The number of joints depends on if
sesamoids are included, age of the human and the definition of joints. However, the number of sesamoids is the same in most people with variations being rare. Joints are mainly classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications.
Clinical, numerical classification • monoarticular – concerning one joint • oligoarticular or pauciarticular – concerning 2–4 joints • polyarticular – concerning 5 or more joints
Structural classification (binding tissue) Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other. •
cartilaginous joint – joined by
cartilage. There are two types:
primary cartilaginous joints composed of
hyaline cartilage, and
secondary cartilaginous joints composed of hyaline cartilage covering the articular surfaces of the involved bones with
fibrocartilage connecting them. •
synovial joint – not directly joined – the bones have a synovial cavity and are united by the dense irregular connective tissue that forms the articular capsule that is normally associated with accessory ligaments.
Functional classification (movement) Joints can also be classified functionally according to the type and degree of movement they allow: Joint movements are described with reference to the basic
anatomical planes. •
amphiarthrosis – permits slight mobility. Most amphiarthrosis joints are
cartilaginous joints. An example is the
intervertebral disc. Individual intervertebral discs allow for small movements between adjacent vertebrae, but when added together, the vertebral column provides the flexibility that allows the body to twist, or bend to the front, back, or side.
condyloid joint and
saddle joint. Joints can also be classified, according to the number of axes of movement they allow, into nonaxial (gliding, as between the proximal ends of the ulna and radius), monoaxial (uniaxial), biaxial and
multiaxial. Another classification is according to the
degrees of freedom allowed, and distinguished between joints with one, two or three degrees of freedom.
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: • Simple joint: two articulation surfaces (e.g.
shoulder joint,
hip joint) • Compound joint: three or more articulation surfaces (e.g.
radiocarpal joint) • Complex joint: two or more articulation surfaces and an
articular disc or
meniscus (e.g.
knee joint)
Anatomical The joints may be classified anatomically into the following groups: •
Joints of hand •
Elbow joints •
Wrist joints •
Axillary joints •
Sternoclavicular joints •
Vertebral articulations •
Temporomandibular joints •
Sacroiliac joints •
Hip joints •
Knee joints •
Articulations of foot Unmyelinated nerve fibers are abundant in joint capsules and ligaments, as well as in the outer part of intra-articular menisci. These nerve fibers are responsible for pain perception when a joint is strained. ==Clinical significance==