Biologic Injections: Evidence and Expectations

Platelet-rich plasma and cell-based therapies are widely marketed. Where the evidence is genuinely supportive, and where it is not yet.

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Platelet-rich plasma, bone marrow aspirate concentrate, and various “stem cell” preparations are among the most aggressively marketed treatments in orthopedics. Some have real, if modest, evidence behind them. Others are sold well ahead of the science. Knowing which is which is the whole point of this article.

What these treatments actually are

Platelet-rich plasma (PRP) — your own blood, centrifuged to concentrate platelets and the growth factors they release. Preparation methods vary widely, which is a major reason study results conflict.

Bone marrow aspirate concentrate (BMAC) — marrow drawn usually from the pelvis and concentrated. Contains a small population of progenitor cells alongside growth factors.

“Stem cell” products — a marketing term more than a clinical one. Commercially sold amniotic and umbilical products generally contain no living stem cells.

If a clinic promises cartilage regrowth from an injection, the claim is ahead of the evidence.

Where the evidence is reasonably supportive

Knee osteoarthritis — PRP outperforms hyaluronic acid and saline for pain and function in multiple trials, with benefit measured in months. It modifies symptoms; it does not regrow cartilage.

Chronic tendinopathy — lateral elbow tendinopathy has the strongest data; patellar and gluteal tendinopathy are promising.

Plantar fasciitis — randomized trials comparing PRP to corticosteroid injection generally show similar early relief but longer-lasting benefit from PRP at six to twelve months.

Hip osteoarthritis — smaller and less consistent than the knee literature, but several trials report pain and function gains comparable to or better than hyaluronic acid.

Achilles tendinopathy — evidence is mixed for the mid-substance form, but PRP is a reasonable option in patients who have failed a proper eccentric loading program.

Rotator cuff tendinopathy — useful for partial tears and chronic tendon pain that has not responded to therapy; it is not a substitute for repair of a full-thickness tear.

As an adjunct in surgery — PRP applied at the time of rotator cuff repair or meniscal repair has shown modest improvements in healing rates in some series.

Where it is not yet convincing

Advanced, bone-on-bone arthritis — injections do not restore a joint surface that is gone.

Acute ligament tears as a substitute for reconstruction when reconstruction is indicated.

Why the results vary so much

Much of the confusion around biologics comes down to the fact that no two injections are the same. Spin speed, spin time, whether white blood cells are included, the volume injected, and the number of sessions all differ between clinics, and none of it is standardized. Two trials can both study “PRP” and be testing meaningfully different products. That variability is the single biggest reason the literature looks inconsistent, and it is why a result reported in one paper does not automatically transfer to the injection offered down the street.

Patient selection matters just as much. A biologic injection asks the body to do the healing; it works best where there is still tissue worth supporting. Early or moderate arthritis with preserved joint space, a chronic tendon problem that has plateaued despite good rehabilitation, a patient who is otherwise healthy and not smoking — those are the settings where the modest benefit reported in trials is most likely to show up in real life.

Cost, coverage, and honest expectations

Because most biologic injections are not covered by insurance, patients are usually paying out of pocket — often for a series rather than a single treatment. That makes clarity about the goal essential. A realistic aim is several months of reduced pain and better function, which can be genuinely valuable: it may make rehabilitation possible, delay an operation, or carry someone through a season. It is not cartilage regrowth, and it is not a substitute for a reconstruction or repair when one is clearly indicated.

Used selectively — the right patient, the right joint, honest expectations — biologics are a reasonable part of a non-operative plan. Used as a universal answer, they are an expensive way to postpone a decision.

This article is general information, not medical advice for your specific case. Discuss your own imaging, history, and goals with Dr. Kunze or your treating physician.

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