The healthy knee joint fluid contains a substance called hyaluronan (hyaluronic acid). Hyaluronan is highly viscous, allowing the cartilage surfaces of the bones to glide upon each other smoothly. It acts like a shock absorber and lubricant in the joint, allowing joints to move smoothly over each other. Patients with osteoarthritis have a lower-than-normal concentration of hyaluronic acid in their joints. Experts believe that adding hyaluronan to the arthritic joint will facilitate movement and reduce pain. Hyaluronan joint injections are quick and relatively painless.
During the procedure, if there is any swelling in the knee, the physician will remove (aspirate) the excess fluids before injecting the hyaluronan. Generally, the aspiration and the injection are done using only one needle injected into the joint.
The effectiveness of hyaluronan injection in treating arthritis is not clear. It has been proposed that hyaluronan is most effective if the arthritis is in its early stages (mild to moderate). However, studies on effectiveness show mixed results.