The results of hyaluronic acid injections for knee osteoarthritis vary with each patient. Some people experience complete relief from knee osteoarthritis symptoms, while others receive partial relief or no relief.1,2
Research Regarding Hyaluronic Acid Injections for Knee Osteoarthritis
Several clinical studies have investigated the effectiveness of hyaluronic acid injections in treating knee osteoarthritis.
A few findings from these studies include:
- Pain relief is not immediate, and usually begins around the fourth week after the initial injection.3-5
- Duration of relief periods may vary from 2 months up to 6 months.1,3-6 The most effective period is usually between weeks 5 and 13.1,7
- Multiple injections regimes may be more effective than a single injection in some people.8,9
- Additional injections may provide longer relief up to 3 years in some patients who show initial improvement with this treatment. This long period of pain relief may help postpone total knee replacement surgery in some cases.1
Not all studies conducted to test the effectiveness of hyaluronic acid injections in treating knee osteoarthritis have reported positive results. For this reason, some doctors may not recommend this treatment.2 Research also shows that these injections may not work in overweight people due to the narrowing of joint space in the knee.10
How Hyaluronic Acid Injections Work in the Osteoarthritic Knee
Research suggests that hyaluronic acid injections may work in several ways to reduce knee osteoarthritis symptoms.1,3 For example, hyaluronic acid injections may reduce inflammation and friction; and the slow the degeneration of cartilage and bone.
Effects on knee pain and inflammation
Hyaluronic acid injections may reduce knee osteoarthritic symptoms by one or more of its following properties:
- Lubrication. In some people, the viscosity of hyaluronic acid may provide better lubrication and shock absorption in the knee joint. These effects may reduce friction within the joint, thereby reducing pain and stiffness, and preventing the loss of cartilage and bone.1,3
- Anti-inflammatory effects. Research shows hyaluronic acid injections may provide anti-inflammatory effects such as reduced pain, inflammation, and/or swelling in the knee.1,3
- Pain-relieving effects. In some people, hyaluronic acid molecules form a boundary around nerve endings, preventing pain signals from being sent to the brain. These molecules also bind to other cells in the knee that signal pain. Through these mechanisms, knee pain may be decreased.1,3
The viscosity of hyaluronic acid may also have positive effects on the cartilage, bone, and other surrounding tissues in the knee.
See Knee Anatomy
Effects on knee cartilage and bone
In general, hyaluronic acid that is injected in the knee stays in the joint for only a few days. However, the results may last for months. Proponents believe this extended pain relief suggests hyaluronic acid injections may actually modify the osteoarthritic disease process—and not just suppress the symptoms.1,3
Specifically, in some people, hyaluronic acid knee injections may act by:
- Aiding the growth and protection of cartilage by stimulating an increase in the growth of cartilage-producing cells, called chondrocytes. These injections also protect existing chondrocytes, thereby increasing the overall cartilage formation.1,3
- Strengthening existing cartilage by producing important proteins (proteoglycans) and carbohydrates (glycosaminoglycans).3
- Strengthening existing bone by altering the density and thickness of the knee’s subchondral bone (bone that lies immediately below the cartilage). The changes in bone structure may help reduce stresses on the cartilage when the knee bears weight.3
- Stimulating the body to produce its own hyaluronic acid, in turn restoring the quantity of hyaluronic acid in the knee and providing long-term effects.1,3
These effects may help prevent the progression of osteoarthritis.
Hyaluronic Acid Injections: Approved Use and Brand Names
The US Food and Drug Administration (FDA) has approved the use of hyaluronic acid injections for knee osteoarthritis. The FDA also states that this injection must be used after other treatments such as physical therapy and the use of pain-relieving medications have been tried and failed.7 Off-label use of hyaluronic acid injections may be considered by some doctors in treating osteoarthritis of the ankle, shoulder, and thumb joints.
Depending on the pharmaceutical brand, there can be one (Synvisc One), three (Euflexxa, Synvisc), four (Orthovisc), or five (Hyalgan) injections of hyaluronic acid for knee osteoarthritis. For brands using more than one injection, each shot is given once a week (for 3 to 5 weeks).7 Generic formulations are also available.