What causes osteoarthritis in the knee?

Arthritis is your knee's biggest enemy, and it can result over time from injury or disease. This is the most common type of osteoarthritis, and there are a number of causes that influence your risk of developing osteoarthritis in the knee. These can be broken down into 2 types: primary osteoarthritis and secondary osteoarthritis.

Primary Osteoarthritis of the knee:

This is a slow, progressive arthritis condition that usually begins after 40 years of age. It mainly affects weight-bearing joints (like knees and hips) as a result of excessive loads placed on normal joint tissues, or reasonable loads applied on inferior joint tissues. The exact cause is not determined however it is believed to be affected by:

• Family history and/or genetics
• Obesity (according to the 2002 National Health Interview Survey, obese adults are up to 4 times more likely to develop knee osteoarthritis than normal weight adults; approximately 66% of adults with arthritis are overweight).
• Aging (reduction and deterioration of cartilage).
• Wear and tear on your joints that results in the release of destructive enzymes which break down the cartilage to the point where the bones of the knee joint rub together and develop sclerosis (a hardening of tissue) as well as tiny fractures, cysts and bone spurs.
• Lack of activity which results in weak muscles and unstable joints (44% of adults diagnosed with arthritis report no participation in physical activity based on findings from the 2002 National Health Interview Survey).

Secondary Osteoarthritis of the knee:

This type of arthritis often appears before 40 years of age. It is the result of a clearly defined cause, such as:

• Acute trauma from a knee injury, loose joints, or joint surgery (bone injury or fracture, ligament, tendon, meniscus or synovial tissue damage), especially if it never healed properly. Osteochondritis dissecans results in fragments of cartilage loose in the joint, and often leads to osteoarthritis.
• Repetitive stress movements or strains that result in excessive bending, excessive walking, or overuse of your knee joint at work or play.
• Blood disorders or joint infections (such as gout or septic arthritis).

• Metabolic imbalances resulting from increased levels of uric acid, calcium deposits, or ongoing use of medications.
• Hormone disturbances as a result of diabetes or growth hormone disorders that affect cartilage wear. Menopause often increases the progression of osteoarthritis of the knee.
• Poor bone alignment or posture (your joints don't line up properly) can result in Chondromalacia patellae (Patella femoral syndrome and Runner's knee), which involves degeneration of the cartilage on the back of the knee cap. Women are more prone to this condition as they tend to have wider hips than men, which creates a wider angle at their knee. This can affect tracking of their knee cap and cause imbalanced weight on their joint, which can pose problems with instability, dislocation or pain (like a tire that is out of alignment, the treads will wear out on one side of the tire). You can often look at your shoe treads to see if one side of your heal is worn out more than the other to determine if you have alignment issues.

Progression of Osteoarthritis:

This can be classified into 5 stages of arthritis severity:

• Grade 0 - Normal
• Grade 1 ­ Chondromalacia involves early onset of osteoarthritis: softening of cartilage, joint surface stress, and fluid filling the joint cavity; as the condition progresses your knee gets inflamed and swollen, but there is no major joint surface damage at this point.
• Grade 2 ­ Fissuring, tearing or cracking of joint cartilage less than _ inch; this damage often goes unnoticed.
• Grade 3 ­ Fibrillation indicates later onset of osteoarthritis: very torn and worn appearance, damaged cartilage covering bone greater than _ inch (bone is still in tact); your damaged joint surface breaks into loose pieces which release enzymes that aid in destructing your joint surface. Up until now minor surgery can help your cartilage to heal.
• Grade 4 - Exposure and damage of underlying bone; healing without surgery is low.