Part 1 - Knee pains due to OA (Hyaluronic Acid Injection - your knee joint all drugged up!)
Updated: Aug 5, 2019
….perhaps the title may be deemed a tad inappropriate but that is how I like to view this topic today.
I had received quite a few DMs regarding Hyaluronic Acid Intra-articular injections in the past 2 weeks.
Most of the DMs were inquiring my personal opinion on them….some asked what were the outcomes I see in patients who had gotten them….some asked if certain brands were better than others. ALL claimed that they had some form of knee osteoarthritis or another (or rather they had knee pain which they attributed it to being osteoarthritis).
This (knee osteoarthritis) is quite a big topic and I will try and cover everything (or at least what I think is important for you to know) in this several-part article (I have yet to decide how much I want to write about this. If the mood strikes, it can go on forever!).
1st part, let’s talk about what Hyaluronic Acid is and knee osteoarthritis.
Objective(s) of this article:
1) what is Hyaluronic Acid (HA)
2) what is knee osteoarthritis (basic description)
3) why do you (possibly) have knee pain
4) how does HA help
We START this off with a more scientific description of Hyaluronic Acid (HA).
Sometimes also known as Hyaluronan, it is a glycosaminoglycan (GAGs) which is a naturally occurring molecule in our bodies. GAGs are actually a polysaccharide (a very long chain complex carbohydrate) and like how you would usually think of carbs, it attracts water thus making it an ideal lubricant.
Some examples of GAGs are – Glucosamine, Chondroitin (sound familiar?) and Hyaluronic Acid. It is widely found in all connective tissues (skin, muscles, ligaments, tendons etc).
As lay-man as I can word this, Hyaluronic Acid (HA) is a substance that is present in the body and is found naturally is in our connective tissues such as our skin and (surprise, surprise!) our joints. The molecule itself “hangs on” to water molecules, which is why it is also commonly use in the beauty products for its hydrating properties (face cream, face mask, eye creams and the list is endless) and in the aesthetic world, commonly used as fillers (plumping up one’s lips like Kylie Jenner).
Personally I use them on a regular basis - as a face cream...not plumping up my lips to be Kylie Jenner.
Because it holds on to water molecules, it has cushioning and lubricating effect, which is IDEAL for our joints (our topic of discussion).
Hyaluronic Acid (HA) is also a main component of the extracellular matrix thus it has a big role in inflammation, angiogenesis (formation of new blood vessels) and tissue regeneration.
Having read the brief run through of what HA is and what it can do, it is really not a huge surprise that it is commonly being used for musculoskeletal (MSK) injuries such as ligamentous sprain, tendinopathies (ailments of the tendons), degenerative joint disorders (that usually comes from “overuse”) AND dermatological/cosmetic enhancements.
But back to the knee joint.
Knee Osteoarthritis (OA) is a disease of breakdown of the cartilage lining the knee joint (I will explain more on this later).
Previously when I was still a junior doctor, it was thought that OA was due to degeneration (meaning it wore off as you age).
However these days, we think of it as an inflammatory process from excessive mechanical load onto the joint.
Our knee joint has cartilage at the ends of both femur (thigh) and tibia (shin) bones. This is the natural “shock absorber” of our knee joints (some might argue it shares this significant role with the meniscus but that is not the point of this article).
The blood circulation within the knee joint itself is almost negligible thus to nourish the cartilage, the knee synovial lining produces Synovial Fluid.
Everyone’s knee joints (or any synovial joint in our body, for that matter) have synovial fluid.
The synovial lining of the knee joints can also become inflamed (due to trauma or excessive unaccustomed mechanical load) and start producing excessive “altered” synovial fluid. The alteration is that is now has a lot of inflammatory cells within it. Inflammatory cells releases substances that can further damage the cartilage and worsening the condition.
Unfortunately, this can be a vicious cycle of pain from unmanaged load onto knee LEADING to inflammation from unmanaged load onto knee LEADING to swelling within the knee LEADING to destruction of cartilage LEADING to more pain (and repeat).
Which is why controlling inflammation and swelling is very important.
Now…the other very important question you should ask is this: WHY do I get pain in knee osteoarthritis?
First thing first….cartilage has NO nerve endings. Which means, your cartilage in the knee joint (or any joint for that matter) can NOT feel pain.
Yes...the cartilage in your knee joints are unable to feel pain as they lack nerve endings. However, many structures around it has plenty of pain nerve fibres such as (1) synovial lining, (2) joint capsule, (3) adjacent knee ligaments and menisci (and the knee has MANY ligaments), (4) bones underneath the cartilage, (5) tendons surrounding the knee, and (6) muscles surrounding the knee.
You may think that you can differentiate a muscle pain from a joint pain but most of the time, it is highly interrelated and may be difficult to differentiate (true story!).
So in knee osteoarthritis, you get swelling from inflamed synovial lining (can cause pain) which distends the knee joint capsule (can cause pain) which may stress the surrounding knee ligaments (can cause pain) and ultimately may alter the way you move/walk/run thus affecting your muscles/tendons/ligaments (definitely can cause pain).
SO how does Hyaluronic Acid injection helps?
Disclaimer: There MAY be a bit of a placebo effect taking place but I refrain from going down that rabbit hole so we stick to the topic at hand.
You now know that the cartilage in your knee joints are important and that synovial fluid brings nourishment to the cartilage and keeps it healthy.
Now think of the HA injection being the “vitamin supplementation” added into your synovial fluid to “nourish” your cartilage.
Since cartilage is needed for the “vitamin supplementation” to work, if your cartilage has worn off to a certain degree, there is nothing for the “vitamin” to work on.
Read and re-read the above 2 sentences.
You NEED to have cartilage in the first place for HA injection to somewhat take effect.
This is PARTIALLY the reason why HA injection works on some people and failed on others.
And this is the reason why sometimes a doctor is hesitant to give HA injection to a patient after looking at his/her xray. The xray may already show bone on bone picture (which tells the doctor that the cartilage is no longer there). Remember that the ends of the bone have plenty of pain nerve fibres. Bone on bone will cause A LOT of pain and HA injection almost never work.
But lets say you only have a mild to moderate osteoarthritic knee and there is still a decent amount of viable cartilage.
In that situation, then yes there is a good chance that HA injection may ease some pain/discomfort. However, like any other supplements out there, when you stop taking it, the effect will also wear off eventually. Which is why you will hear or read that some people have their knees injected on a regular basis (it ranges from 6 months to every few years depending on quite a few factors).
I hear you say….Doc, then is it all doom and gloom for my knees?
Fortunately the proper answer is no, if your knees are not at a severe stage of osteoarthritis yet.
The REAL answer to reducing knee pain long term is actually LOAD MANAGEMENT onto the knees.
Wait for Part 2 of this article where we discuss load management as a long term way to deal with knee discomfort in early to moderate osteoarthritis. We will also look into the different "types" of Hyaluronic Acid injections available in the market, the possible complications from the injections and my opinion if it really is worth the money (coz it ain't cheap!).