PRP vs. Cortisone Injections for Knee Osteoarthritis: Which Lasts Longer?

If you have knee osteoarthritis and your physician has offered an injection, you are almost certainly choosing between two options: a corticosteroid ("cortisone") shot, or platelet-rich plasma (PRP). They are often presented as interchangeable. They are not. They work through different biology, on different timelines, at very different price points.

The short version: corticosteroid tends to relieve pain faster, within days, but the effect commonly fades over weeks to a few months. PRP tends to take several weeks to do anything noticeable, but across randomized trials and systematic reviews it more often retains an advantage at the six- and twelve-month marks. Neither regrows cartilage. Neither is a cure. Both can be reasonable, and the better choice depends on your joint, your timeline and your goals.

How a corticosteroid injection actually works

A corticosteroid is a potent anti-inflammatory. Injected into the joint space, it suppresses the inflammatory cascade that drives synovitis — the swelling of the joint lining that produces much of the day-to-day pain in osteoarthritis. It downregulates inflammatory signaling, reduces effusion and, for many people, produces genuine relief within two to five days.

What it does not do is change the structural situation. Cartilage loss, meniscal degeneration and bone remodeling continue. The medication is managing a symptom, competently and quickly, while the underlying joint carries on as before. That is a legitimate and sometimes ideal goal — particularly when a knee is acutely inflamed and you cannot start rehabilitation until the flare calms down.

There is also a dose ceiling. Most clinicians limit repeat corticosteroid injections in the same joint, commonly to a few per year, because the available evidence raises concerns about cumulative effects on cartilage with frequent, repeated use over time.

How PRP works, and why it is slower

PRP is made from your own blood. A sample is drawn, spun in a centrifuge to concentrate platelets, and the resulting preparation is injected into the joint. Platelets are not just clotting cells — they are storage vessels for growth factors and signaling proteins that participate in tissue repair and in modulating the local inflammatory environment.

The mechanism is therefore biological rather than purely pharmacological. Instead of shutting down inflammation with a drug, PRP is intended to shift the signaling environment inside the joint toward a less inflammatory, more repair-oriented state. That process is not instant. Most protocols warn patients that meaningful change appears somewhere between four and twelve weeks, and that the first week can include a temporary increase in soreness as the joint responds.

A practical complication worth knowing: PRP is not a standardized product. Platelet concentration, the presence or absence of white blood cells (leukocyte-rich versus leukocyte-poor), spin protocol and injection volume all vary between clinics. Much of the inconsistency in the published literature likely reflects this variability rather than a simple yes-or-no answer about whether PRP works.

What the evidence actually shows

Systematic reviews and meta-analyses comparing intra-articular PRP with corticosteroid in knee osteoarthritis have converged on a reasonably consistent pattern.

1. In the first one to four weeks, corticosteroid generally performs as well as or better than PRP for pain reduction. It is the faster option, and that is not really disputed.
2. Between three and six months, the two often look similar, with corticosteroid's advantage having faded.
3. At six to twelve months, several randomized trials and pooled analyses report better pain and function scores in the PRP groups, though effect sizes vary and some trials find no significant difference.
4. Evidence for structural or cartilage-level change with either treatment remains weak. Imaging-based outcomes are inconsistent, and no one should be promised cartilage regrowth from an injection.
5. Studies consistently show larger benefit in mild-to-moderate osteoarthritis than in severe, bone-on-bone disease.

The honest summary is that PRP appears to offer more durable symptomatic benefit in appropriately selected patients, while corticosteroid offers faster but shorter relief — and that the quality of the underlying trials is uneven, with heterogeneous PRP preparations making direct comparison harder than it should be.

Side effects and risks of each

Corticosteroid injections are generally well tolerated. The recognized issues include a post-injection flare in the first 24 to 48 hours, transient elevation of blood glucose — relevant if you have diabetes — skin depigmentation or fat atrophy at the injection site, and concerns about cartilage health with frequent repeated use. Infection is rare but possible with any joint injection.

PRP carries a different risk profile. Because it is autologous, allergic and immune reactions are very unlikely. The common complaints are procedural: pain during and after the injection, stiffness and swelling for several days, and bruising at the blood draw site. The realistic downside of PRP is not usually harm — it is cost and the possibility of no meaningful response.

Both require the same basic precautions: a sterile technique, a pause on certain blood thinners where your physician advises it, and no injection into an actively infected joint. Anti-inflammatory medication is often paused around a PRP injection, since suppressing inflammation may work against the intended signaling effect.

Who is the better candidate for each

Corticosteroid tends to suit the person with an acutely inflamed, swollen knee who needs to function now — a flare before travel, a work deadline, or a joint too irritable to begin physical therapy. It also suits people for whom cost is a decisive factor, since it is dramatically cheaper and frequently covered by insurance.

PRP tends to suit the person with mild-to-moderate osteoarthritis, a knee that is more painful than swollen, a willingness to wait weeks for results, and a plan that extends beyond the injection itself. It is a poor fit for end-stage, bone-on-bone arthritis, where the evidence is weakest and expectations are hardest to manage.

Neither is a substitute for the parts of treatment that reliably matter: progressive strength work around the knee, load management, and body composition. Injections buy a window. What you do inside that window determines much of the result. The same logic underpins the staged, measured structure of our longevity program, and it is worth reading alongside our overview of PRP therapy for joint pain and the broader osteoarthritis treatment guide.

Cost, access and practical logistics

The cost gap is substantial. A corticosteroid injection is a low-cost, widely available procedure, commonly covered by health insurance in most systems. PRP is usually paid out of pocket, often priced per session, and frequently recommended as a series of two or three injections spaced two to four weeks apart — so the total outlay can be many times higher.

Access differs too. Any trained clinician can perform a corticosteroid injection. PRP requires a centrifuge, a preparation protocol and, ideally, ultrasound guidance for accurate intra-articular placement. Clinic-to-clinic quality varies more than most patients expect.

What to ask your physician before choosing

Bring specific questions rather than asking which one is "better."

1. What grade is my osteoarthritis on imaging, and does that grade favour either option?
2. Is my knee currently inflamed and swollen, or primarily painful and stiff? Which of these does each injection target?
3. If we choose PRP, what preparation protocol do you use, is it leukocyte-rich or leukocyte-poor, and is the injection ultrasound-guided?
4. How many sessions do you expect, at what spacing, and what would tell us it is not working?
5. If we choose corticosteroid, how many injections are you willing to give this joint in a year, and what is the plan when they stop helping?
6. What rehabilitation program runs alongside the injection, and when does it start?

A clinician who answers these precisely is giving you a treatment plan. One who promises a cure from a single injection is giving you a sales pitch.

Bringing it together

Corticosteroid and PRP are not rivals so much as tools with different shapes. Cortisone is a fast, cheap, short-acting way to calm an inflamed joint. PRP is a slower, costlier attempt to change the joint's signaling environment, with evidence suggesting better durability at six to twelve months in the right patient. The available evidence supports both as reasonable options within a wider plan, and neither as a replacement for strengthening, load management and medical guidance.

If you are weighing the two, the most useful next step is a proper assessment of your joint rather than a decision made from an article. Any injection may help more, and last longer, when it is chosen for the specific problem your knee actually has.

This article is educational and does not constitute medical advice. Injection decisions should be made with a qualified clinician who has examined your joint and imaging.