the VAS (p= 0.0007) and the total WOMAC (p= 0.0209) scores when comparing the final results between groups. CONCLUSION The triple infiltration of PRP in patients with mild knee osteoarthritis is clinically more effective than the single application at 48 weeks of follow-up.