What is osteoarthritis of the knee?

Osteoarthritis of the knee is a degenerative joint disease in which the destruction of articular cartilage takes place in between the knee joints. Osteoarthritis mostly affects the knee joint as compared to all other joints in the body. Because when you walk the forces on both the knees get 1.5 times of your total body weight.

There are generally 4 stages of osteoarthritis of the knee. During the first stage, minor wearing and tearing of the knee joint will begin. And as the patient reaches stage 2 the articular cartilage that provides the cushioning effect begins to break down. And as the disease progresses to stage 3 bones start to rub against each other which ultimately causes the knee joints to become inflamed and swollen. This will lead to pain and stiffness in the knees.

Knee joint contains synovium also known as the synovial membrane. It is a soft tissue that traces the whole inner surface of the knee joint, only except the place where the knee joint is lined by the articular cartilage. Synovium produces synovial fluid. First, let me explain to you what is synovial fluid?

What is synovial fluid?

• Synovial fluid is composed of hyaluronic acid, lubricin, collagenase, proteinase. Generally hyaluronic acid provides viscosity, elasticity, and lubrication properties to the synovial fluid that’s why hyaluronic acid is viscous.
• Synovial fluid is a Non-newtonian type of fluid because of hyaluronic acid. Non-newtonian means the fluid whose viscosity changes by changes in stress.
• Osteoarthritis causes inflammation in the joints and breakdown of articular cartilage which leads to swelling and disruption of hyaluronic acid so as the swelling increases the synovial fluid will get dilated which in turn decreases the viscosity of the synovial fluid.
• Let me explain with this you by physics –

As the swelling increases, the synovial fluid will get dilated which in turn increases the area and according to formula n = 1/A where n is (viscosity coefficient) and A is (Area). As the area increases, there will decrease in viscosity, and as viscosity decreases lubrication will also decrease which in turn increases the friction and stiffness.

The 4 stages of osteoarthritis of the knee

Let’s take a look at all the 4 stages of osteoarthritis of the knee joint

Stage 1 – (Doubtful)

• Usually, in this stage, OA patients will develop minor wear and tear in the knee joint but it is very unlikely that the patient will feel any pain or discomfort in the affected areas.
• Osteophytes also know as bone spurs may start to develop on the edge of the knee joint.

Stage 2 – (Mild)

• In this stage, OA patients will first encounter the symptoms like pain after waking up in the morning. And also after doing a much amount of walking or running.
• The space between the knee joint will appear normal and also the cartilage and the soft tissues still remain at a healthy size. But the cartilage matrix has started to breakdown due to an increase in the production of degrading enzymes.
• As the articular cartilage has started to breakdown. You will feel mild knee stiffness generally after waking up in the morning or after sitting over a long period.
• Normally progression of the disease is slow at this stage.

Stage 3 – (Moderate)

• Changes in the knees are significantly more evident.
• Cartilage surfaces have become thin, eroded, rough, and worn out. And also there will be the appearance of small tiny cracks that narrows the gap between the bones.
• As the disease progresses there will be an increase in inflammation which leads to an increase in swelling. And as the swelling increases, the synovial fluid will get dilated which in turn increases the area. And as the area increases, there will a decrease in viscosity, and as viscosity decreases lubrication will also decrease. Which in turn increases the friction and stiffness in the knee joint.

↑Swelling= ↑ Dilation of synovial fluid= ↑Area= ↓Viscosity=↓ Lubrication= ↑Friction= ↑Stiffness

• Due to an increase in friction. the patient will begin to feel more frequent pain while performing day to day activities like walking, running, kneeling, and bending. And also there will be an increase in knee stiffness after waking up in the morning or sitting over a long period.
• The subchondral bone that provides moisture and oxygen to the knee joint. And also acts as a shock absorber to the knee articular cartilage also gets affected.
• Osteophytes also are known as bone spurs increase in size as well as in numbers.

 

Stage 4 – (severe)

• The condition becomes very worse, the knee becomes more inflamed and sore, the space between the knee joint became finer and narrower which in turn leads to severe wearing off of the articular cartilage.
• Due to the severe destruction of cartilage, the condition will move to a chronic inflammatory phase in which there is a severe reduction of synovial fluid which leads to a severe decrease in viscosity and lubrication which in turn severely increases the friction and stiffness.

Chronic Inflammation=↓↓Synovial fluid= ↓↓Viscosity= ↓↓Lubrication= ↑↑Friction= ↑↑Stiffness

• The most important thing to remember in this phase is that due to chronic inflammation there will be a severe reduction of synovial fluid rather than the dilation of synovial fluid which takes place in stage 3.
• Due to an increase in friction and stiffness, the OA patient will experience pain consistently. And during this stage, the patient will also feel extreme pain and discomfort while doing simple day to day activities like walking, climbing stairs, or even slightly moving the knee joint.
• Osteophytes ie bone spurs will become more in number. In this stage, there is an increased chance of other tissues of the knee like meniscus to get affected.

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