What it is
Platelet-rich plasma is made from you. A sample of blood is drawn, spun in a centrifuge to separate it by density, and the platelet-rich fraction is drawn off. That concentrate is then injected into the joint or tendon being treated.
Platelets do more than clot. They carry a range of growth factors involved in signalling tissue repair, and the premise of PRP is to deliver a concentrated dose of those signals directly into a tissue that is failing to repair itself adequately.
Where the evidence is, and where it is not
This is the part most sites skip, and it is the part worth reading.
Reasonably supportive: mild to moderate knee osteoarthritis, where several trials show benefit over placebo and over hyaluronic acid, sustained over months. Lateral epicondylitis (tennis elbow) and some other tendinopathies, where the results have been encouraging particularly compared with steroid injection over the medium term.
Weak or unsupportive: severe, bone-on-bone osteoarthritis. PRP does not regrow cartilage that has gone. Someone with an end-stage joint who is offered PRP is being sold something.
Genuinely uncertain: a good deal else. Preparation protocols vary widely between practices, which makes studies hard to compare and is a real limitation of the field rather than a quibble.
Dr. D’Alessio will tell you which of those categories your problem falls into. If it is the second, she will say so.
The appointment
Blood is drawn, as for a routine test. It is centrifuged while you wait — this is most of the forty-five minutes. The injection itself takes a few minutes and is placed with imaging guidance where the target requires it.
Anti-inflammatory medication is generally stopped for a period before and after, because suppressing the inflammatory response works against the mechanism you are paying for. You will be given specific instructions.
Afterwards
Expect an ache, sometimes a pronounced one, for a few days. That is consistent with the intended response. Reduced activity for a short period, then a graded return.
Improvement is gradual, building over six to twelve weeks. Judging it at two weeks will mislead you in both directions.
The framing that matters
PRP is an adjunct. A knee that receives PRP and no change in strength, load or weight has received one input out of four. The rehabilitation programme is not an optional extra sold alongside — in a practice run by a physician board-certified in Physical Medicine & Rehabilitation, it is the main event, and the injection is there to make it possible.