Viscosupplementation injections are when a gel-like fluid called hyaluronic acid is injected into the knee joint. Hyaluronic acid is naturally found in the synovial fluid surrounding the knee joint, and the injection acts as a lubricant in the joint. Patients with arthritis have a smaller amount of hyaluronic acid in their joints, so the theory is that these injections will help with range of motion and pain reduction. Examples of viscosupplementation injections include Supartz, Euflexxa, Synvisc, or Orthovisc.