Anatomy of Joints: Types, Structures, and Disorders

Joint

Point of contact between two bones, permit body movement of the rigid skeleton. May also stabilize the body, help body maintain balance, or protect the skeleton.

Hyoid bone

The only bone that doesn't articulate with another bone.

Arthrology

Study of joints.

General structural classification

Based on the presence or absence of a joint cavity, and the type of connective tissue uniting bones.

General functional classification

Based on the type of movement permitted.

Fibrous joints

Bones united by dense regular connective tissue, no joint cavity; kinds include suture, syndesmosis, and gomphosis.

Suture

A small amount of dense connective tissue fills the space between skull bones; general functional classification is synarthrosis.

Synostoses

Sutures which have become replaced by bone during the aging process.

Syndesmosis

A large amount of dense connective tissues unite bones; general functional classification is amphiarthrosis.

Gomphosis

Dense connective tissue connecting a tooth to its socket; general functional classification is synarthrosis.

Cartilaginous joints

Bones united by cartilage, no joint cavity; kinds include synchondrosis and symphysis.

Synchondrosis

Hyaline cartilage unites bones; general functional classification is synarthrosis.

Symphysis

Fibrocartilage unites bones; general functional classification is amphiarthrosis.

Synovial joints

Largest category of joint types, where a joint cavity is present; general functional classification is diarthrosis.

Synovial structure

Articular cartilage covers ends of both bones; articular joint capsule unites both bones; the capsule is double layered with an outer fibrous capsule and inner synovial membrane.

Fibrous capsule

Outer layer of joint capsule composed of dense irregular connective tissue; continuous with the periosteum of bones.

Synovial membrane

Inner layer of joint capsule composed of areolar and adipose tissue; secretes synovial fluid into the joint cavity.

Synovial fluid

Lubricates joint, nourishes articular cartilage, and contains phagocytic cells that remove microbes and debris resulting from wear and tear.

Water on the knee

Inflammation of the synovial membrane triggering an excess of synovial fluid production and accumulation in the knee.

Reinforcing ligaments

Extracapsular and intracapsular ligaments, menisci, bursae.

Extracapsular ligaments

Ligaments that remain distinct and lie outside the fibrous capsule.

Intracapsular ligaments

Ligaments inside the articular capsule, though not present in every synovial joint.

Menisci

Articular discs; fibrocartilage pads that cushion and deepen the socket on a bone for a more stable articulation with the other bone.

Bursae

Dense fibrous connective tissue sacs lined with synovial membranes and filled with synovial fluid.

Bursitis

Inflammation of bursae.

Tendonitis

Inflammation of tendon sheaths, a bursa completely wrapped around a tendon.

Pivot joints

Allow for rotation around an axis; diarthrosis, monaxial joint.

Hinge joint

Works like a door hinge; diarthrosis, monaxial joint.

Saddle joint

Articulation between trapezium and first metacarpal bone; diarthrosis, biaxial joint.

Plane joint

Allows for limited gliding movements between bones; diarthrosis, nonaxial joint.

Condyloid joint

Like the radiocarpal joint of the wrist; diarthrosis, biaxial joint.

Ball and socket joint

Only the hip and shoulder joints; diarthrosis, triaxial joint.

Arthritis

Joint inflammation.

Osteoarthritis

Articular cartilage breaks down during normal joint use is not replaced; the exposed bone tissue thickens and forms bony spurs that enlarge the bone ends and may restrict joint movement.

Rheumatoid arthritis

The body's immune system attacks synovial membranes; synovial fluid accumulates, causing joint swelling.

Gouty arthritis

Caused by uric acid deposits in joints; eventually bones at affected joints will fuse and joints will be immobile.

Strain

Overstretching of musculature.

Sprain

Ligaments reinforcing a joint are stretched or torn.

Dislocation

A bone is forced out of its normal position at a joint.