Knee pain caused by osteoarthritis (OA) is commonly seen in geriatric patients. Patients with knee OA are often complicated with joint pain, soreness, and weakness. The injection of autologous platelet rich plasma (aPRP) has been proven to be effective in treating mild knee OA. The effect of injecting aPRP in treating moderate to severe degrees of knee OA remains controversial. This study aimed to evaluate the effectiveness of aPRP in treating patients with at least grade 2 on the Kellgren and Lawrence system for the classification of knee OA using a proteomic approach and clinical evaluation tool of Lequesne index. Musculoskeletal ultrasound was used for accurate needle placement into the knee joint, and to the perimeniscal soft tissue for the injection of aPRP. Three monthly aPRP injections were performed. Group 1 patients received intra-articular (IA) injection only, while group 2 received simultaneous IA and pes anserinus aPRP injections. After two monthly aPRP injections, both groups revealed significant drops in average SF total protein concentrations, and increases in the protein concentrations associated with chelation and anti-aging (eg/transthyretin, matrilin, and complement). However, it is group 2 that revealed significant decreases in the protein concentrations associated with inflammation (eg/immunoglobulin and apolipoprotein), and improved knee functional status. SF appeared to become less susceptible to degeneration after aPRP injections in group 2. As a result, at least 2 monthly injection of IA aPRP in conjunction with accurate injection of aPRP to the perimeniscal soft tissue structure such as the pes anserinus may be a viable option in treating patients with moderate to severe degrees of knee OA.