Classification of Joints A joint (also called an articulation) is a point of contact between bones, between cartilage and bones, or between teeth and bone. A joint’s structure determines its combination of strength and flexibility. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Classification of Joints Structural classification of joints is based on two criteria: 1. Presence or absence of a space between the articulating bones, called a synovial cavity, and 2. Type of connective tissue that holds the bones together. Structurally, joints are classified as one of the following types:  Fibrous joints – no synovial cavity and bones are held together by dense irregular connective tissue.  Cartilaginous joints – no synovial cavity and the bones are held together by cartilage.  Synovial joints – united by the dense irregular connective tissue of an articular capsule, and often by ligaments. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Classification of Joints Functional classification of joints relates to the degree of movement they permit. Functionally, joints are classified as one of the following types:  Synarthrosis – An immovable joint.  Amphiarthrosis – A slightly movable joint.  Diarthrosis – A freely movable joint. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Fibrous Joints Fibrous joints permit little or no movement. The three types of fibrous joints are (1) syndesmoses, (2) sutures, and (3) interosseous membranes Syndesmosis – joint permits limited movement (distal tibia and fibula) and gomphosis (dentoalveolar joint) Suture – fibrous joint that may be a slightly movable or immovable (found between skull bones) – need to know Interosseous membranes – permits slight movement (between the radius and ulna and tibia and fibula) Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Cartilaginous Joints Like a fibrous joint, a cartilaginous joint allows little or no movement. Here the articulating bones are tightly connected by either hyaline cartilage or fibrocartilage. The two types of cartilaginous joints are:  Synchondrosis – an immovable joint (epiphyseal plate)  Symphysis – a slightly movable joint (pubic symphysis and intervertebral joints) – need to know Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Synovial Joints The unique characteristic of a synovial joint is the presence of a space called a synovial (joint) cavity between the articulating bones. The synovial cavity allows a joint to be freely movable. The synovial membrane secretes synovial fluid, which forms a thin, viscous film over the surfaces within the articular capsule. Many synovial joints also contain accessory ligaments, articular discs, fibrous & synovial membranes. Bursae are saclike structures, similar in structure to joint capsules, that reduce friction in joints such as the shoulder and knee joints. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Types of Movements at Synovial Joints Gliding is a simple movement, the nearly flat surfaces of bones move back-and-forth and side-to-side. eg. Carpal bones Angular movements, there is an increase or decrease in the angle between bones (flexion–extension, hyperextension, abduction–adduction, and circumduction). Eg. elbow Rotation, is where a bone moves around its own longitudinal axis. eg. atlas/axis Special movements occur only at certain joints in the body. Examples: elevation–depression, protraction–retraction, inversion–eversion, dorsiflexion–plantar flexion, supination–pronation, opposition. – need to know Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Types of Synovial Joints Synovial joints are divided into 6 subtypes: plane, hinge, pivot, condyloid, saddle, and ball-and-socket. In plane (planar) joints the articulating surfaces are flat, and the bones glide back-and-forth and side-to-side (many are biaxial); they may also permit rotation (triaxial). Examples of plane joints are the joints between carpals and the joints between tarsals. In hinge joints, the convex surface of one bone fits into the concave surface of another, and the motion is angular around one axis (uniaxial); examples are the elbow, knee (a modified hinge joint), and ankle joints. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Types of Synovial Joints In pivot joints, a round or pointed surface of one bone fits into a ring formed by another bone and a ligament, and movement is rotational (uniaxial); examples are the atlanto- axial and radioulnar joints. In condyloid joints, an oval projection of one bone fits into an oval cavity of another, and motion is angular around two axes (biaxial); examples include the wrist joint and metacarpophalangeal joints of digits #2–5. In saddle joints, the articular surface of one bone is shaped like a saddle and the other bone fits into the “saddle” like a sitting rider; motion is angular around two axes (biaxial). An example is the carpometacarpal joint between the trapezium and the metacarpal of the thumb. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Types of Synovial Joints In ball-and-socket joints, the ball-shaped surface of one bone fits into the cuplike depression of another; motion is around three axes (triaxial). Examples include the shoulder and hip joints. The knee joint is the largest and most complex joint in the body. It contains an articular capsule, several ligaments within and around the outside of the joint, menisci, and bursae. Arthroplasty refers to the surgical replacement of severely damaged natural joints with artificial joints. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.

Aging and Joints Aging usually results in decreased production of synovial fluid in joints. In addition, the articular cartilage becomes thinner with age, and ligaments shorten and lose some of their flexibility. The effects of aging on joints are influenced by genetic factors and by wear and tear and vary from one person to another. Most individuals experience some degeneration in the knees, elbows, hips, and shoulders due to the aging process. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.