Hyaluronic Acid (HA)
HA is a normal component of cartilage and joint fluid that provides lubrication.
In arthritic joints, the HA molecule is smaller than normal leading to a less viscous fluid. Intra-articular injection of synthetic HA is believed to alter the metabolism of naturally occurring HA and decrease symptoms of OA.
There remains debate in human and veterinary sports medicine as to the efficacy of HA. This debate stems from a wide variety of study designs and products that have been tested. HA products primarily differ in their molecular weight and are categorized as Low Molecular Weight (LMW, 500-730kDA) or High Molecular Weight (HMW, ~6,000kDA).
HMW more closely resembles normal HA in non-arthritic joints (5,000-10,000kDA). A study was conducted in dogs that had experimentally induced OA and compared HMW and LMW products as well as one injection to 3 injections. (Pashuck TD, 2016)
Results found that both products and both treatment protocols were significantly better than saline control; however, the HMW was better than LMW. The maximal benefit in pain, lameness, function, and range of motion was seen 4-8 weeks after injection and began to subside at 6 months.
References
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Canapp SO, Cross AR, Brown MP, et al. Examination of synovial fluid and serum following intravenous injections of hyaluronan for the treatment of osteoarthritis in dogs. Vet Comp Orthop Traumatol 2005;18:19-174.
Smith GN, Mickler EA, Myers SL, Brandt KD. Effect of intraarticular hyaluronan injections on synovial fluid hyaluronan in the early stage of canine post-traumatic osteoarthritis. J Rheumatol 2001;28:1341-1346.
Pashuck TD, Kuroki K, Cook CR, et al. Hyaluronic acid versus saline intra-articular injections for amelioration of chronic knee osteoarthritis: A canine model. J Orthop Res 2016; 34:1772-1779.
Carapebe GOL, Cavaleti P, Nicacio GM, et al. Intra-articular hyaluronic acid compared to traditional conservative treatment in dogs with osteoarthritis associated with hip dysplasia. Evidence-Based Comp Alt Med 2016.