Effect of Intra-articular Platelet-Rich Plasma vs Placebo Injection on Pain and Medial Tibial Cartilage Volume in Patients With Knee Osteoarthritis: The RESTORE Randomized Clinical Trial
Bennell KL · JAMA (2021)
DOI: 10.1001/jama.2021.19415The RESTORE trial was a large, triple-blinded RCT published in JAMA testing whether leukocyte-poor PRP could reduce pain and preserve cartilage in mild to moderate knee osteoarthritis. 288 patients received three weekly injections of either LP-PRP or saline placebo, with 12-month follow-up measuring pain on an 11-point scale and medial tibial cartilage volume via MRI. The study found no significant benefit of PRP over saline for either outcome. However, the trial has been widely criticized for using a very low platelet concentration (approximately 1.6x baseline), which subsequent meta-analyses have identified as a critical factor separating effective from ineffective PRP protocols.
Clinical Relevance
This trial is essential reading for any practitioner considering PRP for knee OA. It demonstrates that simply injecting a product labeled PRP is insufficient. Clinicians must verify that the preparation system delivers adequate platelet concentration (ideally >4x or >1 million/uL) to achieve therapeutic benefit.
Key Takeaways
- No significant pain improvement over saline placebo at 12 months (p=0.17)
- No cartilage structural benefit on MRI
- Platelet concentration was only ~1.6x baseline, far below the >4x threshold associated with efficacy
- The RESTORE trial is now frequently cited as evidence that LOW-concentration PRP fails, not that PRP itself fails
- Highlights the critical importance of adequate platelet dosing
Key Findings
PRP did not result in a significant difference in symptoms (pain -2.1 vs -1.8, p=0.17) or joint structure (cartilage volume -1.4% vs -1.2%, p=0.81) compared to saline placebo at 12 months. The study has been criticized for low platelet concentration.
Clinical Context
Study Design
Randomized Controlled Trial (Triple-Blinded)
Condition
Mild to Moderate Knee Osteoarthritis (KL Grade 2-3)
Sample Size
288 patients
Follow-up
12 months
Control Group
Saline Placebo
Primary Outcome
11-point Knee Pain Scale (0-10) and MRI Medial Tibial Cartilage Volume
PRP Protocol & Intervention
Preparation System
Commercial (LP-PRP product)
Leukocyte Status
LP-PRP
Platelet Concentration
~1.6x (criticized as insufficient concentration)
Injection Frequency
3 injection(s)
Injection Interval
Weekly