Gel shots (hyaluronic acid)...do they work? What are they?

Many different names for this are out there: gel shots, chicken shots, HA injections, viscosupplementation, etc. Approved for use in the US in 1997, this non-surgical treatment modality has become a popular option for many of the 21 million Americans who suffer from osteoarthritis.
First, a quick primer on osteoarthritis. For those of you who eat chicken, speaking of that, look at the end of the drumstick next time. This is part of the knee of the chicken. There is a shiny white surface on there. This is  articular or what I call 'surface' cartilage which is a key component to every joint in the body. When you're born that surface is nice and shiny, round and smooth. Over time it wears down and becomes rough and flat. This cartilage degradation is what is referred to as 'osteoarthritis'. The causes are multifactorial but affect everyone on earth and are mostly mechanical. They include: age > 50, obesity, gender (female > male), injuries, instability, malalignment (like the tires on your vehicle!), and genetics (like the different brands of tires which wear at different rates. In other words, some folks are born with a set of Pirelli tires, others have Goodyear). Now the cartilage degradation that occurs is not necessarily painful. What causes the pain is the inflammation that occurs in the joint lining, the capsule or tissue envelope surrounding the joint. It is pain that drives the treatment for the condition. Why some people have lots of pain and only intermediate degrees of the osteoarthritis and some who have advanced joint surface damage but minimal symptoms is not well understood. The bottom line is that today, the goals of treatment for osteoarthritis are to:
1) Reduce pain 2) Maintain mobility 3) Minimize disability 4) Halt progression. No non-surgical treatments at this time have conclusively demonstrated the capability to make the joint surfaces smooth again. Nothing has been shown to rebuild or regrow articular cartilage.
Current non-operative therapies for osteoarthritis include:
1) Modalities, i.e heat, ice ace bandaging 2) Weight reduction 3) Aerobic exercise 4) Strength training 5) Assistive devices (cane, walker etc) 6) Physical therapy 7) Bracing 8) Medications: tylenol, advil, alleve etc 9) Cortisone injection 10) HA injections.
I will now present this list of HA FAQs which should cover just about everything . References are provided where possible. If you have any other questions left out let me know.
1) What is HA? HA or hyaluronic acid is a major component of joint fluid. It is a protein polymer which provides the shock absorbing and other maintenance functions of the joint. Specifically it enhances viscoelasticity, joint lubrication, anti-inflammatory and anti-nociceptive (anti-pain) properties of the joint fluid. Think of it as the body's version of Pennzoil, Mobil 1 or whatever your favorite motor oil is!
2) How do HA injections work? Chondrocytes are cells that exist in the articular surface (surface cartilage) of the joint and these are the cells that produce the HA normally. When the cartilage wears down, the HA in the joint decreases. HA injections serve to replenish the joint's supply of HA, thereby restoring viscoelastic, lubricating and shock absorbing ability of the joint fluid. However, recent data suggests that HA also has many anti-inflammatory properties. It's not just a 'lube job'!
REFS: Ghosh P Arthritis Rheum August 2002; Balazs, E. J. Rheumatol 1993; Moreland Arthritis Res Ther 2003
3) Does HA rebuild or regrow cartilage? The short answer is no. See the discussion at the top.
4) Why do some HA therapies consist of 1 injection and others are as many as 5? The short answer is that this is the result of the American free market system and competition. Much like Advil vs Alleve vs Motrin, all anti-inflammatory medication with the same reported effects, there are currently 5 approved HA therapies in the US. All are weekly injections ranging from 1 to 5 weeks: Orthovisc, 3-4; Synvisc, 1 or 3; Euflexxa, 3; Hyalgan and Supartz 3-5.No data exists that conclusively demonstrates the superiority of 1 brand or 1 specific amount of injections. In my practice I first started with Synvisc, 3 injections, then went to Supartz 3 injections with no change in outcomes.
5) Where does the injectable HA come from? Orthovisc and Euflexxa are produced form bacterial cells; Synvisc, Hyalgan and Supartz are made from the cartilage in rooster combs. This is why some people refer to these injections as "chicken shots", but don't worry. No one has been seen to grow feathers or start crowing in the early morning following these injections!
6) Is HA more effective than anti-inflammatory medication or cortisone? In a 2005 study, HA was shown to be 66% more effective than placebo whereas NSAID was 30-50%. Longer term benefits were noted in comparison to cortisone. Specifically, < 4 weeks there was no difference between cortisone and HA, but from 4 weeks to 6 months HA injections were superior. REF: Bellamy  N. et al Cochrane Database Sys Rev 2005;2:CD005328
7) Do HA injections work and if so, how long do they last? As in number 6 above, most studies suggest the overall efficacy is comparable or better than NSAID, cortisone, arthroscopy and PT and results in moderate pain relief overall 60-70% of the time. In cases where it is effective, symptoms are usually improved for a minimum of about 6 months, but it can be much longer. In some cases it can last for up to 1-2 years. REFS: Waddell: Drugs Aging, 2007; Divine et al: Clin Orthop Rel Res, 2007
8) If it works for me can it be done again? Yes. There are studies documenting safe and effective repeat usage. REF: Scali JJ. Eur J Rheumatol Inflamm 1995; 15:57-62
9) What are the side effects?
Side effects are generally local at the injection site and include redness (0.4%), swelling (1%), and pain (2.5%). Severe inflammation with knee swelling is rare and usually resolves in 72hrs but can take 1-2 weeks for full resolution.
10) How do I know if HA would be a good option for me? Your doctor can help decide that, but generally HA is reasonable if you have a diagnosis of osteoarthritis, cannot take NSAID (anti-inflammatory meds such as Advil etc) or NSAID is ineffective, cortisone does not last, you're too young or not ready for total joint replacement and other conservative measures have failed. A 'good' candidate in terms of likelihood of success is someone with mild-moderate osteoarthritis, no significant knee malalignment (not too bowlegged or knock-kneed), and no evidence for inflammatory arthritis (rheumatoid etc.). Again, osteoarthritis is the sort of 'wear and tear' variety. Inflammatory arthritis is totally different. That is a condition where there is an intrinsic medical problem that causes joint damage. Rheumatoid arthritis is a disease of the immune system. Gouty arthritis is a metabolic disease. There are a hundred or so conditions such as these falling into the category of inflammatory joint disease where HA is not indicated for treatment. Practically speaking I will recommend HA injections if nothing else has worked before doing a knee replacement, unless they have already tried that or the pain and severity of the arthritis is just too great, which is a clinical judgment call.
11) Do insurances cover it? Just about all insurances cover it, however they may only cover specific brands. Some will cover only Euflexxa, others Supartz, etc. Re-injections are also covered but usually only if administered 6 months or more after the previous series.
12) What is the difference then between cortisone and HA and why would you administer one over the other ? Cortisone is a powerful anti-inflammatory medication that works well for sudden flare-ups of osteoarthritis. It is rapidly effective over days and has an excellent short term response. However it has no appreciable effect on joint function in terms of lubrication, shock absorption etc. and is not usually effective over the course of months. If an individual has moderately severe OA (osteoarthritis) affecting the whole knee and has not had injection therapy before, we will usually recommend cortisone initially as it is only a single injection and occasionally you can get long term relief. If the severity of OA is milder, perhaps only one compartment involved, then HA injections might be suggested first. There is nothing set in stone on this, however, and can vary between doctors as to what they will use when
13) Can HA be used in other joints? HA application for other joints has been studied but as of yet not FDA approved for anything but the knee.
14) Why does my doctor only use cortisone because he/she says HA injections are a waste of time? There is a wealth of data now that does support the use of HA in the ways discussed here. There are some studies mostly older that suggest HA injections are no more effective than NSAID. This is probably why the American Academy of Orthopedic Surgeons' position on HA injections is 'inconclusive' and is perhaps a reason for some skepticism in the medical community. However the Academy does not discourage it's use, i.e. it does not place HA therapy in their category of 'not recommended'.  REF Altman et al. J Rheumatol 1998.
15) Is it an office procedure?  Yes. In the majority of orthopedic practices the injections are administered in a similar manner in terms of set-up to that of cortisone injections. Some physicians may prefer to inject under xray control as an outpatient procedure because they state the placement of the material in the joint is more reproducible. This is unnecessary in my opinion. Those of us that spend a lot of time working in and around the knee joint can easily place this material inside the knee joint with 100% accuracy without the need for xray assistance.
16) What activities are allowed immediately following the injection? Generally you can resume normal activities. If you must return to sports within 1-2 days, ice application to the knee 4-6 times during the 1st 24 hours after injection is recommended for approximately 15-20 minutes at a time. I recently had a Falcons hockey player play in a game the very next day....and he scored a goal!
17) When can I expect results? For the majority of cases, you will not know for sure what the outcome will be for 6 weeks after the final injection. Some people will notice very subtle improvements after perhaps 2 injections, but rarely after 1. Do not get discouraged if , for example, after 1 month you don't notice anything. Improvement can be very sudden as well as gradual.

I think that covers most of the questions that come up on this. Let me know if you have any more and I will add them in here. Thanks for reading!
For more information on osteoarthritis and arthritis in general, you can look here
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