Anatomy and Function of the Knee
The three bones that comprise the knee joint are the femur (thigh bone), the tibia (shin bone) and the patella (knee cap).
The knee may be described as a modified hinge joint, similar to the hinge on a door. However the knee not only bends back and forth like a hinge, it has a complex rotational component that occur with flexion and extension of the knee.
The knee is a major weight-bearing joint that is held together by muscles, ligaments, and other important soft tissue.
Cartilage is the material inside the joint that provides shock absorption to the knee during weight-bearing activities such as walking or stair climbing.
The Arthritic Knee
Arthritis in the knee joint occurs as a result of degeneration of the cartilage in our knee. Osteoarthritis is commonly referred to as “wear and tear” arthritis or degenerative arthritis, and is the most common cause for total knee replacement surgery.
Due to osteoarthritis, the cartilage in the knee breaks down over time and the result is a severely damaged joint surface with bone rubbing on bone. This process may occur as a result of previous trauma to the joint, ligament instability, or abnormal stresses to the joint.
Rheumatoid arthritis is an inflammatory process that results in erosion of the articular cartilage and subsequent damage to the knee joint surface.
What Is Osteoarthritis?
Osteoarthritis, or OA, refers to the breakdown, or degeneration, of cartilage and fluid that cushions and lubricates the bones in your joints.
The degeneration allows your bones to rub together, resulting in pain and further wear and tear. Osteoarthritis is a chronic progressive condition—which means that it gets worse over time.
Osteoarthritis can occur in any joint, but osteoarthritis of the knee is the most common type, affecting more than 10 million Americans.1
Symptoms of knee osteoarthritis
- Look for these common signs and symptoms:
- Joint soreness after overuse or inactivity
- Joint stiffness after resting or in the morning
- Pain when moving your knee
- Pain when using stairs or getting up from a chair
- Pain that prevents you from exercising your leg
- Grating or catching when moving your knee
- Joint pain that feels worse in the evening after a day’s activity
- Deterioration of coordination due to pain and stiffness
- Weakened thigh muscles
Causes of knee osteoarthritis
Knee osteoarthritis usually develops slowly and gets progressively worse over time. It’s commonly observed when people are middle-aged and older. But you can develop it at any age, following a joint injury or another disorder.
- There are certain factors that increase your risk of developing knee osteoarthritis:
- Age. The older you get, the higher your risk
- Weight. Increased body weight increases your risk. Every pound you gain puts 4 more pounds of stress on your knees2
- Injury or overuse. Athletes and people with active jobs are at higher risk
- Genetics. Recent research suggests that knee osteoarthritis is partially caused by your genes3
- Muscle weakness. Weakness in the muscles surrounding the knee increases your risk
- Other diseases. Rheumatoid arthritis, hemochromatosis (having too much iron), and acromegaly (excessive growth hormone) increase your risk
Getting diagnosed with knee osteoarthritis
Think you have knee osteoarthritis? Don’t wait. It’s very important that you see a doctor, get a proper diagnosis, and start treatment right away.
The sooner you start treatment, the easier knee osteoarthritis is to control and the less damage it can cause. Talk to your doctor or use the physician locator to find a specialist.
How is knee osteoarthritis diagnosed?
There are usually 4 steps to making a diagnosis of osteoarthritis:
- Medical history. This is your doctor’s best tool to diagnose osteoarthritis. Use the tips below to talk about your symptoms, family history, and past medical conditions
- Physical exam. Your doctor will look for typical signs of osteoarthritis, such as swelling, tenderness, and loss of motion
- Joint fluid sample. After applying a local anesthetic, your doctor will take a small amount of fluid from your knee joint. Lab test on this fluid can help confirm osteoarthritis and rule out other conditions
- X-rays or MRIs. These images can show damage inside the joint. Your doctor will be looking for the deterioration of cartilage that is typical of osteoarthritis
Talking to your doctor
The more you tell your doctor about your knee pain and how it affects you, the more effective your osteoarthritis treatment will be.
- When talking to your doctor, follow the tips below. It may help to write your thoughts down and bring them to your appointment.
- Describe your knee pain in detail. Are there areas that hurt more than others? At certain times of the day?
- Discuss the effects on your lifestyle. What activities (such as working, exercising, gardening, and/or golfing) cause you pain?
- Tell your doctor about lifestyle changes you’ve tried and their results.
- Mention any medications or treatments you have used for pain relief. What were the results? Were there any side effects?
- Make sure you talk over the treatment plan your doctor recommends. Following the treatment plan is important—ask for it in writing and bring up any concerns you have.
Knee osteoarthritis treatment options
There is no cure for knee osteoarthritis; but there are treatments that can help you manage and live with the condition.4 The goal of treatment is to decrease pain, maintain or improve joint movement, and limit functional loss so you can enjoy an active life.4 No treatment works for everybody—so make sure you talk over the options with your doctor before starting any treatment.
According to the American College of Rheumatology (ACR), drug therapy for pain management of osteoarthritis is most effective when combined with non-pharmacologic strategies.4 In fact, non-pharmacologic measures should be maintained throughout your treatment period.4
More information on knee osteoarthritis
- There is a wealth of information available about osteoarthritis. If you want to learn more, the following Web sites are excellent resources.
- The Arthritis Foundation
- The Centers for Disease Control and Prevention
- Mayo Clinic
- National Institutes of Health: Medline Plus