Comprehensive Guide to Joints: Types, Classifications, and Movements in Anatomy

Joint

An articulation where two or more bones meet.

Structural classification of joints

Classifies joints based on the material that connects the bones and whether a joint cavity is present. The three structural categories are fibrous, cartilaginous, and synovial joints.

Fibrous joints

Joints connected by dense regular connective tissue that have no joint cavity and are immobile or only slightly mobile. The three types are gomphoses, sutures, and syndesmoses.

Three types of fibrous joints

Gomphoses, sutures, and syndesmoses.

Gomphosis

A fibrous joint that is a "peg-in-a-socket" articulation, such as a tooth in the socket of the mandible or maxilla.

Example of a gomphosis

The articulation between a tooth and its socket in the mandible or maxilla.

What holds a tooth in a gomphosis?

Fibrous periodontal ligaments, also called periodontal membranes.

Functional classification of a gomphosis

Synarthrosis, meaning essentially immobile.

Suture

A fibrous joint found between certain skull bones. It has very short fibers and interlocking, irregular edges.

Function of sutures

The interlocking edges increase stability and decrease the risk of fracture while allowing skull growth during childhood.

Functional classification of sutures

Synarthroses, meaning essentially immobile.

What happens to sutures as adults age?

Many sutures become ossified and form synostoses.

Syndesmosis

A fibrous joint in which bones are connected by an interosseous membrane or ligament, which is a broad ligamentous sheet.

Examples of syndesmoses

The joints between the radius and ulna and between the tibia and fibula.

Functional classification of a syndesmosis

Amphiarthrosis, meaning slightly movable.

Function of syndesmoses

They provide a pivot or connection between two long bones while allowing slight movement.

Cartilaginous joints

Joints in which bones are connected by either hyaline cartilage or fibrocartilage. They lack a joint cavity and are immobile or slightly mobile.

Two types of cartilaginous joints

Synchondroses and symphyses.

Synchondrosis

A cartilaginous joint in which bones are joined by hyaline cartilage.

Functional classification of a synchondrosis

Synarthrosis, meaning immobile.

Symphysis

A cartilaginous joint in which bones are connected by a pad of fibrocartilage.

Function of fibrocartilage in a symphysis

It resists compression and acts as a shock absorber.

Functional classification of a symphysis

Amphiarthrosis, meaning slightly movable.

Synovial joint

A joint in which the articulating bones are separated by a fluid-filled joint cavity. Most joints in the body are synovial joints.

Functional classification of synovial joints

Diarthroses, meaning freely movable.

Main features of synovial joints

Articular capsule, joint cavity, synovial fluid, articular cartilage, ligaments, nerves, and blood vessels.

Joint cavity

The space between articulating bones in a synovial joint that contains synovial fluid.

Articular capsule

The capsule surrounding a synovial joint that encloses the joint cavity and helps stabilize the joint.

Synovial fluid

A fluid within the joint cavity that lubricates the joint and helps nourish articular cartilage.

Articular cartilage

Cartilage covering the articulating surfaces of bones in synovial joints. It reduces friction and helps absorb shock.

Ligaments in synovial joints

Bands of connective tissue that connect bones and help stabilize the joint.

Bursa

A small fluid-filled sac that reduces friction between moving structures such as tendons, ligaments, muscles, and bones.

Tendon sheath

A tubular structure containing fluid that surrounds a tendon and reduces friction as the tendon moves.

Why are bursae important?

They reduce friction between moving tissues around joints.

Why are tendon sheaths important?

They reduce friction as tendons move over bones and other structures.

Synovial joint classification by movement

Synovial joints can be classified as uniaxial, biaxial, or multiaxial/triaxial based on the number of planes or axes in which movement occurs.

Uniaxial joint

A synovial joint in which a bone moves in one plane or around one axis.

Biaxial joint

A synovial joint in which a bone moves in two planes or around two axes.

Multiaxial or triaxial joint

A synovial joint in which a bone moves in multiple planes or around multiple axes.

Six types of synovial joints

Plane, hinge, pivot, condylar, saddle, and ball-and-socket joints.

Order of synovial joints from least to most mobile

Plane, hinge, pivot, condylar, saddle, ball-and-socket.

Plane joint

A synovial joint with relatively flat joint surfaces that allows sliding or gliding movements.

Hinge joint

A synovial joint that primarily allows movement in one plane, such as flexion and extension.

Pivot joint

A synovial joint that allows rotation around a single axis.

Condylar joint

A synovial joint that allows movement primarily in two planes.

Saddle joint

A synovial joint in which each articulating surface is concave in one direction and convex in another, allowing movement in two planes.

Ball-and-socket joint

A synovial joint in which a rounded head fits into a cup-like socket, allowing movement in multiple planes and rotation.

Flexion

A movement that decreases the angle between articulating bones.

Extension

A movement that increases the angle between articulating bones.

Lateral flexion

Bending the vertebral column laterally, or to the side.

Abduction

Movement of a body part away from the body's midline.

Adduction

Movement of a body part toward the body's midline.

Circumduction

A circular movement in which the proximal end of an appendage remains relatively stationary while the distal end moves in a circular pattern, creating an imaginary cone shape.

Rotation

Movement in which a bone pivots around its longitudinal axis.

Medial rotation

Rotation of a body part toward the body's midline.

Lateral rotation

Rotation of a body part away from the body's midline.

Biomechanics

The application of mechanical principles to biological systems.

Lever

A rigid structure that moves around a fixed point called a fulcrum when effort is applied against resistance.

Fulcrum

The fixed point around which a lever moves.

Effort

The force applied to a lever.

Resistance

The force or weight that opposes the effort.

First-class lever

A lever in which the fulcrum is located between the effort and resistance.

Example of a first-class lever in the body

The atlanto-occipital joint of the neck.

Example of a first-class lever outside the body

A pair of scissors.

Second-class lever

A lever in which the resistance is located between the fulcrum and the effort.

Example of a second-class lever in the body

Standing on tiptoe.

Example of a second-class lever outside the body

A wheelbarrow.

Why are second-class levers useful?

A relatively small force can balance or move a larger weight.

How common are second-class levers in the body?

They are relatively rare.

Third-class lever

A lever in which the effort is located between the fulcrum and the resistance.

Example of a third-class lever in the body

The elbow joint during flexion.

Why is the elbow a third-class lever?

The elbow joint acts as the fulcrum, the biceps tendon applies the effort, and the weight in the hand provides resistance.

How common are third-class levers in the body?

They are the most common type of lever in the body.

Sternoclavicular joint

The synovial joint between the sternum and clavicle.

Acromioclavicular joint

The joint between the acromion of the scapula and the clavicle.

Glenohumeral joint

The shoulder joint between the head of the humerus and the glenoid cavity of the scapula.

Hip joint

A synovial ball-and-socket joint between the head of the femur and the acetabulum of the pelvis.

Knee joint

A major synovial joint of the lower limb that permits primarily flexion and extension while also allowing limited rotation.

When do joints begin to form during development?

Joints begin to form by approximately the sixth week of development.

Development of future fibrous joints

Mesenchyme differentiates into dense regular connective tissue.

Development of future cartilaginous joints

Mesenchyme differentiates into fibrocartilage or hyaline cartilage.

Development of future synovial joints

Laterally placed mesenchyme forms the articular capsule and supporting ligaments, another layer forms the synovial membrane, and centrally located mesenchyme may be reabsorbed or form menisci or articular discs.

Arthritis

A group of inflammatory or degenerative diseases of the joints that can cause swelling, pain, and stiffness.

Osteoarthritis

A degenerative joint condition commonly associated with aging and wear and tear that involves deterioration of articular cartilage.

Cause of osteoarthritis

Wearing down and degeneration of articular cartilage.

Joints commonly affected by osteoarthritis

Fingers, knuckles, hips, knees, and shoulders.

Gouty arthritis

Arthritis associated with increased levels of uric acid.

Rheumatoid arthritis

An autoimmune disorder in which the immune system attacks joint tissues, beginning with inflammation of the synovial membrane.

Typical age group for rheumatoid arthritis

Younger to middle-aged adults, although it can occur at other ages.

What happens to a joint during rheumatoid arthritis?

Inflammation of the synovial membrane can lead to scar tissue formation, ossification, and eventually fusion of bone ends called ankylosis.

Ankylosis

Abnormal stiffening or fusion of a joint, which can occur in advanced rheumatoid arthritis.

Treatments for rheumatoid arthritis

NSAIDs and corticosteroids can reduce inflammation and pain, while DMARDs suppress or modify immune-system activity.

DMARDs

Disease-modifying antirheumatic drugs that suppress or modify immune-system activity to slow rheumatoid arthritis progression.

Biologics

A type of DMARD made from substances produced by living cells.

Effect of exercise on joint health

Exercise increases the flow of synovial fluid to chondrocytes and strengthens muscles that support and stabilize joints.

Can excessive exercise affect joints?

Yes. Extreme exercise can aggravate existing joint problems and may worsen osteoarthritis.

Synarthrosis

A functionally immobile joint.

Amphiarthrosis

A functionally slightly movable joint.

Diarthrosis

A functionally freely movable joint.

Structural classification vs functional classification

Structural classification is based on how bones are connected and whether a joint cavity is present. Functional classification is based on the amount of movement allowed.