Anatomy of Joints: Types, Movements, and Key Structures

Joint (articulation)

A point where two bones meet; allows movement and provides stability depending on structure.

Arthrology

Study of joints

Biomechanics

Study of movement and mechanical processes in the body

Kinesiology

Study of body movement

Bony joint (synostosis)

An immovable joint formed when two bones fuse, as in the frontal bone of the skull or the epiphyseal line in adults.

Fibrous joint (synarthrosis)

A joint where bones are connected by dense connective tissue, allowing little or no movement (e.g., skull sutures).

Suture

Immovable joint between skull bones

Serrate suture

Interlocking, saw-like edges between bones

Lap suture

Overlapping bones with beveled edges

Plane (butt) suture

Straight, non-overlapping edges

Gomphosis

Attachment of a tooth to its socket

Periodontal ligament

Connective tissue holding tooth in place

Syndesmosis

Joint bound by longer collagen fibers allowing some movement

Cartilaginous joint (amphiarthrosis)

A slightly movable joint where bones are joined by cartilage, such as in the pubic symphysis or intervertebral discs.

Synchondrosis

Bones joined by hyaline cartilage

Symphysis

Bones joined by fibrocartilage

Synovial joint (diarthrosis)

A freely movable joint enclosed by a capsule and filled with lubricating synovial fluid, such as the shoulder or knee.

Articular cartilage

Smooth covering on bone ends in a joint

Synovial fluid

Lubricating fluid in joint cavity

Joint capsule

Encloses joint cavity; includes fibrous capsule and synovial membrane

Articular disc

Pad of fibrocartilage in some synovial joints

Meniscus

C-shaped fibrocartilage pad in the knee that cushions and stabilizes the joint.

Tendon

A tough, fibrous cord connecting muscle to bone, transmitting the force of muscle contraction.

Ligament

A band of connective tissue connecting bone to bone, providing joint stability.

Bursa

A fluid-filled sac that cushions and reduces friction between tissues such as tendons and bones.

Tendon sheath

Elongated bursa surrounding a tendon

Carpal tunnel syndrome

Compression of median nerve in wrist

Lever system

Mechanical structure to move a load using force and fulcrum

Fulcrum

Fixed point a lever pivots on

Effort

Applied force to move a load

Load

Object being moved by the lever

Mechanical advantage (MA)

Ratio of output force to input force

Power lever

Lever with MA > 1, gives force advantage

Speed lever

Lever with MA < 1, gives speed advantage

First-class lever

Fulcrum in the middle (e.g., scissors)

Second-class lever

Load in the middle (e.g., wheelbarrow)

Third-class lever

Effort in the middle (e.g., tweezers)

Range of motion (ROM)

Extent of movement of a joint

ROM-limiting factors

Articular fit, ligaments, and muscle tone

Axis of rotation

Line around which movement occurs

Degrees of freedom

Number of axes a joint can move around

Monaxial

Movement in one plane

Biaxial

Movement in two planes

Multiaxial

Movement in three planes

Ball-and-socket joint

A multiaxial synovial joint allowing movement in all directions, such as the shoulder and hip joints.

Condylar (ellipsoid) joint

Biaxial joint; oval surface fits into depression

Saddle joint

Biaxial joint; both bones have concave and convex surfaces

Plane joint

Gliding, flat surfaces between bones

Hinge joint

A monaxial joint that permits movement in one plane, like the elbow or knee.

Pivot joint

A joint that allows rotation around one axis, such as the joint between the atlas and axis vertebrae.

Gliding movement

Bones slide past each other

Angular movement

Change in angle between bones

Rotation

Movement of a bone around its own axis, such as turning the head left or right.

Flexion

Decreases the angle between two bones, bringing them closer together (e.g., bending the elbow).

Extension

Increases the angle between two bones, moving them farther apart (e.g., straightening the knee).

Hyperextension

Extension beyond normal range

Abduction

Movement away from the body's midline, as when lifting the arm sideways from the body.

Adduction

Movement toward the midline of the body, such as bringing the arms down to the sides.

Elevation

Raises a body part

Depression

Lowers a body part

Protraction

Moves part forward

Retraction

Moves part backward

Circumduction

Circular movement of a limb

Medial rotation

Turns bone inward

Lateral rotation

Turns bone outward

Supination

Rotating the forearm so the palm faces upward or forward.

Pronation

Rotating the forearm so the palm faces downward or backward.

Lateral flexion

Side bending of head or waist

Right/left rotation

Turning head or trunk to side

Lateral excursion

Side-to-side movement of mandible

Medial excursion

Movement of mandible to midline

Ulnar flexion

Tilts hand toward little finger

Radial flexion

Tilts hand toward thumb

Dorsiflexion

Movement that raises the foot upward toward the shin.

Plantar flexion

Movement that points the toes downward, as when standing on tiptoe.

Inversion

Turns sole inward

Eversion

Turns sole outward

Temporomandibular joint (TMJ)

Jaw joint

Articular disc (TMJ)

Fibrocartilage pad in TMJ

TMJ disorder

Pain or dysfunction in jaw joint

Shoulder (glenohumeral) joint

Ball-and-socket joint of shoulder

Glenoid labrum

Fibrocartilage ring around glenoid cavity

Rotator cuff

Group of muscles and tendons that stabilize the shoulder joint and assist with rotation and lifting.

Shoulder dislocation

Humerus displaced from glenoid cavity

Elbow joint

Hinge joint between humerus and ulna

Radial & ulnar collateral ligaments

Stabilize the elbow joint

Knee joint

The largest joint in the body; a hinge joint that includes menisci and ligaments like the ACL and PCL.

Menisci (knee)

Fibrocartilage pads between femur and tibia

Patellar ligament

Connects patella to tibia

ACL (anterior cruciate ligament)

Prevents the tibia from sliding forward relative to the femur; crucial for knee stability.

PCL (posterior cruciate ligament)

Prevents the tibia from sliding backward relative to the femur.

Locked knee

Knee fully extended and stable

Lateral-impact knee injury

Damage from side blow to knee

Talocrural (ankle) joint

Joint between tibia, fibula, and talus

Calcaneal (Achilles) tendon

Attaches calf muscles to heel

Sprain

Torn ligament or tendon

Dislocation

Displacement of a bone from its joint, often caused by trauma.

Bursitis

Inflammation of a bursa, often due to overuse or repetitive motion.

Tendonitis

Inflammation of a tendon, commonly caused by repetitive stress.

Arthritis

Inflammation of a joint causing pain, stiffness, and reduced mobility.