PRP knee injections: everything you actually need to know

A PRP knee injection is a one-hour office visit: a blood draw, fifteen minutes in a centrifuge, and an ultrasound-guided injection of your platelets into the knee. Dr. Paul Morton, a fellowship-trained hip and knee surgeon, uses it for mild-to-moderate arthritis and select tendon and meniscus problems. Expect a sore knee for a day or two, a series of three, and relief often lasting six months or longer in responders.

Platelet-rich plasma is made from your own blood — nothing is added and nothing foreign is introduced. Platelets are the cells that rush to any injury first, and they carry a payload of growth factors, including PDGF (platelet-derived growth factor) and TGF-β1 (transforming growth factor beta), that signal cells to repair tissue and help regulate inflammation.

A PRP treatment simply concentrates that machinery: a small tube of blood, a spin in the centrifuge, and an injection of the platelet-rich layer into your knee. No laboratory-grown cells, no donor material. The clinical detail — and the evidence, with sources named — is on the PRP procedure page.

Here is the honest version: PRP does not regrow cartilage, and no reputable surgeon will promise that it does. What it can do is calm the inflammatory chemistry inside an arthritic or irritated knee, so the joint hurts less and tolerates activity better. Think of it as changing the environment inside the knee, not rebuilding its parts.

The best-studied use is mild-to-moderate knee arthritis — that page covers who responds and how PRP compares with cortisone and gel. PRP is also used for stubborn tendon problems around the knee, such as jumper's knee, and for select degenerative meniscus tears; a torn meniscus that locks or catches is a mechanical problem that needs its own evaluation for meniscus repair, not an injection. A knee that is already bone-on-bone has less to gain, and for those knees an honest conversation about knee replacement serves you better than another shot.

A little preparation protects your result — and one part of it protects your safety.

• Blood test. Dr. Morton may order a complete blood count (CBC) to confirm your platelet levels before the first injection.
• Prescription blood thinners and antiplatelet drugs. Never stop these on your own. If you take one — for a heart stent, atrial fibrillation, a prior clot, or any other reason — the office coordinates with your prescribing physician or cardiologist to decide whether a brief pause is safe, or whether PRP should wait.
• Over-the-counter anti-inflammatories (ibuprofen, naproxen, aspirin) and blood-thinning supplements such as fish oil, flaxseed oil, and bromelain are usually held for about a week beforehand, because they can blunt the healing response PRP depends on. The office confirms exact timing for you.
• Not a candidate if you have a low platelet count or abnormal platelet function, an active infection, severe anemia, or active cancer.
• Bring a photo ID, your insurance card, a medication list, and any prior X-rays or MRI; if your imaging was taken in Hawai‘i, the office can usually retrieve it electronically. Wear or bring shorts.

Plan for about an hour, all in the office. The injection itself takes seconds; most people feel pressure and fullness rather than sharp pain. There is no general anesthesia, no incision, and no need for someone to drive you home unless you'd simply prefer the company. If a needle makes you nervous, tell us — a calm, unrushed visit is part of the job.

Expect the treated knee to feel sore, stiff, and full for a day or two. That's not a complication — it's the point. PRP works partly by provoking a healing response, so a brief flare is normal, and because anti-inflammatory medications can blunt that response, you'll hold NSAIDs and lean on ice and acetaminophen instead.

PRP is offered everywhere from med-spas to franchise clinics, and the injection itself is the easy part. The judgment is not. Getting a real result from PRP starts long before the needle — with an accurate diagnosis. Is your knee pain actually arthritis, or is it a torn meniscus that PRP can't fix? How advanced is the wear? Is there something else going on that a shot would only mask?

A fellowship-trained joint surgeon answers those questions first, places the injection accurately into the right target, and — most importantly — tells you plainly when PRP isn't your best option. If biologics won't help you, someone who can also offer conventional injections and surgery has every reason to say so. PRP here sits inside a complete joint-preservation program, not on a sales menu.

Be clear-eyed on cost: most insurers still classify PRP as investigational, so it is typically a cash-pay treatment. You'll receive a written quote for the recommended series — usually three injections over about six weeks — before you decide, with no packages pushed. The consultation and X-rays that decide candidacy are often covered, and if a hyaluronic acid gel injection fits your knee and your plan covers it, the office handles the authorization so the covered part stays covered.

PRP is usually not the right choice if your knee is end-stage bone-on-bone, if you have an active infection, certain blood disorders, or a bleeding tendency, or if you're seeking a one-and-done cure rather than a management tool.

What happens next. Start with an orthopedic consultation or call (808) 439-6201. PRP is offered at Pacific Bone & Joint in Honolulu (Ala Moana), West O‘ahu (Kunia), Hilo, and Kona; managed-care and Medicaid/Quest plans may need a referral from your primary care physician, which the office checks before your visit. If travel isn't practical, a telehealth consultation can review your imaging first, with the injection done in clinic.