Scientific deep-dive

GLP-1 for Knee Osteoarthritis: STEP-9 Evidence + Surgery Bridge

STEP-9 (Bliddal 2024 NEJM) showed semaglutide reduced WOMAC pain scores in knee OA patients with obesity. We review the trial outcomes, the joint-replacement bridge, and the practical orthopedic + obesity medicine pathway.

By Eli Marsden · Founding Editor
Editorially reviewed & fact-checked against primary sources · How we verify contentLast reviewed
11 min read·9 citations

Knee osteoarthritis affects roughly 14 million US adults. STEP-9 (Bliddal 2024 NEJM) is the first phase-3 randomized trial showing semaglutide 2.4 mg reduces WOMAC pain in patients with both obesity and symptomatic knee osteoarthritis. Not all knee pain in arthritis comes from inside the joint: tenderness on the inner knee below the joint line can be pes anserine bursitis.

Frequently Asked Questions

Yes, in people who also have obesity. STEP-9 (Bliddal 2024 NEJM[1]) was the first phase-3 randomized trial to test this, and once-weekly semaglutide 2.4 mg produced significantly greater reductions in WOMAC knee-pain scores than placebo, alongside roughly 13% body-weight loss and improved physical function. The trial studied symptomatic knee osteoarthritis in adults with obesity, so the finding applies to that overlap population rather than to knee osteoarthritis in people at a healthy weight.
No — semaglutide is not FDA-approved for osteoarthritis and is not an osteoarthritis drug. Its benefit in the knee runs through weight loss reducing joint load rather than any direct action on cartilage. Intensive weight loss reduces knee joint loads, inflammation and pain (Messier 2013 IDEA trial[2]), and the OARSI guidelines recommend weight management as core non-surgical care for knee osteoarthritis in people with overweight or obesity (Bannuru 2019[3]). A GLP-1 is best understood as one tool to achieve that weight loss, adjunctive to exercise and the rest of guideline-based osteoarthritis care, and these decisions should be made with your clinician.
Yes, and this is the best-established lever. The IDEA randomized trial (Messier 2013[2]) showed that intensive diet plus exercise reduced knee joint loads, lowered inflammatory markers, and improved pain and function in overweight and obese adults with knee osteoarthritis — more than either intervention alone. Because the knee carries several times body weight during walking, even a modest weight reduction meaningfully lowers the mechanical load across the joint. Staying active also matters: as little as an hour a week of moderate activity is associated with maintained function in adults with lower-extremity joint symptoms (Dunlop 2019[5]).
No. Nothing in the evidence suggests semaglutide regrows cartilage or reverses the structural damage of osteoarthritis. STEP-9 (Bliddal 2024[1]) measured symptoms — pain and function — not joint structure, and the improvement is attributable to weight loss reducing joint load and inflammation rather than to disease modification. Osteoarthritis remains a chronic condition; the realistic goal with weight loss is meaningful symptom relief and better function, potentially delaying or reducing reliance on other interventions, not a cure.
Semaglutide is not established as a cause of joint pain, and in the population that matters here — adults with obesity and knee osteoarthritis — it reduced knee pain rather than worsening it (Bliddal 2024[1]). The more relevant caution during any rapid weight loss is loss of muscle mass, which can undercut the joint support that strong muscles provide (Cava 2017[9]). That is why pairing a GLP-1 with adequate protein and resistance exercise is sensible for someone using it to help their knees. Any new or persistent joint pain on treatment should be evaluated by your clinician.

References

  1. 1.Bliddal H, Bays H, Czernichow S, Uddén Hemmingsson J, Hjelmesæth J, et al. Once-Weekly Semaglutide in Persons with Obesity and Knee Osteoarthritis. N Engl J Med. 2024. PMID: 39476339.
  2. 2.Messier SP, Mihalko SL, Legault C, Miller GD, Nicklas BJ, et al. Effects of intensive diet and exercise on knee joint loads, inflammation, and clinical outcomes among overweight and obese adults with knee osteoarthritis: the IDEA randomized clinical trial. JAMA. 2013. PMID: 24065013.
  3. 3.Bannuru RR, Osani MC, Vaysbrot EE, Arden NK, Bennell K, et al. OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis. Osteoarthritis Cartilage. 2019. PMID: 31278997.
  4. 4.de Ree RHGM, de Jong LD, Hazebroek EJ, Somford MP. Optimal timing of hip and knee arthroplasty after bariatric surgery: A systematic review. J Clin Orthop Trauma. 2024. PMID: 38766387.
  5. 5.Dunlop DD, Song J, Hootman JM, Nevitt MC, Semanik PA, et al. One Hour a Week: Moving to Prevent Disability in Adults With Lower Extremity Joint Symptoms. Am J Prev Med. 2019. PMID: 30902564.
  6. 6.Murphy LB, Cisternas MG, Theis KA, Brady TJ, Bohm MK. All-Cause Opioid Prescriptions Dispensed: The Outsized Role of Adults With Arthritis. Am J Prev Med. 2020. PMID: 32763134.
  7. 7.Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, et al.; SURMOUNT-1 Investigators. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022. PMID: 35658024.
  8. 8.Wilding JPH, Batterham RL, Calanna S, Davies M, Van Gaal LF, et al.; STEP 1 Study Group. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021. PMID: 33567185.
  9. 9.Cava E, Yeat NC, Mittendorfer B. Preserving Healthy Muscle during Weight Loss. Adv Nutr. 2017. PMID: 28507015.

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