Arthritis in knee (or any joint) results from degeneration (wear & tear) of the lining cartilage tissue in the joint. This results in pain, inflammation in the joint, reduced range of movement and occasionally locking/instability.
While "arthritis" is typically used synonymously with osteoarthritis, it is important to differentiate PRIMARY arthritis from SECONDARY arthritis.
What is primary arthritis?
Typically primary arthritis has no identifiable cause. It results in degeneration of the cartilage of the joint due to wear and tear over several years or due to advancing age. Patients develop gradual onset of pain usually over the age of 60-65 years and the disease progressively gets worse over time. X-rays are usually diagnostic, but MRI may be helpful in early stages. Advanced arthritis results from significant neglect of an arthritic joint
What is unicompartmental and tricompartmental arthritis?
Another terminology used is Tri-compartmental arthritis for knee. This simply means that the arthritis affects the medial and lateral part of the knee joint along with patello-femoral joint (the joint behind the knee cap). It is a common occurrence that the medial side of the knee joint is affected first followed by other parts of the joint. In this early stage of arthritis if the symptoms are severe, then a unicompartmental knee replacement is a reasonable option of treatment.
What is SECONDARY ARTHRITIS?
Arthritis of the knee can also result secondary to another affection of the knee such infection, previous fracture, or rheumatoid arthritis.
Any such insult to the knee can result in cartilage degeneration and arthritis. The typical presentation is that patients have a fracture around the knee that is fixed or an infection in the knee that resolves with treatment, but a few years later, the joint degeneration becomes apparent. Typically secondary arthritis presents in a younger population.
It is important to understand that all chronic pain in the knee is not secondary to arthritis. Untreated injury to meniscus or ligaments in the knee can cause chronic pain in the knee which is unrelated to cartilage degeneration.
It is also important to remember that rheumatoid arthritis and other inflammatory arthropathies such as gout can also cause chronic pain without there being cartilage damage, although arthritis eventually sets in in long standing/untreated cases.
Arthritis in knee is one of the commonest orthopaedic problems, but not all chronic pain is due to arthritis
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