Platelet-rich plasma (PRP) injections currently offer the longest-lasting relief among widely available knee injections, with measurable improvements in pain and function persisting up to 12 months. That said, the best option for you depends on the severity of your arthritis, how quickly you need relief, and what your insurance covers. Here’s how each type compares.
PRP: Up to 12 Months of Relief
PRP is made from your own blood. A sample is drawn, spun in a centrifuge to concentrate the platelets and growth factors, then injected into your knee. A large meta-analysis of randomized controlled trials found that PRP provided clinically meaningful improvements in both pain and function at 3, 6, and 12 months compared to placebo. At one year, patients still showed significant gains in joint function, stiffness, and overall symptom scores.
Not all PRP is equal. Preparations with a higher platelet concentration performed better. High-platelet PRP maintained clinically significant pain relief at 3, 6, and 12 months, while low-platelet formulations lost their edge over placebo by the one-year mark. If you’re considering PRP, it’s worth asking your provider about the concentration they use.
In head-to-head comparisons with hyaluronic acid, PRP consistently came out ahead. A systematic review of dozens of randomized trials found that PRP produced lower pain scores and better function scores at every follow-up point through 12 months. By one year, patients who received hyaluronic acid had noticeably more stiffness than those who received PRP.
Hyaluronic Acid: 6 Months Per Course
Hyaluronic acid (sometimes called viscosupplementation or “gel shots”) works differently from PRP. It supplements the natural lubricant in your joint, and its onset is slower, typically taking several weeks before you notice a difference. But the relief tends to be more durable than a standard steroid shot.
A large U.S. health claims study found that a single course of hyaluronic acid injections pushed the median time to knee replacement from about 4 months to over a year. Patients who received five or more courses over time delayed surgery by an average of 3.6 years. That doesn’t mean each injection lasts years, but it suggests that repeated courses can meaningfully extend the life of your natural knee. Most patients (about 73%) receive just one course before moving on to other treatments or surgery.
The typical treatment cycle involves three to five weekly injections, with benefits generally lasting around six months. You can repeat the cycle, though many insurance plans have specific rules about how often they’ll cover it.
Standard Corticosteroids: About 3 Months
Corticosteroid injections are the fastest-acting option. Some of their effects begin within minutes, and most people feel substantial relief within a day or two. A meta-analysis of eight randomized trials found that steroids provide mild to moderate pain reduction for up to three months, with the benefit approaching zero around the four-month mark.
That makes steroids useful when you need quick relief for a flare-up or want to buy time before a procedure, but they’re not a long-term solution. Repeated steroid injections are also associated with cartilage changes over time, which is why most doctors limit how frequently they’re given.
Extended-Release Steroids: 5 to 6 Months
An extended-release formulation of triamcinolone (sold as Zilretta) was designed to address the short lifespan of traditional steroid injections. Instead of rapidly leaking out of the joint, the medication is embedded in tiny microspheres that dissolve slowly, keeping the drug inside the knee longer.
Clinical trial data shows this version provides 5 to 6 months of pain relief, roughly double what standard steroids offer. It also outperformed both placebo and traditional steroid injections in symptom scores. The tradeoff is cost: it’s significantly more expensive, and insurance coverage varies.
Bone Marrow Aspirate Concentrate: Potentially 24+ Months
Bone marrow aspirate concentrate (BMAC) is the newest and least established option. It involves drawing bone marrow (usually from your pelvis), concentrating the stem cells and growth factors, and injecting them into the knee. The evidence base is still growing, but early results are intriguing.
A systematic review of randomized controlled trials found that BMAC produced significant pain improvement starting at one month, with benefits sustained through 12 months. When compared directly to hyaluronic acid, BMAC showed better pain scores at both 6 and 12 months. More notably, while hyaluronic acid’s benefits declined significantly after 12 months, BMAC’s results remained stable out to 24 months in one study and 48 months in another.
The catch is that the evidence is limited to a small number of trials, and one study found no difference between BMAC and a simple saline injection at 12 months. This is promising but not yet definitive, and BMAC is typically expensive and rarely covered by insurance.
How Arthritis Severity Affects Duration
The stage of your osteoarthritis plays a major role in how long any injection will work. Doctors grade knee arthritis on a scale from 0 (no signs) to 4 (bone-on-bone). Most injection therapies are recommended for grades 2 and 3, where there’s clear evidence of bone spurs and some joint space narrowing but the joint isn’t completely worn out.
Patients with grade 2 arthritis tend to respond better and longer than those with grade 3. In one study tracking outcomes over three years, 75% of grade 2 patients were still responding at 12 months compared to about 67% of grade 3 patients. By grade 4, injections of any type offer limited and short-lived relief, and knee replacement becomes the more reliable path forward.
Comparing Your Options at a Glance
- Standard corticosteroids: fastest relief (hours to days), lasts about 3 months, widely covered by insurance
- Extended-release steroids: similar fast onset, lasts 5 to 6 months, higher cost and variable coverage
- Hyaluronic acid: slow onset (weeks), lasts about 6 months per course, can be repeated multiple times
- PRP: gradual onset, lasts up to 12 months, rarely covered by insurance, high-platelet formulations work best
- BMAC: gradual onset, early evidence suggests 12 to 24+ months, limited research, highest out-of-pocket cost
If pure duration is your priority and cost isn’t a barrier, PRP with a high platelet concentration has the strongest evidence for lasting relief through a full year. BMAC may eventually prove to last longer, but the research isn’t mature enough to make that claim confidently. For people who need insurance to cover the treatment, hyaluronic acid offers the best balance of duration and accessibility, while corticosteroids remain the go-to for fast, short-term relief.