In children

chronic knee problems are not very common.

In the young adult

Injuries due to sports or accidents while driving a two wheeler causing tear of the ligaments of the knee joint is common. Ligaments are structures which stabilize joints. They are cord like bands of connective tissue and resist abnormal movements between the bones of the joints. When their endurance limit is exceeded, they fail and this leads to instability. In the knee there are four ligaments binding the thigh bone to the shin bone. These are the anterior cruciate, the posterior cruciate, the medial collateral and the lateral collateral.

Two of them run within the knee joint cavity, the ACL (anterior cruciate ligament) being one of the two. It prevents the shin bone from sliding forward from the thigh bone in activities like coming downstairs. A hard twist or excessive pressure on the ACL can tear it, so that the knee gives out and can no longer support the body. Unless an injured ACL is accurately diagnosed and treated, the cushioning cartilage (the menisci) in the knee could be seriously damaged. Without this cushion, the thighbone and the shinbone would rub against each other, leading to further damage. - The majority of ACL injuries occur in females aged 15-25.

The PCL (posterior cruciate ligament) arises from the top of the tibia and is inserted to the inner aside of the lower end of the femur at the front. It prevents the thigh bone from sliding forwards on the leg bone or it prevents the leg bone from sliding too backwards on the thigh bone. An injury to the posterior cruciate ligament is the rarest of all ligament injuries in the knee.This is common in contact sports like football, and Kabaddi in which there is the risk of a blow to the front of the knee or twisting injury.

Post Traumatic Arthritis can follow a serious knee injury. A knee fracture or severe tears of the knee's ligaments may damage the articular cartilage over time, causing knee pain and limiting knee function.

Rheumatoid Arthritis is a autoimmune disease in which the synovial membrane becomes thickened and inflamed, producing too much synovial fluid, which over-fills the joint space. This chronic inflammation damages the cartilage and eventually causes cartilage loss, pain and stiffness. RA strikes 3% of women and 1% of men, usually between the ages of 20 and 55 years. Ankylosing spondylitis affects men between 20 and 30 years.

In the older age group the most common cause of chronic knee pain and disability is osteoarthritis, Osteoarthritis usually occurs after the age of 50 and often in an individual with a family history of arthritis. It is twice as common in women. Osteoarthritis is a degenerative joint disease, characterized by progressive wearing away of the cartilage of the joint. Due to the protective cartilage being worn away by knee arthritis, bare bone is exposed within the joint.