In general, the term arthritis can refer to any alteration of the normal, smooth articulating surfaces (those surfaces that touch and move in contact with each other) of the knee joint. This can be caused by disease, infection, injury and heredity. Oftentimes the terminology describing the arthritis can give a clear picture as to the causative factors leading to the arthritic condition.
Osteoarthritis
Osteoarthritis is widely classified as the garden variety, wear-and-tear form of arthritis. The main causes of osteoarthritis are obesity, overuse, injury, previous surgery to the knee and the aging process. Regardless of which one of these causes is evident, the end results are the same: loss of the smooth cartilage that covers the ends of the bones, pain, inflammation of the joint lining, excess joint fluid production (effusion) and ultimate alteration of mobility.
Osteoarthritis can present itself in various degrees of severity, from mild aching to severe pain and loss of mobility with deformity of the joint in severe cases.
Rheumatoid Arthritis
Rheumatoid arthritis is a hereditary, autoimmune disease that manifests itself through destructive, inflammatory responses inflicted upon different tissues and organ structures within the body.
In the case of joint involvement, rheumatoid arthritis responses involve the development of severely inflamed tissues of the joint lining, or synovium. As this process worsens, the synovitis (inflamed joint lining) becomes increasingly invasive and destructive to the joint cartilage, encroaching into the joint itself and destroying the cartilage cells, thus causing the arthritic process to progress and worsen.
Gouty Arthritis
Gout is a condition, frequently passed along through heredity, that involves the overproduction or under-excretion (removal) of uric acid in the blood stream. Uric acid is a chemical compound that occurs naturally in the body and exists to help in the digestion and breakdown of many foods, mainly proteins. This condition is frequently exacerbated (made worse) with poor diet habits, over-consumption of alcohol and chronic dehydration.
Uric acid is typically in crystalline form and, for any number of reason, can leach out of the blood and into joints, typically those of the lower extremities, causing significant pain, inflammation and swelling. When levels of circulating uric acid crystals become significant enough to warrant problems, they often leach into the aforementioned joints and can cause destruction of normal joint cartilage due to the crystalline deposits of uric acid, causing what is commonly known as a "gouty attack."
Attacks that are frequent or left untreated over a period of time can lead to multiple joint involvement and progressive worsening of joint cartilage destruction, thus increasing the severity of the arthritic condition.
Septic Arthritis
Septic arthritis is arthritis that has been caused by infection in the knee joint. When an infection is present in the knee joint, the microorganisms will typically produce what is called an exudate, or a by-product of their growth and metabolism. The common name for this exudate is pus.
When pus is present in an enclosed space, such as the knee joint, it can ultimately exert increasing pressure upon the interior components of the knee as its volume steadily grows and it has nowhere to go. As this pressure increases, it begins to cause destruction of the cartilage cells that make up the smooth joint coverings. If the pus and pressure are present for any length of time, it can lead to total destruction of the knee joint surfaces and progression of the infection to locations deep within the bone itself.
Traumatic Arthritis
Traumatic arthritis occurs whenever the knee join cartilage surfaces have been significantly disrupted and damaged because of injury. Injuries that involve fractures that extend into the joint can leave those surfaces uneven and distorted to the point that rubbing of these surfaces during walking and other activities will cause significant wear and tear of the cartilage.
Similarly, ligament injuries that leave the knee unstable can cause abnormal wear on the surfaces due to excessive laxity of the components of the knee, especially the cartilage surfaces of the femur (thigh bone) and tibia (shin bone).
