The real difference is not potency. It is what you go through to get it.

CHOOSING BETWEEN THE TWO

Both treatments take tissue from you, concentrate it, and put it back the same day. That is where the similarity ends. They differ in what is delivered, how it is obtained, what it costs, and — the point most often skipped — in infection risk and therefore in whether antibiotics belong anywhere near them.

Where each comes from

PRP comes from a venous blood draw. A tube of blood, a centrifuge, a concentrate of platelets, back into the target under image guidance. Total time about an hour, and the draw itself is unremarkable.

BMAC comes from your iliac crest. Marrow is aspirated through a trocar under local anesthetic, concentrated, and injected. It is a genuinely different order of procedure, and the harvest site typically aches for several days — sometimes more than the joint being treated.

What is in each

PRP delivers concentrated platelets and the growth factors in their alpha granules: PDGF, TGF-β, VEGF, EGF, IGF-1. No cells that could become tissue — signal only.

BMAC delivers a mixed nucleated cell population plus platelets and signaling molecules. The mesenchymal stromal fraction that gives it its reputation is a small minority, well under one percent of nucleated cells. It is more than PRP contains, and considerably less than the phrase “stem cell treatment” implies.

Infection risk, and the antibiotic decision

One correction to a claim this page used to make more loosely. Pooled randomized data across six trials and 860 patients puts the complication rate for BMAC at about 42% against 41% for comparator injections — no significant difference, with effusion the most common event. Marrow is not more likely to cause a problem. What differs is severity: an infection seeded at or near bone is a more serious problem than a soft-tissue one, which is what changes the technique and the antibiotic decision.

This is the difference that changes clinical practice, and it should be stated without hedging.

BMAC carries a more serious infection risk, not a more frequent one — pooled randomized data puts complication rates at about 42% against 41% for comparator injections, with no significant difference. The distinction is severity if it happens, because an infection near bone is a harder problem than a soft-tissue one. Harvesting marrow means entering bone, and an infection seeded at or near bone is a far more serious problem than a soft-tissue infection — longer treatment, worse consequences, occasionally surgical. That elevated risk is mitigated by prophylactic antibiotics, and they are used for this procedure.

PRP carries a low infection risk, and antibiotics do not help it. A venous draw and a soft-tissue injection performed under sterile technique do not reach the threshold where prophylaxis changes outcomes. Giving antibiotics anyway adds gastrointestinal side effects, allergy risk and resistance pressure while subtracting nothing from the risk. So we do not give them.

If a clinic consents you for both procedures with a single risk conversation and a single antibiotic policy, it has not distinguished between them, and that is worth noticing before you agree to either.

Discomfort, honestly

PRP: a blood draw, a local anesthetic, an injection, and a flare lasting a few days at the treated site.

BMAC: the same at the treated site, plus a harvest. Local anesthesia handles the skin and periosteum well, but the sensation of marrow being aspirated is distinctive and briefly unpleasant for most people. The crest is sore to lie on for several days. People should be told this plainly rather than discovering it.

What the head-to-head evidence shows

Fewer direct comparisons exist than either side of the argument implies. In knee osteoarthritis the picture has moved. Earlier head-to-head trials generally found no statistically significant difference in pain and function at twelve months. A more recent single-center trial of 175 patients spanning Kellgren–Lawrence grades II to IV found otherwise: BMAC produced the greatest quality-of-life gains, ahead of both PRP and hyaluronic acid, with the difference most marked in physical health and mobility.

The reconciliation is about disease stage rather than one being wrong. The two run close in earlier joints, and marrow pulls ahead as the joint gets worse — which is also where the four-year BMAC data in grade III and IV knees was earned. So for an earlier-stage joint, where the results are comparable and BMAC is the more demanding procedure costing several times more, that is a real argument for starting with PRP. For a joint further along, it stops being one.

For tendinopathy there is essentially no comparative evidence favoring BMAC, and PRP has a substantial literature. For osteonecrosis the position reverses: marrow-derived treatment has the better case there than anywhere else discussed on this site.

A side-by-side summary

• Source. PRP: venous blood. BMAC: iliac crest marrow.
• Delivered. PRP: platelets and growth factors. BMAC: mixed cells plus signal.
• Infection risk. PRP: low. BMAC: higher, and bone-adjacent.
• Antibiotic prophylaxis. PRP: no, it does not help. BMAC: yes, it does.
• Recovery from the procedure itself. PRP: a flare. BMAC: a flare plus a sore harvest site.
• Cost. PRP lower; BMAC several times higher.
• Evidence in tendinopathy. PRP substantially better supported.
• Evidence in knee arthritis. Comparable at a year.
• Evidence in osteonecrosis. BMAC better supported.

How we actually choose

PRP first for earlier-stage joints, because it performs comparably there at lower cost and with far less to endure. Marrow where the joint is further along, where PRP has already been tried and underdelivered, or where the indication is specific to it — osteonecrosis of the femoral head has no plasma equivalent. BMAC considered when the joint is further gone, when PRP has produced a partial response worth building on, when subchondral bone is part of the picture, or when the diagnosis is osteonecrosis.

Escalating on evidence is a better sequence than starting with the larger procedure because it is described more impressively. If someone recommends BMAC as a first move for a tennis elbow, ask them why.

What neither one does

Neither regrows cartilage in an arthritic joint. Neither repairs a large retracted tendon tear. Neither substitutes for a joint replacement where the structure is the problem — though both are used in end-stage disease to buy time and reduce medication burden — and neither removes the need for the loading program afterward. Any comparison that leaves those out is selling rather than explaining.

Why “more cells” is not obviously better

The intuitive argument for BMAC is that it delivers cells and PRP does not, so it must do more. That intuition assumes the cells engraft and become tissue, and the current understanding is that they largely do not.

What the delivered cells appear to do is signal — releasing growth factors, cytokines and extracellular vesicles that modulate inflammation and influence the cells already living in the tissue — and then disappear within days. If signaling is the mechanism, then a preparation dense in growth factors is competing on the same terms, which is exactly what the head-to-head results suggest.

That does not make cell content irrelevant. It does mean the cell count is a proxy for signaling capacity rather than a measure of how much new tissue you are buying, and it explains why a several-fold price difference has not translated into a several-fold outcome difference in any trial so far.

Practical differences on the day

• Time. PRP is comfortably an hour. BMAC takes longer, with the harvest, processing and positioning.
• Positioning. The harvest requires lying prone or on your side for a period, which matters if that is difficult for you.
• Driving home. Most people drive after PRP. After a marrow harvest, particularly with any sedation, plan for someone to take you.
• Time off. PRP rarely needs any. BMAC often warrants a day, and longer if your work involves lifting or prolonged sitting on the harvest side.
• Repeatability. A second PRP injection is a minor undertaking. A second marrow harvest is not, and that asymmetry should factor into a plan that may need more than one round.

Choosing between the two

Is BMAC stronger than PRP?

Not demonstrably, in knee arthritis at a year. It is more invasive and more expensive. What BMAC actually is.

Why antibiotics for one and not the other?

Entering bone justifies prophylaxis; a soft-tissue injection does not, and antibiotics do not reduce PRP’s risk. Risks and side effects.

Is BMAC the same as stem cell therapy?

It is what most clinics mean by it, though the stem cell fraction is very small. What that phrase actually means.

Which should I start with?

PRP, for most indications. Escalate on evidence rather than on marketing. Candidacy.

Related reading

• Bone marrow aspirate concentrate
• PRP compared with stem cell treatments
• Risks and side effects
• PRP for knee osteoarthritis