Who Responds Best to PRP Injections for Knee Arthritis? | Dr. Jeffrey Peng MD
- 15 hours ago
- 4 min read
Medically reviewed by Dr. Jeffrey Peng, MD — Board-Certified Sports Medicine Physician
Published: February 26, 2026 | Last Updated: February 26, 2026
Platelet-rich plasma (PRP) injections have become one of the most promising non-surgical treatments for knee osteoarthritis. However, not every patient experiences the same degree of improvement. In my practice, I have treated thousands of patients with PRP, and while the majority respond well, there are clear patterns in who benefits most and who may need a different approach.
A 2025 study published in Frontiers in Physiology (Sun et al.) analyzed 140 patients with knee osteoarthritis to identify which baseline characteristics predict a successful response to PRP therapy. The findings offer valuable guidance for both patients considering PRP and clinicians optimizing treatment protocols.
How Effective Is PRP for Knee Osteoarthritis?
Across multiple clinical trials and meta-analyses, PRP injections for knee osteoarthritis consistently demonstrate a response rate of approximately 80 percent. This particular study confirmed that finding: 114 out of 140 patients (81 percent) achieved the minimal clinically important difference (MCID) for pain scores on the Visual Analog Scale, and 109 out of 140 patients (78 percent) reached the MCID for functional outcomes on the WOMAC scale at the six-month follow-up.
Each PRP treatment in the study involved drawing 45 milliliters of blood, which was processed and concentrated down to roughly 5 milliliters containing approximately 7 to 8 billion platelets per injection. The study included patients across the full spectrum of radiographic severity, from Kellgren-Lawrence grade 1 (mild) through grade 4 (severe).
Three Key Factors That Predict PRP Response
Using multivariate analysis, the researchers identified three baseline characteristics that significantly influenced PRP outcomes. Understanding these factors can help set realistic expectations and guide treatment planning.
Number of PRP Injections
The single most influential factor was the number of injections received. Patients who had two or more PRP injections were approximately four times more likely to achieve significant pain relief compared to those who received only a single treatment (odds ratio 4.285). This finding aligns with clinical experience: repeated doses likely sustain growth factor release and extend the biological repair process over time.
Body Mass Index (BMI)
For every one-point increase in body mass index, the effectiveness of PRP treatment decreased by approximately 13 percent (odds ratio 0.867). Higher BMI is associated with greater mechanical load on the knee joint and increased levels of chronic, low-grade systemic inflammation—both of which can counteract the healing effects of PRP.
This trend is not unique to PRP. Across orthopedics broadly, patients with metabolic syndrome, diabetes, or obesity tend to experience worse outcomes after nearly any musculoskeletal treatment, whether surgical or non-surgical. The underlying chronic inflammatory state accelerates cartilage degradation and reduces the body's ability to respond to regenerative therapies.
Duration of Symptoms
Each additional year of symptomatic knee arthritis reduced the likelihood of functional improvement by roughly 9 percent (odds ratio 0.905). In other words, patients who sought treatment earlier in their disease course responded more robustly to PRP. This reinforces a principle I emphasize frequently with my patients: earlier intervention generally leads to better outcomes with regenerative treatments.
What Does Not Predict PRP Outcomes
Perhaps one of the most clinically meaningful findings was that age and radiographic severity (Kellgren-Lawrence grade) were not predictive of treatment response. This means that older adults can still experience substantial benefit from PRP, and moderate-to-severe arthritis on X-ray can improve just as much as milder disease.
What appears to drive PRP success is not how the X-ray looks, but how biologically active the joint environment still is—how much residual cartilage remains and how responsive the synovial tissue is. PRP works primarily by modulating the joint environment through anti-inflammatory signaling and growth factor release, rather than by reversing end-stage structural damage.
Should Patients with Higher BMI or Long-Standing Arthritis Avoid PRP?
Absolutely not. In my practice, I have treated patients with BMIs well above 40 and others who have been managing arthritis pain for more than 10 or even 15 years—and many of them have responded remarkably well to PRP. For several of these patients, PRP was the first treatment that provided meaningful, lasting relief.
However, consistent with this study's findings, these patients often needed more than one PRP injection to reach a point of significant improvement. A series of treatments may be necessary to sustain the regenerative environment within the joint and unlock the full benefits of PRP therapy.
How to Maximize Your PRP Results
Based on the evidence and my clinical experience, there are several strategies that can help optimize PRP outcomes:
Consider a series of injections. The data strongly supports multiple PRP treatments over a single session. In my practice, I typically recommend a series of two to three injections spaced several weeks apart for knee osteoarthritis.
Address modifiable risk factors. Optimizing body weight, managing metabolic conditions, and reducing systemic inflammation through diet, exercise, and supplementation can all improve the likelihood of a positive response.
Seek treatment early. The longer arthritis progresses untreated, the more difficult it becomes to achieve meaningful improvement. If you are considering PRP, earlier intervention is generally better.
Follow a structured rehabilitation program. PRP injections are most effective when combined with targeted physical therapy and progressive strengthening. The injection creates a window of enhanced healing—rehabilitation helps the body take full advantage of that window.
The Bottom Line
PRP remains one of the most effective non-surgical treatment options for knee osteoarthritis, with approximately 80 percent of patients experiencing clinically meaningful improvement. The number of injections, BMI, and symptom duration are the strongest predictors of response—while age and X-ray severity are not. This study, published in Frontiers in Physiology (DOI: 10.3389/fphys.2025.1678037), provides further evidence that patient selection and treatment protocol optimization can meaningfully improve outcomes.
Schedule a Consultation
If you are dealing with knee osteoarthritis and want to learn whether PRP injections may be right for you, I encourage you to schedule a consultation. As a board-certified sports medicine physician, I specialize in non-surgical, evidence-based treatments for joint pain and arthritis. My clinic is located in Campbell, California, serving the greater San Francisco Bay Area.
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