What are platelet-rich plasma (PRP) injections?

What Are Platelet-Rich Plasma (PRP) Injections?

Platelet-rich plasma (PRP) injections are an autologous blood-derived therapy that delivers concentrated platelets—typically at supraphysiological levels (at least 2-3 times above normal)—to injured or degenerating tissues, where activated platelets release growth factors and cytokines that promote tissue regeneration, angiogenesis, and healing. 1, 2

Preparation and Composition

PRP is prepared through a straightforward centrifugation process of the patient's own blood:

• Blood is drawn and anticoagulated, then centrifuged using gravitational techniques or standard cell separators to concentrate platelets based on density gradients 3, 1
• The resulting product contains concentrated platelets, plasma proteins, cytokines, thrombin, and various growth factors 4
• Different preparation methods (varying g-force, centrifugation time, and activation techniques) produce significantly different products with variable platelet yields, concentration, purity, and activation status 5
• The International Society on Thrombosis and Haemostasis has established a classification system that categorizes PRP based on leukocyte content (L-PRP if ≥1%), red blood cell content (Red-PRP if ≥10%), activation method, platelet concentration, and preparation technique 3

Biological Mechanisms of Action

Upon activation, PRP releases bioactive proteins and growth factors from platelet α-granules that directly stimulate multiple regenerative pathways:

• Promotes local angiogenesis (new blood vessel formation) in treated tissues 5, 1
• Stimulates stem cell recruitment, cell migration, proliferation, and differentiation 5, 1
• Enhances deposition of matrix proteins, particularly collagen, supporting structural tissue repair 5, 1
• Creates a fibrin scaffold that acts as a temporary three-dimensional matrix for cellular regeneration and tissue remodeling 5, 1
• Key growth factors include vascular endothelial growth factor (VEGF) and tissue growth factor β (TGF-β), while inflammation is modulated through inhibition of the nuclear factor-κB pathway 6

Clinical Applications

PRP has been used across multiple medical specialties, though evidence quality varies considerably by indication:

Established or Promising Applications:

• Dental and maxillofacial procedures: enhancing bone regeneration and wound healing, particularly in poorly vascularized areas 1
• Knee osteoarthritis: recent randomized controlled trials demonstrate superiority over both corticosteroids and hyaluronic acid for symptom relief 6
• Patellar tendinopathies and lateral epicondylitis: convincingly shown to be efficacious 6
• Rotator cuff repair (small to medium tears): substantial analgesic effects and enhanced healing rates 6
• Anterior cruciate ligament reconstruction: improved autograft maturation, reduced donor site morbidity, and better allograft incorporation 4

Applications with Uncertain Evidence:

The International Society on Thrombosis and Haemostasis rates the following as uncertain (median scores 4-6.5 out of 10):

• Burn injuries, tendon injuries, acute muscle injuries 3
• Bone healing in orthopedics 3
• Sports injuries and osteoarthritis treatment (though newer evidence for osteoarthritis is more favorable) 3
• Skin aging prevention as beauty therapy 3

Critical Limitations and Caveats

The field suffers from poor standardization that directly impacts clinical outcomes:

• Preparation methods, terminology, purity, content, and quality of PRP products vary dramatically across studies and clinical settings 5
• This variability makes mechanism elucidation challenging and results in inconsistent clinical efficacy 5
• Many clinical trials have been conducted without clear definition or quantification of PRP biological properties, making it difficult to compare results or establish optimal protocols 5
• The International Society on Thrombosis and Haemostasis emphasizes that future trials must be appropriately controlled, adequately powered, and include rigorous quality control of platelet preparations 3

Safety Profile

PRP demonstrates excellent safety characteristics due to its autologous nature:

• Minimal immunogenicity risk and negligible foreign body reactions since it's derived from the patient's own blood 7, 2
• Few complications reported in clinical literature 7, 8
• Proper sterile technique during preparation and application remains essential 1, 7
• Commercial PRP preparation devices should be used according to manufacturer specifications 1

Practical Considerations

For clinicians considering PRP therapy:

• The autologous origin, ease of preparation, cost-effectiveness, and excellent safety profile make PRP an attractive therapeutic option 3, 4
• However, the lack of standardization means that specific protocols, dosing, timing, and application techniques remain poorly defined 4
• Further mechanistic studies are needed to identify the optimal combination of bioactive factors for maximal regenerative activity 3, 5
• High-quality randomized controlled trials with standardized protocols and objective outcome measures are necessary to support broader clinical applications 1, 7