The Science of Knee Gel Injections: How They Work and Why They're Effective
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Last Updated On: March 29, 2024

The Science of Knee Gel Injections: How They Work and Why They’re Effective

Published on: Mar 6, 2023

Knee gel injections, also known as viscosupplementation, have gained popularity as a treatment option for knee pain due to conditions like osteoarthritis and injuries. Our upcoming blog post delves into the scientific mechanisms of how these injections work to alleviate inflammation and pain.


Osteoarthritis (OA) is a collective term for conditions caused by degenerative-inflammatory joint changes, namely cartilage and bone tissue. The cause of this condition is mainly the physiological process of aging, but osteoarthritis can develop at any age. 

It occurs in one in three people aged 45-64 years old and is present in 60-70% of people over 65 years old. Most often, OA affects women. A decrease in estrogen levels usually facilitates this after the age of 40 years old.

The main symptom of osteoarthritis, which forces the patient to consult a doctor, is pain in the joint. It can be severe, limiting mobility, or moderate, occurring only during particular movements. 

Several factors contribute to the development of osteoarthritis, even at a young age:

  • Mismatch of physical load on the joint and its compensatory capabilities;
  • Transferred inflammatory lesions of the joints: arthritis, bursitis, etc.;
  • Hemorrhages into the joint cavity;
  • Endocrine gland diseases;
  • Congenital disorders, hereditary predisposition;
  • Vascular disorders, as a result of which the blood supply to the joint is disturbed;
  • Flat Feet;
  • Overweight;
  • Joint dysplasia.

Unfortunately, aging, as a process, is irreversible. However, joint changes are responsive to appropriate treatment.

There are the following solutions for the medical treatment of osteoarthritis:

  • NSAIDs;
  • Opioids (in some cases);
  • Corticosteroids (in the acute stage);
  • Chondroprotectors;
  • Viscosupplementation (intra-articular injections of hyaluronic acid) like when you buy Synvisc.

What Are Knee Gel Injections?

Intra-articular injections of hyaluronic acid (IAHA or viscosupplementation) are a modern and effective treatment method used to treat the arthrosis of various joints (primarily knees), especially in the early stages. 

The Knee Gel Injections are effective in the rehabilitation period after surgical interventions to restore homeostasis in the joint quickly. 

They relieve inflammation and pain syndrome. They make the intra-articular fluid more dense and viscous, which results in the cartilage tissue being better protected and recovering more quickly.

How Do Knee Injections Work?

In older adults or those who suffer from joint diseases, the quantity of lubricant found in the joints decreases sharply; It ceases to perform its protective and lubricating functions, which leads to cartilage tissue destruction. This process results in a worsening of the situation by provoking inflammation and increasing joint pain.

Introducing knee injection gel into the joint cavity reduces these detrimental effects by replacing the diminished synovial fluid, increasing its viscosity.

Gel injections also help when osteoarthritis has not yet developed, but when there is a deficiency of synovial fluid, a heavy load on the joint (for example, during power sports), or when the joint needs additional lubrication.

IAHA Benefits And Side Effects

Advantages of knee gel injections:

  • Pain syndrome and swelling quickly decrease;
  • Shortened duration of the treatment process;
  • Reduction of oral painkillers, helping to avoid unwanted side effects;
  • Increased range of motion in the joint;
  • The normalization of the composition and physiological properties of synovial fluid;
  • Postponed need for joint replacement surgery;
  • A prolonged period of remission of chronic diseases;
  • Long-term therapeutic effects are visible for a year.

Although knee injections for painful joints have many benefits, it’s essential to understand the possible risks of any treatment performed. IAHA may result in some minor side effects, but they are significantly less severe compared with the prolonged use of prescription drugs or corticosteroid injections. These may include knee pain, bruising, swelling at the injection site, skin irritation, rash or itching around the knee, headache, nausea, and muscle pain. 

In most cases, the side effects from knee gel injection usually resolve within a few days. However, it’s essential to instruct your patient to inform you immediately if they experience any adverse complications so that you can switch to a different knee arthritis treatment.

Patient Selection for Knee Gel Injections

Based on data presented by systemic reviews and MAs on the use of IAHA, the ideal patient should meet the following criteria for viscosupplementation:

  • Meet the ACR criteria for OA (pain in the knee and at least 3 of the following: over 50 years old, crepitus, bony tenderness, bony enlargement, and no palpable warmth).
  • Have a documented diagnosis of primary OA of the target knee.
  • Demonstrate radiographic evidence of OA in the tibiofemoral compartment of the target knee.
  • Have a recent history of continued OA pain in the target knee, despite attempted nonpharmacological and pharmacological treatments.
  • Have an abnormal arthritis outcome score (on WOMAC or other evidence-based OA index).
  • Not be overweight.
  • Younger than 65 years old.

Treatment with HA is ideal for patients who have not had adequate pain relief from oral medications (NSAID, acetaminophen), exercise and physical therapy.

Other candidates for knee gel injections include patients with existing renal or gastrointestinal intolerance for NSAID and those with severe OA who are either poor surgical candidates or must postpone total knee replacement. In this subset of patients who are less-than-ideal candidates for surgery, IAHA injections can provide both pain relief and improved function.

Administering Hyaluronic Injections To The Knee

Before the procedure, the patient must undergo the necessary examinations and tests to determine any contraindications, after which a treatment program is designed.  

Not many contraindications to the procedure exist. 

  • Pregnancy and lactation;
  • Young age;
  • Infectious diseases in the acute period.
  • Inflammation of the joints;
  • Skin diseases around the joint;
  • Broken integrity of the skin at the injection site;
  • Increased sensitivity to any of the components of the medicine.

Manipulation must be performed by a surgeon or orthopedic traumatologist, using only disposable syringes with a special needle for injection. The primary difficulty in the procedure is reaching the joint gap accurately. For this, the use of ultrasound control is essential.

Analgesia is unnecessary as the sensations are similar to a regular intramuscular injection. However, at the request of the patient, local anesthesia is possible.Ā 

Immediately after the injection, we recommend moving the joint to distribute the gel evenly. A tight bandage is then applied, and post-treatment recommendations should be given, namely avoiding physical exertion for a certain period and specific changes in the diet. The recovery time for knee gel injection is usually two days.

Products to Consider

There are several dozen hyaluronic acid preparations for intra-articular injections for sale on the pharmaceutical market. They differ in molecular weight, the percentage of hyaluronic acid, the method of obtaining the molecule, etc. However, no universal drug would suit all patients and be the most effective for all cases; doctors, therefore, need to consult each patient individually and choose the most suitable treatment depending on the stage and course of the osteoarthritis.

We recommend you try the products from the orthopedic injections page on our website. One example of a product in this category is Synvisc and its newer version Synvisc One.


It’s essential to note that IAHA injections do not cure all knee conditions which cause pain. Nevertheless, these injections have shown great potential in treating osteoarthritis, improving patients` mobility, and relieving pain for up to six months.

Viscosupplementation gives the possibility of avoiding a radical surgical intervention to replace the affected joint or, at least, postponing the operation for a later date.


How long do knee gel injections last?

After knee gel injections, most patients have pain relief for 4-6 months. 

Individuals can have hyaluronic acid injections approximately every six months. Many patients report that the injections provide enough relief to delay or even avoid knee replacement surgery.

Can a patient walk after a gel injection in the knee?

After a hyaluronic acid gel injection, patients must rest and not strain the knee joint for at least 48 hours and avoid prolonged walking or standing.

They need to refrain from activities such as:

  • jogging,
  • soccer,
  • tennis,
  • heavy lifting,
  • standing for a long time. 

Are gel injections good for the knee?

The knees can experience gradual degeneration due to arthritis; This leads to reduced lubrication and cushioning within the joints. HA gel injections can address this issue, helping to restore the proper lubrication and cushioning within the joints. The gel injections are also effective in reducing inflammation and preventing further wear and tear of the joint cartilage. 

Are gel injections for knees painful?

Generally, there is no pain when using ultrasound guidance to perform the injection.

If the pain felt by the patient is excruciating, the injection probably has not gotten into the joint. Also, failing to get in the joint means the risk of a severe reaction such as ‘pseudo-sepsis’ increases.


Bhadra, A. K., Altman, R., Dasa, V., Myrick, K., Rosen, J., Vad, V., Peter Vitanzo, J., Bruno, M., Kleiner, H., & Just, C. (2017). Appropriate Use Criteria for Hyaluronic Acid in the Treatment of Knee Osteoarthritis in the United States. Cartilage, 8(3), 234-254.

Kolasinski, S. L., et al. (2020). 2019 American College of Rheumatology/Arthritis Foundation guideline for the management of osteoarthritis of the hand, hip, and knee.

Jared R.H. Foran, MD, FAAOS, Stuart J. Fischer, MD, FAAOS. Viscosupplementation Treatment for Knee Arthritis. OrthoInfo. American Academy of Orthopaedic Surgeons.

FAQs about arthritis. Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Division of Population Health. (2021).

Abin Puravath, MD. Hyaluronic acid. American College of Rheumatology (2020).

Fusco, G., Gambaro, F. M., Matteo, B. D., & Kon, E. (2021). Injections in the osteoarthritic knee: A review of current treatment options. EFORT Open Reviews, 6(6), 501-509.

Divine, J. G., & Shaffer, M. D. (2011). Use of Viscosupplementation for Knee Osteoarthritis. Current Sports Medicine Reports, 10(5), 279ā€“284.