Long-Term Efficacy of Intra-Articular Platelet-Rich Plasma in Knee Osteoarthritis: A 6-Year Follow-up of a Prospective Cohort.

This prospective study evaluated the long-term efficacy, radiographic progression, and predictors of deterioration in patients with knee osteoarthritis (KOA) treated with intra-articular platelet-rich plasma (PRP) injections. Seventy-eight patients (118 knees) with Kellgren-Lawrence (KL) grade I-III KOA received 3 monthly PRP injections and were followed at 4 and 6 years. Pain and function were assessed with the Visual Analogue Scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Radiographic progression, analgesic use, and predictors of clinical worsening were analysed using linear mixed-effects modeling and survival analysis. At 4 years, significant improvements were observed in VAS (6.72 ± 1.82 to 4.47 ± 1.32, p < 0.0001) and WOMAC (58.32 ± 17.58 to 39.67 ± 10.37, p < 0.0001). By 6 years, outcomes regressed toward baseline (VAS 6.31 ± 1.47, p = 0.079; WOMAC 56.45 ± 14.35, p = 0.41). Benefits were more sustained in KL I-II compared with KL III, who showed earlier decline and greater analgesic use. KL progression was the strongest predictor of worsening (β = +14.2 WOMAC points, p < 0.001), with each baseline KL grade increase adding +6.5 WOMAC points (p = 0.002); BMI also contributed modestly (p = 0.018). Survival analysis showed KL III had a 3.1-fold higher failure risk than KL I (median 3.5 vs. 5.1 years, p < 0.001). PRP provides meaningful symptom relief and functional improvement for up to 4 years in mild-to-moderate KOA, but benefits decline by 6 years, particularly in advanced disease.