PRP Therapy: Is It Effective for Knee Osteoarthritis?

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Abstract

Welcome to our educational series. I’m Dr. Alex Jimenez. In this post, we delve into the intricate world of Platelet-Rich Plasma (PRP) therapy, specifically for treating knee osteoarthritis (OA). We will explore the ongoing debate surrounding the optimal composition of PRP, questioning long-held beliefs about the role of white blood cells (leukocytes) and the importance of platelet concentration. Drawing on cutting-edge research from leading scientists, we will review several landmark studies to determine whether leukocyte-rich (LR-PRP) or leukocyte-poor (LP-PRP) PRP is superior and how the absolute platelet count affects clinical outcomes. This discussion will highlight that in an inflammatory environment like knee OA, even leukocyte-rich PRP can exert powerful anti-inflammatory effects. We will also examine how variability in clinical trial results might be explained by platelet dose. Ultimately, this journey aims to provide a clearer, evidence-based understanding of how to optimize PRP therapy to improve patient outcomes, which is central to our integrative approach at Injury Medical Clinic.

A New Chapter in Integrative Care: Introducing Our Medical Director

I am thrilled to announce a significant and exciting development for our practice. Dr. Maria Guadalupe Cardenas, MD, a distinguished and board-certified internist with over 40 years of invaluable experience, has joined our team as the Medical Director and Collaborative Physician at Injury Medical Clinic PA. Dr. Cardenas (NPI #1164426749, Texas MD License #J2933) brings a wealth of medical knowledge and a deep commitment to patient care that perfectly aligns with our clinic’s philosophy.

This collaboration establishes a powerful multidisciplinary framework right here in El Paso, Texas. My expertise in chiropractic care, functional medicine, and rehabilitation will now be seamlessly integrated with Dr. Cardenas’s comprehensive medical oversight. This partnership allows us to offer a truly holistic and robust treatment model, especially for complex cases involving personal injury, chronic pain, and degenerative conditions like osteoarthritis. Together, we are committed to delivering the highest standard of care by combining chiropractic, medical, and functional medicine to create personalized, effective treatment plans for our community.

Unpacking the PRP Puzzle: Beyond the Basics

Over the years, the conversation around Platelet-Rich Plasma (PRP) has become increasingly complex. We often hear about networks of platelets, cytokines, and growth factors, creating a whirlwind of information. Today, I want to simplify this and focus on a few fundamental questions that directly impact how we treat our patients, particularly those with knee osteoarthritis (OA). I was asked to select some of my favorite research papers on this topic, and the ones I’ve chosen help illuminate some of the most debated aspects of PRP therapy.

For a long time, the consensus, or what I call the “dogma” in our field, has been that for conditions like knee OA, you want to use leukocyte-poor PRP (LP-PRP). The thinking was that leukocytes, or white blood cells, are pro-inflammatory and would worsen the already inflamed environment of an arthritic joint. This led to a very rudimentary approach: remove as many white blood cells as possible. However, as our understanding evolves, it’s clear we need a much more refined and nuanced analysis. Let’s look at what the latest evidence says.

The Role of Leukocytes: Friend or Foe in Knee OA?

The question of whether to include or exclude leukocytes in PRP for knee OA has been a major point of contention. The conventional wisdom has been to avoid them. However, several high-quality studies now challenge this assumption, suggesting that leukocyte content might not adversely affect outcomes—and could even be beneficial.

Giuseppe Filardo’s Landmark Studies

Two of my favorite papers on this subject come from the brilliant researcher Dr. Giuseppe Filardo, formerly of the Rizzoli Institute in Italy. He conducted two separate double-blind, randomized controlled trials on patients with moderate knee OA.

• Study Design:

• • The first study involved 192 patients, and the second involved 132 patients.
  • Patients received a series of three injections.
  • They were randomly assigned to receive either leukocyte-rich (LR-PRP) or leukocyte-poor (LP-PRP).
  • Both PRP preparations had a similar platelet concentration (about 4x baseline).
  • The key difference was the leukocyte concentration: the LR-PRP had a significantly higher white blood cell count compared to the LP-PRP.
  • One study used cryopreserved PRP, while the other used fresh PRP.

• The Findings: The results were striking. Both groups—those who received LR-PRP and those who received LP-PRP—experienced significant improvements in their clinical scores. Most importantly, there was no statistically significant difference in outcomes between the two groups. This research strongly suggests that the presence of leukocytes did not lead to worse results, directly contradicting the old dogma.

This leads to another fascinating concept: PRP’s effect is context-dependent. In a healthy, non-inflamed tissue, introducing a high concentration of leukocytes might indeed trigger an inflammatory response. However, in a chronically inflamed environment, like an osteoarthritic knee, PRP may act as an anti-inflammatory agent. Dr. Filardo’s work supports the idea that in an inflamed joint, even leukocyte-rich PRP can help quell the fire rather than fuel it.

The Anti-Inflammatory Power of Leukocyte-Rich PRP

To further explore this, let’s examine a compelling study published in the Journal of Orthopedic & Sports Physical Therapy. Researchers, including Brendan Lee, collected blood from 12 patients with knee OA and prepared both LR-PRP and LP-PRP from each patient. This method eliminates patient-to-patient variability and provides a direct comparison.

• What They Measured: They analyzed the levels of various biochemical mediators in both PRP preparations, including:

• • Anti-inflammatory cytokines: molecules that help reduce inflammation.
  • Pro-inflammatory cytokines: These are molecules that promote inflammation.
  • Nociceptive pain mediators: substances involved in pain signaling.

• Key Discoveries: The study found that leukocyte-rich PRP expressed significantly higher levels of anti-inflammatory mediators, including Interleukin-1 receptor antagonist (IL-1ra), IL-4, and IL-10. IL-1ra is a potent anti-inflammatory agent that directly blocks the action of the major pro-inflammatory cytokine, IL-1?. We often talk about the importance of IL-1ra in managing arthritis, and here we see that LR-PRP is a rich source of it.
• No Increase in Inflammation: Crucially, there was no significant difference in levels of the major pro-inflammatory cytokines, IL-1? and IL-6, between the LR-PRP and LP-PRP groups. There was also no difference in the levels of nociceptive pain mediators, such as nerve growth factor.

The conclusion from this molecular-level analysis is profound: leukocyte-rich PRP may be beneficial for patients with knee OA because it can deliver a powerful anti-inflammatory punch without increasing pro-inflammatory signals. This reinforces the idea that in a chronically inflamed joint, PRP’s primary role can shift to becoming powerfully anti-inflammatory.

So, where do we go from here? Perhaps the debate shouldn’t be about simply including or excluding all leukocytes. We need a much more sophisticated analysis. Instead of a blanket removal, we should focus on differential counts. We should eliminate neutrophils (a type of white blood cell often associated with acute inflammation) and focus on specific monocyte and macrophage populations, which are crucial for tissue remodeling and healing. The ratio of different leukocyte subtypes could be more important than the total count. This is a question for future research, but these papers clearly demonstrate that the old “leukocytes are bad” theory is overly simplistic.

The Numbers Game: Does Platelet Dose Matter?

If leukocyte content isn’t the deciding factor, what is? Evidence is mounting that the total number of platelets delivered to the target tissue may be the most critical variable for success. This concept isn’t new; early papers by researchers like Baskin hinted at it. In one study of 150 patients randomized to receive either PRP or hyaluronic acid (HA), both groups improved, but the PRP formulation contained approximately ten billion platelets. This high dose became a benchmark.

More Platelets, Lower Failure Rate

Dr. Giuseppe Filardo and his team explored this very question. In another well-designed study, they took 250 patients with knee OA and divided them into three groups based on the platelet concentration of their PRP injections:

• Low Platelet Group: Lower concentration of platelets.
• Medium Platelet Group: Moderate concentration of platelets.
• High Platelet Group: High concentration of platelets.

The results were clear: the groups that received higher platelet concentrations had a significantly lower failure rate. This provides direct evidence that platelet dose matters.

Meta-Analysis Confirms the Dose-Dependent Effect

Following this, the same research group published a meta-analysis—a study that pools data from multiple previous trials. They analyzed 18 randomized controlled trials focused on PRP for knee OA. Their findings solidified the dose-response relationship: PRP formulations with higher platelet concentrations led to greater pain relief and more durable improvement.

So, quite simply, the numbers count. It’s also worth noting that many commercial systems that produce higher platelet yields often concentrate white blood cells. This might be why the leukocyte debate became so confused: perhaps the positive effects observed with some LR-PRP preparations were actually due to the higher platelet dose they coincidentally contained, rather than the leukocytes themselves.

Explaining Variability in Clinical Research

This dose-dependent effect may also explain the tremendous variability we see in the PRP literature. Let’s look at two high-profile examples.

The JAMA Study: A Case of Low Dosage?

A widely cited study published in the prestigious journal JAMA in 2021 concluded that PRP was no better than a placebo (saline injection) for knee OA. This was a well-conducted, double-blind trial with 288 patients. However, when you look closer at the methods, they used a particular commercial PRP system known to produce a very low platelet yield. I have no relationship with any of these companies, but the data is public. The lack of a positive effect in this prominent study may not have been due to PRP not working, but to the platelet dose being too low to produce a therapeutic effect.

The Meniscectomy Study: Another Example of Low Yield

Similarly, another study examined the use of PRP after arthroscopic meniscectomy. This was also a double-masked, randomized trial. Here, they used a system from Arthrex known as ACP, which also yields relatively low platelet yields. And again, the study found no significant effect.

These trials, while well-designed, highlight a critical flaw in much of the existing research: the failure to standardize or even report the platelet dose. It’s like comparing studies on a new drug without knowing if patients received 10 mg or 100 mg.

The UC San Francisco Systematic Review: A Clear Dose-Response

Finally, a recent systematic review from Dr. Drew Lansdown and his team at UC San Francisco provides some of the clearest evidence to date. They analyzed 29 randomized trials of PRP for knee OA and looked at the data through the lens of platelet dosage.

• They charted the variability across all studies, which was immense.
• They separated patients into responders (those who achieved a clinically significant improvement) and non-responders.
• The responders received an average platelet dose of approximately 5 billion platelets.
• The non-responders received about half that dose, around 2.7 billion platelets.
• Furthermore, improvements in objective biomarkers (such as changes seen on MRI) also seemed greater with a higher platelet dose.

The data are becoming increasingly clear: there is a dose-response relationship between platelet count and clinical outcomes in patients with knee OA.

Integrating These Findings into Our Chiropractic and Medical Practice

At Injury Medical Clinic, these findings are not just academic—they directly inform how we approach patient care. As a Doctor of Chiropractic with advanced training as a Family Nurse Practitioner and in functional medicine, I see patients struggling with the debilitating effects of knee osteoarthritis every day. Our goal is to use the most effective, evidence-based tools available.

Our integration of chiropractic care and PRP therapy, under the medical direction of Dr. Maria Cardenas, creates a powerful synergy.

• Chiropractic Adjustments and Mobilization: Before any regenerative procedure, it’s essential to ensure the joint mechanics are optimized. Chiropractic adjustments can help restore proper alignment and mobility in the knee, hip, and spine, reducing abnormal stress on the arthritic joint. This creates a better biomechanical environment for the PRP to work effectively.
• Functional Medicine and Nutrition: We use functional medicine principles to address the systemic inflammation that often drives osteoarthritis. We analyze diet, gut health, and micronutrient status to create a personalized anti-inflammatory plan, which complements the local anti-inflammatory effects of PRP.
• Targeted PRP Therapy: Guided by the research we’ve discussed, we prioritize PRP preparations that deliver a therapeutic dose of platelets—ideally 5 to 10 billion per injection. Under the medical oversight of Dr. Cardenas, we ensure the procedure is performed safely and effectively.
• Rehabilitation and Physical Therapy: Following the PRP injection, a structured rehabilitation program is crucial. We design customized exercise protocols to strengthen the supporting muscles, improve range of motion, and protect the healing joint, ensuring long-term success and a return to function.

This comprehensive, multidisciplinary model allows us to address osteoarthritis from every angle—mechanically, biochemically, and functionally—giving our patients the best possible chance for meaningful and lasting relief. Thank you for joining me on this deep dive into the science of PRP.

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