Osteoarthritis (OA) is a musculoskeletal condition that commonly affects the knee and/or hip joint(s). There is no cure for OA and most treatment options focus on alleviating pain and preventing functional decline. Hyaluronic acid (HA) and corticosteroids are common intra-articular therapies for OA. If conservative treatments fail, a common procedure for advanced hip or knee OA is a total joint arthroplasty.
Platelet-rich-plasma (PRP) injections are a biologic therapy for treatment of OA receiving increased research interest. PRP is an autologous blood product with a higher concentration of platelets than whole blood which is created by centrifuging it. PRP is easy to use, minimally-invasive, safe, and does not have as many regulatory requirements as traditional therapeutic pharmaceuticals.
The authors in the article, Platelet-Rick Plasma for the Management of Hip and Knee Osteoarthritis, provide a review of the literature and clinical guidelines regarding the use of PRP as a treatment option for hip and knee OA.
Proposed Biological Mechanisms of PRP in the Context of Osteoarthritis
Osteoarthritis is a disease which causes breakdown of joint tissue including cartilage, bone, ligament, and muscle. The pathophysiology of OA is thought to be caused by an imbalance between anabolic and catabolic mechanisms and is characterized by the presence of increased inflammatory cells.
Although the biology of PRP is not completely understood, it may be able to interfere with the progression of OA by promoting an anabolic response. PRP has been shown to have an initial proinflammatory action followed by a reduction in inflammatory molecules. There is evidence that PRP has analgesic effect as well as a role in inflammation. PRP enhances the joint repair and slows deterioration of tissue.
Effects on Osteoarthritis Symptoms
The first randomized control trial (RCT) on PRP was published in 2012. Fifteen knee OA and three hip OA RCT’s have been published since 2012. The studies are difficult to interpret and methodological concerns include questionable blinding, failure to conceal allocation, selective reporting, small sample sizes and inappropriate statistical analyses. While some studies have shown promise, more rigorous studies need to be performed to determine if PRP is clinically significant.
Three studies compared PRP to a placebo and all reported significant benefits of PRP at 6 or 12 months but small sample sizes limit the influence of the studies. Most studies reported greater improvements in clinical outcomes with PRP over HA for knee OA. These benefits have been seen up until 12 months but appear to decline over time. While results may be statistically significant, there is question about the clinical relevance of the improvements.
Little research attention has been given to comparing PRP to treatments commonly used in the management of OA, such as exercise and analgesics. One small study in knee OA found no difference between PRP and exercise plus transcutaneous electrical nerve stimulation while another trial showed that PRP resulted in better clinical outcomes compared to acetaminophen.
While most studies have evaluated PRP as a monotherapy for OA, PRP could be given in combination with other therapies in clinical practice. It has been postulated that PRP may have an additive effect with HA. In a knee OA study, the combination of PRP and HA led to better pain and function outcomes at one year when compared with HA alone and better function outcomes at three months when compared with PRP alone. Another hip OA trial found that PRP alone was actually more effective than the combination of PRP and HA at two-, six- and 12-months follow-up.
Effects on Joint Structure
One study, reported that nearly 50% of their 13 patients with knee OA showed improved cartilage volume (assessed using ultrasonography) at the lateral and medial femoral condyles, as well as the intercondylar notch, at six months following three PRP injections administered at monthly intervals. Another uncontrolled trial involving 15 patients with no or early knee OA received a single PRP injection. The study found no significant structural worsening at 12-months follow-up (assessed using magnetic resonance imaging) in 73% of those with medial compartment involvement, 80% of those with patellofemoral involvement and 83% of those with lateral compartment involvement. Due to the lack of a control group in both studies, no conclusions can be made at this time about the ability of PRP to slow structural disease progression in those with knee or hip OA.
Current clinical guidelines either do not mention or are unable to recommend the use of PRP for the management of OA, based on the lack of high-quality studies and questions regarding statistical significance. Clarity around the efficacy and appropriate protocol for PRP is required before clinical guidelines are likely to be updated.
Overall, the authors of this study recommend that knee OA be managed through education, exercise and, if appropriate, weight loss. If PRP is offered, it is suggested that clinicians inform patients about PRP’s inconclusive evidence so patients can make informed decisions about whether or not to consent to this currently unproven therapy.
Basic science and clinical studies suggest that PRP could be a promising non-operative treatment for OA but more robust studies are needed. Evidence from studies of low to moderate quality show that intra-articular PRP injection therapy is a safe treatment with potential to provide symptomatic benefit for OA up to 12 months, and more effective than HA. While there is some evidence that younger patients and those with less structural change may be more responsive to PRP, further research is needed to establish whether older patients respond effectively to PRP. Effects of PRP on OA structural disease progression are unknown due to lack of studies in this area. No recommendations can currently be made about the optimal PRP protocol for patients with OA.
Physical Therapy First Implications
Physical therapy remains a valuable option for reducing pain and improving function in knee and hip OA while additional research is conducted on alternative treatment options. While the therapists at Physical Therapy First remain up to date on the latest research, it is important to talk with your physician regarding research implications for alternative treatments such as PRP when considering treatment options for knee and hip OA.
Bennell, K., Hunter, D., Paterson, K. (2017). Platelet-Rich Plasma for the Management of Hip and Knee Osteoarthritis. Complementary and Alternative Medicine, Current Rheumatology Report. 19:24