Cortisone Injections for Knee Arthritis
What a cortisone injection does for an arthritic knee, how long the benefit actually lasts, the evidence on repeated injections and cartilage, and the timing rule that matters if you may have a knee replacement later.
Cortisone injections are the most common intervention offered for a painful arthritic knee, and the one most surrounded by half-truths — both from people who think they are miraculous and from people who think they destroy joints.
The Australian guideline’s position is measured: a corticosteroid injection may be appropriate for some people with knee osteoarthritis, for short-term symptom relief. Not a core treatment, not forbidden.
What it actually does
Cortisone is a potent anti-inflammatory. Injected into the joint, it suppresses the inflammatory component of arthritis pain — the swelling, the heat, the ache that follows use.
What it does not do is repair anything, change the arthritis, or affect the joint surface. It treats the symptom, well, for a while.
How long it lasts — honestly
This is where expectations most often part company with the evidence.
Across trials, the average benefit over a placebo injection is around two to four weeks. Individual experience varies a lot: some people get several months, some get very little, and the response is difficult to predict beforehand.
A useful way to think about it is as a window, not a treatment. The window is genuinely useful — it can settle a flare, get you through a holiday or a daughter’s wedding, or create enough relief to start the exercise programme that will do the longer-term work. Using the window for something is the difference between an injection that helps and one that merely passes.
The repeated-injection question
The concern people have heard about is real but frequently mangled in the retelling.
A trial gave patients corticosteroid injections every three months for two years. At the end, the injected group had greater cartilage volume loss on MRI than a saline-injected group — and no better pain relief.
What that supports: not using injections on an automatic repeating schedule.
What it does not support: the idea that a cortisone injection damages your knee. One injection, or occasional injections spaced by symptoms, is a different thing from eight injections on a fixed timetable.
The practical position most surgeons take is to space injections by at least three months, and to treat a knee that needs them more often than that as a knee telling you something. If it requires injecting every few months to stay tolerable, the productive conversation is about what comes next rather than about the next injection.
The timing rule that matters
If a knee replacement is anywhere on your horizon, this is the paragraph to remember.
An injection given shortly before knee replacement surgery is associated with an increased risk of infection afterwards. Because of that, most surgeons want a clear interval — commonly around three months — between the last injection into a knee and replacing it.
This catches people out. It is not unusual for someone to have an injection while waiting for a surgical opinion and then find their surgery has to be deferred to clear the interval. If replacement is being discussed at all, say so before agreeing to an injection.
Practicalities
The injection takes a few minutes and needs no anaesthetic — a local anaesthetic is usually mixed with the steroid, which is why relief is often immediate before wearing off and returning as the steroid takes effect over a few days.
Some knees are injected in rooms; some are done under ultrasound guidance, which improves accuracy particularly in larger knees or where the anatomy is difficult.
Expect local soreness for a day or two. Occasionally the knee is briefly more painful for 24 to 48 hours before improving — a steroid flare, which is uncomfortable rather than dangerous. If you have poorly controlled diabetes, be aware blood sugar commonly rises for several days afterwards and plan for it. If the knee becomes hot, swollen and increasingly painful several days later rather than settling, that needs urgent assessment rather than waiting.
Where it fits
A cortisone injection is a reasonable, evidence-supported tool for a flare or a defined period. It is a poor long-term strategy, and it is not a substitute for the things that actually change the trajectory.
The people who get the most from injections tend to be the ones who use the relief to do something — start the exercise programme, get through a period they could not otherwise, or make an unhurried decision about surgery rather than a cornered one.
Next: gel injections (hyaluronic acid) — or back to the overview.
How long does a cortisone injection last in the knee?+
On average, less time than most people expect. Across trials the benefit over a placebo injection averages around two to four weeks, though individual experience varies widely — some people get a few months, some get very little. It is best understood as a way to settle a flare or get through a specific period, rather than as ongoing treatment.
Are cortisone injections bad for your knee?+
In moderation, no. The concern comes from a trial in which injections given every three months for two years produced greater cartilage volume loss on MRI than saline injections, and no better pain relief. That is a specific and fairly aggressive schedule rather than evidence that any injection harms the joint. The practical conclusion drawn from it is to use injections for symptom relief when needed, rather than on a routine repeating schedule.
How many cortisone injections can you have in a knee?+
There is no absolute limit, but injections are generally spaced at least three months apart, and a pattern of needing them more often than that is a signal worth acting on rather than continuing. If a knee requires injecting every few months to remain tolerable, the useful conversation is about what comes next, not about the next injection.
Does a cortisone injection delay knee replacement surgery?+
It can defer it, sometimes for a long time, which is a legitimate reason to have one. What it does not do is change the underlying arthritis. There is also a timing consideration — an injection given shortly before a knee replacement is associated with increased infection risk, so most surgeons want a clear interval, commonly around three months, between the last injection and surgery. If a replacement is on the horizon, say so before having an injection.
What does a cortisone injection into the knee feel like?+
The injection itself takes a few minutes and needs no anaesthetic beyond the local anaesthetic usually mixed with the steroid. Most people describe pressure rather than sharp pain. Local soreness for a day or two afterwards is common and occasionally the knee is briefly more painful before it improves — the so-called steroid flare. Relief typically begins within a few days.
Who should not have a cortisone injection in the knee?+
Anyone with a suspected infection in or around the joint should not be injected, and injections are used cautiously in people with poorly controlled diabetes because blood sugar commonly rises for several days afterwards. Anyone due for knee replacement surgery in the near future should discuss timing first, because of the infection-risk interval.