7 Key Insights into Gel Shots for Knees: Side Effects, Benefits

What is a gel shots in the knee?

There are several types of injections that can be administered in the knee. Here are the four main ones:

1. Corticosteroid injections (cortisone),
2. Hyaluronic acid injections = gel shots,
3. Local injections of lidocaine or Xylocaine,
4. Platelet-Rich Plasma (PRP) injections.

In this article, I am focusing on hyaluronic acid injections (gel shots).

Where does the injected hyaluronic acid come from?

Hyaluronic acid is a natural substance found in our joints and skin. When injected into the knee, it acts as a lubricant to reduce pain and improve mobility. (We will see later if it really works.)

A significant portion of the injected hyaluronic acid is synthetically manufactured in a laboratory. This type of hyaluronic acid is produced through bioengineering processes to create a substance that is similar to what is naturally produced by the human body.

Another historical source of hyaluronic acid was extraction from the combs of roosters 🐓. This method is less common nowadays due to ethical concerns and the possibility of allergic reactions.

Why are gel shots performed?

Most often, hyaluronic acid is injected in the case of knee osteoarthritis (femoro-tibial osteoarthritis or femoro-patellar osteoarthritis in medical terms!).

This is the same substance used in medicine and cosmetic surgery, for example, to address wrinkles.

Less frequently, these injections are also recommended for meniscus problems, cartilage issues, unexplained knee inflammation, or other knee problems such as synovitis.

Is knee viscosupplementation the same thing?

Knee viscosupplementation is a specific type of hyaluronic acid injection. It’s simply the name given to these injections when performed for knee arthritis.

Whether called “viscosupplementation” or “hyaluronic acid injection,” it’s the same substance injected. The same procedure, effects, and aftercare apply.

How to perform a knee shot?

Sports doctors or rheumatologists typically administer these injections.

Here’s how the injection is carried out:

1. Your doctor disinfects the area.
2. Sometimes, local anesthesia is applied.
3. Your doctor inserts a fine needle into the knee joint and injects hyaluronic acid directly into the joint.
4. You can return home immediately with some instructions.

The quantity of hyaluronic acid and the number of injections may vary depending on the product brand and the practices of your healthcare professional.

In United-States, physical therapists are not authorized to perform injections.

What are the proven effects of gel shots for knee?

Gel shots for knee have been quite well studied in research. These studies compare the progress of people who received these injections versus those who received nothing, a placebo, or another treatment.

This helps provide a bit more certainty that any observed improvement (or side effects) is due to the injection and not something else. For example, it could be related to the natural fluctuation of symptoms over time, regardless of any intervention!

Here’s an overview of studies on the effects of hyaluronic acid injections for knee osteoarthritis, gathered from the “Google of medical studies,” PubMed.

What do studies say about the effects of hyaluronic acid injections?

When there are numerous studies on a subject, some research teams publish comprehensive reviews of these studies, selecting the most reliable ones.

In the table below, I precisely summarize the results of the latest reviews of studies conducted on hyaluronic acid injections.

Then, I share my insights on the matter.

For What Issue	Research Team Conclusions	Reference
Knee Osteoarthritis (21,163 participants)	Strong conclusive evidence indicates that viscosupplementation leads to a slight reduction in knee osteoarthritis pain compared to a placebo, but the difference is less than the clinically important minimum difference between groups. Strong conclusive evidence also suggests that viscosupplementation is associated with an increased risk of serious adverse events compared to a placebo. The results do not support widespread use of viscosupplementation for knee osteoarthritis treatment.	🇨🇦 🇬🇧 🇨🇭 🇨🇳 Pereira 2022
Knee Osteoarthritis	In the majority of studies, hyaluronic acid (HA) was administered in a single injection (52.6% of studies) or in three weekly injections (28.9% of studies). Intra-articular hyaluronic acid injections have a limited role in the treatment of knee osteoarthritis in patients who do not achieve sufficient pain relief with topical or oral medications and physiotherapy. They are safe and effective, except for minor side effects such as local pain and short-term swelling. Severe allergic reactions are extremely rare. They provide adequate pain relief and functional improvement for up to six months, regardless of the number of injections and the type of preparations used.	🇦🇪 Chavda 2022
Athletes with degenerative cartilage lesions or knee osteoarthritis	Clinical evidence available remains limited, with only a few published studies and an overall low level of evidence.	🇮🇹 Marziani 2023
Injection after knee arthroscopy	Although hyaluronic acid injection after knee arthroscopy is safe, the available evidence does not support its effectiveness for pain relief and functional recovery.	🇨🇳 Mao 2023
Knee Osteoarthritis	Investigators’ conflicts of interest (and study funding) did not significantly influence the frequency of favorable outcomes or the level of evidence in studies.	Via 2023 🇺🇲
Knee Osteoarthritis	From a healthcare system perspective, data show a favorable cost profile for hyaluronic acid injections, a reduction in the use of opioids and corticosteroids, and a delay in the need for total knee replacement compared to taking anti-inflammatory or corticosteroid. This is especially true for early-stage osteoarthritis.	Ranawat 2023 🇺🇲

I grant you, it’s a lot of information, and some of it is contradictory.

Here’s what I take away from it and why.

In the face of contradictory data of this kind (some syntheses concluding an interest, others not), I tend to align with the more skeptical results.

This means that I place more trust in publications that observe an unfavorable benefit/risk balance for hyaluronic acid knee injections at the individual level.

Why? For at least these two reasons:

1. Studies concluding that hyaluronic acid injections do not have a clinically significant effect on knee osteoarthritis rely on a more cautious data analysis.
2. Negative results are less likely to be published than positive results. This can lead to an overestimation of the effect of a treatment, a well-known bias in research, the publication bias.

This bias has been specifically highlighted for studies on hyaluronic acid knee injections:

We found evidence of the non-publication of many industry-funded trials, despite their adequate statistical power.

Pereira 2022

I’m not the only one adopting this approach.

For instance, the independent French medical journal Prescrire, of which I am one of the numerous reviewers since 2018, says this about hyaluronic acid knee injections:

“Knee Osteoarthritis: Avoid intra-articular hyaluronic acid. Intra-articular injections of hyaluronic acid modestly relieve patients suffering from knee osteoarthritis at best, at the cost of local reactions, and sometimes serious adverse effects.”

Prescrire 2013

Of course, when considering the value of injections for YOU, you are the only one who can decide their relevance to you. Perhaps, for you, these potential small benefits outweigh the potential risks.

We all assess the benefit/risk balance differently.

On average, people receiving a hyaluronic acid knee injection rate their pain 5 points lower than those receiving a placebo, on a scale from 0 to 100. For example:

• People receiving a placebo may report pain at 35/100.
• People receiving the injections may report pain at 30/100.

Can we expect a change in these conclusions if new studies are conducted? Clearly, no. Here’s what a research team says about this:

“There has been a spectacular increase in the number of clinical trials after 2009, when sufficient evidence was already available to refute the benefits of viscosupplementation beyond those obtained with a placebo.”

Pereira 2022

Does one injection of hyaluronic acid in the knee suffice?

A single injection of hyaluronic acid in the knee can be sufficient.

Some studies assess whether the effectiveness of injections on pain or other parameters is influenced by the number of injections received.

It appears not to be the case (Chavda 2022).

Often, your doctor may still suggest additional injections if there is no effect after the first one.

How long does it take for the injection to have an effect?

People who feel relief after a knee injection typically experience it within a few days, at most a few weeks.

The effects of the injection last at best for 6 months (even if you’ve had multiple injections).

Source: Chavda 2022

When and why doesn’t the injection work?

The established primary factor for the lower effectiveness of injections is having knee osteoarthritis already at an advanced stage.

However, even people with mild osteoarthritis may not feel any improvement. That’s why one of the main reviews of studies on the subject does not recommend the use of hyaluronic acid knee injections for osteoarthritis.

Is it normal to have knee pain after gel injections?

It is common and not alarming to experience pain after a hyaluronic acid injection. Even if you are among those for whom the injection “will eventually work” and provide more relief than average.

Why?

Here are some possible reasons:

• Inflammatory reaction: the injection itself can cause slight irritation and a local inflammatory reaction in the knee joint. This reaction can lead to temporary pain (a few hours or a few days).
• Expansion of synovial fluid: hyaluronic acid is injected directly into the knee joint. As there is more fluid, this can exert pressure on the surrounding tissues, causing a sensation of tension and temporary pain.

Much more rarely, it could be a side effect related to an allergy or infection.

Are there side effects of gel injection in knee? Is it dangerous?

The possible side effects of hyaluronic acid knee injections and their frequency are quite well-known since there are hundreds of studies on the subject, in addition to cases reported outside clinical trials.

3.7% of people receiving viscosupplementation had a side effect classified as severe, compared to 2.5% in the placebo group.

Here are the side effects categorized as severe that occur most frequently in people receiving a hyaluronic acid injection for knee osteoarthritis compared to those receiving a placebo (Pereira 2022).

Category	Medical Term	Simple Explanation
Digestive Issues	Diverticulitis	Inflammation of small pouches in the colon wall, called diverticula.
	Esophagitis	Inflammation of the esophagus, the tube that carries food from the mouth to the stomach.
	Cholecystitis	Inflammation of the gallbladder, the organ that stores bile produced by the liver.
Metabolic Issues	Hyperglycemia	High levels of sugar in the blood, often associated with diabetes.
Cardiac Issues	Atrial Fibrillation	Irregular heartbeat.
	Congestive Heart Failure	Inability of the heart to pump blood effectively.
Circulatory Issues	Deep Vein Thrombosis	Formation of a blood clot in a deep vein of the body.
Respiratory Issues	Pneumonia	Lung infection.
Pulmonary Issues	Asthma	Chronic respiratory disease characterized by episodes of difficult breathing.
Prostate Problems	Prostate Disorders	Various conditions affecting the prostate, a gland in the male reproductive system.
Cancer-Related Issues	Carcinoma	Type of cancer that develops from epithelial cells.
Gallbladder Issues	Cholecystitis	Inflammation of the gallbladder.

As you have noticed, these types of effects also occur in people receiving a placebo. That’s why there may not necessarily be a established causal link between the injection and the event (establishing such a link is challenging).

These side effects are, therefore, rare. The more common side effects after a hyaluronic acid injection in the knee include:

• Short-lived pain.
• Mild inflammation of the knee, becoming red and warm.
• Stiffness and difficulty bending the knee.

Source: InformedHealth 2021

What kind of rest after knee gel shots?

Your doctor may advise you to “take it easy” or not to “overdo it” after your knee infiltration. What does this mean specifically?

In international recommendations, nothing very precise is mentioned on this subject.

The injection can cause mild inflammation of the knee, and excessive physical activity can too.

It is better to avoid excessive physical activity for at least a few days.

However, if you are accustomed to, for example, walking for an hour every day, that is not considered excessive physical activity!

See also: Can you walk after knee injection?

Can you play sports after a hyaluronic acid knee injection?

Yes, it’s the same reasoning.

If you are used to regularly exercising, there’s no problem with resuming activity in the days following the injection, if you feel up to it.

However, if you are relying on the injection to get back into sports and haven’t done any for years, you should start very gradually.

But this advice applies even if you haven’t had a hyaluronic acid injection!

Does Medicare cover the cost of knee gel injections?

Medicare will cover knee injections that approved by the FDA. This includes hyaluronan injections.

The coverage is good for one injection every 6 months. In general, patients will be responsible for paying a portion of the costs associated with knee gel injections, even if Medicare does cover the procedure. This includes things like deductibles, copayments, and coinsurance.

How much does an injection cost? You need to consider:

• The cost of the product.
• The cost of the consultation.

Original Medicare will cost 20% coinsurance. Knee gel injections covered by insurance will vary based on the carrier and plan you have.

On average in the United States you can expect that each injection could be about $1,200.

What to do instead of a hyaluronic acid knee injection?

Browsing my website, you will find many articles on various pathologies for which injections are sometimes used.

These articles generally cover different types of existing treatments.

For example:

• PRP knee injections: Does it work?
• How to walk for your arthritic knee?
• My articles on knee replacement

***

Any more questions? An experience to share, a viewpoint to express? Head to the comments section 🙂!

 📚 SOURCES

Pereira TV, Jüni P, Saadat P, Xing D, Yao L, Bobos P, Agarwal A, Hincapié CA, da Costa BR. Viscosupplementation for knee osteoarthritis: systematic review and meta-analysis. BMJ. 2022 Jul 6;378:e069722. doi: 10.1136/bmj-2022-069722. PMID: 36333100; PMCID: PMC9258606.

Chavda S, Rabbani SA, Wadhwa T. Role and Effectiveness of Intra-articular Injection of Hyaluronic Acid in the Treatment of Knee Osteoarthritis: A Systematic Review. Cureus. 2022 Apr 26;14(4):e24503. doi: 10.7759/cureus.24503. PMID: 35651409; PMCID: PMC9135165.

De Marziani L, Sangiorgio A, Bensa A, Boffa A, Andriolo L, Filardo G. Intra-articular injections in sport-active patients with degenerative cartilage lesions or osteoarthritis of the knee: a systematic review. J Exp Orthop. 2023 Nov 8;10(1):112. doi: 10.1186/s40634-023-00674-0. PMID: 37938446.

Mao B, Pan Y, Zhang Z, Yu Z, Li J, Fu W. Efficacy and Safety of Hyaluronic Acid Intra-articular Injection after Arthroscopic Knee Surgery: A Systematic Review and Meta-analysis. Orthop Surg. 2023 Jan;15(1):16-27. doi: 10.1111/os.13602. Epub 2022 Nov 21. PMID: 36411508; PMCID: PMC9837239.

Via GG, Brueggeman DA, Lyons JG, Frommeyer TC, Froehle AW, Krishnamurthy AB. Funding has no effect on studies evaluating viscosupplementation for knee osteoarthritis: A systematic review of bibliometrics and conflicts of interest. J Orthop. 2023 Apr 4;39:18-29. doi: 10.1016/j.jor.2023.03.015. PMID: 37089621; PMCID: PMC10114245.

Ranawat A, Guo K, Phillips M, Guo A, Niazi F, Bhandari M, Waterman B. Health Economic Assessments of Hyaluronic Acid Treatments for Knee Osteoarthritis: A Systematic Review. Adv Ther. 2023 Oct 30. doi: 10.1007/s12325-023-02691-y. Epub ahead of print. PMID: 37899384.

Acide hyaluronique intra-articulaire : à éviter dans la gonarthrose” Rev Prescrire 2013 ; 33 (357) : 528. (pdf, réservé aux abonnés)

InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Osteoarthritis of the knee: Do knee injections help? 2019 Jul 18. Available from: https://www.ncbi.nlm.nih.gov/books/NBK544975/