Inflamed Joints (Arthritis) Causes, Pathophysiology, Symptoms

What is arthritis?

Arthritis is the term for inflammation of the joint. It is usually characterized by pain and stiffness of the joint. While arthritis is more frequently seen in the elderly and often associated with wear and tear on the joint, it can also afflict young people and even children. The two more common types of arthritis seen are osteoarthritis (OA) and rheumatoid arthritis (RA) which affects the elderly and young adults respectively. A joint is a site where two bones articulate with each other. It provides flexibility, mobility and stability to the different parts of the body and the body as a whole. It is made up of several different types of tissue n a configuration which is ideally suited for flexibility, bearing weight and providing stability to the site.

Types of Joints

Joints may be classified either as synovial (cavitated) or non-synovial (solid).

Synovial joints have a greater degree of movement. The two bones are separated by a space with a surrounding synovial lining and capsule. The synovial lining (synovial membrane/synovium) produces synovial fluid which occupies the joint space and acts as a lubricant and shock absorber. The fluid also provides oxygen and nutrients to the cartilage of the joints. Cartilage at either end of the bone ensures that the bones do not rub together and also acts as a shock absorber.

Non-synovial joints have very limited movement which is often barely visible. These joints are anatomically simpler than synovial joints and are also known as synarthroses. It lacks a joint space. Instead the two bones are bridged by firm but somewhat flexible tissue like fibrous tissue or cartilage.

Arthritis may involves the articular cartilage, synovial membrane and/or bone.

Causes of Arthritis

In order for the joints to be working optimally, all the structures mentioned above that make up the joint need to be healthy and functioning. Inflammation may arise for various reasons including :

  • Age
  • Autoimmune factors
  • Genetic
  • Injury
  • Infection
  • Biomechanical stress – obesity, joint dislocation and instability, muscle strain

A large number of cases of arthritis, however, arise for no known reason or unidentified genetic and possibly environmental factors. These different causes may lead to changes in the joint structure. Some of these changes include :

  • Worn articular cartilage
  • Reduced synovial fluid
  • Thickening and stiffening of the synovial lining
  • Stiffness of the joint capsule

Gradually these changes impair the normal structure and functioning of the joint and inflammation sets in. It may be further exacerbated by other pathological processes that promotes the inflammatory reaction.

Pathophysiology

The pathophysiology largely depends on the cause. Arthritis may affect one joint (monoarthritis), two to four joints (oligoarthritis) or five or more joints (polyarthritis).

Rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder that affects many organs and structures in the body (systemic) but mainly the joints. There are a number of changes that occur in the joint with RA. Initially there is inflammation of the synovium. The membrane becomes swollen and thick and loses its normally smooth surface. Blood flow increases (hypervascularity) and white blood cells accumulate in the synovial fluid. Fibrin starts aggregating on parts of the synovium and floats freely in the synovial fluid. With time these components in the synovial fluid congregate to a form a mass (pannus) that deposits over the articular cartilage. In this way the cartilage is gradually eroded. Eventually the cartilage is destroyed and the underlying bone is exposed in the joint cavity. The pannus forms a tough fibrous tissue that essentially bridges the two apposing bones thereby stiffening the joint. Inflammation often extends to the surounding capsule, ligaments, tendons and muscles.

Osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by erosion of the articular cartilage. Unlike other forms of arthritis, the inflammation is not prominent despite the presence of inflammatory cells. Osteoarthritis instead is a cartilage disease. In OA the chondrocytes that are responsible for maintaining and replenishing the cartilage initially proliferate and then die. The structure of the cartilage is compromised and without chondrocytes to repair it the cartilage continues to degenerate. The cartilage cracks and then small pieces  break off into the joint space. Small portions of the underlying bone tissue (subchondral tissue) may also break off. Small fractures occur at the articulating surface of the bones and synovial fluid seeps into the bone tissue. This causes bony outgrowths as the tissue expands. the entire articular surface is damaged and some parts are remodeled in a manner that does not allow for healthy functioning of the joints.

Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA), also known as juvenile rheumatoid arthritis, is a group of  disorders that are characterized by chronic joint inflammation. As the name suggests it occurs in children usually before the age of 16 years and the cause is unknown. There are several different categories including :

  • Systemic-onset JIA
  • Persistent or extended oligoarthritis
  • Rheumatoid factor (RF)–positive polyarthritis
  • Rheumatoid factor (RF)-negative polyarthritis
  • Enthesitis-related arthritis
  • Psoriatic juvenile idiopathic arthritis
  • Undifferentiated arthritis

Seronegative Spondyloarthropathies

Inflammation of the joint is immune-mediated and directed against an unidentified antigen. There is a lack of antibodies, hence the term seronegative, and it is believed that many of these types of arthritis are triggered by an infection.

  • Ankylosing spondyloarthritis
  • Reactive arthritis
  • Reiter syndrome
  • Enteritis-associated arthritis
  • Psoriatic arthritis
  • Arthritis associated with inflammatory bowel disease

Infectious Arthritis

This type of arthritis is a result of an infection and is also known as septic arthritis. Microorganisms enter the joint space and infect the articular structures. These pathogens may directly enter the joint through an injury or reach the joint from a surrounding site of infection or even from a distant site by traveling through the bloodstream (hematogenous spread).

  • Bacterial arthritis
  • Tuberculous arthritis
  • Lyme arthritis
  • Viral arthritis
  • Fungal arthritis

Crystal-Induced Arthritis

This type of arthritis arises with the deposition of crystals in the joint. These crystals may be endogenous like monosodium urate (in gout), calcium pyrophosphate dihydrate (pseudo-gout) or calcium phosphate (same as the bone mineral) or it may be exogenous like corticosteroid ester crystals, talcum and the biomaterials polyethylene and methyl methacrylate. The presence of these crystals lead to joint disease.

  • Gout and gouty arthritis
  • Calcium pyrophosphate crystal deposition disease (pseudo-gout)

Traumatic Arthritis

Traumatic or post-traumatic arthritis is joint inflammation due to injury. The trauma may affect the entire joint or just parts of its like the cartilage or bone. It may be caused by a fall, sporting injury like a kick, motor vehicle accident, assault, bullet or knife wound and so on.

Signs and Symptoms

Joint pain and joint stiffness are the main symptoms. It is important to note that not all cases of joint pain (arthralgia) are arthritis. The following symptoms may also be present in most types of arthritis but this can be vary.

  • Swollen joints
  • Redness of the surrounding skin
  • Tender joints
  • Grating sound when moving joints
  • Lumps or nodules in and around joints
  • Deformity of joints
  • Fever

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