Platelet-Rich Plasma Injections for Knee Pain: What Patients Should Know
What PRP Is and How It Works
Platelet-rich plasma (PRP) is a preparation derived from your own blood. After a small volume of blood is drawn — typically 30–60 mL — it is placed in a centrifuge that separates red blood cells from plasma and concentrates the platelets. Platelets are not just clotting agents; they carry a dense store of growth factors, including platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-β), and vascular endothelial growth factor (VEGF). These proteins regulate cell proliferation, tissue repair, and new blood vessel formation.
When this concentrated preparation is injected into the knee, the growth factors interact with local cells to modulate inflammation and stimulate repair processes in cartilage, tendon, and other joint structures. Because PRP is autologous — made from the patient's own blood — the risk of allergic reaction or disease transmission is essentially zero.
The procedure itself is straightforward. Blood is drawn, processed, and injected into the knee under sterile technique, often with ultrasound guidance to confirm accurate placement. The entire process takes about an hour, and patients typically return home the same day.
When PRP Is Appropriate for the Knee
PRP is most commonly considered for two knee conditions: knee osteoarthritis and patellar tendinopathy (jumper's knee).
In knee osteoarthritis, PRP injections target the inflammatory mediators within the joint fluid that accelerate cartilage breakdown. Several randomized controlled trials and systematic reviews have found that PRP outperforms hyaluronic acid injections and placebo for pain relief and functional improvement in early-to-moderate osteoarthritis, particularly in younger patients and those with less severe joint degeneration. Results generally last six months to a year, and some patients benefit from repeat treatment.
In patellar tendinopathy, PRP addresses the degenerative tendon changes that underlie this chronic overuse condition. Evidence supports PRP as an effective adjunct to physical therapy when conservative care alone has not produced adequate improvement.
PRP is not a substitute for surgery when structural damage — such as a large meniscus tear or grade IV cartilage loss with bone-on-bone contact — is the primary problem. Your surgeon will help determine whether PRP is appropriate based on imaging findings, symptom severity, and your prior treatment history.
Setting Realistic Expectations
PRP is not a cure for knee arthritis. It does not reverse cartilage loss or regenerate the joint surface. What it can do is reduce pain, decrease the inflammatory burden within the joint, and improve functional capacity — often for a meaningful period of time. Many patients describe gradual improvement over the four to eight weeks following injection as the growth factors exert their effects.
Patients who combine PRP with a concurrent physical therapy program tend to experience better outcomes than those who rely on the injection alone. Building strength in the quadriceps and hip abductors reduces compressive loads on the joint and makes the biological environment more favorable for the repair processes PRP initiates.
Not every patient responds equally. Factors that predict better outcomes include younger age, lower body mass index, earlier-stage disease, and adherence to rehabilitation.
The Procedure and Recovery
Most patients tolerate PRP injection well. There may be increased soreness at the injection site for two to five days following the procedure — a normal response to the concentrated growth factors. This temporary flare typically resolves on its own without requiring specific treatment beyond ice and limited activity.
You should avoid anti-inflammatory medications (NSAIDs and corticosteroids) for two to four weeks before and after PRP, as they can neutralize the growth factor activity that makes PRP effective.
Your surgeon will discuss the appropriate number of injections for your situation. Some patients benefit from a series of two or three injections spaced a few weeks apart; others respond well to a single treatment.
If you're experiencing knee pain and want to explore whether PRP is an appropriate option for you, the specialists at Maryland Orthopedic Specialists can help. Call (301) 515-0900 or [schedule an appointment online](https://www.mdorthospecialists.com/contact).
