Platelet-rich plasma (PRP) is a non-surgical option for individuals experiencing persistent knee discomfort. This treatment utilizes components from the patient’s own blood to encourage healing within the joint. This article explores what PRP is and examines the clinical evidence regarding its effectiveness for knee conditions, particularly osteoarthritis.
Understanding Platelet-Rich Plasma
Platelet-rich plasma is a concentration of platelets derived from the patient’s own blood, which is then injected into the injured area. Platelets are cell fragments known primarily for their role in blood clotting, but they also contain hundreds of signaling proteins and growth factors. Normal blood typically contains about 150,000 to 450,000 platelets per microliter, while PRP is prepared to contain a concentration significantly above this baseline, often two to nine times higher.
The preparation process begins with drawing a small amount of blood from the patient, similar to a standard blood test. This blood sample is then placed into a device called a centrifuge. Spinning the blood at high speeds separates its components into distinct layers: red blood cells at the bottom, platelet-poor plasma at the top, and a thin middle layer called the “buffy coat” containing the concentrated platelets and white blood cells.
The practitioner extracts this concentrated platelet layer to create the final PRP solution for injection. The exact composition of the resulting PRP can vary significantly depending on the preparation technique used, such as whether a single or double centrifugation is performed. This variability affects the final platelet concentration and whether the product is leukocyte-rich (contains more white blood cells) or leukocyte-poor (contains fewer white blood cells).
The Biological Rationale
The theoretical foundation for using PRP stems from the high concentration of growth factors released by the activated platelets. These growth factors, such as Platelet-Derived Growth Factor (PDGF), Transforming Growth Factor-beta (TGF-β), and Insulin-like Growth Factor-1 (IGF-1), are naturally involved in tissue repair and regeneration. When injected into the knee joint, these molecules are intended to initiate or accelerate the body’s healing cascade.
The signaling proteins promote the proliferation of cells like chondrocytes, which maintain cartilage health. By delivering a concentrated dose of these factors, PRP aims to reduce the destructive inflammatory environment present in degenerative conditions like osteoarthritis. This anti-inflammatory action helps restore the balance between cartilage breakdown and production. These factors also stimulate the recruitment of reparative cells and promote new blood vessel formation (angiogenesis), supporting tissue restoration within the joint.
Clinical Evidence and Efficacy
The question of whether PRP works for knees is largely focused on its efficacy in treating knee osteoarthritis (OA), the most common application. Current research suggests that PRP injections offer a statistically and clinically significant benefit over a placebo for patients with mild to moderate knee OA. Multiple meta-analyses of randomized controlled trials indicate that PRP can provide noticeable improvements in pain reduction and functional outcomes, such as walking and daily activities.
The duration of this improvement is often substantial, with patients reporting sustained pain relief and better function for up to 6 to 12 months following the injection. The effectiveness of the treatment appears to be directly related to the quality of the product, as studies show that high-platelet concentration PRP provides superior and more durable relief compared to lower-concentration preparations. When compared to other common treatments like hyaluronic acid injections, PRP frequently shows a superior benefit in terms of both pain relief and functional improvement over the long term.
However, the efficacy of PRP is not uniform across all knee conditions or all stages of OA. The evidence for PRP’s benefit in cases of severe, end-stage OA with extensive cartilage loss is limited and inconsistent. The lack of standardized preparation protocols across the medical field also makes it difficult to compare results between different studies. Despite these variations, the bulk of clinical evidence supports PRP as a safe and effective treatment choice for individuals with early to moderate knee OA.
The Treatment Process and Recovery
The PRP procedure for the knee is performed in an outpatient setting and typically takes less than 30 minutes, though preparation time can vary. After the blood is drawn and the plasma is processed in the centrifuge, the concentrated solution is ready for injection. The physician often uses ultrasound guidance to ensure the precise delivery of the PRP directly into the joint space or to the specific injured tendon or ligament.
Patients may experience mild to moderate discomfort during the injection, and the area is often numbed with a local anesthetic beforehand. Following the procedure, it is common to have mild soreness, swelling, or temporary stiffness at the injection site for the first one to two days. This temporary discomfort is a sign that the body’s healing response has been activated.
Patients are generally advised to rest the knee and avoid strenuous activity for the first 24 to 48 hours. It is usually recommended to avoid non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, during the initial recovery period, as these medications can potentially interfere with the platelet activity.
Light activity and gentle range-of-motion exercises may be introduced within the first week, with a gradual increase in activity over the following weeks. Noticeable improvements in pain and function typically begin to emerge between three to six weeks, with peak benefits often observed around two to three months as the regenerative process takes hold.