Gel injections before knee replacement are often presented as a way to reduce osteoarthritis pain and postpone surgery. They are also called hyaluronic acid injections or viscosupplementation.
Some people report useful relief after these injections, while others notice little or no difference. Research findings and professional guidelines also vary, which makes it important to understand what is being injected, what the treatment may change, and what it cannot accomplish.
What are gel injections?
Hyaluronic acid is a substance that occurs naturally in synovial fluid, the fluid inside a healthy joint. It contributes to the fluid’s viscosity and helps joint surfaces move against one another.
Osteoarthritis changes more than the amount of cartilage inside your knee. It can also affect the composition and mechanical properties of the synovial fluid. Viscosupplementation involves injecting a manufactured hyaluronic acid product into your knee joint.
Depending on the product, treatment may involve one injection or a series of injections. The molecular weight, formulation, dosage, and treatment schedule can vary. These differences are one reason gel injections should not all be treated as though they are identical.
What hyaluronic acid may do
The proposed effects include changing the viscoelastic properties of joint fluid and influencing inflammatory or pain-related activity inside your knee. The common description that an injection simply “lubricates your knee” is easy to understand, but it is incomplete.
Hyaluronic acid does not remain inside your knee permanently, and its possible effects involve more than placing a lasting layer of lubrication between two joint surfaces.
If an injection helps, improvement may develop gradually rather than immediately. Some people report reduced pain or improved activity tolerance over the following weeks. Others do not experience a clinically useful change.
A gel injection may change symptoms for some people, but it does not replace lost cartilage or reverse osteoarthritis.
Unlike a local anesthetic, hyaluronic acid is not expected to provide immediate numbness. A lack of improvement during the first few days does not necessarily predict the final response. Your clinician can explain the expected timeframe for the specific product being used.
Why the research appears inconsistent
Studies of gel injections have reached different conclusions. Some report modest improvements in pain or function. Others find that the average benefit compared with a placebo injection is small and may not reach a level that patients would consider clinically important.
A large 2022 systematic review published in BMJ concluded that viscosupplementation produced a small reduction in pain compared with placebo, but the difference was below the study’s threshold for a clinically important improvement.
Professional recommendations also differ. The American Academy of Orthopaedic Surgeons does not recommend hyaluronic acid injections for routine use in symptomatic knee osteoarthritis. The American College of Rheumatology conditionally recommends against them. In contrast, the Osteoarthritis Research Society International includes them as an option for selected people with knee osteoarthritis.
These differences do not mean that every person will have the same result. They show that average study findings, product differences, osteoarthritis severity, expense, individual response, and patient preferences all contribute to the decision.
Who may be more likely to notice a benefit?
Research has not identified a guaranteed profile of a successful responder. Some evidence suggests that people with mild to moderate osteoarthritis may be more likely to notice improvement than people with advanced joint changes, but this is not a reliable prediction for an individual person.
If your joint space is severely reduced, your leg alignment has changed substantially, or pain and limited function have progressed despite other treatment, a gel injection may be less likely to provide enough improvement to alter your longer-term plan.
That does not make the decision automatic. Your imaging, symptoms, previous treatments, health history, goals, insurance coverage, and surgical timeline need to be considered together.
For practical education throughout the knee replacement process, be a Total Knee Success Insider. You will receive new podcast episodes, articles, and useful resources by email.
Measure function, not only pain
If you decide to try a gel injection, pain is not the only outcome worth observing. Consider whether you can walk farther, tolerate strengthening more comfortably, manage stairs with better control, sleep with fewer interruptions, or participate more fully in daily activities.
Choose a few functional markers before the injection and observe them over the timeframe provided by your clinician. This gives you more useful information than trying to remember whether your knee feels generally better.
If the injection reduces symptoms, the improved period may provide an opportunity to strengthen your legs, improve stamina, and prepare for future demands. Prehabilitation remains valuable whether surgery is approaching or you are trying to maintain your current function.
What gel injections do not change
Hyaluronic acid does not regrow cartilage, correct a joint deformity, or restore a severely narrowed joint space. It is a symptom-management option, not a structural cure for osteoarthritis.
Relief also does not prove that surgery will never be needed. It may provide additional time before surgery, but the duration and degree of improvement cannot be predicted with certainty.
If total knee replacement is already being considered, ask your surgeon whether receiving an injection would affect the proposed surgical date. Evidence about infection risk and preoperative injections continues to develop, and surgeons may have specific policies regarding the interval between an injection and surgery.
Potential drawbacks and side effects
Temporary soreness, swelling, warmth, or stiffness can occur after an injection. A more substantial inflammatory reaction is uncommon but possible. Infection is rare and requires prompt medical attention. Cost can also be significant when insurance does not cover the treatment.
Before proceeding, ask which product will be used, how many injections are required, what improvement is realistic, how long you should wait before evaluating the result, and what symptoms should prompt a call to the office.
Making the decision fit your larger plan
The central question is not whether gel injections work for everyone. They do not. The useful question is whether the expected possibility of improvement is reasonable for your knee, goals, expense, and timeline.
If surgery is becoming more likely, the free 2-Week Knee Replacement Launch Plan can help you organize essential preparations. You can also explore The Knee Replacement Game Plan™ for a more complete framework for preparing before surgery.
The next episode in this injection series examines platelet-rich plasma, commonly called PRP, including what it contains, what current evidence shows, and how to evaluate regenerative medicine claims.
Join the free Total Knee Success Insider for practical knee replacement education, new podcast episodes, and helpful resources. You can also sign up using the form at the bottom of this page.
References
- American Academy of Orthopaedic Surgeons. Management of Osteoarthritis of the Knee (Non-Arthroplasty): Evidence-Based Clinical Practice Guideline. 3rd ed. Published August 31, 2021.
- Brophy RH, Fillingham YA. AAOS clinical practice guideline summary: management of osteoarthritis of the knee (nonarthroplasty), third edition. J Am Acad Orthop Surg. 2022;30(9):e721-e729. doi:10.5435/JAAOS-D-21-01233
- Pereira TV, Jüni P, Saadat P, et al. Viscosupplementation for knee osteoarthritis: systematic review and meta-analysis. BMJ. 2022;378:e069722. doi:10.1136/bmj-2022-069722
- Kolasinski SL, Neogi T, Hochberg MC, et al. 2019 American College of Rheumatology/Arthritis Foundation guideline for the management of osteoarthritis of the hand, hip, and knee. Arthritis Care Res (Hoboken). 2020;72(2):149-162. doi:10.1002/acr.24131
- Bannuru RR, Osani MC, Vaysbrot EE, et al. OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis. Osteoarthritis Cartilage. 2019;27(11):1578-1589. doi:10.1016/j.joca.2019.06.011
Educational Disclaimer: This article provides general educational information and is not medical advice. It does not determine whether an injection is appropriate for a specific person, diagnose the source of symptoms, or replace guidance from a surgeon, physician, physical therapist, or other licensed healthcare professional. Injection decisions and timing before surgery must be individualized. Seek prompt medical attention for severe pain, increasing redness, drainage, fever, or other concerning symptoms after an injection.