Joint disorders of the knee fall under two categories:

• mechanical knee problems
• inflammatory knee problems

Mechanical knee problems are caused by injuries like a hard jolt or an abrupt wrenching movement which can force the knee to go beyond its normal capacity of motion. Inflammatory knee problems stem from arthritis.
In most cases, arthritis of the knee is often diagnosed as osteoarthritis, a degenerative disease that causes gradual joint erosion.

Osteoarthritis of the knee can cause deterioration of the joint. The accompanying inflammation, as is common in most rheumatic diseases, also results in joint impairment.
Rheumatoid arthritis of the knee is characterized by joint inflammation and damage to the supporting cartilage. Other ancillary parts of the knee, like the muscles, tendons and ligaments are not spared from the disease.
Osteoarthritis can be triggered by an inordinate amount of strain on the joint caused by deformity, recurring injuries, or being overweight. The disease often strikes during middle age or older, however, younger people are also at risk of developing the disease due to the following:

• genetics is involved - heredity is also a factor when children and young adults develops osteoarthritis.
• sports-related injuries - frequent damage directly affecting the knee’s cartilage disk (meniscus) can also lead to osteoarthritis in young athletes.
• Rheumatoid arthritis – Osteoarthritis in the young starts out as Rheumatoid arthritis.