For most adults with mild-to-moderate knee arthritis, PRP injections provide longer-lasting relief than cortisone, while cortisone still wins for fast, short-term pain control. Cortisone tends to work within days but fades within weeks; PRP builds more slowly but can hold its benefit for six months to a year in randomized trials. The right choice depends on your Kellgren-Lawrence grade, how urgently you need relief, and whether you have already tried conservative care.
TL;DR:
- PRP injections provide longer-lasting relief for knee arthritis, with benefits persisting up to a year, especially when administered as a series of two to three injections.
- Cortisone offers faster pain relief within days but typically fades within weeks, making it suitable for urgent flare-ups rather than sustained improvement.
- Evidence shows PRP is more effective than cortisone after about six months, particularly in symptom reduction and biomarker improvements in joint health.
- Patients with mild to moderate arthritis (Kellgren-Lawrence grade I to III) and those who have exhausted conservative care are better candidates for PRP.
- Repeated cortisone injections pose long-term cartilage risks, while PRP’s main concern is transient soreness, with no proven tissue regrowth yet demonstrated.
Table of Contents
- PRP Injections Versus Cortisone For Knee Arthritis: The Basics Compared
- How Strong Is the Evidence for PRP Therapy in the Knee?
- Who Is a Good Candidate for PRP or Cortisone?
- What Happens After Each Injection?
- How Do You Choose Between PRP and Cortisone?
- How We Apply the Evidence at Nowak Orthopedic Associates
- What Are the Long-Term Risks Beyond a Year?
- What the Research Actually Tells Us to Prioritize
- Ready to Discuss Your Options? Here’s How to Start
- Sources
- FAQ
PRP Injections Versus Cortisone For Knee Arthritis: The Basics Compared
Cortisone (a corticosteroid) and platelet-rich plasma work through almost opposite mechanisms, and that difference explains nearly every outcome pattern seen in the research. Cortisone floods the joint with a synthetic anti-inflammatory hormone that shuts down the immune signals causing swelling and pain. PRP takes a sample of your own blood, concentrates the platelets, and injects that concentrate back into the joint to release growth factors that may support tissue repair and dial down inflammatory chemicals like IL-6 and TNF-alpha.
That mechanical difference shows up clearly in how fast each treatment acts and how long it lasts:
- Onset: Cortisone typically relieves pain within 24 to 72 hours. PRP can also produce rapid analgesic effects within the first week in some patients, though its full benefit usually builds over several weeks.
- Duration: Cortisone’s relief commonly fades within several weeks. PRP benefits often peak around three to six months and, in some trials, persist through 12 months.
- Protocol: Cortisone is usually a single injection, sometimes repeated at intervals of several months. PRP is frequently given as a short series, often two to three injections spaced roughly a week apart, since series protocols tend to outperform single injections in clinical outcomes.
- Safety pattern: Cortisone carries cumulative risks with repeated use, including possible cartilage effects. PRP’s main downside is a transient flare of joint swelling in the first few days after injection.
Neither option is universally “better.” Cortisone remains the faster tool for a flare-up. PRP is the more durable tool for patients trying to change the trajectory of their arthritis rather than just quiet it down for a month.
How Strong Is the Evidence for PRP Therapy in the Knee?
The evidence base for PRP therapy in the knee has grown substantially, and the newer trials are more convincing than the early, small studies that once made PRP look like a coin flip. A 2021 systematic review and meta-analysis pooling eight studies and 648 patients found PRP produced significantly greater symptom reduction than corticosteroid injections at three, six, and nine months, with the largest gap appearing at six to nine months. That analysis reported a notable improvement on the WOMAC and VAS pain scales for PRP over cortisone at six months, comfortably above what most researchers consider a minimally clinically important difference. Triple-injection PRP protocols outperformed single injections in that same review, reinforcing why most clinics now favor a short series over a one-shot approach.
A separate single-center randomized controlled trial followed patients for a full year and found something clinically useful: at one week, PRP and cortisone performed about the same. By 15 weeks, PRP had pulled ahead on both pain and function, and it held that advantage through the full 12-month follow-up. That trial also documented transient synovitis in some early PRP recipients, a detail worth knowing before treatment rather than after.
More recent biomarker research adds a mechanistic layer to the pain-score data. A randomized trial in patients with late-stage knee osteoarthritis compared two weekly PRP injections against a single corticosteroid injection plus NSAID therapy, and PRP produced favorable changes not just in pain scores but in inflammatory and cartilage-degradation biomarkers including COMP, MMP-3, IL-6, IL-18, and TNF-alpha at three and six months. Patients in the PRP group also used less opioid medication over that window, a functional outcome that matters as much as any lab value.
None of this makes PRP a settled science. Study heterogeneity is real. Trials differ in whether they use leukocyte-rich or leukocyte-poor PRP, how many injections they give, and what Kellgren-Lawrence grades they enroll. That variability is exactly why consensus statements from groups like ESSKA-ICRS matter: they translate inconsistent trial designs into practical selection rules. The AAPM&R guidance statement reflects the same caution, offering eleven evidence-informed best practices while openly acknowledging where the data still falls short. Momentum is building, though. Recent tracking of the literature shows the volume and quality of PRP research climbing year over year, with guidelines gradually catching up to what the newer RCTs are showing.
Who Is a Good Candidate for PRP or Cortisone?
Not every knee benefits equally from either treatment, and matching the therapy to the patient is where outcomes improve most.
- Kellgren-Lawrence grade 0 to III describes the sweet spot for PRP, according to ESSKA-ICRS consensus guidance; severe grade IV arthritis typically responds poorly and is not considered a first-line PRP indication.
- Age matters too. The same consensus statement generally caps ideal PRP candidacy around age 80, since biologic response tends to diminish with advanced age.
- Active patients who have already tried physical therapy and possibly a first cortisone shot, without lasting relief, are often the best fit for a PRP series.
- Bleeding disorders, active joint infection, or recent systemic steroid use can rule out or delay either treatment and should always come up during your evaluation.
- Cortisone still has a clear role for urgent flare-ups, for patients who need fast relief before an event or surgery, and as a diagnostic tool to confirm the knee joint itself is the pain source.
If you are weighing surgery down the road, a diagnostic cortisone injection can also help your surgeon confirm the joint, rather than a nearby tendon or nerve, is generating your pain.
What Happens After Each Injection?
The first week after treatment looks different depending on which injection you receive, and knowing what is normal helps you avoid unnecessary worry.
- Days 1 to 3: Cortisone typically brings noticeable relief quickly. PRP may cause soreness, warmth, or mild swelling as the concentrated platelets trigger a localized inflammatory response, a reaction some patients mistake for the treatment “not working.”
- Days 3 to 7: Cortisone relief usually plateaus. PRP soreness typically settles, and some patients report the first signs of pain improvement within this first week.
- Weeks 2 to 6: Cortisone benefit often begins fading. PRP benefit continues building, especially if you received the recommended two or three injections rather than just one.
- Months 3 to 6: This is typically where PRP’s advantage becomes most visible, with pain and function scores often surpassing what cortisone achieved at its peak.
Light activity is fine after either injection, but high-impact exercise should generally wait 48 to 72 hours. Most clinics schedule a follow-up visit within two to four weeks to gauge response and decide whether additional PRP injections in the series are warranted.
Pro Tip: If your knee feels puffier or warmer than usual in the first three days after a PRP injection, that is usually transient synovitis, not a sign of infection or failure. Ice, rest, and over-the-counter acetaminophen typically resolve it within days. Call your clinician if you develop fever, spreading redness, or pain that worsens rather than improves.
Repeat cortisone injections are typically spaced at least three months apart because of cumulative joint risks, while a PRP series is usually reevaluated for a repeat course only after six months to a year, depending on how long the initial benefit lasted. For a deeper look at what steroid injections can do to joint tissue over time, see this breakdown of cortisone injection side effects.
How Do You Choose Between PRP and Cortisone?
A short checklist can turn this decision from confusing to concrete before you even walk into a consultation.
- How severe is the arthritis? Mild-to-moderate (KL I to III) generally favors PRP; advanced KL IV often responds better to other approaches.
- How urgent is the pain? A flare that needs fast control before a trip, event, or surgery usually points toward cortisone.
- What have you already tried? If physical therapy and one cortisone shot have not produced lasting relief, a PRP series is a reasonable next step.
- Are you planning surgery soon? A diagnostic cortisone injection can help confirm the knee joint is the actual pain source.
- Do you have contraindications? Bleeding disorders and active infection affect PRP eligibility; recent or frequent steroid use raises cumulative-risk concerns for cortisone.
When you sit down with your clinician, ask directly: How many injections do you recommend, and why that number? What specific improvement should I expect, and by when? How does my Kellgren-Lawrence grade affect my odds of benefiting? What does this cost out of pocket, and does insurance typically cover it? PRP is often billed as self-pay since coverage varies by carrier and plan, while cortisone is more consistently covered. Asking about cost transparently, rather than assuming, avoids surprises after treatment.
How We Apply the Evidence at Nowak Orthopedic Associates
Our Regenerative Clinic approaches this decision the same way the research does: match the treatment to the patient, not the other way around. A typical evaluation includes a physical exam, imaging to confirm Kellgren-Lawrence grade, and a conversation about what you have already tried and what you are hoping to achieve.
For patients with mild-to-moderate arthritis who want a longer-lasting option and have exhausted basic conservative care, we often recommend a PRP injection series rather than a single dose, consistent with the trial data showing multiple injections outperform one. For patients dealing with an acute flare, or who need a bridge to a planned procedure, cortisone remains a legitimate, faster tool in the same toolkit.
What Are the Long-Term Risks Beyond a Year?
Repeated cortisone injections over years carry the most consistent long-term concern: some research has linked frequent, ongoing steroid use to accelerated cartilage thinning, which is part of why most clinicians cap how often it can be repeated in the same joint. Cortisone’s biggest long-term risk is less about any single shot and more about frequency over time.
PRP’s long-term risk profile looks different. Because it uses your own blood components rather than a synthetic drug, it does not carry the same cumulative cartilage concerns tied to repeated steroid dosing. The bigger open question with PRP beyond 12 months is durability. The one-year data from the RCT following patients through a full year of follow-up is reassuring, but fewer studies have tracked outcomes past that point, so how PRP performs at two or three years is still being defined.
Neither treatment reverses established structural damage in an arthritic knee. Both are symptom-management tools, not cures, and severe arthritis (KL IV) that has progressed significantly may eventually need a surgical conversation regardless of which injection route you try first. Tracking your response honestly, and revisiting the plan with your clinician if relief keeps shrinking, matters more over the long run than which injection you started with.
What the Research Actually Tells Us to Prioritize
The conventional advice on this topic treats PRP and cortisone like a coin flip, “try one and see.” That undersells what the last several years of trial data actually show. Multiple RCTs and a meta-analysis pooling nearly 650 patients now point in the same direction: PRP’s advantage compounds over months, while cortisone’s advantage is real but front-loaded and short.
Where I think patients get misled is assuming these are interchangeable substitutes for the same problem. They are not. Cortisone is a fire extinguisher. PRP is closer to a maintenance strategy. The mistake I see most often is a patient defaulting to whichever option their insurance makes easiest, rather than the one that matches their actual goal, whether that is getting through a wedding next month or staying active for the next five years.
If there is one priority worth taking from the evidence, it is this: match the injection to the timeline you actually care about, and do not let a single steroid shot’s fast relief distract from what a properly dosed PRP series can do over six to twelve months.
— Dr. Roger Nowak
Ready to Discuss Your Options? Here’s How to Start
You can access both sides of this decision under one roof, rather than being sent to a separate injection clinic after a rushed referral. Our board-certified orthopedic team evaluates your imaging, your Kellgren-Lawrence grade, and your activity goals in the same visit where we discuss whether a PRP injection series or a cortisone shot fits your situation better, and we can pivot to arthroscopic options if regenerative or steroid treatment isn’t enough.
A first visit typically includes a physical exam, a review of prior imaging or new X-rays if needed, and a direct conversation about expected timelines and potential out-of-pocket costs before you commit to anything. If you want to understand what that first appointment involves and how to prepare, review our first visit guide and schedule a consultation with our Regenerative Clinic team today.
This article is general information, not a substitute for advice from a qualified doctor. Consult a qualified healthcare professional about your own circumstances before acting on anything here.
FAQ
What Is the Downside of PRP Injections?
The main downside is a temporary flare of swelling and soreness in the first few days, known as transient synovitis, plus a slower onset than cortisone and often out-of-pocket cost since insurance coverage varies.
Can PRP Regrow Knee Cartilage?
Current evidence supports PRP’s anti-inflammatory and biomarker-modifying effects rather than proven cartilage regrowth; trials show favorable changes in cartilage-degradation markers like COMP and MMP-3, but that is different from confirmed tissue regeneration.
Can You Walk After PRP in the Knee?
Yes, most patients walk normally right after treatment, though clinicians typically recommend avoiding high-impact activity for 48 to 72 hours while any mild soreness settles.
Is PRP Worth It for Knee Pain?
For patients with mild-to-moderate arthritis (Kellgren-Lawrence grade I to III) who have tried conservative care, PRP is often worth considering, since trial data shows it outperforming cortisone on pain and function from around 15 weeks through 12 months.