Why is PRP Treatment Important for Knee OA?
There is a long chain of events in cartilage breakdown, but early in the process, inflammatory mediators are produced that lead to further breakdown of the joint and surrounding tissues. There are treatments in traditional medicine that dampen symptoms but fail to reverse the disease process. Total knee replacement is effective for late-stage OA, but over one third of joint recipients experience chronic pain. Poor outcome rates are estimated to be 20% (Beswick, 2012).
Clearly, it is important to treat and reverse OA before the late stage when joint replacement is the only option.
PRP Described
PRP is obtained from the patient’s own blood, which is centrifuged one or two times to obtain platelet concentrations that are one to three times greater than whole blood. The one-spin system has a short preparation time, while the two-spin system concentrates the buffy coat layer and results in a higher platelet concentration but takes longer to prepare.
Platelets contain growth factors that respond in a site-specific manner. Approximately 70% of these growth factors are secreted within the first ten minutes of administration. These factors and other proteins stimulate chondrocyte and stem cell proliferation and dampen inflammation. Tissue growth factor-β (TGF-β) stimulates stem cells to differentiate into cartilage cells and suppresses a potent inflammatory cytokine (IL-1). Insulin-like growth factor-1 (IL-1) promotes proliferation of cartilage cells and cartilage matrix. Bone morphogenic protein (BMP) assists in chondrocyte migration, and fibroblast growth factor (FGF) plays a major role in cartilage repair. Platelet-derived growth factor (PDGF) increases cartilage cell proliferation. Vascular endothelial growth factor stimulates the growth of new blood vessels, thereby increasing nutrient flow to the injured area.
All PRP is not the same. It can be prepared with low white cell counts (leukocyte-poor) or high white cell counts (leukocyte-rich). There is controversy over these preparations, as some believe the leukocyte-rich preparations lower the risk of infection, while others believe leukocyte-rich preparations enhance pro-inflammatory cytokines and enzymes. Most of the studies in the literature document positive outcomes with leukocyte-poor preparations, and these preparations are usually less painful than leukocyte-rich preparations.
Results
Laboratory studies have shown positive effects of PRP on cartilage cell proliferation and collagen II production. PRP appears to increase hyaluron production (the lubricating fluid of the joint) and to support stem cell survival and proliferation. PRP also contains lubricin, a component that contributes to cartilage integrity.
With respect to drugs, leukocyte-poor PRP is documented as having significantly better and more sustained outcomes than acetaminophen. The effects of PRP are comparable to corticosteroid injections in relieving pain in late-stage OA, but PRP effects are sustained up to 12 months versus 4 months for steroids. Furthermore, PRP has none of the toxic effects of steroid drugs.
According to Cook (2018), saline injections have a powerful placebo effect with reported beneficial outcomes lasting up to six months. It is crucial, therefore, that interventional therapies outperform saline injections. Multiple randomized controlled studies have consistently shown PRP to be more effective than saline injections. Some studies showed positive PRP effects up to 12 months.
Several studies compared PRP to Visco supplementation with hyaluronic acid. Twelve studies reported superior outcomes with PRP, while three studies reported no difference between the two. Leukocyte-poor PRP was found to be more effective than hyaluron, with PRP showing decreased levels of inflammatory cytokines at 12 weeks. There is some indication that PRP may be more effective in less severe cases of knee OA.
Clinical Application
PRP injections are usually administered as a series of injections, a week or up to three months or more apart. Patients are instructed to apply ice to the site and refrain from exercise for a week. Based on the author’s experience, patients report pain relief for six to 12 months following the three-injection protocol. It is not known how many PRP injections are necessary for each patient. It may be that the number of injections needed should be based on OA severity, as some patients with mild OA improve after only one or two injections. PRP therapy is safe, and it is effective in many patients.
Summary
Leukocyte-poor PRP significantly improves pain and function in knee OA. It compares favorably to other currently available therapies, especially in milder forms of OA. It is safe, effective, minimally invasive, and can be used early in the treatment of osteoarthritis.
References
Cook, C. & Smith, P. (2018). Clinical update: Why PRP should be your first choice for injection therapy in treating osteoarthritis of the knee. Current Reviews Musculoskeletal Med, 11:583-592.
Beswick A, Wylde V, Gooberman-Hill R, et al. (2012). What proportion of patients report long-term pain after total hip or knee replacement for osteoarthritis? A systematic review of prospective studies in unselected patients. BMJ Open, 2 (e000435). doi: 10.1136/bmjopen-2011-000435.
