00:00So osteoarthritis forms part of a bunch of conditions called degenerative joint disease.
00:19Osteoarthritis is not the only pathology that causes joints to become degenerate.
00:24Joints can become degenerate following trauma or inflammatory disease such as rheumatoid arthritis.
00:29But osteoarthritis is the most common cause.
00:31So what is osteoarthritis?
00:33Now osteoarthritis affects around one in five people over the age of 45.
00:38And because of osteoarthritis more than 80,000 knee replacements are performed each year.
00:43The knee is composed of the femur and the tibia.
00:47These are two bones.
00:49There is the patella which is a small sesamoid bone which is encased in the quads tendon and the patella tendon.
00:55And the patella articulates with the front of the femur in an area called the trochlea.
01:02The joint is moved by muscles and tendons and is stabilized by ligaments.
01:07So the medial collateral ligament, the lateral collateral ligament and internally it has the ACL and PCL ligaments.
01:14The inside of the joint where the movement takes place is covered in a substance called cartilage.
01:21Then inside the knee joint, for example, this is highline cartilage.
01:25And this is quite amazing stuff because you're born with it.
01:30You can't regenerate it.
01:32The highline cartilage doesn't have a blood supply or a nerve supply.
01:36So whatever you're born with and as an adult, that's what you have for the rest of your life.
01:40So it's important to look after it.
01:41But unfortunately, in a lot of situations, the cartilage can break down.
01:46For example, osteoarthritis.
01:47Now, osteoarthritis is a condition which is characterized by an imbalance in the enzymes that exist within the cartilage that produce the substance of the cartilage, which is called the matrix.
02:00In osteoarthritis, some of these enzymes, the NMPs or matrix metalloproteinases, they're known as, are working too hard.
02:10So that causes an imbalance in the homeostasis or the balance of the cartilage.
02:14And over time, the matrix starts to break down because these enzymes are working too hard.
02:20And that results in a thinning of the cartilage that covers the end of the bone.
02:24So the depth of this cartilage in a healthy joint is around 5 to 8 millimeters in the knee.
02:32And over time, this thins out.
02:34And underlying this cartilage is the bone, where there are some nerve endings.
02:39So what the cartilage does is it allows smooth gliding of the knee joint with every step that you take in every day of your life.
02:47And when you go for a jog or for a run or you play any sport, all of these structures are coming under a lot of strain.
02:53And the cartilage is able to withstand the forces of your body weight during all these kinds of movements and sports, which is quite amazing.
03:02Osteoarthritis doesn't just affect the cartilage.
03:04It affects all the tissues around the joint.
03:06So this structure here is the meniscus, and we can talk more about that later.
03:12So the meniscus is affected and can become degenerate as part of osteoarthritis.
03:16The tendons and the ligaments and the lining of the joint are all affected, and this results in increasing pain, a reduced range of movement, night pain, and just a loss of function of the joint as the osteoarthritis becomes more and more severe.
03:32There are different grades of osteoarthritis, so in the grade 1 osteoarthritis, you don't really notice a change radiographically, as in on the x-rays, and it goes up all the way to grade 4.
03:44So grade 1 is a softening.
03:46Grade 2 is a fissuring of the cartilage.
03:49Grade 3 is a thinning, but there is some cartilage remaining.
03:52And grade 4 is a complete loss of the cartilage in a particular area of the knee joint.
03:58The medial side of the joint is usually most affected, but in severe arthritis, the medial compartment, the lateral compartment, as well as the patellofemoral compartment are degenerate.
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