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The most obvious of the knee pain causes is injury. Not only can a sudden knee injury cause immediate pain, but it can also affect your knee health in the long term if not treated properly. An injury may weaken your knee and make it more vulnerable to wear and tear. This can result in chronic conditions like osteoarthritis developing much more rapidly.

Sudden Knee Pain Without Injury

Sudden Knee Pain Without Injury

Not all knee pain is the result of an obvious injury. Activity is one of the most common knee pain causes. This is because highly active people put more stress on their knees. The knee joint absorbs a lot of force during physical activity, especially during activities like running, bending, squatting, or walking on an incline.

Figure 1. Squatting applies multiple forces on the knee joint. Repetitive squatting over time can lead to gradual wear and tear of the joint.

Body weight is another factor that contributes to knee pain. Since the knee joint absorbs a lot of body weight during daily activities, a higher body weight puts extra pressure on the knee. Over time, this can cause the support and cushioning in your knee to wear down at a faster rate and make you more likely to develop chronic knee pain.

• Knee Pain When Bending and Squatting
• Knee Pain When Running – Top Five Causes

• Knee Pain When Bending and Squatting
• Knee Pain When Running – Top Five Causes

Bone on bone knee pain is caused by wear and tear on the joint over time. A combination of activity, body weight, or prior injury gradually wears away the cartilage that cushions the knee joint. Without that cushioning, bone begins to touch bone, which causes severe knee pain and stiffness.

Three Areas of Knee Pain

Three Areas of Knee Pain

Bone on bone knee pain can occur in one or more of the three knee compartments where bones meet:

1. 1. Medial compartment: where the thigh bone (femur) meets the shin bone (tibia).
   2. Lateral compartment: where the femur meets the tibia.
   3. Patellofemoral compartment: underneath the kneecap (patella) where it meets the femur.

Figure 2. There are three compartments (also called joints) inside the knee. They are located in the spaces where bones interact.

Figure 2. There are three compartments (also called joints) inside the knee. The knee pictured has arthritis in all three compartments – a disease pattern known as multicompartmental osteoarthritis.

In a healthy knee, the surfaces where these bones meet are protected by cartilage, which forms a smooth surface to help your joint move more easily. Knee pain and stiffness occurs when the cartilage wears away, leaving less joint space and unprotected bone that grinds together as you move.

• Bone on Bone Knee Pain – What You Need to Know
• How Bone Spurs Form

• Bone on Bone Knee Pain – What You Need to Know
• How Bone Spurs Form

Bone on bone knee pain is one of the main features of severe knee osteoarthritis. Osteoarthritis is a chronic condition that affects the entire joint, but is mainly caused by cartilage degeneration. It can result in knee pain and stiffness, inflammation, instability, and limited range of motion.

Figure 3. A knee with advanced stage osteoarthritis will feel very stiff and painful. The joint space will be narrower than usual, the cartilage will be mostly worn away, and bone spurs will be present.

Figure 3. A knee with advanced stage osteoarthritis will have narrower joint space than normal, which can be detected through x-ray imaging.

Types of Osteoarthritis

Types of Osteoarthritis

How Osteoarthritis Progresses

How Osteoarthritis Progresses

Figure 4. Osteoarthritis commonly begins in the patellofemoral compartment, the space between the patella and the femur.

Figure 4. Osteoarthritis commonly begins in the patellofemoral compartment, the space between the patella and the femur.

There are four stages used to classify the severity of osteoarthritis. The early stages may include some knee soreness and stiffness, especially during and after activity. Then, as more cartilage wears away and joint space decreases, pain and inflammation increase. Severe osteoarthritis is characterized by severe bone on bone knee pain, which can make everyday activities difficult.

• Osteoarthritis: Diagnosis, Symptoms, Treatment

• Osteoarthritis: Diagnosis, Symptoms, Treatment

What’s Next?

Assessing Knee Pain

The next section will review potential knee pain causes based on the location of the pain and the activities that trigger it. You will gain a better ability to assess your symptoms and a deeper understanding of possible underlying causes.