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What is Knee Arthritis?

Arthritis is a painful joint, and its a condition that can affect any joint in our body, although its more common in some, like the hip or the knee.  Today we will talk about knee arthritis.  Arthritis occurs when the cartilage wears out.  Our cartilage lines our bones within a joint, and it creates a very slippery surface so that our bones can smoothly glide against each other when we bend our knee, for example.  Cartilage is so slippery that there is less friction when you bend your knee than an ice cube sliding on a sheet of ice.  Smoother than ice on ice.  Now that’s smooth.  However, as we get older, our cartilage starts to wear out.  And unfortunately, our body is not very good at replacing it once its gone.  Therefore, as we start to loose cartilage, our knee joint experiences more friction with bending, and that friction is painful.  Arthritis is pain caused by more friction

There are many things associated with the loss of cartilage.  Aging is the most common cause.  No matter how hard we try, our body will slowly lose cartilage over time.  But being overweight increases cartilage loss.  Injury to the knee from trauma will also cause faster cartilage loss because some of our cartilage cells can be destroyed.  Jobs that require hard labor, like working construction, also put a lot of stress across the knees and can accelerate the loss of cartilage.  Your genetics, and family history also play a role.  Some people just inherit “bad knees” and will start developing pain at an earlier age.

The knee is a pretty complex joint and the cartilage can wear away in different patterns.  The knee is actually one joint made up of three compartments: 1) a compartment where the kneecap (patella) rubs against the thigh bone (femur); and two compartments where the thigh bone rubs against the leg bone (tibia): 2) a medial and 3) a lateral compartment.

How is Knee Arthritis diagnosed?

Knee arthritis is suspected in people that report worsening knee pain over many months to years, without a recent fall or traumatic injury.  It is mostly seen in the elderly population, and younger people with knee pain usually have injuries to their ligaments, like the ACL (see talk) or meniscus (see talk).  People will have tenderness along their knee joint (due to the inflammation from too much friction), and they will commonly have knee swelling.  Additionally, as arthritis worsens, people will lose motion in their knee and the knee will not be able to bend like a health knee should.  All of these findings will lead your doctor to suspect arthritis.

Knee arthritis is diagnosed with basic x-rays of the knees taken while a person is standing up.  Three views are taken: a side view of the knee (“lateral”) and front view (called an “A.P.”), and a view of the kneecap (“Sunrise view”). 

Although you cannot see cartilage directly on x-ray, you see a space between the bones on x-ray, and this space represents the cartilage (even though you cannot see cartilage, you know its there). As the space between the bones becomes smaller, this is an indication of worsening arthritis.  When there is no space at all and the two bones (femur and tibia) are directly touching, its labeled “bone-on-bone arthritis” , which is a term for end stage arthritis (no cartilage remains). 

MRIs and CAT scans are not required for the diagnosis and treatment planning for arthritis (although some new technology uses MRIs of the knee to create custom knee replacement implants, more on that later).

How is Knee Arthritis treated?

Knee arthritis should be treated with a stepwise approach from least invasive to more aggressive.  While current technology does not exist to reverse arthritis, the process of cartilage loss can be slowed.  The most common symptom of arthritis is pain, and therefore, the main goal of treatment is pain relief.

Initial treatment consists of physical therapy (to maintain full motion of the knee, and strengthen the surrounding muscles), anti-inflammatory medication, and lifestyle changes.  The goal lifestyle changes are to minimize risk factors for the progression of arthritis.  If you are overweight, then a lifestyle change would be to diet so that you lose weight and your remaining cartilage has less force put on it with every step.  Or if you are doing hard labor every day, a goal may be to get involved in work that puts less stress on your knees.  The combination of these treatments can be very effective in treating the knee pain and delaying the progression of arthritis. 

However with time arthritis typically progresses and more invasive treatments are required.  Before talking surgery, a lot of doctors will recommend knee injections.  There are two types of injections on the market.  A steroid injection works be reducing inflammation and is often effective in reducing pain for a few weeks to months.  A steroid injection can be repeated every few months as long as its providing pain relief.  Remember that this injection is not treating the underlying disease, it is treating the symptom: pain.  After a few years (or less) the arthritis often becomes too severe to be effectively treated with this type of injection.  A second type of injection is a visco-supplement injection.  The idea here is to inject a lubricating fluid into the knee to reducing the friction that causes arthritic pain.  This approach targets more of the cause for pain (the increasing friction with loss of cartilage), however, while it sounds great in theory, its real-world efficacy has mixed-results (some people like it, others feel little relief).

With time, arthritis will slowly continue its march toward worsening joint destruction and increased pain.  Knee injections often lose their impact and people return to their doctors looking for the next level of treatment. This is typically the time to begin discussing surgery.  X-rays will show the bones in the knee close together, if not directly touching, and the knee itself malaligned from the excessive wear.  Knee replacements are the gold standard for treating end-stage knee arthritis. They have proven to be very effective and have a high success rate.  But they are also big procedures, with possible significant complications, and they should be considered only once the above-mentioned treatments are no longer effective, and the pain is significantly affecting daily function and life-style.  Many orthopedic surgeons will tell their patients: "You have knee arthritis, that will eventually require a knee replacement.  You will know when you are ready.  Come to me when you feel the pain is too much and its preventing you from performing your daily activities."

As we mentioned earlier, the knee has three compartments, and arthritis can develop in one, two or all three of these compartments. If its only seen in one compartment, a partial knee replacement (called a Unicondylar Knee replacement, or Uni for short) can be considered.  The recovery time is much less than a full replacement because it preserves more of the knees natural structures so that people require less rehab .  

However, arthritis isolated to one compartment is uncommon (only about 7-10% of people with knee arthritis are good candidates for a partial replacement) and therefore, the majority of people electing for surgery to treat knee arthritis undergo a total (meaning all three knee compartments) knee replacement. 

What is the long term outcome?  

While arthritis is a progressive disease, there are great treatments at every stage of progression that can effectively reduce symptoms.  A knee replacement has excellent to good outcomes in about 90% of people even at 10 and 15 years after surgery.  Its an effective way get rid of pain, and to allow people to resume their normal lives. And with improving technology, those outcomes are only expected to get better and last longer. 

Stopping the progression, or even reversing the process and setting back the clock is a wonderful goal for the future of medicine.  A lot of research is going into projects that strive to understand how cartilage heals and how it can be regrown.  Stay tuned to learn more about the progress of this research.


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