Answering the two questions patients ask most
Once patients decide PRP is worth considering for knee osteoarthritis, the two most common follow-up questions are practical: how many injections will I need, and how long can I expect the benefit to last? Recent trial data gives a clearer answer to both than was available even a few years ago.
Durability of benefit
The 2025 American Journal of Sports Medicine meta-analysis of 18 randomised trials found that PRP’s advantage over placebo was present at every measured time point from 1 month through 12 months. However, a sub-analysis by platelet concentration found an important distinction: high-platelet preparations maintained a clinically meaningful benefit all the way to 12 months, while low-platelet preparations lost their clinically meaningful edge earlier, around the 6-month mark, even though a statistical difference from placebo could still be detected.
A separate 2025 retrospective study of 140 patients reported pain scores roughly halving and function scores improving significantly at the six-month mark, with only a handful of mild, self-limiting side effects such as temporary post-injection soreness.
This pattern — meaningful medium-term relief that may fade without a repeat course — is broadly consistent with how PRP is understood to work: it modulates inflammation and stimulates a healing response but does not permanently alter the structural course of osteoarthritis.
How many injections, and how often to repeat
Most of the higher-quality randomised trials in the current evidence base used a short course of 2 to 3 injections spaced roughly one to two weeks apart, rather than a single injection, and this multi-injection protocol is what most of the strongest efficacy data is based on.
Because benefit tends to plateau around 6 to 12 months (again, depending on preparation), many treating specialists plan for the possibility of a repeat course roughly once a year for patients who respond well, similar to how hyaluronic acid is often re-dosed periodically.
A separate 2025 retrospective study of 140 patients reported pain scores roughly halving and function scores improving significantly at the six-month mark, with only a handful of mild, self-limiting side effects such as temporary post-injection soreness.
This pattern — meaningful medium-term relief that may fade without a repeat course — is broadly consistent with how PRP is understood to work: it modulates inflammation and stimulates a healing response but does not permanently alter the structural course of osteoarthritis.
What this means for you
- Expect a course of injections (commonly 2–3), not a single shot, if following the protocols behind the strongest trial evidence.
- Realistic expectation: meaningful relief for roughly 6 to 12 months, with higher-platelet preparations trending toward the longer end.
- If benefit fades, a repeat course — rather than assuming the treatment has permanently failed — is a reasonable and evidence-consistent next step.
- PRP works best as part of an overall plan that includes activity modification and appropriate strengthening, not as a stand-alone fix.
This article summarises published research for general information and does not replace individual medical advice. Outcomes vary between patients — talk to your treating specialist about whether PRP is appropriate for your specific condition.
References
Bensa A, Previtali D, Sangiorgio A, et al. PRP Injections for the Treatment of Knee Osteoarthritis: The Improvement Is Clinically Significant and Influenced by Platelet Concentration — A Meta-analysis of Randomized Controlled Trials. Am J Sports Med. 2025;53(3):745–754.
Retrospective cohort study of PRP for knee osteoarthritis, 140 patients, 6-month outcomes. 2025.