A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.

Classification

Terms ending in the suffix -sis are singular and refer to just one joint, while -ses is the suffix for pluralization.

Structural classification

Structural classification names and divides joints according to how the bones are connected to each other. There are three structural classifications of joints:

• fibrous joint - joined by fibrous connective tissue
• cartilaginous joint - joined by cartilage
• synovial joint - not directly joined

Functional classification

Joints can also be classified functionally, by the degree of mobility they allow:

• synarthrosis - permits little or no mobility. Most synarthrosis joints are fibrous joints (eg The Skull).
• amphiarthrosis - permits slight mobility. Most amphiarthrosis joints are cartilaginous joints (eg. Vertebrae).
• diarthrosis - permits a variety of movements. All diarthrosis joints are synovial joints (eg. Shoulder, Hip, Elbow, Knee etc), and the terms "diarthrosis" and "synovial joint" are considered equivalent by Terminologia Anatomica.

Biomechanical classification

Joints can also be classified based on their anatomy or on their biomechanical properties. According to the anatomic classification, joints are subdivided into simple and compound, depending on the number of bones involved, and into complex and combination joints:

1. Simple Joint: 2 articulation surfaces (eg. shoulder joint, hip joint)
2. Compound Joint: 3 or more articulation surfaces (eg. radiocarpal joint)
3. Complex Joint: 2 or more articulation surfaces and an articular disc or meniscus (eg. knee joint)

Anatomical

The joints may be classified anatomically into the following groups:

1. Articulations of hand
2. Elbow joints
3. Wrist joints
4. Axillary articulations
5. Sternoclavicular joints
6. Vertebral articulations
7. Temporomandibular joints
8. Sacroiliac joints
9. Hip joints
10. Knee joints
11. Articulations of foot

Arthritis

Main: Arthritis Arthritis and direct physical trauma to a joint are the causes of joint damage. Arthritis is a group of conditions where there is damage caused to the joints of the body. Arthritis is the leading cause of disability in people over the age of 55.

There are many different forms of arthritis, each of which has a different cause. The most common form of arthritis, osteoarthritis (also known as degenerative joint disease) occurs following trauma to the joint, following an infection of the joint or simply as a result of aging. Furthermore, there is emerging evidence that abnormal anatomy may contribute to early development of osteoarthritis. Other forms of arthritis are rheumatoid arthritis and psoriatic arthritis, which are autoimmune diseases in which the body is attacking itself. Septic arthritis is caused by joint infection. Gouty arthritis is caused by deposition of uric acid crystals in the joint that results in subsequent inflammation. Additionally, there is a less common form of gout that is caused by the formation of rhomboidal shaped crystals of calcium pyrophosphate. This form of gout is known as pseudogout.