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Knee Injections: Steroid and PRP

Knee injections in Houston for arthritis: how long a cortisone shot lasts, how often to repeat it, PRP with honest caveats, and when genicular RFA is next.

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In short

Knee injections put medication directly inside an arthritic knee to reduce pain and let you walk and exercise. We offer two options, and they are not interchangeable: corticosteroid works within days and lasts 4–12 weeks; platelet-rich plasma is self-pay with fair but mixed evidence. These are treatments, not tests. When injections give shorter and shorter relief, a genicular nerve block and radiofrequency ablation are the next non-surgical step.

Medically reviewed by Purvi Patel, MD · Updated September 27, 2026

Key facts

Treats	Knee osteoarthritis; flares of inflammatory arthritis; pes anserine bursitis; persistent swelling after injury
Test or treatment?	Treatment. Relief from the first steroid injection also confirms the joint, rather than a nearby nerve or the hip, as the source
Procedure time	5–10 minutes at an office visit
Anesthesia	Local anesthetic in the skin or cold spray; no sedation
Downtime	Rest for 24–48 hours; most people walk out and drive themselves
When relief starts	Steroid: 1–3 days. PRP: 4–8 weeks
How long relief lasts	Steroid: typically 4–12 weeks. PRP: 6–12 months in responders
How often it can be repeated	Steroid: no more than 3–4 per year, at least 3 months apart. PRP: a course of 1–3 injections, repeated no more than about once a year
Insurance	Steroid is covered. PRP is not covered and is self-pay

Who it is for

Good candidates

Knee osteoarthritis on X-ray with pain that limits walking, stairs, sleep or exercise despite oral or topical anti-inflammatories, weight management and activity changes
A swollen knee where drawing off fluid and injecting steroid will relieve pressure and inflammation
Patients who want to delay knee replacement, are waiting for a surgery date more than 3 months away, or are not surgical candidates
Patients who need a pain-free window to complete physical therapy
PRP: mild-to-moderate knee arthritis in patients who cannot have or do not want repeated steroid and can self-pay

Usually not the right choice

A knee replacement scheduled within the next 3 months (steroid raises infection risk in the new joint) or an existing knee replacement, unless arranged with the surgeon
A hot, red, swollen knee with fever, which must be tested for infection or gout before any steroid
Mechanical symptoms (locking, giving way) from a meniscal or ligament tear that surgery would address; an injection can settle swelling but not the mechanical problem
Skin infection over the knee
Uncontrolled diabetes or a steroid injection in any joint within the past 3 months (steroid)

Steroid vs PRP, honestly

Corticosteroid. The knee's lining (synovium) becomes inflamed in osteoarthritis, and that inflammation drives much of the pain and swelling. Steroid injected into the joint settles it within days. A Cochrane review found moderate pain relief for a few weeks, fading by 3 months; in practice most patients get 4–12 weeks. Steroid does not rebuild cartilage, and a randomized trial (McAlindon and colleagues, JAMA 2017) of triamcinolone every 3 months for 2 years found more cartilage loss than placebo and no lasting pain advantage. Steroid remains the most reliable short-term option; the trial is the reason we limit it to 3–4 injections a year, space them at least 3 months apart, and stop repeating an injection that gives less than 4–6 weeks of relief.

Platelet-rich plasma (PRP). Your own blood, spun to concentrate platelets and growth factors, injected into the knee. Several randomized trials show PRP at least as good as the lubricant injections it was compared against at 6–12 months, but the largest placebo-controlled trial (RESTORE, JAMA 2021) found no benefit over saline for pain or cartilage at 12 months, and the ACR recommends against it. PRP is not covered by insurance. Read PRP injections for the full picture, including what it costs and what it cannot do.

What about gel shots? Hyaluronic acid (gel shot) injections are another option some clinics offer; we do not perform them, and the evidence for them is mixed (AAOS 2021 recommends against routine use).

Both injections are done under ultrasound guidance when possible; landmark injections miss the knee joint about 1 in 3 times, and medication in the fat pad does nothing.

Illustration of knee injections: steroid and prp

When injections stop working: the path to genicular block and RFA

Most knees with moderate-to-severe arthritis reach a point where steroid gives a few weeks, then a few days, then little. Continuing to inject at that point spends the yearly limit and, over years, costs cartilage. Two better options exist. For patients ready for surgery, knee replacement is definitive, and we coordinate timing so no steroid is given in the 3 months before it. For patients not ready or not eligible (age, weight, heart or lung disease, preference), a genicular nerve block tests whether the knee's sensory nerves can be silenced; if it gives at least 50% relief, genicular radiofrequency ablation typically gives 6–12 months of relief, can be repeated, and does not interfere with a later replacement. The same pathway is used for persistent pain after a knee replacement once the surgeon has excluded infection and loosening. Knee injections are performed at our Houston and Webster offices, and in Pearland when that office opens in November 2026.

What happens on procedure day

Check-in: we confirm your blood-thinner plan, glucose if diabetic, allergies, any planned knee replacement and any recent steroid injection. Knee injections are usually done at a regular office visit.
Positioning: sitting with the knee bent or lying with the knee slightly bent over a roll. The skin is cleaned with antiseptic.
Guidance: ultrasound shows the joint recess, any fluid, and the needle path; the knee is entered from the outer side below or beside the kneecap.
Numbing: a small amount of lidocaine in the skin or a cold spray.
Injection: if the knee is swollen, fluid is drawn off first, which relieves pressure and can be sent for analysis if infection or gout is a question. The medication (steroid with local anesthetic, or PRP) is then injected; a feeling of fullness is normal.
After: a bandage, a few minutes of observation, and home. No driver is needed; the knee may feel slightly numb from the local anesthetic for an hour or two.

After the procedure

Day 0. Rest the knee, ice 15 minutes at a time, and avoid stairs and long walks. The local anesthetic may give a few hours of relief that then fades.

Days 1–3. Steroid: a flare of pain for 24–48 hours is possible before relief begins; flushing, poor sleep and higher blood sugar are common for a few days. PRP: expect the knee to be more painful for 3–7 days; do not take anti-inflammatories, which blunt the platelets.

Week 1–2 (steroid) or weeks 3–8 (PRP). This is when to judge the response. Resume physical therapy and quadriceps strengthening; the injection creates the window and strength is what keeps the knee working.

Judging the response. Steroid: 50% or more relief for at least 4–6 weeks justifies repeating when it wears off, within the yearly limit; relief of days only means the joint needs a different approach. PRP: judge at 8 weeks; do not repeat a course that did not help.

Call us for a knee that becomes hot, red, very swollen or much more painful 2–7 days after an injection, fever, or drainage at the site.

What the evidence shows

The knee is the most studied joint for injections, and the picture is clear enough to state in a few lines. Steroid works, for weeks rather than months, and repeated use has a measurable cost to cartilage. PRP has fair evidence against other injections and weak evidence against placebo, and it costs the patient. Ultrasound guidance improves accuracy and outcomes for both. Genicular radiofrequency ablation, for knees that no longer respond to injections, gave at least 50% relief at 6 months in about 3 in 4 patients versus 1 in 6 with steroid in a randomized trial. Finally, a steroid injection within 3 months of knee replacement raises the risk of infection in the new joint, which is why timing is part of every injection decision.

Alternatives and what comes next

Exercise, weight management, a brace or cane, and topical or oral anti-inflammatories are the foundation, and the AAOS and ACR guidelines put them first. Pes anserine bursitis on the inner knee is treated with a small steroid injection into the bursa rather than the joint. When injections fade, the genicular nerve block and RFA pathway or a surgical opinion about replacement are the next steps. Compare medications and joints on the joint injections hub, and read knee pain for the condition, including pain after knee replacement.

Safety and preparation

Blood thinners: knee injections are low bleeding-risk procedures and most patients continue aspirin and other blood thinners. Tell us what you take; a hold is arranged only in specific cases with your prescriber. Never stop a blood thinner on your own.
Diabetes: steroid raises blood sugar for 1–3 days, occasionally up to a week. Check more often, keep taking your medication, and call if readings stay above 300. We may postpone if your glucose is very high on the day.
Infection or fever: we reschedule for fever, an active infection anywhere, or a skin problem over the knee. A hot, red, swollen knee is tested for infection or crystals before any steroid.
Allergies (contrast, steroid, local anesthetic): tell us about reactions to cortisone, lidocaine or dental numbing. Contrast is not needed for ultrasound-guided knee injections.
Pregnancy: tell us if you are or could be pregnant; knee injections use ultrasound, not X-ray.
Sedation and driving: no sedation is used and most people drive themselves home.
Planned knee replacement: tell us the date. No steroid injection is given into the knee within 3 months of a planned replacement, and we notify your surgeon of any injection.
PRP: stop anti-inflammatory medications (ibuprofen, naproxen, meloxicam and similar) for 1–2 weeks before and 2 weeks after, because they blunt platelet function; acetaminophen is fine. Drink plenty of water the day before the blood draw.
Recent steroids: a steroid injection into any joint within 3 months, or an epidural or oral steroid course within 2 weeks, usually means we wait.

Risks and side effects

Common and expected

Soreness at the site for 1–2 days
Steroid flare: increased knee pain for 24–48 hours in a small number of people
Increased knee pain for 3–7 days after PRP
Blood sugar rise for 1–3 days, sometimes up to a week, in people with diabetes (steroid)
Facial flushing, poor sleep or a racing feeling for a day or two (steroid)

Uncommon

Skin thinning, lightening or a dimple of fat loss at the site (steroid)
Bruising or bleeding into the joint, particularly on blood thinners
Allergic reaction to local anesthetic or steroid
No benefit, or relief lasting only days

Rare but serious

Joint infection (septic arthritis), roughly 1 in 3,000 to 1 in 50,000 injections; needs same-day treatment
Cartilage loss with frequent repeated steroid over years, and rapidly progressive arthritis or bone collapse reported in a small number of patients
Tendon weakening or rupture if steroid is injected into the patellar tendon (avoided with guidance)
Increased infection risk in a subsequent knee replacement when steroid is given within 3 months of surgery
Nerve or blood vessel injury from the needle, prevented with ultrasound

Frequently asked questions

How long does a knee cortisone shot last?

Typically 4–12 weeks, starting within 1–3 days. Some patients get longer relief early in the course of arthritis and shorter relief as it advances. If a steroid injection helps for only a few days, repeating it is not worthwhile and we discuss the genicular block and ablation pathway or a surgical opinion.

How often can you get a cortisone shot in your knee?

No more than 3–4 times a year, at least 3 months apart, and only when the previous one gave meaningful relief. A trial of injections every 3 months for 2 years showed more cartilage loss than placebo without lasting pain benefit, so we treat the limit as a ceiling.

Is PRP better than cortisone for the knee?

PRP has matched or beaten the lubricant injections it was compared against at 6–12 months in several trials, but the largest placebo-controlled trial found no advantage over saline, and the American College of Rheumatology recommends against it. It is not covered by insurance. Cortisone works faster and more predictably in the short term. See our PRP page for a detailed comparison.

Can I get a knee injection before knee replacement surgery?

Not a steroid injection within about 3 months of the surgery date; it raises the risk of infection in the new joint and most surgeons will postpone the operation. Tell your surgeon about every injection you have had, whatever the type.

What can I do when knee injections stop working?

Two paths: knee replacement if you are ready and eligible, or a genicular nerve block followed by genicular radiofrequency ablation, which silences the knee's sensory nerves for typically 6–12 months, can be repeated, and does not interfere with a later replacement.

Does a knee injection hurt?

A brief sting from the skin numbing, then pressure or fullness as the medication goes in. It takes a few minutes. Ultrasound guidance lets us enter the joint where there is fluid, which is the least painful path. PRP causes a few days of increased pain afterward; steroid usually does not.

Sources

Next step

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