A cortisone shot will not repair a torn ACL. The ACL has almost no blood supply, so it cannot heal itself, and cortisone does nothing to rebuild torn ligament fibers. What a cortisone injection can do is temporarily reduce the pain and swelling that follow an ACL tear, buying you some short-term relief while you and your doctor figure out a longer-term plan.
What Cortisone Actually Does in Your Knee
When you tear your ACL, blood floods the joint (a condition called hemarthrosis), triggering a wave of inflammation. That inflammation causes the intense swelling, stiffness, and pain you feel in the days after the injury. It can also damage the cartilage surfaces inside the knee if it persists. A cortisone shot works by suppressing that inflammatory cascade, which dials down swelling and provides pain relief.
A pilot randomized controlled trial found that injecting a corticosteroid into the knee after an ACL injury helped protect the joint’s cartilage from the damaging effects of that post-injury inflammation. So the shot isn’t just masking symptoms. It may offer a real, if limited, protective benefit for the rest of your knee in the acute phase after injury.
How Long the Relief Lasts
The pain relief from a cortisone shot is temporary, and shorter than many people expect. Research consistently shows that the strongest benefit lasts about one week after injection. Some patients get relief for a few weeks to a month, but in studies comparing cortisone to placebo injections, there was no meaningful difference in pain scores between the two groups by three to four weeks. The published range is anywhere from 1 to 24 weeks, but the realistic expectation for most people is a few weeks of noticeable improvement followed by a gradual return of symptoms.
Why Cortisone Can’t Fix the Tear
Cortisone is a powerful anti-inflammatory, but it comes with a tradeoff: it interferes with the body’s tissue repair processes. Animal studies on ligaments and tendons have found that corticosteroid exposure is associated with collagen bundle fragmentation, tissue thinning, reduced tensile strength, and delayed healing. In injured tissue, cortisone appears to alter the normal progression of collagen remodeling, keeping the tissue in an earlier, weaker repair state for longer than it would otherwise remain.
This is why cortisone is used only for symptom management, not as a treatment for the structural damage itself. It quiets inflammation while potentially slowing the limited healing your knee might otherwise attempt.
Timing Matters If Surgery Is Planned
If you’re heading toward ACL reconstruction surgery, the timing of a cortisone injection is critical. A 2025 study analyzing nearly 5,000 matched patients found that receiving a cortisone shot within eight weeks before ACL reconstruction doubled the rate of postoperative infection. The infection rate was 1.2% in patients who had received a recent injection, compared to 0.6% in those who had not. At six months post-surgery, that gap persisted: 1.3% versus 0.6%.
These are still small absolute numbers, but a doubled infection risk after knee surgery is significant enough that most surgeons will want to know about any recent cortisone injections. If reconstruction is likely in your near future, this is a conversation worth having before agreeing to a shot.
When a Cortisone Shot Makes Sense
Cortisone is most useful in a few specific situations after an ACL tear. If your knee is severely swollen and painful in the first days or weeks after injury, a cortisone injection (often combined with aspiration, where the doctor drains excess fluid from the joint) can make you more comfortable and allow you to start physical therapy sooner. It’s also sometimes used for patients who are managing a torn ACL without surgery, particularly older or less active individuals who need periodic relief from flare-ups of swelling and pain.
It is not a substitute for the two treatments that actually address ACL instability: structured physical therapy to strengthen the muscles around your knee, or surgical reconstruction to replace the torn ligament with a graft.
How PRP Injections Compare
Platelet-rich plasma (PRP) injections are sometimes offered as an alternative to cortisone for knee pain and inflammation. A systematic review comparing the two found that cortisone and PRP perform similarly in the first month. After that, PRP pulls ahead. At three, six, and nine months, PRP was significantly better at reducing pain and stiffness. The greatest difference appeared at six to nine months, with PRP patients reporting meaningfully lower pain scores on standard scales.
A series of three PRP injections, typically spaced a week apart, was more effective than a single injection over a 12-month follow-up. PRP also showed a trend toward better return to sporting activities at six months compared to cortisone, though the difference just missed statistical significance. PRP costs more and is rarely covered by insurance, but for patients looking for longer-lasting relief without surgery, it may be worth discussing.
Neither PRP nor cortisone will regrow a torn ACL. Both are tools for managing symptoms around the joint, not for fixing the underlying structural problem.
Partial Versus Complete Tears
Whether your ACL is partially or completely torn doesn’t change what cortisone can offer. In both cases, the injection targets inflammation in the joint, not the ligament itself. A partial tear may heal enough with physical therapy alone to restore functional stability, and cortisone can help manage pain during that rehab process. A complete tear almost never heals on its own regardless of what’s injected into the knee. The decision about cortisone is really about managing your symptoms and protecting your cartilage in the short term, not about the degree of the tear.