ObjectiveTo explore the clinical efficacy of the ultrasound-guided intra-articular injection of platelet-rich plasma (PRP) in the treatment of patients with different stages of knee osteoarthritis.MethodsWe retrospectively analyzed the clinical characteristics and X-ray data of patients with knee osteoarthritis who received ultrasound-guided intra-articular injection of PRP in the Department of Rehabilitation Medicine at Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University between May 2018 and June 2019. The patients were grouped according to the Kellgren & Lawrence Classification (K&L 0, Ⅰ, Ⅱ, Ⅲ, and Ⅳ). All the patients received four injections with a one-week interval. The Visual Analogue Scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were used to evaluate the clinical efficacy before the injection, and 3 and 6 months after the injection. Adverse reactions were recorded.ResultsA total of 102 patients were included without any grade 0 cases. There were 20 patients in K&L Ⅰ group, 37 in Ⅱ group, 31 in Ⅲ group, and 14 in Ⅳ group. No adverse event was reported. Significant differences of VAS scores and WOMAC index were observed in Ⅰ, Ⅱ and Ⅲ groups at the 3rd and 6th month follow-up (P<0.05). VAS and WOMAC scores of the three groups at the 3rd and 6th month after the treatment were significantly improved compared with those before the treatment (P<0.05). There was no significant difference in VAS score at the 3rd or 6th month after the treatment three groups (P>0.05). For K&L Ⅰ group, there was no statistically significant difference in WOMAC score at the 3rd or 6th month after the treatment (P>0.05). However, the WOMAC scores at the 3rd month after the treatment were better than those at the 6th month in K&L Ⅱ and Ⅲ groups (P<0.05). There was no significant time-depended changes in VAS score or WOMAC score in K&L Ⅳ group (P>0.05).ConclusionThe ultrasound-guided intra-articular PRP injection is safe and effective for pain relief and function improvement in patients with knee osteoarthritis at the early and middle stage.