Want to read more about joint injections? Check out our overview article here.
Below, you can read more about two types of joint injections, Hyaluronic Acid, and Steroids.
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 et al) 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.
Steroid injections are a common treatment of arthritis in people and animals. However, we know that repeated steroid injections can be detrimental to cartilage. We typically recommend reserving steroid injections as a last resort for “end-stage” disease when there is little to no cartilage remaining.
Steroids can be effective in decreasing inflammation and pain in the joint. Steroids are typically combined with HA when administered. One study showed equivalent results of HA plus steroids vs. ACP (Arthrex brand of PRP). Improvements were seen as soon as 1 week after injection and lasted at least 12 weeks (Franklin et al).