Objective: The efficacy of platelet-rich plasma (PRP) injections for knee osteoarthritis (OA) is often reported, despite parameters closely correlated with symptomatic relief not being definitely established. We assessed correlations between symptomatic relief induced by PRP and five parameters.

Methods: Thirty-nine patients with knee OA were treated with PRP. A 6.0-ml sample of an autologous leukocyte-reduced PRP was obtained from 40 mL of whole blood by Cell Source Co. Ltd. Two intra-articular injections of this PRP were given at a 2-week interval. The following five parameters were evaluated: age, disease duration, body mass index (BMI), radiographic femorotibial angle (FTA) and the protrusion of the medial meniscus with displacement of the medial collateral ligament (meniscal protrusion) as seen on the ultrasound screen.

The improvement rate was calculated by dividing the difference between 12 week assessment and baseline scores of the Lequesne index by the baseline score and multiplying by 100.

Results: All patients returned for the final follow-up visit. Percent remission was not significantly correlated with age, disease duration, BMI and FTA (P>0.05). The correlation between meniscal protrusion and improvement rate was significant (P=0.026, R=0.36).

Conclusion: In the current study, improvement rate induced by PRP decreased with increase of meniscal protrusion. The correlation suggested that patients with knee OA who had less meniscal protrusion could expect good improvement from intra-articular injections of PRP.