by Walter I Sussman

If you have knee arthritis, chances are you’ve been offered a cortisone injection. For decades, cortisone has been one of the most common treatments for knee pain.

But today, many patients are asking:

• Is "stem cell" therapy better than cortisone for knee arthritis?

• What about PRP vs "stem cell" knee injections?

• Are there better knee injection alternatives to cortisone?

The answer isn’t one-size-fits-all. These treatments work very differently, and understanding those differences is critical before making a decision.

Let’s break it down clearly.

Understanding Knee Arthritis

Knee osteoarthritis happens when the joint begins to break down over time. Cartilage thins, inflammation increases, and the bone beneath the cartilage (the subchondral bone) becomes stressed (learn more about knee osteoarthritis here).

Common symptoms include:

• Aching pain with walking or stairs

• Stiffness in the morning

• Swelling

• Decreased range of motion

• Sharp pain with pivoting

Traditional treatment often starts conservatively:

• Physical therapy

• Activity modification

• Anti-inflammatory medications

• Cortisone injections

But newer biologic treatments like PRP and stem cell therapy (BMAC) aim to do more than temporarily reduce inflammation.

What Is a Cortisone Injection?

Intra-articular corticosteroids are potent anti-inflammatory agents that reduce inflammation, decrease swelling, and provide pain relief. They have been a standard therapy for knee osteoarthritis since the 1950s.

How It Works

Cortisone:

• Reduces inflammation

• Decreases swelling

• Temporarily calms pain signals

How Long Does It Last?

For many patients corticosteroid relief is temporary and diminishes over time:

• Relief begins within days

• Effects last 4–8 weeks

• Some experience relief up to 3 months

However, relief is often temporary.

• A Cochrane meta-analysis of 27 trials (1,767 participants) found pain benefits were moderate at 1-2 weeks (SMD -0.48), small to moderate at 4-6 weeks (SMD -0.41), small at 13 weeks (SMD -0.22), and no evidence of effect at 26 weeks (SMD -0.07). This supports the claim that relief typically lasts 4-8 weeks, with some patients experiencing benefit up to 3 months. (Jüni et al, 2015; da Costa et al, 2016)

• An NEJM review confirms that intraarticular glucocorticoid injections are "efficacious for short-term pain relief, commonly lasting a few weeks."(Sharma, 2021)

Limitations of Cortisone

Repeated cortisone injections may:

• Provide diminishing returns

• Potentially accelerate cartilage thinning with frequent use

• Mask pain without addressing underlying joint degeneration

Cortisone treats inflammation — it does not support tissue repair. The evidence regarding repeated injections shows:

• Cartilage volume loss with repeated injections: A landmark RCT found that 2 years of triamcinolone administered every 3 months resulted in significantly greater cartilage volume loss than saline injections (between-group difference of −0.11 mm, corresponding to a moderate effect size), with no significant difference in knee pain. (McAlindon et al, 2017)
• Observational data: A 2025 analysis from the Osteoarthritis Initiative found corticosteroid injections were associated with greater OA progression on MRI compared to controls (mean WORMS difference 0.39; P = .02) and hyaluronic acid (0.42; P = .04) over 2 years. A cohort study found multiple corticosteroid injections associated with worsening joint space narrowing (HR 3.02) and increased risk of joint replacement (HR 2.54). (Bharadwaj et al, 2025; Ayub et al, 2021)

What Is "Stem Cell" Therapy for Knee Arthritis?

When people search for "stem cell"injections knee arthritis, they are usually referring to Bone Marrow Aspirate Concentrate (BMAC), learn more about BMAC here.

BMAC is created by harvesting bone marrow (typically from the iliac crest of the pelvis) and processing it via centrifugation to concentrate the cellular constituents. The concentration process enriches multiple cell populations and bioactive factors:

• Mesenchymal stromal cells (often called “stem cells”): BMAC processing significantly enriches MSC populations, with approximately 4-fold increases in compared to unprocessed bone marrow aspirate. These cells are capable of chondrogenic, osteogenic, and adipogenic differentiation (El-Jawhari et al, 2020)

• Platelets: BMAC processing significantly enriches platelet concentrations (Schäfer et al, 2019; Cassano et al, 2018)

• Anti-inflammatory signaling molecules: BMAC hassignificantly higher IL-1Ra concentrations than PRP (13,432 pg/mL vs. 588 pg/mL; P = 0.0018), making it a potent anti-inflammatory source. (Cassano et al, 2018; Koyanagi et al, 2023)

The goal is not simply to suppress inflammation — unlike corticosteroids, which provide only anti-inflammatory effects, BMAC provides a complex mixture of cells and signaling molecules support a healthier joint environment.

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References

Ayub S, Kaur J, Hui M, Espahbodi S, Hall M, Doherty M, Zhang W. Efficacy and safety of multiple intra-articular corticosteroid injections for osteoarthritis-a systematic review and meta-analysis of randomized controlled trials and observational studies. Rheumatology (Oxford). 2021 Apr 6;60(4):1629-1639. doi: 10.1093/rheumatology/keaa808. PMID: 33432345.

Bharadwaj UU, Lynch JA, Joseph GB, Akkaya Z, Nevitt MC, Lane NE, McCulloch CE, Link TM. Intra-articular Knee Injections and Progression of Knee Osteoarthritis: Data from the Osteoarthritis Initiative. Radiology. 2025 May;315(2):e233081. doi: 10.1148/radiol.233081. PMID: 40423542; PMCID: PMC12127947.

Cassano JM, Kennedy JG, Ross KA, Fraser EJ, Goodale MB, Fortier LA. Bone marrow concentrate and platelet rich plasma differ in cell distribution and interleukin 1 receptor antagonist protein concentration. Knee Surg Sports Traumatol Arthrosc. 2018 Jan;26(1):333-342. doi: 10.1007/s00167-016-3981-9. Epub 2016 Feb 1. PMID: 26831858.

da Costa BR, Hari R, Jüni P. Intra-articular Corticosteroids for Osteoarthritis of the Knee. JAMA. 2016 Dec 27;316(24):2671-2672. doi: 10.1001/jama.2016.17565. PMID: 28027351.

El-Jawhari JJ, Ilas DC, Jones W, Cuthbert R, Jones E, Giannoudis PV. Enrichment and preserved functionality of multipotential stromal cells in bone marrow concentrate processed by vertical centrifugation. Eur Cell Mater. 2020 Aug 4;40:58-73. doi: 10.22203/eCM.v040a04. PMID: 32749666.

Jüni P, Hari R, Rutjes AW, Fischer R, Silletta MG, Reichenbach S, da Costa BR. Intra-articular corticosteroid for knee osteoarthritis. Cochrane Database Syst Rev. 2015 Oct 22;2015(10):CD005328. doi: 10.1002/14651858.CD005328.pub3. PMID: 26490760; PMCID: PMC8884338.

Koyanagi M, Fujioka-Kobayashi M, Inada R, Yoneyama Y, Satomi T. Skin and Bone Regeneration of Solid Bone Marrow Aspirate Concentrate Versus Platelet-Rich Fibrin. Tissue Eng Part A. 2023 Mar;29(5-6):141-149. doi: 10.1089/ten.TEA.2022.0175. Epub 2023 Feb 21. PMID: 36416223.

McAlindon TE, LaValley MP, Harvey WF, Price LL, Driban JB, Zhang M, Ward RJ. Effect of Intra-articular Triamcinolone vs Saline on Knee Cartilage Volume and Pain in Patients With Knee Osteoarthritis: A Randomized Clinical Trial. JAMA. 2017 May 16;317(19):1967-1975. doi: 10.1001/jama.2017.5283. PMID: 28510679; PMCID: PMC5815012.

Samuels J, Pillinger MH, Jevsevar D, Felson D, Simon LS. Critical appraisal of intra-articular glucocorticoid injections for symptomatic osteoarthritis of the knee. Osteoarthritis Cartilage. 2021 Jan;29(1):8-16. doi: 10.1016/j.joca.2020.09.001. Epub 2020 Sep 7. PMID: 32911075.

Schäfer R, DeBaun MR, Fleck E, Centeno CJ, Kraft D, Leibacher J, Bieback K, Seifried E, Dragoo JL. Quantitation of progenitor cell populations and growth factors after bonemarrow aspirate concentration. J Transl Med. 2019 Apr 8;17(1):115. doi: 10.1186/s12967-019-1866-7. PMID: 30961655; PMCID:PMC6454687.

Sharma L. Osteoarthritis of the Knee. N Engl J Med. 2021 Jan 7;384(1):51-59. doi:10.1056/NEJMcp1903768. PMID: 33406330.