Optimal PRP Preparation for Knee Joint Infiltration

1. Blood Collection

2. Centrifugation Protocol — The Core Decision

Double-Spin is Superior for Platelet Concentration

• Spin 1 (soft spin): 100–160 × g for 10–15 min → separates red blood cells (RBCs) from platelet-rich plasma supernatant
• Spin 2 (hard spin): 250–400 × g for 10–15 min → pellets platelets, discard upper platelet-poor plasma (PPP), resuspend pellet in small volume

Critical platelet concentration threshold: ASRA 2025 analysis of 8 clinical trials found all 4 positive trials used PRP at ≥3× baseline platelet concentration; all 4 negative trials had only 1.2–1.7× baseline. Target ≥3× baseline (ideally ~1,000,000–1,500,000 platelets/µL).

3. Leukocyte Content — LP-PRP vs LR-PRP

Current Consensus (2024–2026):

Practical recommendation:

4. Activation Status

• Exogenously activated PRP showed significantly greater pain relief (SMD −1.05, 95% CI −1.58 to −0.52) and functional improvement (SMD −1.21, 95% CI −1.75 to −0.67)
• Non-activated PRP did not show statistically significant benefit

Activation agents:

• Calcium chloride (CaCl₂) — most widely used and studied; mimics the natural coagulation cascade, triggering alpha-granule degranulation
• Calcium gluconate — alternative
• Thrombin — effective but risk of bovine thrombin antibodies if bovine-derived; autologous thrombin preferred
• Activation is done immediately before injection (within minutes), not during preparation

5. Volume and Injection Protocol

6. Pre- and Post-Injection Protocol

• Avoid NSAIDs for at least 5 days before blood draw and injection (inhibit platelet function via COX inhibition)
• Post-injection: Avoid NSAIDs for at least 1–2 weeks — critical, as PRP's mechanism requires prostaglandin-mediated signalling pathways
• Activity restriction: 24–48 hours of relative rest post-injection; avoid high-impact loading
• Corticosteroids: Should not be used within 4–6 weeks before PRP (suppress the local immune environment required for PRP action)

7. Optimal PRP Preparation Summary

Blood draw: 20–60 mL in ACD anticoagulant (19–21G needle)
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Spin 1 (soft): ~130 × g × 10–15 min
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Transfer platelet-rich supernatant (avoid buffy coat for LP-PRP)
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Spin 2 (hard): ~300–400 × g × 10–15 min
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Discard upper PPP, resuspend platelet pellet in 5–6 mL plasma
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Verify: platelet count ≥3× baseline (ideally ~1,000,000–1,500,000/µL)
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Activate with CaCl₂ immediately before injection
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Inject under ultrasound guidance into knee joint

Key Takeaways

1. Double-spin centrifugation is superior to single-spin for platelet concentration and durability of benefit.
2. Platelet concentration ≥3× baseline is the most critical predictor of clinical success — more important than leukocyte content.
3. LP-PRP is preferred for knee joints due to equivalent efficacy and lower post-injection inflammatory reaction; the joint's intra-articular environment is susceptible to cytokine-driven inflammation from granulocytes.
4. Exogenous activation with CaCl₂ significantly improves outcomes over non-activated PRP.
5. Avoid NSAIDs perioperatively — this single step is frequently overlooked and can undermine the entire treatment.
6. 3 weekly injections appears optimal; the benefit extends to at least 12 months and may reach 60 months for cartilage preservation.

RPM = 1000 × √(RCF ÷ (1.118 × r_cm))

RPM Values for Standard 10 cm Rotor

Most Cited Protocol-Specific RPM Values

Practical standard for a generic bench centrifuge with 10 cm rotor:

• Spin 1: 1200 RPM × 10 min
• Spin 2: 1800 RPM × 10 min

Important Caveats

1. Always convert RCF → RPM using your specific rotor radius. If your rotor radius differs from 10 cm, use:

   RPM = 1000 × √(RCF ÷ (0.01118 × r_mm))

2. Do not exceed 400 × g (~1900 RPM at 10 cm) in either spin — higher speeds activate and degranulate platelets prematurely, destroying growth factor payload before injection.
3. Acceleration and deceleration should be set to low/medium — abrupt stops (brake on) shear platelets. Use no-brake or slow-brake deceleration.
4. Temperature: Room temperature (20–22°C) — do not refrigerate the centrifuge. Cold temperatures induce platelet shape change and premature activation.
5. If your machine only displays × g (RCF), target 130 × g for Spin 1 and 340 × g for Spin 2 regardless of rotor size.