Can PRP Injections Slow Down Knee Arthritis?
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By Dr. Jeffrey Peng, MD · Published March 5, 2026 · 7 min read
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Platelet-rich plasma (PRP) injections have become one of the most effective non-surgical treatments for reducing pain and improving function in patients with knee osteoarthritis. But an important question remains: can PRP actually slow down the progression of arthritis itself? A landmark randomized controlled trial by Chu et al. (2022) set out to answer that question — and the results were remarkable.
What Did This PRP Clinical Trial Find?
This multicenter, double-blind, sham-controlled randomized clinical trial enrolled 610 patients with mild to moderate knee osteoarthritis. Participants were randomly assigned to receive either three PRP injections or three saline placebo injections, spaced one week apart. The study followed patients for up to five years — making it one of the longest follow-up periods in any PRP trial to date.
The results were striking. PRP reduced pain scores by approximately 80 to 90 percent and improved functional outcomes by nearly 50 percent compared to baseline. More importantly, MRI imaging at the five-year mark demonstrated that PRP slowed cartilage loss by roughly 50 percent compared to the placebo group.
How Was This PRP Study Designed?
The study recruited patients from nine hospitals across China, including five tertiary medical centers. All participants had mild to moderate osteoarthritis; patients with severe grade 4 disease were excluded. A total of 308 patients were randomized to the PRP group and 302 to the saline placebo group.
Outcomes were measured using the WOMAC osteoarthritis index, the International Knee Documentation Committee (IKDC) subjective score, and the visual analog scale (VAS) for pain. The authors also analyzed synovial fluid biomarkers at six and twelve months and obtained MRI scans at baseline and at the five-year follow-up to evaluate cartilage volume changes.
For the PRP group, each treatment session began with a 50 cc blood draw, which yielded approximately 5 cc of concentrated PRP. The mean platelet concentration was 4.3 times that of whole blood, translating to roughly 8 to 9 billion platelets per injection. All injections were performed under ultrasound guidance. The placebo group also had blood drawn, but the sample was discarded and sterile saline was injected instead — an excellent study design that helps control for the placebo effect.
How Much Pain Relief Can You Expect from PRP?
The WOMAC osteoarthritis score ranges from 0 (no symptoms) to 96 (worst possible symptoms). Both groups showed initial improvement from baseline to three months. However, only the PRP group continued to improve, with sustained benefits lasting through the full two-year clinical follow-up. The saline group returned to baseline by six months and progressively worsened over time.
Pain scores told a similar story. Using the visual analog scale (0 to 10), PRP-treated patients saw their average pain drop from approximately 5 out of 10 down to 1 out of 10 — an 80 to 90 percent improvement. Functional scores improved by close to 50 percent. These are substantial, clinically meaningful improvements that can transform a patient's quality of life.
In my practice, I find that this level of pain relief is often the key that unlocks everything else. Many patients with osteoarthritis are stuck in a vicious cycle: arthritis causes pain, pain prevents exercise, lack of exercise accelerates arthritis, and the cycle repeats. PRP can break that cycle by reducing pain enough for patients to re-engage with cardiovascular exercise and strength training — both of which are critically important for managing arthritis long-term.
How Does PRP Affect Inflammation Inside the Knee?
The researchers analyzed synovial fluid — the fluid inside the knee joint — to assess the inflammatory environment. They measured key inflammatory cytokines, including tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β), both of which are elevated in arthritic joints and drive cartilage breakdown.
At six months after treatment, TNF-α and IL-1β levels in the PRP group were significantly lower than before the injections, indicating a healthier joint environment. The placebo group showed no change in inflammatory markers, which is expected — saline does not alter the inflammatory cascade inside the knee.
However, by twelve months, the inflammatory markers in the PRP group had returned to baseline. This finding has important clinical implications. It suggests that while PRP effectively reduces inflammation for several months, the beneficial anti-inflammatory effects are temporary — which is why booster injections become relevant.
Does PRP Slow Down the Progression of Knee Arthritis?
This is perhaps the most exciting finding from the study. The authors measured tibiofemoral cartilage volume on MRI at baseline and again at the five-year follow-up. In the PRP group, cartilage volume decreased by a mean of 1,171 mm³. In the saline group, cartilage volume decreased by a mean of 2,311 mm³. The difference between groups was statistically significant, suggesting that PRP reduced the rate of cartilage loss by approximately 50 percent over five years (Chu et al., 2022).
This is a meaningful finding because slowing cartilage loss is the key to preventing the progression from moderate arthritis to bone-on-bone disease — which is when patients often require a total knee replacement. A separate retrospective study by Sánchez et al. (2020) found that 85.7 percent of patients who received PRP did not undergo knee replacement during a five-year follow-up, with a median delay to surgery of 5.3 years in those who eventually did (Sánchez et al., 2020).
How Many Platelets Do You Need for Effective PRP?
This study used a 50 cc blood draw to produce PRP with a mean platelet concentration of 4.3 times whole blood — approximately 8 to 9 billion platelets per injection. This appears to be the therapeutic ballpark for treating most orthopedic conditions with PRP.
Prior research has demonstrated that using too few platelets results in no meaningful clinical benefit. What remains unclear is the upper limit of the dose-response curve. Some practitioners are now starting with 120 cc blood draws to achieve even higher platelet concentrations, but we need more studies to determine whether this provides additional benefit over the standard 50 cc protocol.
How Many PRP Injections Do You Need?
The optimal number of PRP injections remains somewhat debated, but the evidence is becoming clearer. Multiple studies have shown that a single PRP injection containing 8 to 10 billion platelets can provide symptom relief lasting approximately one year, after which symptoms typically return to baseline.
This clinical trial used a protocol of three PRP injections spaced one week apart, which produced more substantial and longer-lasting improvements. The number of injections a patient needs depends on several factors: the severity of their arthritis, their baseline pain level, and their treatment goals. Patients with mild arthritis may respond well to a single injection, while those with moderate to severe disease or significant pain may benefit from a series of two or three.
Cost is also a practical consideration. PRP is not currently covered by most insurance plans, so the financial burden falls on patients. Some patients opt for the full three-injection series upfront. Others take a more conservative approach, starting with one injection and reassessing every four weeks to determine if additional treatments are warranted.
Do You Need Booster PRP Injections?
Based on this study's cytokine analysis, I currently recommend booster PRP injections at approximately one-year intervals. The data showed that inflammatory markers (TNF-α and IL-1β) dropped significantly after PRP treatment but returned to baseline by twelve months. Since elevated inflammatory cytokines drive cartilage breakdown and symptom progression, maintaining low levels of these markers through periodic booster treatments is a logical strategy for keeping the joint as healthy as possible.
Even patients who feel relatively symptom-free at the one-year mark should consider a booster injection. The inflammatory markers are silently accumulating, and proactive treatment helps prevent the arthritis from progressing to a point where surgical intervention becomes necessary. I would argue that the study's already impressive results on cartilage preservation would have been even better if yearly boosters had been part of the protocol.
If you are considering PRP treatment for knee arthritis, I encourage you to schedule a consultation to discuss whether this approach is appropriate for your specific situation.
References
1. Chu J, Duan W, Yu Z, et al. Intra-articular injections of platelet-rich plasma decrease pain and improve functional outcomes than sham saline in patients with knee osteoarthritis. Knee Surg Sports Traumatol Arthrosc. 2022;30(12):4063-4071. doi:10.1007/s00167-022-06887-7
2. Sánchez M, Jorquera C, Sánchez P, et al. Platelet-rich plasma injections delay the need for knee arthroplasty: a retrospective study and survival analysis. Int Orthop. 2020;45(2):401-410. doi:10.1007/s00264-020-04669-9
Medical Disclaimer: This content is for educational purposes only and does not substitute for the medical advice of a physician. Always consult your healthcare provider before beginning any new treatment program. The information presented reflects the opinion of Dr. Jeffrey Peng and does not represent the views of his employers or affiliated hospital systems.
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