Patho - part 1 - PCL week 4

What is a joint:
- “the place of union, usually more or less movable, between two or more bones. Joints between skeletal elements exhibit a great variety of form and function, and are classified into three general morphologic types: fibrous joints; cartilaginous joints; and synovial joints.” – Stedman’s Medical Dictionary 2005.

Types of joint:
Fibrous joints.
- Solid with no joint cavity
- Types of fibrous joint
o Suture – “A form of fibrous joint in which two bones formed in membrane are united by a fibrous membrane continuous with the periosteum.” Eg between bones of the skull, which form a synostosis with age.
o Syndemosis – “A form of fibrous joint in which opposing surfaces that are relatively far apart are united by ligaments.” eg holds distal ends of tibia and fibula together with a strong interosseous ligament.
o Gomphosis – “A form of fibrous joint in which a peglike process fits into a hole, as the root of a tooth into the socket in the alveolus.”

Cartilaginous joints.
- Solid with no joint cavity
- Primary cartilaginous joints:
o Two areas of bone are bridged by hyaline cartilage.
o Don’t allow movement but do allow growth
o Include epiphysial plates during growth, costochondral joint.
- Secondary cartilaginous joints
o Thin layer of hyaline cartilage covers the bone with thick fibrocartilage in between.
o Also called symphyses
o Located exclusively in the midline of the body

Synovial joints.
- Allow for extensive movement
- Characterised by a joint cavity and hyaline cartilage covering bony surfaces
- Types of synovial joints:
o Plane – surfaces are almost flat and parallel. Movements are simple gliding movements
o Uni-axial – have a pair of movements around one axis. Can be either hinge (elbow) or pivot (radioulnar joints)
o Bi-axial – pair of movements around two axes which are usually perpendicular to each other. Can be condylar/ ellipsoid (wrist joint) or saddle (carpometacarpal joint of the thumb)
o Multi-axial/ ball and socket joints – two pairs of movement (as per bi-axial) and an extra pair of movements
- Simple and compound joints
o Simple = one pair of articular surfaces (most synovial joints)
o Compound = more than one pair (eg elbow and knee)
- Complex joints have a joint cavity subdivided into more than one compartment. Can be complete (by fibrocartilage) or incomplete (by menisci)

- Fern.