Biologic treatments are collections of proteins, growth factors, and cells from a donor that can be injected to treat a variety of clinical conditions. Most treatments are stand-alone injections, but certain patients may benefit from biologic augmentation during surgical procedures. The three main categories of biologic treatment are platelet-rich plasma (PRP), stem cells, and cartilage transplantation.

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Platelet-rich plasma (PRP) therapy has emerged as a promising treatment modality for knee osteoarthritis (OA), offering a less invasive alternative to surgery for managing pain and improving function. The rationale behind its use stems from the concentrated growth factors and cytokines present in platelets, which stimulate tissue regeneration and reduce inflammation. These factors, including platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-β), and vascular endothelial growth factor (VEGF), are believed to promote cartilage repair, reduce pain, and improve joint function in individuals with knee OA. However, the efficacy of PRP remains a topic of ongoing investigation, with varying results reported across different studies. Several studies have evaluated the effectiveness of PRP injections for knee OA, revealing statistically significant improvements in pain and functional scores compared to placebo in many cases [1, 2], although the magnitude of effect varies considerably and further research with standardized protocols is needed.

Prognostic indicators for successful PRP therapy are not definitively established, but factors such as the severity of OA, the presence of significant inflammatory components, and the patient's overall health status are likely to influence the outcome. Patients with early-stage OA and minimal structural damage may experience greater benefit than those with advanced disease characterized by significant cartilage loss and joint deformity. The presence of significant inflammation could also affect the effectiveness of PRP. The expected outcomes of PRP therapy include pain reduction, improved functional capacity, and enhanced quality of life, with a gradual improvement in symptoms over several weeks post-injection. The duration of the therapeutic effect can vary, with some studies reporting sustained benefits for up to 12 months or longer, while others observe a shorter duration.

The recovery timeline following PRP injection is generally short, with mild discomfort or swelling at the injection site for a few days that typically resolves without intervention. Most patients return to normal activities within a few days to a week, although strenuous exercise should be avoided initially. PRP, however, is not a cure for knee OA; it aims to slow disease progression and improve symptoms, not reverse the underlying degenerative process. Surgical interventions may still be necessary if PRP therapy fails to provide adequate relief. Limitations in the current literature include small study sizes, inconsistent PRP preparation, and the potential influence of the placebo effect. Large-scale, randomized controlled trials with standardized protocols and longer follow-up are crucial to better understand PRP's efficacy.

Comparing PRP to other common intra-articular injections for knee OA, such as hyaluronic acid (HA) and cortisone, reveals distinct mechanisms and outcomes. HA injections act primarily as viscosupplementation, lubricating the joint and improving its shock-absorbing capacity. Cortisone injections, on the other hand, exert a strong anti-inflammatory effect, providing rapid but often short-lived pain relief. PRP, unlike HA, aims to stimulate tissue regeneration, offering a potentially longer-lasting benefit, although this remains under investigation [2]. Compared to cortisone, PRP avoids the potential systemic side effects associated with corticosteroids and potentially provides a more sustained effect. However, cortisone offers much more rapid and noticeable pain relief. The optimal choice of treatment depends on the individual patient's clinical presentation, stage of OA, and response to prior therapies. Some clinicians may even utilize a combination of these therapies depending on the patient's needs. A direct comparison of PRP and HA is presented in Gilat et al. [2], highlighting the distinct mechanisms and potential benefits of each approach.

In conclusion, PRP therapy offers a promising, minimally invasive treatment option for knee OA. While the evidence supports a potential benefit in pain reduction and functional improvement, further research is needed to establish optimal protocols. Individualized treatment plans should consider the patient's specific clinical presentation and expectations, with careful consideration given to the advantages and limitations when comparing PRP to other injection therapies such as HA and cortisone.

References:

[1] Sanchez, M., et al. (2014). Platelet-rich plasma for the treatment of knee osteoarthritis: A meta-analysis. Osteoarthritis and Cartilage, 22(10), 1532-1540.

[2] Gilat, R., Haunschild, E.D., Knapik, D.M. et al. Hyaluronic acid and platelet-rich plasma for the management of knee osteoarthritis. International Orthopaedics (SICOT) 45, 345–354 (2021). https://doi.org/10.1007/s00264-020-04801-9