Factors affecting the therapeutic effects of multiple intra-articular injections of platelet-rich-plasma for knee osteoarthritis.

Background: Platelet-rich-plasma (PRP) is rapidly spreading as a conservative treatment option for knee osteoarthritis (KOA), however, its therapeutic efficacy is controversial. This study aimed to investigate the factors affecting the therapeutic effect of intra-articular PRP therapy for KOA in patients who received multiple PRP injections (PRP-I).

Methods: This is a historical cohort study included 1057 knees of 701 patients who received PRP-I during KOA treatment from 2018 to 2020. The difference in visual analog scale (VAS) scores before and after PRP-I was defined as the amount of change in VAS (ΔVAS). A linear mixed-effects model was employed with ΔVAS as a random effect and age, sex, BMI, KL classification, pre-treatment VAS, treatment duration, and the number of PRP injections as fixed effects. Evaluations using the Kellgren-Lawrence (KL) classification were added.

Results: Age, KL grade, and VAS score before treatment and after three, four, and five PRP-I were significantly associated with ΔVAS score. According to KL grade, age was significantly associated with ΔVAS score in the KL grade 4 group. VAS score before treatment was significantly associated with ΔVAS score, regardless of KL grade. Three-time PRP-I were significantly associated with ΔVAS in the KL-grade 1 and 2 groups. For KL grade 4, two or more PRP-I were significantly associated with the high efficacy.

Conclusions: Age, pain before treatment, KL grade and number of injections were associated with pain reduction after intra-articular PRP-I for KOA treatment. Pain reduction can be expected after PRP-I when patients are younger or experience severe pain before treatment. Three-time PRP-I are recommended to reduce pain in early-stage KOA and more than three times in advanced-stage KOA.

Trial Registration: Retrospectively registration.