Tuesday afternoon. Second appointment. Three weeks since the MRI. The PA pulled up an injection diagram on a tablet, the cortisone shot from two months ago still partly visible in the patient’s chart on the next screen over. The cortisone had quieted the inflammation. The cortisone had not changed the underlying tissue. The PA explained that what came next was a different kind of injection, prepared from the patient’s own blood, and built around a different premise. Repair rather than suppression.
The premise behind platelet-rich plasma, or PRP, sits inside the broader regenerative medicine field. The therapy uses platelets concentrated from a small blood draw, reinjected at the target tissue site, to deliver growth factors and other bioactive proteins that the body uses in normal tissue repair. PRP is not a cell-based therapy in the way bone marrow or adipose stem cell concentrate is. PRP is a blood-derived product. The mechanism, the preparation, and the research base each have their own profiles.
Platelets and Growth Factors: The Biology Behind PRP
Platelets are small, anucleate cell fragments in the blood that play a primary role in clotting and tissue repair. Beyond their familiar role in stopping bleeding, platelets carry hundreds of bioactive proteins in granules that release into surrounding tissue when the platelet activates. The published literature on NIH PubMed Central documents that platelets contain more than 1100 different proteins with multiple post-translational modifications, generating over 1500 protein-based bioactive factors that include growth factors, immune messengers, enzymes, and other tissue repair components.
Several growth factors drive the therapeutic premise behind PRP:
- VEGF (vascular endothelial growth factor), which supports new blood vessel formation
- PDGF (platelet-derived growth factor), which stimulates cell proliferation and migration
- TGF-β (transforming growth factor beta), which influences extracellular matrix synthesis
- IGF-1 (insulin-like growth factor 1), which supports cell growth and survival
When PRP is injected into a target tissue, the platelets activate, release their granule contents, and contribute growth factors and immunomodulatory mediators to the local environment. The mechanism is not pure cell replacement. The mechanism is biological reinforcement of the body’s own repair pathways through concentrated delivery of factors the body already uses.
How PRP Is Prepared in Clinical Settings
PRP preparation runs through a short clinical sequence, with variation in technique that affects the product the patient receives. The variation matters more than most patients first realize, since two clinics can both call their product “PRP” and deliver concentrates that differ substantially in platelet count, white blood cell content, and biological activity.
A standard preparation arc:
- Blood draw, typically 10 to 60 milliliters from the patient’s arm vein
- Centrifugation, in one or two stages, that separates blood components by density
- Collection of the platelet-rich plasma layer, with or without inclusion of leukocytes (white blood cells)
- Optional activation step, using calcium chloride or thrombin
- Reinjection at the target tissue, often under ultrasound guidance
Two technical variables shape the product profile:
- Leukocyte-rich versus leukocyte-poor PRP. The presence or absence of white blood cells in the final product affects the immunological profile and may matter differently for different target tissues. Recent meta-analyses suggest leukocyte-poor PRP is associated with more favorable response patterns for knee osteoarthritis specifically.
- Single-spin versus double-spin protocols. Double-spin systems generally produce higher platelet concentrations than single-spin approaches, with corresponding differences in growth factor delivery.
A clinic that can describe its PRP system, the platelet concentration the system produces, and the leukocyte profile of its final product is operating at the documentation level the published research describes. A clinic that markets PRP without specifying these variables is using a category label rather than a product specification.
Where PRP Has the Strongest Research Support
The PRP research base spans multiple clinical applications, with the depth of supporting data varying by target tissue. A short calibration helps:
| Application | Research support level | Common clinical use |
|---|---|---|
| Lateral epicondylitis (tennis elbow) | Stronger for chronic cases | Common |
| Knee osteoarthritis (mild to moderate) | Growing, with leukocyte-poor PRP showing favorable patterns | Common |
| Rotator cuff partial tears | Mixed, with some favorable findings for chronic cases | Common |
| Patellar tendinopathy | Promising, less consistently demonstrated | Less common |
| Achilles tendinopathy | Mixed, individual studies variable | Less common |
| Hip osteoarthritis | Limited research, less consistent findings | Less common |
| Plantar fasciitis | Mixed evidence, some favorable studies | Less common |
The AAOS PRP for Knee Osteoarthritis Technology Overview, the academy’s published guidance for the field, treats the supporting research as inconclusive due to inconsistent results across studies and lack of standardized protocols. More recent meta-analyses, including comparisons of PRP against hyaluronic acid and corticosteroids for knee osteoarthritis, have shown more favorable patterns for PRP at 12-month follow-up, particularly in patients with mild to moderate disease.
The AOSSM, in its sports medicine literature, treats PRP as effective for chronic tennis elbow and as showing promising but less consistently demonstrated patterns for Achilles and patellar tendon conditions. The clinical bottom line for the patient is that PRP has stronger documented support in some applications than in others, and the marketing claims of clinics often outpace the research support for the specific application the patient is considering.
How PRP Compares to Cortisone Injections for Joint Pain
The comparison the patient most often wants to make is between PRP and cortisone, since cortisone is the most familiar joint injection and the one many patients have already tried before considering PRP. The two work through different mechanisms, on different timescales, with different effect profiles.
| Dimension | Cortisone | PRP |
|---|---|---|
| Mechanism | Anti-inflammatory, suppresses local immune response | Pro-repair, delivers growth factors |
| Onset of effect | Days to one to two weeks | Weeks to months |
| Duration | Weeks to a few months in most cases | Months, with response patterns extending beyond a year in some studies |
| Cartilage effect | May contribute to cartilage degradation with repeated use | Generally not associated with cartilage harm |
| Number of injections | Limited per joint per year due to cartilage concerns | Series of one to three injections common |
| Cost | Lower, often insurance-covered | Higher, generally out-of-pocket |
| Research base | Long-established, with documented short-term effects | Growing, with stronger findings in specific applications |
Cortisone remains useful for short-term symptom control. PRP attempts something different, with a longer onset and a different mechanism, and the patient who has cycled through repeated cortisone injections without lasting response may be a candidate for the alternative. The choice depends on the specific condition, the patient’s response history, and the clinical fit the consultation establishes.
What Patients Typically Experience During and After Treatment
The procedure day for PRP runs through a familiar sequence for patients who have had blood drawn or received an injection before, with one or two additions specific to PRP.
A typical sequence:
- Blood draw at the start of the appointment, usually 10 to 60 milliliters depending on the system
- A 15 to 30 minute wait while the centrifuge processes the sample
- The injection itself, typically under ultrasound guidance for joint or tendon targets
- Brief observation period before discharge
The post-procedure experience runs through several phases. The first 24 to 48 hours often involve more soreness at the injection site than the underlying condition was producing before, since the procedure is meant to stimulate local inflammatory and repair processes. The first one to two weeks typically include activity restrictions, with most patients returning to baseline activity by week two to three. Functional response, when it occurs, often becomes visible between weeks four and twelve, with continued improvement possible up to six months.
Two practical points worth carrying:
- The post-injection soreness is generally a feature, not a bug. The pro-repair mechanism involves local inflammatory response. Anti-inflammatory medications such as NSAIDs are usually avoided for the first week or two for this reason, since they may dampen the very response the procedure is meant to stimulate.
- The response timeline runs longer than cortisone. Patients evaluating PRP at three weeks tend to undervalue the procedure. Patients evaluating at three to six months tend to have a clearer read.
Why PRP May Not Be the Right Choice for Some Patients
PRP is not universally indicated, and several factors shape candidacy in ways the consultation should surface:
- Severe, advanced disease. For high-grade osteoarthritis, particularly Kellgren-Lawrence grade IV, the underlying joint structure may be too compromised for the regenerative premise to apply meaningfully.
- Active infection or systemic immunological condition. Active infection is generally a contraindication, and certain systemic conditions may complicate the response.
- Anticoagulant therapy. Patients on blood thinners may need protocol adjustments or may not be candidates depending on the anticoagulant and the procedure setting.
- Specific blood disorders. Conditions affecting platelet function or count may make the procedure unsuitable.
- Realistic expectations. The patient who is hoping for an outcome cortisone delivers, on a timeline cortisone delivers, may not be a candidate for what PRP is designed to do. The procedures answer different questions.
When a clinic recommends PRP without surfacing these candidacy factors, the consultation is operating below the candidacy-evaluation level. When a clinic walks through them and concludes that PRP is or is not the right fit for the patient’s specific case, the consultation is operating at the level the procedure deserves.
Tuesday afternoon at the orthopedic office ends with the PA closing the tablet and handing the patient a printout that lists the platelet concentration the system produces and the post-injection protocol for the first two weeks. The injection diagram is no longer the abstract image the appointment started with. The patient knows what platelet concentration the system delivers and what the post-injection week tends to look like. None of those items is a guarantee. All of them together often tend to be the difference between an injection chosen on the basis of what cortisone is not and one chosen on the basis of what PRP is designed to do.
Important note on regenerative therapy: No regenerative therapy is fully predictable in outcome, and any guidance that promises otherwise overstates what current evidence supports. The realistic question for a patient considering treatment is what level of preliminary or emerging evidence the patient and clinician find sufficient and what specific practices keep the decision aligned with that evidence base.
Sources:
- Platelet-Rich Plasma for Knee Osteoarthritis Technology Overview, American Academy of Orthopaedic Surgeons
- Platelet-Rich Plasma for Osteoarthritis: Sports Medicine Update, American Orthopaedic Society for Sports Medicine
- Platelet-Rich Plasma: Molecular Mechanisms, Actions and Clinical Applications, NIH PubMed Central