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Gel Shots (hyaluronic acid) for Knee Arthritis: What are they and do they work?
Many different names for knee arthritis injections are out there: gel shots, chicken shots, HA injections, viscosupplementation, etc. Approved for use in the U.S. in 1997, this non-surgical treatment modality has become a popular option for many of the 21 million Americans who suffer from knee osteoarthritis.
The goals of treatment for osteoarthritis are to reduce pain, maintain mobility, minimize disability and halt progression. No non-surgical treatments, at this time, have conclusively demonstrated the capability to make the joint surfaces smooth again. Nothing has been proven to rebuild or regrow articular cartilage.
Current non-operative therapies for osteoarthritis include: Modalities (heat, ice, ace bandaging), weight reduction, aerobic exercise, strength training, assistive devices (cane, walker, etc.), physical therapy, bracing, medications (Tylenol, Advil, Aleve, etc.), cortisone injection, HA (gel) injections.
The following list of HA “FAQs” should cover just about everything you need to know. References have been included in a few instances:
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.
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’.
Does HA rebuild or regrow cartilage?
The short answer is no. See the discussion above.
Why do some HA therapies consist of one injection and others are as many as five?
This is the result of the American free market system and competition. Much like Advil vs. Aleve vs. Motrin, all anti-inflammatory medication with the same reported effects, there are currently five approved HA therapies in the U.S. All are weekly injections ranging from one to five weeks: Orthovisc, 3-4; Synvisc, 1 or 3; Euflexxa, 3; Hyalgan and Supartz 3-5. No data exists that conclusively demonstrates the superiority of one brand or one specific amount of injections. In my practice, I first started with Synvisc, three injections and then I went to Supartz, three injections with no change in outcomes.
Where does the injectable HA come from?
Orthovisc and Euflexxa are produced from 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.
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. From 4 weeks to 6 months HA injections were superior.
(Bellamy N. et al Cochrane Database Sys Rev 2005;2:CD005328)
Do HA injections work and if so, how long do they last?
Asmentioned 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 six months, but it can be much longer. In some cases it can last for up to 1-2 years. (Waddell: Drugs Aging, 2007; Divine et al: Clin Orthop Rel Res, 2007)
If it works for me can it be done again?
Yes. There are studies documenting safe and effective repeat usage.
(Scali JJ. Eur J Rheumatol Inflamm 1995; 15:57-62)
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 72 hours but can take 1-2 weeks for full resolution.
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,). 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.
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 six months or more after the previous series.
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.
Is it an office procedure?
Yes. In the majority of orthopedic practices the injections are administered in the office.
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 first 24 hours after injection is recommended for approximately 15-20 minutes at a time.
When can I expect results?
For the majority of cases, you will not know for sure what the outcome will be for six weeks after the final injection. Some people will notice very subtle improvements after perhaps two injections, but rarely after one. Do not get discouraged if, for example, after a month you don’t notice anything. Improvement can be very sudden as well as gradual.