Arthritis
The word arthritis is derived from the Greek words “arthon” meaning joint, and “itis” meaning inflammation. Therefore, anything that causes joint inflammation is technically arthritis. Medicine recognizes a variety of different categories of arthritis, including: osteoarthritis, inflammatory arthritis, crystal arthritis, and septic (infection) arthritis.
The Anatomy of a Joint
Given that arthritis is specific to a joint it is important to understand what makes up a joint. A joint is formed when two bones meet. Most joints allow for movement, although there are some joints that move very little, or not at all. The bones that make up a joint are covered with smooth gliding cartilage called hyaline cartilage. This hyaline cartilage is smooth and very slippery — just like ice. It allows the joint to move with minimal friction. The entire joint is usually contained by a synovial lining. Imagine a thin plastic wrap around the joint. The synovial cells in this lining normally secrete a small amount of lubricating synovial fluid to help the joint move easily. Some joints have a different type of cartilage called fibrocartilage in the middle of the joint (ex. the meniscus in the knee) to serve as a shock absorber, or on the edge of the joint (ex. the labrum in the hip or shoulder joints) to give the joint more support.
Different Types of Arthritis
There are many different types of arthritis. Each form of arthritis affects the joint in a different way. However, the end result of many types of arthritis is often a joint that is painful, swollen, and stiff. Some of the most common types of arthritis include:
Osteoarthritis
Osteoarthritis is sometimes called wear and tear arthritis or degenerative arthritis. It occurs when some, or all, of the smooth gliding hyaline cartilage is lost. Imagine a road that is covered with a smooth sheet of ice following freezing rain. The ice would be the equivalent of the cartilage and the road directly beneath the ice would be the equivalent of the bone. Loss of some, or all, of the ice exposing the road beneath would be the equivalent of osteoarthritis. Loss of ice in a few areas would be the equivalent of mild osteoarthritis. Whereas, loss of most or all of the ice would be the equivalent of severe osteoarthritis. There are a few common ways that the smooth cartilage is lost leading to osteoarthritis, including:
- Post-traumatic arthritis: In post-traumatic arthritis an injury to the joint such as an associated fracture causes direct or secondary cartilage loss in the joint. For example, a bad ankle fracture often leads to ankle osteoarthritis.
- Osteoarthritis Due to Malalignment: Another common cause of osteoarthritis is malalignment leading to concentrated load through one area of the joint. This overloaded area causes the cartilage to wear thin resulting in osteoarthritis. This is why people with knock knees or bow legs are at higher risk of knee osteoarthritis over time compared to those with neutral alignment. A slight malalignment of the hip joint socket is also the reason why many people develop hip arthritis.
Inflammatory Arthritis
Inflammatory arthritis occurs when the synovial lining surrounding the joint becomes inflamed. This leads to joint discomfort, and over time the joint cartilage can be worn away if the inflammation is not controlled. Commonly, the inflammation of the joint lining is caused by the patient’s immune system attacking the synovial lining. There are a variety of types of inflammatory arthritis including: rheumatoid arthritis, psoriatic arthritis, reactive arthritis, and ankylosing spondylitis.
Crystal Arthritis
Crystal arthritis occurs when certain molecules in the blood crystallize in the joint (synovial) lining which elicits an intense inflammatory response leading to pain, swelling, and potentially destruction of the joint cartilage. The most common type of crystal arthritis is gout which occurs when increased amounts of uric acid in the bloodstream crystallize to form crystals, reading an intensely painful joint.
Hemophilic Arthritis (Arthritis due to bleeding in the joint)
Blood in a joint is harmful to the joint cartilage. Bleeding into a joint that occurs numerous times can eventually lead to arthritis from destruction of the joint cartilage. Repeated episodes of bleeding within a joint may be seen in patients with hemophilia.
Septic Arthritis (Arthritis due to an infection in the joint)
Pus and other products of a bacterial infection are quite damaging to a joint. If a joint becomes infected, the smooth gliding joint cartilage can be damaged leading to long-term arthritis. Quick and effective treatment of a joint infection is important to minimize the risk of long-term arthritis.
July 12th, 2024