Review patient history for anticoagulation therapy. Obtain written informed consent. Confirm absence of active skin infection at the injection site. Perform baseline pain and functional assessment. No fasting required.
Apply ice pack to the knee for 15 minutes post-procedure. Advise patient to avoid strenuous activity or high-impact exercise for 48 hours. Resume normal activity as tolerated. Monitor for signs of infection such as excessive swelling or fever. Discharge patient immediately post-observation.
Comprehensive Clinical Guide: Intra-articular Knee Injection (Platelet-Rich Plasma)
1. Introduction & Overview
Platelet-Rich Plasma (PRP) therapy has emerged as a cornerstone of regenerative orthopedics. As a biological, autologous treatment, PRP utilizes the patient’s own blood to stimulate healing and reduce inflammation within the knee joint. Unlike traditional corticosteroid injections, which primarily mask pain, PRP aims to modulate the intra-articular environment, potentially slowing the progression of degenerative joint disease.
This guide serves as a clinical reference for orthopedic specialists, sports medicine physicians, and clinical staff involved in the administration and management of intra-articular PRP injections for knee pathology.
2. Technical Specifications & Mechanism of Action
PRP is defined as a volume of autologous plasma that has a platelet concentration above baseline. The therapeutic efficacy is predicated on the release of growth factors from the alpha-granules of platelets.
The Biological Cascade
Upon injection, activated platelets degranulate, releasing a concentrated cocktail of bioactive proteins, including:
* TGF-β (Transforming Growth Factor-beta): Promotes collagen synthesis and matrix remodeling.
* PDGF (Platelet-Derived Growth Factor): Stimulates angiogenesis and fibroblastic mitogenesis.
* VEGF (Vascular Endothelial Growth Factor): Enhances vascular permeability and endothelial cell proliferation.
* IGF-1 (Insulin-like Growth Factor-1): Supports chondrocyte proliferation and cartilage matrix maintenance.
Classification of PRP
Not all PRP is identical. Clinical outcomes are often dependent on the preparation protocol:
| Classification | Platelet Concentration | Leukocyte Content | Clinical Primary Use |
| :--- | :--- | :--- | :--- |
| L-PRP | High | High | Tendinopathy / Soft Tissue |
| P-PRP | High | Low | Intra-articular (Knee) |
| L-PRP (Rich) | Moderate | High | Chronic Degeneration |
Expert Note: For intra-articular knee injections, Leukocyte-Poor PRP (P-PRP) is generally preferred to minimize the inflammatory response associated with neutrophils within the joint space.
3. Clinical Indications & Patient Selection
PRP is indicated for patients who have failed conservative management (physical therapy, NSAIDs, weight loss) but are not yet candidates for, or wish to delay, total knee arthroplasty (TKA).
Primary Indications
- Knee Osteoarthritis (OA): Specifically Kellgren-Lawrence Grades I, II, and III.
- Meniscal Tears: Degenerative tears in the white-white zone or non-surgical traumatic tears.
- Chondromalacia Patellae: Early-stage cartilage softening.
- Post-Surgical Healing: Adjunct therapy following arthroscopic meniscectomy or ligament reconstruction.
Patient Exclusion Criteria
- Active systemic infection or local skin infection at the injection site.
- Platelet count <100,000/μL.
- History of metastatic cancer or active malignancy.
- Recent corticosteroid injection (requires 4-6 week washout period).
4. Pre-Operative Preparation & The Procedure
Patient Preparation
- Medication Review: Patients must discontinue NSAIDs (Ibuprofen, Naproxen, Aspirin) at least 7 days prior to the procedure to ensure optimal platelet function.
- Hydration: Advise patient to increase water intake 48 hours prior to blood draw.
- Informed Consent: Clearly outline that PRP is often considered "off-label" or "investigational" by some insurance providers and that outcomes are variable.
The Procedural Steps
- Blood Draw: Venipuncture is performed (typically 20–60mL of whole blood).
- Centrifugation: The blood is placed in a centrifuge. The goal is to separate the red blood cells (RBCs) from the plasma and buffy coat.
- Preparation: The platelet-rich layer is extracted via sterile technique.
- Injection:
- Position patient supine with the knee in 30° of flexion (using a bolster).
- Perform a sterile prep with Chlorhexidine or Betadine.
- Guidance: Ultrasound-guided injection is the gold standard, targeting the suprapatellar pouch or the lateral mid-patellar portal to ensure intra-articular placement.
- Technique: A 22-gauge needle is used to enter the joint capsule. If an effusion is present, perform arthrocentesis prior to the injection.
5. Post-Operative Recovery Protocol
The post-injection period is critical for maximizing the biological benefit of the growth factors.
- Days 1–3: Relative rest. Avoid strenuous activity. Use ice packs for 15 minutes, 3 times daily, to manage post-injection soreness. Strictly avoid NSAIDs for at least 2 weeks post-injection, as they may inhibit the inflammatory-mediated healing process.
- Days 4–14: Gradual return to activities of daily living. Gentle range-of-motion exercises.
- Weeks 2–6: Initiation of structured physical therapy focusing on quadriceps strengthening and proprioceptive training.
- Long-term: Evaluation at 3 months for functional improvement.
6. Risks, Side Effects, and Complications
While PRP is autologous and carries a low risk of systemic reaction, the following must be monitored:
* Post-Injection Flare: An acute inflammatory response lasting 24–72 hours is common and represents the activation of the healing cascade.
* Infection: Septic arthritis is a rare but serious risk (<0.1% incidence).
* Neurovascular Injury: Rare, usually associated with improper needle placement.
* Synovitis: Transient synovial irritation.
7. Alternative Treatments
When discussing PRP, the clinician should provide a comparative analysis of standard care:
* Corticosteroids: Provide rapid, short-term pain relief (weeks) but may negatively affect chondrocyte health over time.
* Hyaluronic Acid (HA) Viscosupplementation: Acts as a lubricant and shock absorber; better for mechanical symptoms than biological healing.
* Prolotherapy: Uses dextrose to induce a controlled inflammatory response.
* Bone Marrow Aspirate Concentrate (BMAC): A more invasive regenerative option containing mesenchymal stem cells, often used for advanced degenerative cases.
8. Frequently Asked Questions (FAQ)
1. How many injections are required?
Most clinical studies suggest a series of 1 to 3 injections, spaced 2–4 weeks apart, for optimal outcomes in knee OA.
2. Is the procedure painful?
The blood draw is routine. The injection itself can cause pressure or aching, but most patients tolerate it well with local anesthesia (lidocaine) applied to the skin.
3. Will insurance cover this?
Coverage varies significantly. Many commercial insurers categorize PRP as "experimental." Always verify benefits prior to scheduling.
4. How long until I see results?
Unlike steroids, PRP is not an immediate pain reliever. Patients typically report improvement between 4 and 8 weeks post-injection.
5. Can I take Tylenol if I am in pain?
Yes. Acetaminophen is the preferred analgesic post-procedure as it does not interfere with platelet function or the inflammatory healing cascade.
6. Are there specific supplements I should stop?
Yes, high-dose Omega-3 fish oils and Vitamin E supplements should be paused for 7 days prior, as they can also impact platelet aggregation.
7. How long does the effect last?
Clinical durability is variable. Many patients experience relief for 6 to 12 months, though this depends on the severity of the underlying osteoarthritis.
8. Does age affect the outcome?
While younger patients with higher-quality platelets may see faster results, studies indicate that PRP is effective across multiple age demographics for knee OA.
9. What is the difference between PRP and Stem Cells?
PRP contains growth factors derived from platelets. Stem cell therapies (like BMAC) involve harvesting progenitor cells that have the potential to differentiate into various tissue types.
10. Can I drive after the procedure?
Most patients can drive immediately afterward, provided they are not experiencing significant post-injection discomfort.
9. Conclusion
Intra-articular PRP injection represents a paradigm shift in the management of knee osteoarthritis. By harnessing the body's intrinsic healing mechanisms, clinicians can offer a viable, low-risk alternative to invasive surgery. Success is highly dependent on patient selection, precise ultrasound-guided delivery, and strict adherence to the post-injection recovery protocol. As regenerative medicine continues to evolve, PRP remains the bedrock of non-surgical biologic intervention for the knee.
Disclaimer: This guide is intended for educational and professional clinical reference only. It does not replace institutional policy, clinical judgment, or specific manufacturer instructions for PRP preparation kits.