Platelet-Rich Plasma and the Biologic Toolbox
- PRP is an AUTOLOGOUS blood product: the patient's own blood is centrifuged to CONCENTRATE platelets (typically several-fold above baseline) in a small plasma volume; activated platelets release a cocktail of GROWTH FACTORS (PDGF, TGF-β, VEGF, IGF-1, EGF, bFGF) intended to promote healing.
- PRP is prepared by centrifuging anticoagulated blood to separate plasma, the platelet/leukocyte 'buffy coat', and red cells; single- versus double-spin protocols, the anticoagulant, and whether platelets are activated (e.g. with calcium/thrombin) all vary - which is why products differ widely.
- The most important classification axis is LEUKOCYTE content: LEUKOCYTE-POOR (LP) versus LEUKOCYTE-RICH (LR) PRP; formal systems include PAW (Platelets, Activation, White cells) and Mishra.
- Best evidence is in KNEE OSTEOARTHRITIS: level-1 meta-analyses show intra-articular PRP gives better pain and function than hyaluronic acid at 6-12 months, without increased adverse events, and LEUKOCYTE-POOR PRP appears superior to leukocyte-rich for knee OA.
- In TENDINOPATHY the evidence is mixed but PRP is used (e.g. recalcitrant lateral epicondylitis); evidence for rotator cuff repair augmentation and many other indications is inconsistent.
- The wider ORTHOBIOLOGICS toolbox includes bone marrow aspirate concentrate (BMAC), mesenchymal stromal cells, autologous conditioned serum (ACS) and hyaluronic acid - all limited by HETEROGENEITY and a lack of standardisation/regulation, the central caveat for the whole field.
- “Name the growth factors: PDGF, TGF-β, VEGF, IGF-1, EGF, bFGF - released from platelet alpha-granules on activation.
- “For knee OA, level-1 data favour PRP over HA, and leukocyte-POOR over leukocyte-rich PRP (less inflammatory intra-articularly).
- “The honest exam answer always flags the lack of standardisation - platelet dose, leukocyte content, activation and spin protocols all vary, so trials are hard to compare.
Preparations differ in platelet concentration (dose), leukocyte content (LP vs LR), red-cell contamination, activation (none vs calcium/thrombin), spin protocol (single vs double), and volume. Two "PRP" injections can be biologically very different products.
This heterogeneity is the main reason trial results conflict and meta-analyses are limited. Reporting systems (PAW, Mishra, PLRA) exist to standardise description, and good studies now specify the leukocyte content and platelet dose so results can be compared.
What PRP Is & What It Delivers
Platelet-rich plasma (PRP) is an autologous preparation in which the patient's own blood is centrifuged to concentrate platelets (commonly several-fold above the whole-blood baseline) into a small plasma volume. Platelets store growth factors in their alpha-granules; on activation they release PDGF (platelet-derived growth factor), TGF-β, VEGF (angiogenesis), IGF-1, EGF and bFGF, among others. The rationale is that delivering a bolus of these factors to an injured or degenerate tissue promotes cell proliferation, matrix synthesis, angiogenesis and modulation of inflammation - in short, augments the local healing environment.
| 0 | 1 |
|---|---|
| PDGF | Chemotaxis and proliferation of mesenchymal cells; angiogenesis |
| TGF-β | Matrix synthesis (collagen); chondrocyte/osteoblast effects; modulates inflammation |
| VEGF | Angiogenesis (new blood vessel formation) |
| IGF-1 | Cell proliferation/survival; matrix production |
| EGF / bFGF | Proliferation, angiogenesis and tissue remodelling |
Preparation
PRP is made at the point of care: anticoagulated whole blood is centrifuged so that it separates by density into plasma (top), a thin buffy coat of platelets and leukocytes (middle), and red cells (bottom). A single spin ('soft') concentrates platelets in plasma while keeping some red/white cells; a double spin ('hard', then a second spin) achieves higher platelet concentration and lets the operator include or exclude the leukocyte layer to make leukocyte-rich or leukocyte-poor PRP. The product may be used as a liquid (often activated with calcium chloride/thrombin to trigger granule release) or as a fibrin matrix (PRF).
Classification (Leukocyte-Poor vs Leukocyte-Rich)
Low white-cell content ('pure' PRP). Generally preferred for intra-articular use (e.g. knee OA) because leukocytes (and their catabolic enzymes/cytokines) can provoke a more inflammatory flare in a joint. Level-1 data favour LP-PRP over LR-PRP for knee OA.
Higher white-cell content; more pro-inflammatory. Has been advocated for some tendinopathies (where a controlled inflammatory/anabolic stimulus may help), though comparative evidence is limited.
Because products vary so much, classification systems standardise reporting: PAW (Platelets, Activation, White cells - DeLong), Mishra, and PLRA (Platelet, Leukocyte, Red cell, Activation). For the exam, the headline distinction is LP vs LR, and you should always state the leukocyte content when describing a study's PRP.
Clinical Evidence
This is where the evidence is best. Level-1 meta-analyses show that intra-articular PRP gives better pain relief and function than hyaluronic acid (HA) at 6 and 12 months, with no increase in adverse events, and that leukocyte-poor PRP is associated with better outcomes than leukocyte-rich PRP. PRP is therefore used as a non-operative option, particularly in mild-to-moderate OA, to provide symptomatic relief and potentially delay surgery (it does not regrow cartilage or replace arthroplasty for end-stage disease).
The Wider Orthobiologics Toolbox
| 0 | 1 | 2 |
|---|---|---|
| PRP | Autologous concentrated platelets + growth factors | Knee OA (LP-PRP), tendinopathy; best-studied |
| Bone marrow aspirate concentrate (BMAC) | Concentrated marrow (cells + growth factors) | Cartilage/bone defects, OA; variable evidence |
| Mesenchymal stromal cells (MSCs) | Culture-expanded or concentrated stromal cells | Investigational; regulatory constraints |
| Autologous conditioned serum (ACS) | Serum enriched in anti-inflammatory IL-1Ra | OA/radiculopathy; limited evidence |
| Hyaluronic acid (HA) | Viscosupplement (not strictly a 'biologic') | Knee OA - the usual comparator for PRP |
| BMP-2/7 | Recombinant osteoinductive growth factors | Spinal fusion / selected nonunion (see Bone Signaling) |
Across all orthobiologics the limiting issue is lack of standardisation and regulation: dose, cell/ platelet content, processing and activation vary between systems and studies, outcomes are heterogeneous, and many indications rest on low-level evidence. The mature position is to use the best-supported indications (e.g. LP-PRP for knee OA), specify the preparation, counsel honestly about uncertainty and cost, and avoid overselling unproven uses.
Evidence & Key Studies
Platelet-rich plasma versus hyaluronic acid for knee osteoarthritis: a systematic review and meta-analysis of randomized controlled trials
- Meta-analysis of 18 level-1 RCTs (811 PRP vs 797 HA patients): mean WOMAC improvement was significantly higher with PRP (44.7%) than HA (12.6%).
- Several trials showed significantly less pain (VAS) and better IKDC scores with PRP at latest follow-up.
- Leukocyte-POOR PRP was associated with significantly better subjective IKDC scores than leukocyte-rich PRP.
Platelet-rich plasma versus hyaluronic acid in the treatment of knee osteoarthritis: a meta-analysis
- Meta-analysis of 20 RCTs: intra-articular PRP reduced pain (WOMAC/VAS) more effectively than HA at 6 and 12 months.
- PRP gave better functional recovery (WOMAC function) at 1, 3, 6 and 12 months than HA.
- PRP did not increase the risk of adverse events compared with HA.
According to PubMed, the knee-OA efficacy statements (PRP superior to HA; leukocyte-poor better than leukocyte-rich) come from the cited level-1 meta-analyses. The growth-factor list and preparation/ classification details are standard, well-established descriptions used throughout the orthobiologics literature; the lack of standardisation is a consistently reported limitation.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 55-year-old with mild-to-moderate knee osteoarthritis asks about a PRP injection. What is PRP, how is it made, and what does the evidence say compared with hyaluronic acid?”
“What are the main limitations of the PRP/orthobiologics evidence base, and what other orthobiologics might you mention?”
Mnemonics & Memory Aids
PRP-VIDE
Hook:PRP-VIDE: the platelet factors (PDGF, TGF-β, VEGF, IGF-1, EGF, bFGF) and the standardisation caveat.
LP-JOINT
Hook:LP-JOINT: leukocyte-poor PRP into the joint is the best-supported PRP use.
What it is
- Autologous concentrated platelets (several-fold above baseline) in plasma
- Releases PDGF, TGF-β, VEGF, IGF-1, EGF, bFGF from alpha-granules
- Made by centrifugation -> plasma / buffy coat / red cells
Classification
- Leukocyte-poor (LP) vs leukocyte-rich (LR) - the key axis
- Pure PRP (liquid) vs platelet-rich fibrin (PRF, matrix)
- Reporting systems: PAW (DeLong), Mishra, PLRA
Evidence
- Knee OA: level-1 PRP > HA at 6-12 months; LP-PRP > LR-PRP; no extra adverse events
- Tendinopathy (e.g. lateral epicondylitis): mixed but used when conservative care fails
- Most other indications: variable/low-level evidence
Wider toolbox & caveat
- BMAC, MSCs, ACS (IL-1Ra), HA comparator, recombinant BMP
- Central problem: lack of standardisation/regulation
- Counsel honestly; specify the preparation; use best-supported indications