Anatomy of Joints

Articulation and Classification of Joints

• A joint is the place where a bone meets another bone, cartilage, or teeth, varying in stability and mobility.
• Joints are classified into three categories based on their structure: fibrous, cartilaginous, and synovial.

Fibrous Joints

• Fibrous joints are held together by dense regular connective tissue.
• There are three specific types of fibrous joints: gomphoses, sutures, and syndesmosis.

Cartilaginous Joints

• Cartilaginous joints are bones attached by cartilage.
• There are two specific types of cartilaginous joints: synchondroses and symphyses.

Synovial Joints

• Synovial joints are freely mobile diarthroses.
• Articulating bones are separated by a joint cavity containing synovial fluid.
• Synovial joints have a general anatomy consisting of an articular capsule, joint cavity, and synovial fluid.

Accessory Structures of Synovial Joints

• Bursae are sacs outside most synovial joints where ligaments, muscle, tendons, and/or bones rub.
• Tendon sheaths are elongated bursae around tendons, particularly in confined areas.
• Fat pads are packing material that provides some protection.

Types of Synovial Joints

• Synovial joints are classified by the shapes of articulating surfaces and the amount of movement allowed.
• Uniaxial joints move in one plane or axis, biaxial joints move in two planes or axes, and multiaxial joints move in three planes or axes.
• The six classes of synovial joints, in order of increasing movement, are: plane joints, hinge joints, pivot joints, condylar joints, saddle joints, and ball-and-socket joints.

Movements of Synovial Joints

• Gliding motion involves articular surfaces sliding back and forth or side to side.
• Angular motion increases or decreases the angle between bones.
• Rotational motion involves a bone turning on its longitudinal axis.
• Special movements occur only at specific joints, including depression, elevation, dorsiflexion, plantar flexion, inversion, eversion, protraction, and retraction.