Permanent damage to joint cartilage or loss of joint cartilage with exposure of underlying bone is known as arthritis. Osteoarthritis, rheumatoid arthritis, and traumatic arthritis are the most common forms of this disease.
The joint surfaces, where bones move against each other are covered with an approx. 3-4 cm thick articular cartilage, a smooth tissue that cushions the bones and enables them to move easily without much friction. It does not have any nerve supply to carry sensation for pain. But once the cartilage is damaged or worn out, the underlying bone starts to rub against each other. This bone does have nerve supply and it starts to emit pain sensation to the brain as soon as the bone rubs against bone.
Cartilage damage is divided into four different levels of severity:
Grade 1: slight superficial fibrillation
Grade 2: deeper tear and large surface fibrillation
Grade 3: deeper defect (to the bone) with strong fibrillation, mechanically not acceptable
Grade 4: exposed subchondral bone
Osteoarthritis (OA) usually occurs after age 50. The articular cartilage covering & cushioning the bones of the knee softens & wears away. This is mainly caused by mal-alignment of the lower extremities. If one or more parts of the knee are damaged, mobility will decrease. Over time the cartilage is worn away. The damage increases because the cartilage is unable to regenerate on its own. As a result, the joint space diminishes and the bones start to contact each other. This causes inflammation of the soft tissues and severe pain and also restricts mobility. Several factors which influence osteoarthritis apart from age related wear and tear are:
Typical Indian lifestyle with floor sitting habits, sitting cross-legged
Overzealous use of knee joint like playing contact sports, jogging, excessive walking in order to maintain fitness
Rheumatoid Arthritis (RA) is a disease in which the synovial membrane becomes thickened & inflamed producing excessive synovial fluid. Chemicals inside this pathological tissue (pannus) eat into the healthy cartilage and surrounding bone. This destructive process leads to pain and stiffness.
Traumatic Arthritis can follow a serious knee injury like fracture or ligament tears. Injury leads to direct or indirect damage to the articular cartilage, leading to arthritis.
Other less occurring causes of arthritis are:
Malalignment, eg. in cases of deformities- varus, valgus
Coagulation disorder like haemophilia
Metabolic diseases like gout