Viscosupplementation is a good choice of treatment in knee osteoarthritis

Although I have not as yet carried out an analysis of my knee osteoarthritis patients’ data whom I have treated with intraarticular (IA) hyaluronic acid (HA), it is something I fully intend to to. My practical experience suggests that IA HA effectively decreases knee pain and improves function and patient’s well-being.

Knee osteoarthritis (OA) is a progressive degenerative disease. As a synovial joint, in normal healthy states there are 2-3 mls of synovial fluid in the knee. HA is an important component of the synovial fluid with viscoelastic properties, protecting cartilage cells against physical and biochemical damage, providing a healthy, painless function. In knee OA viscoelasticity deteriorates, cartilage becomes overloaded, cartilage cells are lost, function and mobility decreases. Exogeneous HA replaces and supplements synovial fluid and provides viscosupplementation, a process whereby physiological conditions of the joint tissues are restored. HA also binds to synovial cells to stimulate biosynthesis of endogenous HA molecules. The result is a decrease in pain, better functionality and mobility, and a better quality of life.

Viscosupplementation with IA HA is an effective treatment for knee OA. There is good evidence of its effectiveness from randomized controlled trials. Compared to continuous NSAID treatment, IA HA proved equally efficient and demonstrated a more favorable safety profile in certain cases, i.e. in older patients and in those at greater risk of NSAID-induced side effects. HA is indicated in mild to moderate knee OA or in advanced stages of OA when surgical treatment is contraindicated.   

HA is not a rapidly acting agent, but rather the clinical effect on pain and function extends for a long period after administration, up to 6-12 months post-injection. The slow onset of its effect begins at week 4. Real-life evidence for long-term effectiveness comes from observational studies. IA HA injections were highly effective in improving resting and walking pain for up to 6 months and the patient’s concomitant analgesia could be reduced by  30-5o%. Adverse events of IA HA are very rare, the most common being transient and mild pain and swelling at the injection site.

Different HA preparations, with various molecular weights (MW) are known. Hyalgan (Fidia, Italy) is a linear low MW HA, whereas Synvisc (Genzyme, US) is a cross-linked high MW HA approved by the FDA, which equals the elastoviscous properties of the knee of a healthy, 18-27 year old man. Some clinical trials find no priority with respect to symptomatic efficacy between the HA preparations of various MWs. Some favor cross linked high MW HAs (hylans), based on their prolonged joint residence time. The optimal binding to synovial cell receptors occurs with intermediate MW HA.  

HAs are mainly produced synthetically by bacterial fermentation. They are highly purified, sterile and nonpyrogenic viscoelastic fluids. To achieve maximum effect 3-5 injections at weekly intervals are required, but at present there are ”mono” preparations providing therapeutic doses in one injection (e.g. Monovisc, Synvisc Mono). Injection technique is of prime importance for both efficacy and tolerance.

Recent consensus statements on the management of knee OA have been published. According to the statement of the European Society for Clinical and Economic Aspects of Osteoarthritis (ESCEO) IA HAs are ranked in step 3 when chondroprotective agents + paracetamol or topical NSAIDs (step 1) and oral NSAIDs (step 2) are ineffective. Nevertheless according to another Expert Group from Europe viscosupplementation should not only be used in patients who have failed to respond adequately to other modalities, but rather as a positive indication of knee OA therapy.