Joints
1.1.7 - Define the term joint.
1.1.8 - Distinguish between the different types of joint in relation to movement permitted.
1.1.9 - Outline the features of a synovial joint.
1.1.10 - List the different types of synovial joint.
Joint Definition
A joint is a structure in the body where two bones articulate.
Types of Joints
There are 3 types of joints you need to know about:
Fibrous
No movement, very stable. Bones are joined by strong fibers (sutures)
Cartilaginous
Slight movement. The ends of bones are covered with white pads of fibrocartilage that act as shock absorbers
Synovial
Wide range of movement. Most common joints. Subdivided according to movement possibilities. Characterized by the presence of a joint capsule and cavity lined with synovial membrane
Synovial Joint Structure
Synovial joints have the following structures and functions:
Articular cartilage
Structure - Smooth and spongy. Covers the ends of bones
Function - Prevents friction, absorbs shock, protects the bones
Articular capsule
Structure - Fibrous capsule: tough and fibrous. Synovial membrane: covers all internal surfaces
Function - Fibrous capsule: to strengthen joints. Synovial membrane: to secrete synovial fluid
Synovial fluid
Structure - Slippery fluid (looks like egg whites) that fills the joint capsule
Function - Reduces friction, nourishes cartilage, and gets rid of waste from the joint
Ligaments
Structure - Bands of strong fibrous connective material
Function - Joins bone to bone, providing stability
Bursae
Structure - Fluid filled sac found between tendon and bone
Function - Found in body areas of high stress. Reduces friction
Meniscus
Structure - Wedge of tough flexible discs of fibrocartilage
Function - Improves fit between bone ends. Increases stability. Reduces wear and tear to joint surfaces
Types of Synovial Joints
There are several types of synovial joints that you need to know about:
Gliding
Description: Flat or slightly curved bones
Glide back and forth and slide across each other. Least amount of movement of all synovial joints.
Examples: Tarsal bones, Carpal bones
Hinge
Description: Flex or extend in one direction only
Convex surface fits into a concave surface
Examples: Elbow joints, Knee joint
Pivot
Description: Rounded surface of one bone rolls around a ring formed by bone and ligament
Examples: Radioulnar joint, Bottom of skull
Condyloid
Description: Oval or egg shaped bone fits into a cup
Examples: Between the radius and carpal bones
Saddle
Description: Saddle shaped bone. Fits against another bone shaped like the legs of a rider sitting on a saddle
Examples: Between the carpal bone and metacarpal of the thumb
Ball and Socket
Description: Sphere shaped head of one bone fits into a rounded cavity on the other bone
Examples: Shoulder, Hip