If you've lived with arthritis for long enough, you've likely been told about "the gel shot" or "the rooster shot" or "the natural shot." What all of these are talking about is an injection of hyaluronic acid (HA). What is hyaluronic acid? Sounds like something a dermatologist might market (and some do as skin creams), but for our purposes here it's a viscous substance that is made up of glycosaminoglycans (GAGs) to be technical. What these GAGs do are essentially act as a cushion or binding substance in the body's joints. Along with a compound called lubricin, hyaluronic acid is a major constituent part of normal joint fluid as both a cushion and lubricant.
In aged and arthritic joints, the size of the hyaluronic acid molecules are smaller than those of young, healthy joints. This contributes to the decreased ability of the molecules to cushion and lubricate. What these HA injections do is introduce large molecule hyaluronic acid back into the knee, hip, shoulder, etc. Note that some HA injections only contain small HA molecules (low molecular weight is the technical terminology), and these have been found less effective than those injections of large HA molecules (high molecular weight HA).
Interestingly, HA has been used in equine sciences for years. The indications are for horses which typically pull heavy loads or have synovitis (inflammation of the inner lining of the joint capsule). Also, there's some data to suggest that HA exerts an anti-inflammatory effect in settings with high levels of inflammation! Given that the destruction of articular cartilage is likely linked to inflammation, this could propose a secondary mechanism for HA's efficacy. Last, it has a very low side-effect profile. One manufacturer, Synvisc, makes it's HA from the comb of the rooster. Yes, that fleshy, red crown on the head of a rooster is a rich source of HA. Don't worry though, more chickens aren't harmed by the utilization of the comb as it was previously a throwaway portion of commercially grown chickens anyhow. Why do I tell you this? Well, because the HA that Synvisc makes can potentially cause an allergic reaction in those who have chicken or egg allergies. Other side effects are a transient synovitis or irritation of the knee capsule which can be quickly quelled with a steroid shot as well as some injection-related pain if the HA isn't injected into the knee but instead into the surrounding soft tissue. For this reason, I commonly use ultrasound guidance for HA shots in which I wish to confirm my needle placement.
So what's the story? Can you get one? Should you? Well, the answer to the latter is more personal, but hopefully I can elucidate some of the details. Hyaluronic acid has been shown to improve knee pain in knee OA; this is what the original research was done for. Due to the fact that osteoarthritis can be present in multiple joints, many providers will offer injections into other, typically larger, joints as well. However, most if not all insurances will only pay for injections into the knees since that was where the original research was done. What does this mean for you? First, it's an option for your knee OA pain and a reasonable one. Second, if you want it elsewhere, you'll have to pay out of pocket (about $500-$600, ouch!).
What's my take? I tell my patients that it's a low-risk option for refractory knee pain and one that is paid for by most insurances. In my opinion, if it keeps you from a surgeon's knife for a few more years, then it's a no-brainer to at least try it.