A joint. or articulation, is the place where two bones come together. All bones except one - the hyoid - form a joint with another bone. joints hold bones together and allow the rigid skeleton to move.

Classification of joints

Based on function (the amount of movement they allow) there are three types of joints:

Immovable joints (synarthroses): the bones are in very close contact. separated onIy by a thin layer of fibrous connective
tissue (eg skull sutures. costochondral junction) Slightty
movable joints (amphiarthroses): characterised by bones
connected by hyaline cartilage (eg manubriostenal joint

freely movable joints (diarthrosis): characterised by synovial-lined joint cavity and hyaline articular cartilage

There are six types of freely movable joints:

Ball and socket eg shoulder, hip

Condyloid: eg metacarpophalangeal joints - oval-shaped condyle fits into ellipti­cal cavity of another, allowing angular motion but not rotation

Saddle: eg carpometacarpal joint of thumb

Pivot eg atlantoaxial joint
Hinge: eg elbow, knee

Gliding: eg vertebral column - flat or slightly flat surfaces move against each other allowing sliding or twisting without any circular movement

Joint structure 

Based on structure. there are three types of joint:

Fibrous joints

Cartilaginous joints

Synovial joints

Fibrous joints characterized by

• lack joint cavity

• Fibrous tissue unites bones

There are three types of fibrous joints

, Sutures eg cranial
Syndesmosis (eg inferior tibiofibular joint
 Gomphosis (eg roots of teeth in alveolar socket

Cartilaginous joints which characterized by

There are two types of cartilaginous joints

Primary (synchrondrosis): where bone and hyaline cartilage meet eg between rib and costal cartilage

Secondary (symphysis): where hyaline-covered articular surfaces of two bones are united by fibrous tissue or fibrocartilage (eg pubic symphysis and Inter-vertebral joints

Synovial joints 

Synovial joints are characterised by

• Presence of a joint cavity

• Bones are covered With a layer of smooth hyaline cartilage to reduce function (occasionally fibrocartilage) eg menisci of knee

• Joint is enclosed by capsular ligament. lined with synovial membrane

• Synovial membrane produces synovial fluid to lubricate the joint

• Articulating surfaces of adjacent bones are reciprocally shaped

Hyaline cartilage is composed of chondrocytes, cartilage, gel matrix, water, collagen ann proteoglycans. Articular cartilage has no blood or nerve supply and relies on diffu­sion for nutrition.

Bone dystrophies

These diseases of bone are characterised by a disturbance of bone development, growth or structure, and can be congenital or acquired

Congenital: eg achondroplasia, fibrous dysplasia, osteogenesis imperfecta. osteopetrosis

Acquired: eg vitamin deficiencies (rickets, osteomalacia), osteoporosis. endocrine disease (acromegaly, gigantism, hyperparathyroidism), Paget'sdisease, hypertrophic osteoarthropathy, metaphyseal fibrous defect 


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